diff --git a/.forgejo/workflows/deps.yml b/.forgejo/workflows/deps.yml
index ffaca53..b29723c 100644
--- a/.forgejo/workflows/deps.yml
+++ b/.forgejo/workflows/deps.yml
@@ -12,10 +12,10 @@ jobs:
     outputs:
       cache-primary-key: ${{ steps.restore-deps.outputs.cache-primary-key }}
     steps:
-      - uses: https://code.forgejo.org/actions/checkout@v3
+      - uses: https://git.libre-chip.org/mirrors/checkout@v3
         with:
           fetch-depth: 0
-      - uses: https://code.forgejo.org/actions/cache/restore@v3
+      - uses: https://git.libre-chip.org/mirrors/cache/restore@v3
         id: restore-deps
         with:
           path: deps
@@ -58,19 +58,19 @@ jobs:
       - name: Get SymbiYosys
         if: steps.restore-deps.outputs.cache-hit != 'true'
         run: |
-          git clone --depth=1 --branch=yosys-0.45 https://github.com/YosysHQ/sby.git deps/sby
+          git clone --depth=1 --branch=yosys-0.45 https://git.libre-chip.org/mirrors/sby deps/sby
       - name: Build Z3
         if: steps.restore-deps.outputs.cache-hit != 'true'
         run: |
-          git clone --depth=1 --recursive --branch=z3-4.13.3 https://github.com/Z3Prover/z3.git deps/z3
+          git clone --depth=1 --recursive --branch=z3-4.13.3 https://git.libre-chip.org/mirrors/z3 deps/z3
           (cd deps/z3; PYTHON=python3 ./configure --prefix=/usr/local)
           make -C deps/z3/build -j"$(nproc)"
       - name: Build Yosys
         if: steps.restore-deps.outputs.cache-hit != 'true'
         run: |
-          git clone --depth=1 --recursive --branch=0.45 https://github.com/YosysHQ/yosys.git deps/yosys
+          git clone --depth=1 --recursive --branch=0.45 https://git.libre-chip.org/mirrors/yosys deps/yosys
           make -C deps/yosys -j"$(nproc)"
-      - uses: https://code.forgejo.org/actions/cache/save@v3
+      - uses: https://git.libre-chip.org/mirrors/cache/save@v3
         if: steps.restore-deps.outputs.cache-hit != 'true'
         with:
           path: deps
diff --git a/.forgejo/workflows/test.yml b/.forgejo/workflows/test.yml
index e83c668..49fb3e4 100644
--- a/.forgejo/workflows/test.yml
+++ b/.forgejo/workflows/test.yml
@@ -9,7 +9,7 @@ jobs:
     runs-on: debian-12
     needs: deps
     steps:
-      - uses: https://code.forgejo.org/actions/checkout@v3
+      - uses: https://git.libre-chip.org/mirrors/checkout@v3
         with:
           fetch-depth: 0
       - run: |
@@ -41,7 +41,7 @@ jobs:
           curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain 1.82.0
           source "$HOME/.cargo/env"
           echo "$PATH" >> "$GITHUB_PATH"
-      - uses: https://code.forgejo.org/actions/cache/restore@v3
+      - uses: https://git.libre-chip.org/mirrors/cache/restore@v3
         with:
           path: deps
           key: ${{ needs.deps.outputs.cache-primary-key }}
@@ -52,7 +52,7 @@ jobs:
           make -C deps/yosys install
           export PATH="$(realpath deps/firtool/bin):$PATH"
           echo "$PATH" >> "$GITHUB_PATH"
-      - uses: https://github.com/Swatinem/rust-cache@v2
+      - uses: https://git.libre-chip.org/mirrors/rust-cache@v2
         with:
           save-if: ${{ github.ref == 'refs/heads/master' }}
       - run: cargo test
diff --git a/crates/fayalite-proc-macros-impl/src/hdl_bundle.rs b/crates/fayalite-proc-macros-impl/src/hdl_bundle.rs
index 79326e2..b0fe498 100644
--- a/crates/fayalite-proc-macros-impl/src/hdl_bundle.rs
+++ b/crates/fayalite-proc-macros-impl/src/hdl_bundle.rs
@@ -83,6 +83,7 @@ impl ParsedBundle {
             custom_bounds,
             no_static: _,
             no_runtime_generics: _,
+            cmp_eq: _,
         } = options.body;
         let mut fields = match fields {
             syn::Fields::Named(fields) => fields,
@@ -437,6 +438,7 @@ impl ToTokens for ParsedBundle {
             custom_bounds: _,
             no_static,
             no_runtime_generics,
+            cmp_eq,
         } = &options.body;
         let target = get_target(target, ident);
         let mut item_attrs = attrs.clone();
@@ -765,6 +767,69 @@ impl ToTokens for ParsedBundle {
             }
         }
         .to_tokens(tokens);
+        if let Some((cmp_eq,)) = cmp_eq {
+            let mut where_clause =
+                Generics::from(generics)
+                    .where_clause
+                    .unwrap_or_else(|| syn::WhereClause {
+                        where_token: Token![where](span),
+                        predicates: Punctuated::new(),
+                    });
+            let mut fields_cmp_eq = vec![];
+            let mut fields_cmp_ne = vec![];
+            for field in fields.named() {
+                let field_ident = field.ident();
+                let field_ty = field.ty();
+                where_clause
+                    .predicates
+                    .push(parse_quote_spanned! {cmp_eq.span=>
+                        #field_ty: ::fayalite::expr::ops::ExprPartialEq<#field_ty>
+                    });
+                fields_cmp_eq.push(quote_spanned! {span=>
+                    ::fayalite::expr::ops::ExprPartialEq::cmp_eq(__lhs.#field_ident, __rhs.#field_ident)
+                });
+                fields_cmp_ne.push(quote_spanned! {span=>
+                    ::fayalite::expr::ops::ExprPartialEq::cmp_ne(__lhs.#field_ident, __rhs.#field_ident)
+                });
+            }
+            let cmp_eq_body;
+            let cmp_ne_body;
+            if fields_len == 0 {
+                cmp_eq_body = quote_spanned! {span=>
+                    ::fayalite::expr::ToExpr::to_expr(&true)
+                };
+                cmp_ne_body = quote_spanned! {span=>
+                    ::fayalite::expr::ToExpr::to_expr(&false)
+                };
+            } else {
+                cmp_eq_body = quote_spanned! {span=>
+                    #(#fields_cmp_eq)&*
+                };
+                cmp_ne_body = quote_spanned! {span=>
+                    #(#fields_cmp_ne)|*
+                };
+            };
+            quote_spanned! {span=>
+                #[automatically_derived]
+                impl #impl_generics ::fayalite::expr::ops::ExprPartialEq<Self> for #target #type_generics
+                #where_clause
+                {
+                    fn cmp_eq(
+                        __lhs: ::fayalite::expr::Expr<Self>,
+                        __rhs: ::fayalite::expr::Expr<Self>,
+                    ) -> ::fayalite::expr::Expr<::fayalite::int::Bool> {
+                        #cmp_eq_body
+                    }
+                    fn cmp_ne(
+                        __lhs: ::fayalite::expr::Expr<Self>,
+                        __rhs: ::fayalite::expr::Expr<Self>,
+                    ) -> ::fayalite::expr::Expr<::fayalite::int::Bool> {
+                        #cmp_ne_body
+                    }
+                }
+            }
+            .to_tokens(tokens);
+        }
         if let (None, MaybeParsed::Parsed(generics)) = (no_static, &self.generics) {
             let static_generics = generics.clone().for_static_type();
             let (static_impl_generics, static_type_generics, static_where_clause) =
diff --git a/crates/fayalite-proc-macros-impl/src/hdl_enum.rs b/crates/fayalite-proc-macros-impl/src/hdl_enum.rs
index 1d16177..9174566 100644
--- a/crates/fayalite-proc-macros-impl/src/hdl_enum.rs
+++ b/crates/fayalite-proc-macros-impl/src/hdl_enum.rs
@@ -155,7 +155,11 @@ impl ParsedEnum {
             custom_bounds,
             no_static: _,
             no_runtime_generics: _,
+            cmp_eq,
         } = options.body;
+        if let Some((cmp_eq,)) = cmp_eq {
+            errors.error(cmp_eq, "#[hdl(cmp_eq)] is not yet implemented for enums");
+        }
         attrs.retain(|attr| {
             if attr.path().is_ident("repr") {
                 errors.error(attr, "#[repr] is not supported on #[hdl] enums");
@@ -211,6 +215,7 @@ impl ToTokens for ParsedEnum {
             custom_bounds: _,
             no_static,
             no_runtime_generics,
+            cmp_eq: _, // TODO: implement cmp_eq for enums
         } = &options.body;
         let target = get_target(target, ident);
         let mut struct_attrs = attrs.clone();
diff --git a/crates/fayalite-proc-macros-impl/src/hdl_type_alias.rs b/crates/fayalite-proc-macros-impl/src/hdl_type_alias.rs
index e5d5f7b..97501e7 100644
--- a/crates/fayalite-proc-macros-impl/src/hdl_type_alias.rs
+++ b/crates/fayalite-proc-macros-impl/src/hdl_type_alias.rs
@@ -49,10 +49,14 @@ impl ParsedTypeAlias {
             custom_bounds,
             no_static,
             no_runtime_generics: _,
+            cmp_eq,
         } = options.body;
         if let Some((no_static,)) = no_static {
             errors.error(no_static, "no_static is not valid on type aliases");
         }
+        if let Some((cmp_eq,)) = cmp_eq {
+            errors.error(cmp_eq, "cmp_eq is not valid on type aliases");
+        }
         let generics = if custom_bounds.is_some() {
             MaybeParsed::Unrecognized(generics)
         } else if let Some(generics) = errors.ok(ParsedGenerics::parse(&mut generics)) {
@@ -95,6 +99,7 @@ impl ToTokens for ParsedTypeAlias {
             custom_bounds: _,
             no_static: _,
             no_runtime_generics,
+            cmp_eq: _,
         } = &options.body;
         let target = get_target(target, ident);
         let mut type_attrs = attrs.clone();
diff --git a/crates/fayalite-proc-macros-impl/src/hdl_type_common.rs b/crates/fayalite-proc-macros-impl/src/hdl_type_common.rs
index 6193dc3..2da0915 100644
--- a/crates/fayalite-proc-macros-impl/src/hdl_type_common.rs
+++ b/crates/fayalite-proc-macros-impl/src/hdl_type_common.rs
@@ -26,6 +26,7 @@ crate::options! {
         CustomBounds(custom_bounds),
         NoStatic(no_static),
         NoRuntimeGenerics(no_runtime_generics),
+        CmpEq(cmp_eq),
     }
 }
 
@@ -2069,11 +2070,16 @@ macro_rules! impl_bounds {
             $(
                 $Variant:ident,
             )*
+            $(
+                #[unknown]
+                $Unknown:ident,
+            )?
         }
     ) => {
         #[derive(Clone, Debug)]
         $vis enum $enum_type {
             $($Variant(known_items::$Variant),)*
+            $($Unknown(syn::TypeParamBound),)?
         }
 
         $(impl From<known_items::$Variant> for $enum_type {
@@ -2086,28 +2092,54 @@ macro_rules! impl_bounds {
             fn to_tokens(&self, tokens: &mut TokenStream) {
                 match self {
                     $(Self::$Variant(v) => v.to_tokens(tokens),)*
+                    $(Self::$Unknown(v) => v.to_tokens(tokens),)?
                 }
             }
         }
 
         impl $enum_type {
             $vis fn parse_path(path: Path) -> Result<Self, Path> {
+                #![allow(unreachable_code)]
                 $(let path = match known_items::$Variant::parse_path(path) {
                     Ok(v) => return Ok(Self::$Variant(v)),
                     Err(path) => path,
                 };)*
+                $(return Ok(Self::$Unknown(syn::TraitBound {
+                    paren_token: None,
+                    modifier: syn::TraitBoundModifier::None,
+                    lifetimes: None,
+                    path,
+                }.into()));)?
                 Err(path)
             }
+            $vis fn parse_type_param_bound(mut type_param_bound: syn::TypeParamBound) -> Result<Self, syn::TypeParamBound> {
+                #![allow(unreachable_code)]
+                if let syn::TypeParamBound::Trait(mut trait_bound) = type_param_bound {
+                    if let syn::TraitBound {
+                        paren_token: _,
+                        modifier: syn::TraitBoundModifier::None,
+                        lifetimes: None,
+                        path: _,
+                    } = trait_bound {
+                        match Self::parse_path(trait_bound.path) {
+                            Ok(retval) => return Ok(retval),
+                            Err(path) => trait_bound.path = path,
+                        }
+                    }
+                    type_param_bound = trait_bound.into();
+                }
+                $(return Ok(Self::$Unknown(type_param_bound));)?
+                Err(type_param_bound)
+            }
         }
 
         impl Parse for $enum_type {
             fn parse(input: ParseStream) -> syn::Result<Self> {
-                Self::parse_path(Path::parse_mod_style(input)?).map_err(|path| {
-                    syn::Error::new_spanned(
-                        path,
+                Self::parse_type_param_bound(input.parse()?)
+                    .map_err(|type_param_bound| syn::Error::new_spanned(
+                        type_param_bound,
                         format_args!("expected one of: {}", [$(stringify!($Variant)),*].join(", ")),
-                    )
-                })
+                    ))
             }
         }
 
@@ -2115,6 +2147,7 @@ macro_rules! impl_bounds {
         #[allow(non_snake_case)]
         $vis struct $struct_type {
             $($vis $Variant: Option<known_items::$Variant>,)*
+            $($vis $Unknown: Vec<syn::TypeParamBound>,)?
         }
 
         impl ToTokens for $struct_type {
@@ -2126,42 +2159,63 @@ macro_rules! impl_bounds {
                     separator = Some(<Token![+]>::default());
                     v.to_tokens(tokens);
                 })*
+                $(for v in &self.$Unknown {
+                    separator.to_tokens(tokens);
+                    separator = Some(<Token![+]>::default());
+                    v.to_tokens(tokens);
+                })*
             }
         }
 
         const _: () = {
             #[derive(Clone, Debug)]
-            $vis struct Iter($vis $struct_type);
+            #[allow(non_snake_case)]
+            $vis struct Iter {
+                $($Variant: Option<known_items::$Variant>,)*
+                $($Unknown: std::vec::IntoIter<syn::TypeParamBound>,)?
+            }
 
             impl IntoIterator for $struct_type {
                 type Item = $enum_type;
                 type IntoIter = Iter;
 
                 fn into_iter(self) -> Self::IntoIter {
-                    Iter(self)
+                    Iter {
+                        $($Variant: self.$Variant,)*
+                        $($Unknown: self.$Unknown.into_iter(),)?
+                    }
                 }
             }
 
             impl Iterator for Iter {
                 type Item = $enum_type;
 
-
                 fn next(&mut self) -> Option<Self::Item> {
                     $(
-                        if let Some(value) = self.0.$Variant.take() {
+                        if let Some(value) = self.$Variant.take() {
                             return Some($enum_type::$Variant(value));
                         }
                     )*
+                    $(
+                        if let Some(value) = self.$Unknown.next() {
+                            return Some($enum_type::$Unknown(value));
+                        }
+                    )?
                     None
                 }
 
                 #[allow(unused_mut, unused_variables)]
                 fn fold<B, F: FnMut(B, Self::Item) -> B>(mut self, mut init: B, mut f: F) -> B {
                     $(
-                        if let Some(value) = self.0.$Variant.take() {
+                        if let Some(value) = self.$Variant.take() {
                             init = f(init, $enum_type::$Variant(value));
                         }
                     )*
+                    $(
+                        if let Some(value) = self.$Unknown.next() {
+                            init = f(init, $enum_type::$Unknown(value));
+                        }
+                    )?
                     init
                 }
             }
@@ -2173,6 +2227,9 @@ macro_rules! impl_bounds {
                     $($enum_type::$Variant(v) => {
                         self.$Variant = Some(v);
                     })*
+                    $($enum_type::$Unknown(v) => {
+                        self.$Unknown.push(v);
+                    })?
                 });
             }
         }
@@ -2191,6 +2248,7 @@ macro_rules! impl_bounds {
                     $(if let Some(v) = v.$Variant {
                         self.$Variant = Some(v);
                     })*
+                    $(self.$Unknown.extend(v.$Unknown);)*
                 });
             }
         }
@@ -2244,6 +2302,8 @@ impl_bounds! {
         Size,
         StaticType,
         Type,
+        #[unknown]
+        Unknown,
     }
 }
 
@@ -2257,6 +2317,8 @@ impl_bounds! {
         ResetType,
         StaticType,
         Type,
+        #[unknown]
+        Unknown,
     }
 }
 
@@ -2270,6 +2332,7 @@ impl From<ParsedTypeBound> for ParsedBound {
             ParsedTypeBound::ResetType(v) => ParsedBound::ResetType(v),
             ParsedTypeBound::StaticType(v) => ParsedBound::StaticType(v),
             ParsedTypeBound::Type(v) => ParsedBound::Type(v),
+            ParsedTypeBound::Unknown(v) => ParsedBound::Unknown(v),
         }
     }
 }
@@ -2284,6 +2347,7 @@ impl From<ParsedTypeBounds> for ParsedBounds {
             ResetType,
             StaticType,
             Type,
+            Unknown,
         } = value;
         Self {
             BoolOrIntType,
@@ -2295,6 +2359,7 @@ impl From<ParsedTypeBounds> for ParsedBounds {
             Size: None,
             StaticType,
             Type,
+            Unknown,
         }
     }
 }
@@ -2330,6 +2395,7 @@ impl ParsedTypeBound {
                 ParsedTypeBound::Type(known_items::Type(span)),
             ]),
             Self::Type(v) => ParsedTypeBounds::from_iter([ParsedTypeBound::from(v)]),
+            Self::Unknown(v) => ParsedTypeBounds::from_iter([ParsedTypeBound::Unknown(v)]),
         }
     }
 }
@@ -2364,6 +2430,7 @@ impl From<ParsedSizeTypeBounds> for ParsedBounds {
             Size,
             StaticType: None,
             Type: None,
+            Unknown: vec![],
         }
     }
 }
@@ -2391,6 +2458,7 @@ impl ParsedBounds {
     fn categorize(self, errors: &mut Errors, span: Span) -> ParsedBoundsCategory {
         let mut type_bounds = None;
         let mut size_type_bounds = None;
+        let mut unknown_bounds = vec![];
         self.into_iter().for_each(|bound| match bound.categorize() {
             ParsedBoundCategory::Type(bound) => {
                 type_bounds
@@ -2402,15 +2470,37 @@ impl ParsedBounds {
                     .get_or_insert_with(ParsedSizeTypeBounds::default)
                     .extend([bound]);
             }
+            ParsedBoundCategory::Unknown(bound) => unknown_bounds.push(bound),
         });
-        match (type_bounds, size_type_bounds) {
-            (None, None) => ParsedBoundsCategory::Type(ParsedTypeBounds {
+        match (type_bounds, size_type_bounds, unknown_bounds.is_empty()) {
+            (None, None, true) => ParsedBoundsCategory::Type(ParsedTypeBounds {
                 Type: Some(known_items::Type(span)),
                 ..Default::default()
             }),
-            (None, Some(bounds)) => ParsedBoundsCategory::SizeType(bounds),
-            (Some(bounds), None) => ParsedBoundsCategory::Type(bounds),
-            (Some(type_bounds), Some(size_type_bounds)) => {
+            (None, None, false) => {
+                errors.error(
+                    unknown_bounds.remove(0),
+                    "unknown bounds: must use at least one known bound (such as `Type`) with any unknown bounds",
+                );
+                ParsedBoundsCategory::Type(ParsedTypeBounds {
+                    Unknown: unknown_bounds,
+                    ..Default::default()
+                })
+            }
+            (None, Some(bounds), true) => ParsedBoundsCategory::SizeType(bounds),
+            (None, Some(bounds), false) => {
+                // TODO: implement
+                errors.error(
+                    unknown_bounds.remove(0),
+                    "unknown bounds with `Size` bounds are not implemented",
+                );
+                ParsedBoundsCategory::SizeType(bounds)
+            }
+            (Some(bounds), None, _) => ParsedBoundsCategory::Type(ParsedTypeBounds {
+                Unknown: unknown_bounds,
+                ..bounds
+            }),
+            (Some(type_bounds), Some(size_type_bounds), _) => {
                 errors.error(
                     size_type_bounds
                         .Size
@@ -2427,6 +2517,7 @@ impl ParsedBounds {
 pub(crate) enum ParsedBoundCategory {
     Type(ParsedTypeBound),
     SizeType(ParsedSizeTypeBound),
+    Unknown(syn::TypeParamBound),
 }
 
 impl ParsedBound {
@@ -2441,12 +2532,14 @@ impl ParsedBound {
             Self::Size(v) => ParsedBoundCategory::SizeType(ParsedSizeTypeBound::Size(v)),
             Self::StaticType(v) => ParsedBoundCategory::Type(ParsedTypeBound::StaticType(v)),
             Self::Type(v) => ParsedBoundCategory::Type(ParsedTypeBound::Type(v)),
+            Self::Unknown(v) => ParsedBoundCategory::Unknown(v),
         }
     }
     fn implied_bounds(self) -> ParsedBounds {
         match self.categorize() {
             ParsedBoundCategory::Type(v) => v.implied_bounds().into(),
             ParsedBoundCategory::SizeType(v) => v.implied_bounds().into(),
+            ParsedBoundCategory::Unknown(v) => ParsedBounds::from_iter([ParsedBound::Unknown(v)]),
         }
     }
 }
@@ -3325,7 +3418,7 @@ impl ParsedGenerics {
                                 | ParsedTypeBound::EnumType(_)
                                 | ParsedTypeBound::IntType(_)
                                 | ParsedTypeBound::ResetType(_) => {
-                                    errors.error(bound, "bound on mask type not implemented");
+                                    errors.error(bound, "bounds on mask types are not implemented");
                                 }
                                 ParsedTypeBound::StaticType(bound) => {
                                     if bounds.StaticType.is_none() {
@@ -3337,6 +3430,12 @@ impl ParsedGenerics {
                                     }
                                 }
                                 ParsedTypeBound::Type(_) => {}
+                                ParsedTypeBound::Unknown(_) => {
+                                    errors.error(
+                                        bound,
+                                        "unknown bounds on mask types are not implemented",
+                                    );
+                                }
                             }
                         }
                         bounds.add_implied_bounds();
diff --git a/crates/fayalite-proc-macros-impl/src/lib.rs b/crates/fayalite-proc-macros-impl/src/lib.rs
index 6ba177b..5fe3ae8 100644
--- a/crates/fayalite-proc-macros-impl/src/lib.rs
+++ b/crates/fayalite-proc-macros-impl/src/lib.rs
@@ -72,13 +72,14 @@ mod kw {
     custom_keyword!(cfg);
     custom_keyword!(cfg_attr);
     custom_keyword!(clock_domain);
+    custom_keyword!(cmp_eq);
     custom_keyword!(connect_inexact);
     custom_keyword!(custom_bounds);
     custom_keyword!(flip);
     custom_keyword!(hdl);
     custom_keyword!(hdl_module);
-    custom_keyword!(input);
     custom_keyword!(incomplete_wire);
+    custom_keyword!(input);
     custom_keyword!(instance);
     custom_keyword!(m);
     custom_keyword!(memory);
diff --git a/crates/fayalite/src/array.rs b/crates/fayalite/src/array.rs
index f617f91..0d9b63f 100644
--- a/crates/fayalite/src/array.rs
+++ b/crates/fayalite/src/array.rs
@@ -2,8 +2,11 @@
 // See Notices.txt for copyright information
 
 use crate::{
-    expr::{ops::ArrayIndex, Expr, ToExpr},
-    int::{DynSize, KnownSize, Size, SizeType, DYN_SIZE},
+    expr::{
+        ops::{ArrayLiteral, ExprFromIterator, ExprIntoIterator, ExprPartialEq},
+        CastToBits, Expr, HdlPartialEq, ReduceBits, ToExpr,
+    },
+    int::{Bool, DynSize, KnownSize, Size, SizeType, DYN_SIZE},
     intern::{Intern, Interned, LazyInterned},
     module::transform::visit::{Fold, Folder, Visit, Visitor},
     source_location::SourceLocation,
@@ -12,7 +15,7 @@ use crate::{
     },
     util::ConstUsize,
 };
-use std::ops::Index;
+use std::{iter::FusedIterator, ops::Index};
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
 pub struct ArrayType<T: Type = CanonicalType, Len: Size = DynSize> {
@@ -148,10 +151,8 @@ impl<T: Type, Len: Size> Type for ArrayType<T, Len> {
         this: Expr<Self>,
         source_location: SourceLocation,
     ) -> Self::MatchVariantsIter {
-        let base = Expr::as_dyn_array(this);
-        let base_ty = Expr::ty(base);
         let _ = source_location;
-        let retval = Vec::from_iter((0..base_ty.len()).map(|i| ArrayIndex::new(base, i).to_expr()));
+        let retval = Vec::from_iter(this);
         std::iter::once(MatchVariantWithoutScope(
             Len::ArrayMatch::<T>::try_from(retval)
                 .ok()
@@ -184,9 +185,7 @@ impl<T: Type, Len: Size> Type for ArrayType<T, Len> {
 
 impl<T: Type, Len: Size> TypeWithDeref for ArrayType<T, Len> {
     fn expr_deref(this: &Expr<Self>) -> &Self::MatchVariant {
-        let base = Expr::as_dyn_array(*this);
-        let base_ty = Expr::ty(base);
-        let retval = Vec::from_iter((0..base_ty.len()).map(|i| ArrayIndex::new(base, i).to_expr()));
+        let retval = Vec::from_iter(*this);
         Interned::into_inner(Intern::intern_sized(
             Len::ArrayMatch::<T>::try_from(retval)
                 .ok()
@@ -218,3 +217,131 @@ impl<T: Type, L: SizeType> Index<L> for ArrayWithoutLen<T> {
         Interned::into_inner(Intern::intern_sized(ArrayType::new(self.element, len)))
     }
 }
+
+impl<Lhs: Type, Rhs: Type, Len: Size> ExprPartialEq<ArrayType<Rhs, Len>> for ArrayType<Lhs, Len>
+where
+    Lhs: ExprPartialEq<Rhs>,
+{
+    fn cmp_eq(lhs: Expr<Self>, rhs: Expr<ArrayType<Rhs, Len>>) -> Expr<Bool> {
+        let lhs_ty = Expr::ty(lhs);
+        let rhs_ty = Expr::ty(rhs);
+        assert_eq!(lhs_ty.len(), rhs_ty.len());
+        lhs.into_iter()
+            .zip(rhs)
+            .map(|(l, r)| l.cmp_eq(r))
+            .collect::<Expr<Array<Bool>>>()
+            .cast_to_bits()
+            .all_one_bits()
+    }
+
+    fn cmp_ne(lhs: Expr<Self>, rhs: Expr<ArrayType<Rhs, Len>>) -> Expr<Bool> {
+        let lhs_ty = Expr::ty(lhs);
+        let rhs_ty = Expr::ty(rhs);
+        assert_eq!(lhs_ty.len(), rhs_ty.len());
+        lhs.into_iter()
+            .zip(rhs)
+            .map(|(l, r)| l.cmp_ne(r))
+            .collect::<Expr<Array<Bool>>>()
+            .cast_to_bits()
+            .any_one_bits()
+    }
+}
+
+impl<T: Type, Len: Size> ExprIntoIterator for ArrayType<T, Len> {
+    type Item = T;
+    type ExprIntoIter = ExprArrayIter<T, Len>;
+
+    fn expr_into_iter(e: Expr<Self>) -> Self::ExprIntoIter {
+        ExprArrayIter {
+            base: e,
+            indexes: 0..Expr::ty(e).len(),
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct ExprArrayIter<T: Type, Len: Size> {
+    base: Expr<ArrayType<T, Len>>,
+    indexes: std::ops::Range<usize>,
+}
+
+impl<T: Type, Len: Size> ExprArrayIter<T, Len> {
+    pub fn base(&self) -> Expr<ArrayType<T, Len>> {
+        self.base
+    }
+    pub fn indexes(&self) -> std::ops::Range<usize> {
+        self.indexes.clone()
+    }
+}
+
+impl<T: Type, Len: Size> Iterator for ExprArrayIter<T, Len> {
+    type Item = Expr<T>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.indexes.next().map(|i| self.base[i])
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.indexes.size_hint()
+    }
+
+    fn count(self) -> usize {
+        self.indexes.count()
+    }
+
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        self.indexes.nth(n).map(|i| self.base[i])
+    }
+
+    fn fold<B, F>(self, init: B, mut f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        self.indexes.fold(init, |b, i| f(b, self.base[i]))
+    }
+}
+
+impl<T: Type, Len: Size> DoubleEndedIterator for ExprArrayIter<T, Len> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.indexes.next_back().map(|i| self.base[i])
+    }
+
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        self.indexes.nth_back(n).map(|i| self.base[i])
+    }
+
+    fn rfold<B, F>(self, init: B, mut f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        self.indexes.rfold(init, |b, i| f(b, self.base[i]))
+    }
+}
+
+impl<T: Type, Len: Size> ExactSizeIterator for ExprArrayIter<T, Len> {
+    fn len(&self) -> usize {
+        self.indexes.len()
+    }
+}
+
+impl<T: Type, Len: Size> FusedIterator for ExprArrayIter<T, Len> {}
+
+impl<A: StaticType> ExprFromIterator<Expr<A>> for Array<A> {
+    fn expr_from_iter<T: IntoIterator<Item = Expr<A>>>(iter: T) -> Expr<Self> {
+        ArrayLiteral::new(
+            A::TYPE,
+            iter.into_iter().map(|v| Expr::canonical(v)).collect(),
+        )
+        .to_expr()
+    }
+}
+
+impl<'a, A: StaticType> ExprFromIterator<&'a Expr<A>> for Array<A> {
+    fn expr_from_iter<T: IntoIterator<Item = &'a Expr<A>>>(iter: T) -> Expr<Self> {
+        iter.into_iter().copied().collect()
+    }
+}
diff --git a/crates/fayalite/src/bundle.rs b/crates/fayalite/src/bundle.rs
index 995510e..9807b92 100644
--- a/crates/fayalite/src/bundle.rs
+++ b/crates/fayalite/src/bundle.rs
@@ -2,7 +2,11 @@
 // See Notices.txt for copyright information
 
 use crate::{
-    expr::{ops::BundleLiteral, Expr, ToExpr},
+    expr::{
+        ops::{ArrayLiteral, BundleLiteral, ExprPartialEq},
+        CastToBits, Expr, ReduceBits, ToExpr,
+    },
+    int::{Bool, DynSize},
     intern::{Intern, Interned},
     sim::{SimValue, ToSimValue},
     source_location::SourceLocation,
@@ -325,7 +329,19 @@ macro_rules! impl_tuple_builder_fields {
 }
 
 macro_rules! impl_tuples {
-    ([$({#[num = $num:literal, field = $field:ident, ty = $ty_var:ident: $Ty:ident] $var:ident: $T:ident})*] []) => {
+    (
+        [$({
+            #[
+                num = $num:tt,
+                field = $field:ident,
+                ty = $ty_var:ident: $Ty:ident,
+                lhs = $lhs_var:ident: $Lhs:ident,
+                rhs = $rhs_var:ident: $Rhs:ident
+            ]
+            $var:ident: $T:ident
+        })*]
+        []
+    ) => {
         impl_tuple_builder_fields! {
             {}
             [$({
@@ -498,6 +514,29 @@ macro_rules! impl_tuples {
                 Self::into_sim_value(*self, ty)
             }
         }
+        impl<$($Lhs: Type + ExprPartialEq<$Rhs>, $Rhs: Type,)*> ExprPartialEq<($($Rhs,)*)> for ($($Lhs,)*) {
+            fn cmp_eq(lhs: Expr<Self>, rhs: Expr<($($Rhs,)*)>) -> Expr<Bool> {
+                let ($($lhs_var,)*) = *lhs;
+                let ($($rhs_var,)*) = *rhs;
+                ArrayLiteral::<Bool, DynSize>::new(
+                    Bool,
+                    FromIterator::from_iter([$(Expr::canonical(ExprPartialEq::cmp_eq($lhs_var, $rhs_var)),)*]),
+                )
+                .cast_to_bits()
+                .all_one_bits()
+            }
+
+            fn cmp_ne(lhs: Expr<Self>, rhs: Expr<($($Rhs,)*)>) -> Expr<Bool> {
+                let ($($lhs_var,)*) = *lhs;
+                let ($($rhs_var,)*) = *rhs;
+                ArrayLiteral::<Bool, DynSize>::new(
+                    Bool,
+                    FromIterator::from_iter([$(Expr::canonical(ExprPartialEq::cmp_ne($lhs_var, $rhs_var)),)*]),
+                )
+                .cast_to_bits()
+                .any_one_bits()
+            }
+        }
     };
     ([$($lhs:tt)*] [$rhs_first:tt $($rhs:tt)*]) => {
         impl_tuples!([$($lhs)*] []);
@@ -507,18 +546,18 @@ macro_rules! impl_tuples {
 
 impl_tuples! {
     [] [
-        {#[num = 0, field = field_0, ty = ty0: Ty0] v0: T0}
-        {#[num = 1, field = field_1, ty = ty1: Ty1] v1: T1}
-        {#[num = 2, field = field_2, ty = ty2: Ty2] v2: T2}
-        {#[num = 3, field = field_3, ty = ty3: Ty3] v3: T3}
-        {#[num = 4, field = field_4, ty = ty4: Ty4] v4: T4}
-        {#[num = 5, field = field_5, ty = ty5: Ty5] v5: T5}
-        {#[num = 6, field = field_6, ty = ty6: Ty6] v6: T6}
-        {#[num = 7, field = field_7, ty = ty7: Ty7] v7: T7}
-        {#[num = 8, field = field_8, ty = ty8: Ty8] v8: T8}
-        {#[num = 9, field = field_9, ty = ty9: Ty9] v9: T9}
-        {#[num = 10, field = field_10, ty = ty10: Ty10] v10: T10}
-        {#[num = 11, field = field_11, ty = ty11: Ty11] v11: T11}
+        {#[num = 0, field = field_0, ty = ty0: Ty0, lhs = lhs0: Lhs0, rhs = rhs0: Rhs0] v0: T0}
+        {#[num = 1, field = field_1, ty = ty1: Ty1, lhs = lhs1: Lhs1, rhs = rhs1: Rhs1] v1: T1}
+        {#[num = 2, field = field_2, ty = ty2: Ty2, lhs = lhs2: Lhs2, rhs = rhs2: Rhs2] v2: T2}
+        {#[num = 3, field = field_3, ty = ty3: Ty3, lhs = lhs3: Lhs3, rhs = rhs3: Rhs3] v3: T3}
+        {#[num = 4, field = field_4, ty = ty4: Ty4, lhs = lhs4: Lhs4, rhs = rhs4: Rhs4] v4: T4}
+        {#[num = 5, field = field_5, ty = ty5: Ty5, lhs = lhs5: Lhs5, rhs = rhs5: Rhs5] v5: T5}
+        {#[num = 6, field = field_6, ty = ty6: Ty6, lhs = lhs6: Lhs6, rhs = rhs6: Rhs6] v6: T6}
+        {#[num = 7, field = field_7, ty = ty7: Ty7, lhs = lhs7: Lhs7, rhs = rhs7: Rhs7] v7: T7}
+        {#[num = 8, field = field_8, ty = ty8: Ty8, lhs = lhs8: Lhs8, rhs = rhs8: Rhs8] v8: T8}
+        {#[num = 9, field = field_9, ty = ty9: Ty9, lhs = lhs9: Lhs9, rhs = rhs9: Rhs9] v9: T9}
+        {#[num = 10, field = field_10, ty = ty10: Ty10, lhs = lhs10: Lhs10, rhs = rhs10: Rhs10] v10: T10}
+        {#[num = 11, field = field_11, ty = ty11: Ty11, lhs = lhs11: Lhs11, rhs = rhs11: Rhs11] v11: T11}
     ]
 }
 
diff --git a/crates/fayalite/src/enum_.rs b/crates/fayalite/src/enum_.rs
index 2ed0b8e..70c58c0 100644
--- a/crates/fayalite/src/enum_.rs
+++ b/crates/fayalite/src/enum_.rs
@@ -2,7 +2,10 @@
 // See Notices.txt for copyright information
 
 use crate::{
-    expr::{ops::VariantAccess, Expr, ToExpr},
+    expr::{
+        ops::{ExprPartialEq, VariantAccess},
+        Expr, ToExpr,
+    },
     hdl,
     int::Bool,
     intern::{Intern, Interned},
@@ -360,6 +363,60 @@ pub enum HdlOption<T: Type> {
     HdlSome(T),
 }
 
+impl<Lhs: Type + ExprPartialEq<Rhs>, Rhs: Type> ExprPartialEq<HdlOption<Rhs>> for HdlOption<Lhs> {
+    #[hdl]
+    fn cmp_eq(lhs: Expr<Self>, rhs: Expr<HdlOption<Rhs>>) -> Expr<Bool> {
+        #[hdl]
+        let cmp_eq = wire();
+        #[hdl]
+        match lhs {
+            HdlSome(lhs) =>
+            {
+                #[hdl]
+                match rhs {
+                    HdlSome(rhs) => connect(cmp_eq, ExprPartialEq::cmp_eq(lhs, rhs)),
+                    HdlNone => connect(cmp_eq, false),
+                }
+            }
+            HdlNone =>
+            {
+                #[hdl]
+                match rhs {
+                    HdlSome(_) => connect(cmp_eq, false),
+                    HdlNone => connect(cmp_eq, true),
+                }
+            }
+        }
+        cmp_eq
+    }
+
+    #[hdl]
+    fn cmp_ne(lhs: Expr<Self>, rhs: Expr<HdlOption<Rhs>>) -> Expr<Bool> {
+        #[hdl]
+        let cmp_ne = wire();
+        #[hdl]
+        match lhs {
+            HdlSome(lhs) =>
+            {
+                #[hdl]
+                match rhs {
+                    HdlSome(rhs) => connect(cmp_ne, ExprPartialEq::cmp_ne(lhs, rhs)),
+                    HdlNone => connect(cmp_ne, true),
+                }
+            }
+            HdlNone =>
+            {
+                #[hdl]
+                match rhs {
+                    HdlSome(_) => connect(cmp_ne, true),
+                    HdlNone => connect(cmp_ne, false),
+                }
+            }
+        }
+        cmp_ne
+    }
+}
+
 #[allow(non_snake_case)]
 pub fn HdlNone<T: StaticType>() -> Expr<HdlOption<T>> {
     HdlOption[T::TYPE].HdlNone()
diff --git a/crates/fayalite/src/expr.rs b/crates/fayalite/src/expr.rs
index f0008f4..016ec8e 100644
--- a/crates/fayalite/src/expr.rs
+++ b/crates/fayalite/src/expr.rs
@@ -16,6 +16,7 @@ use crate::{
         transform::visit::{Fold, Folder, Visit, Visitor},
         Instance, ModuleIO,
     },
+    phantom_const::PhantomConst,
     reg::Reg,
     reset::{AsyncReset, Reset, ResetType, ResetTypeDispatch, SyncReset},
     ty::{CanonicalType, StaticType, Type, TypeWithDeref},
@@ -109,6 +110,7 @@ expr_enum! {
         UIntLiteral(Interned<UIntValue>),
         SIntLiteral(Interned<SIntValue>),
         BoolLiteral(bool),
+        PhantomConst(PhantomConst),
         BundleLiteral(ops::BundleLiteral),
         ArrayLiteral(ops::ArrayLiteral<CanonicalType, DynSize>),
         EnumLiteral(ops::EnumLiteral),
@@ -755,3 +757,27 @@ pub fn repeat<T: Type, L: SizeType>(
     )
     .to_expr()
 }
+
+impl<T: ?Sized + crate::phantom_const::PhantomConstValue> ToExpr for PhantomConst<T> {
+    type Type = Self;
+
+    fn to_expr(&self) -> Expr<Self::Type> {
+        Expr {
+            __enum: ExprEnum::PhantomConst(self.canonical_phantom_const()).intern_sized(),
+            __ty: *self,
+            __flow: Flow::Source,
+        }
+    }
+}
+
+impl<T: ?Sized + crate::phantom_const::PhantomConstValue> GetTarget for PhantomConst<T> {
+    fn target(&self) -> Option<Interned<Target>> {
+        None
+    }
+}
+
+impl<T: ?Sized + crate::phantom_const::PhantomConstValue> ToLiteralBits for PhantomConst<T> {
+    fn to_literal_bits(&self) -> Result<Interned<BitSlice>, NotALiteralExpr> {
+        Ok(Interned::default())
+    }
+}
diff --git a/crates/fayalite/src/expr/ops.rs b/crates/fayalite/src/expr/ops.rs
index 15c195e..e794a68 100644
--- a/crates/fayalite/src/expr/ops.rs
+++ b/crates/fayalite/src/expr/ops.rs
@@ -11,14 +11,15 @@ use crate::{
             GetTarget, Target, TargetPathArrayElement, TargetPathBundleField,
             TargetPathDynArrayElement, TargetPathElement,
         },
-        CastTo, Expr, ExprEnum, Flow, HdlPartialEq, HdlPartialOrd, NotALiteralExpr, ReduceBits,
-        ToExpr, ToLiteralBits,
+        CastBitsTo as _, CastTo, CastToBits as _, Expr, ExprEnum, Flow, HdlPartialEq,
+        HdlPartialOrd, NotALiteralExpr, ReduceBits, ToExpr, ToLiteralBits,
     },
     int::{
         Bool, BoolOrIntType, DynSize, IntType, KnownSize, SInt, SIntType, SIntValue, Size, UInt,
         UIntType, UIntValue,
     },
     intern::{Intern, Interned},
+    phantom_const::{PhantomConst, PhantomConstValue},
     reset::{
         AsyncReset, Reset, ResetType, ResetTypeDispatch, SyncReset, ToAsyncReset, ToReset,
         ToSyncReset,
@@ -1892,6 +1893,26 @@ impl ExprCastTo<Clock> for Clock {
     }
 }
 
+impl<T: ?Sized + PhantomConstValue> ExprCastTo<()> for PhantomConst<T> {
+    fn cast_to(src: Expr<Self>, to_type: ()) -> Expr<()> {
+        src.cast_to_bits().cast_bits_to(to_type)
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> ExprCastTo<PhantomConst<T>> for () {
+    fn cast_to(src: Expr<Self>, to_type: PhantomConst<T>) -> Expr<PhantomConst<T>> {
+        src.cast_to_bits().cast_bits_to(to_type)
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue, U: ?Sized + PhantomConstValue> ExprCastTo<PhantomConst<T>>
+    for PhantomConst<U>
+{
+    fn cast_to(src: Expr<Self>, to_type: PhantomConst<T>) -> Expr<PhantomConst<T>> {
+        src.cast_to_bits().cast_bits_to(to_type)
+    }
+}
+
 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
 pub struct FieldAccess<FieldType: Type = CanonicalType> {
     base: Expr<Bundle>,
@@ -2708,3 +2729,47 @@ impl<T: Type> ToExpr for Uninit<T> {
         }
     }
 }
+
+pub trait ExprIntoIterator: Type {
+    type Item: Type;
+    type ExprIntoIter: Iterator<Item = Expr<Self::Item>>;
+
+    fn expr_into_iter(e: Expr<Self>) -> Self::ExprIntoIter;
+}
+
+impl<T: ExprIntoIterator> IntoIterator for Expr<T> {
+    type Item = Expr<T::Item>;
+    type IntoIter = T::ExprIntoIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        T::expr_into_iter(self)
+    }
+}
+
+impl<T: ExprIntoIterator> IntoIterator for &'_ Expr<T> {
+    type Item = Expr<T::Item>;
+    type IntoIter = T::ExprIntoIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        T::expr_into_iter(*self)
+    }
+}
+
+impl<T: ExprIntoIterator> IntoIterator for &'_ mut Expr<T> {
+    type Item = Expr<T::Item>;
+    type IntoIter = T::ExprIntoIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        T::expr_into_iter(*self)
+    }
+}
+
+pub trait ExprFromIterator<A>: Type {
+    fn expr_from_iter<T: IntoIterator<Item = A>>(iter: T) -> Expr<Self>;
+}
+
+impl<This: ExprFromIterator<A>, A> FromIterator<A> for Expr<This> {
+    fn from_iter<T: IntoIterator<Item = A>>(iter: T) -> Self {
+        This::expr_from_iter(iter)
+    }
+}
diff --git a/crates/fayalite/src/firrtl.rs b/crates/fayalite/src/firrtl.rs
index ea76cf8..dd5fc2e 100644
--- a/crates/fayalite/src/firrtl.rs
+++ b/crates/fayalite/src/firrtl.rs
@@ -15,7 +15,7 @@ use crate::{
         target::{
             Target, TargetBase, TargetPathArrayElement, TargetPathBundleField, TargetPathElement,
         },
-        Expr, ExprEnum,
+        CastBitsTo, Expr, ExprEnum,
     },
     formal::FormalKind,
     int::{Bool, DynSize, IntType, SIntValue, UInt, UIntValue},
@@ -447,6 +447,7 @@ impl TypeState {
             CanonicalType::AsyncReset(AsyncReset {}) => "AsyncReset".into(),
             CanonicalType::SyncReset(SyncReset {}) => "UInt<1>".into(),
             CanonicalType::Reset(Reset {}) => "Reset".into(),
+            CanonicalType::PhantomConst(_) => "{}".into(),
         }
     }
 }
@@ -1152,6 +1153,7 @@ impl<'a> Exporter<'a> {
             | CanonicalType::Clock(_)
             | CanonicalType::AsyncReset(_)
             | CanonicalType::Reset(_) => format!("asUInt({value_str})"),
+            CanonicalType::PhantomConst(_) => "UInt<0>(0)".into(),
         }
     }
     fn expr_cast_bits_to_bundle(
@@ -1357,6 +1359,12 @@ impl<'a> Exporter<'a> {
             CanonicalType::AsyncReset(_) => format!("asAsyncReset({value_str})"),
             CanonicalType::SyncReset(_) => value_str,
             CanonicalType::Reset(_) => unreachable!("Reset is not bit castable to"),
+            CanonicalType::PhantomConst(_) => {
+                let retval = self.module.ns.make_new("_cast_bits_to_phantom_const_expr");
+                definitions.add_definition_line(format_args!("{extra_indent}wire {retval}: {{}}"));
+                definitions.add_definition_line(format_args!("{extra_indent}invalidate {retval}"));
+                return retval.to_string();
+            }
         }
     }
     fn expr_unary<T: Type>(
@@ -1395,6 +1403,11 @@ impl<'a> Exporter<'a> {
             ExprEnum::UIntLiteral(literal) => self.uint_literal(&literal),
             ExprEnum::SIntLiteral(literal) => self.sint_literal(&literal),
             ExprEnum::BoolLiteral(literal) => self.bool_literal(literal),
+            ExprEnum::PhantomConst(ty) => self.expr(
+                UInt[0].zero().cast_bits_to(ty.canonical()),
+                definitions,
+                const_ty,
+            ),
             ExprEnum::ArrayLiteral(array_literal) => {
                 self.array_literal_expr(array_literal, definitions, const_ty)
             }
diff --git a/crates/fayalite/src/lib.rs b/crates/fayalite/src/lib.rs
index 88fe169..512572d 100644
--- a/crates/fayalite/src/lib.rs
+++ b/crates/fayalite/src/lib.rs
@@ -96,6 +96,7 @@ pub mod int;
 pub mod intern;
 pub mod memory;
 pub mod module;
+pub mod phantom_const;
 pub mod prelude;
 pub mod reg;
 pub mod reset;
diff --git a/crates/fayalite/src/memory.rs b/crates/fayalite/src/memory.rs
index 2f0ec47..1101157 100644
--- a/crates/fayalite/src/memory.rs
+++ b/crates/fayalite/src/memory.rs
@@ -1082,6 +1082,7 @@ pub fn splat_mask<T: Type>(ty: T, value: Expr<Bool>) -> Expr<AsMask<T>> {
             )
             .to_expr(),
         )),
+        CanonicalType::PhantomConst(_) => Expr::from_canonical(Expr::canonical(().to_expr())),
     }
 }
 
diff --git a/crates/fayalite/src/module.rs b/crates/fayalite/src/module.rs
index 5a18ac9..446746a 100644
--- a/crates/fayalite/src/module.rs
+++ b/crates/fayalite/src/module.rs
@@ -1490,6 +1490,9 @@ impl TargetState {
                         })
                         .collect(),
                 },
+                CanonicalType::PhantomConst(_) => TargetStateInner::Decomposed {
+                    subtargets: HashMap::new(),
+                },
                 CanonicalType::Array(ty) => TargetStateInner::Decomposed {
                     subtargets: (0..ty.len())
                         .map(|index| {
diff --git a/crates/fayalite/src/module/transform/deduce_resets.rs b/crates/fayalite/src/module/transform/deduce_resets.rs
index fe518a5..a70dc33 100644
--- a/crates/fayalite/src/module/transform/deduce_resets.rs
+++ b/crates/fayalite/src/module/transform/deduce_resets.rs
@@ -155,6 +155,7 @@ impl ResetsLayout {
                     CanonicalType::SyncReset(_) => ResetsLayout::SyncReset,
                     CanonicalType::Reset(_) => ResetsLayout::Reset,
                     CanonicalType::Clock(_) => ResetsLayout::NoResets,
+                    CanonicalType::PhantomConst(_) => ResetsLayout::NoResets,
                 }
             }
         }
@@ -407,7 +408,8 @@ impl Resets {
             | CanonicalType::Bool(_)
             | CanonicalType::AsyncReset(_)
             | CanonicalType::SyncReset(_)
-            | CanonicalType::Clock(_) => Ok(self.ty),
+            | CanonicalType::Clock(_)
+            | CanonicalType::PhantomConst(_) => Ok(self.ty),
             CanonicalType::Array(ty) => Ok(CanonicalType::Array(Array::new_dyn(
                 self.array_elements().substituted_type(
                     reset_graph,
@@ -998,7 +1000,8 @@ fn cast_bit_op<P: Pass, T: Type, A: Type>(
                             CanonicalType::Array(_)
                             | CanonicalType::Enum(_)
                             | CanonicalType::Bundle(_)
-                            | CanonicalType::Reset(_) => unreachable!(),
+                            | CanonicalType::Reset(_)
+                            | CanonicalType::PhantomConst(_) => unreachable!(),
                             $(CanonicalType::$Variant(ty) => Expr::expr_enum($arg.cast_to(ty)),)*
                         }
                     };
@@ -1010,6 +1013,7 @@ fn cast_bit_op<P: Pass, T: Type, A: Type>(
                             | CanonicalType::Enum(_)
                             | CanonicalType::Bundle(_)
                             | CanonicalType::Reset(_) => unreachable!(),
+                            CanonicalType::PhantomConst(_) => Expr::expr_enum(arg),
                             $(CanonicalType::$Variant(_) => {
                                 let arg = Expr::<$Variant>::from_canonical(arg);
                                 match_expr_ty!(arg, UInt, SInt, Bool, AsyncReset, SyncReset, Clock)
@@ -1040,6 +1044,7 @@ impl<P: Pass> RunPass<P> for ExprEnum {
             ExprEnum::UIntLiteral(expr) => Ok(expr.run_pass(pass_args)?.map(ExprEnum::from)),
             ExprEnum::SIntLiteral(expr) => Ok(expr.run_pass(pass_args)?.map(ExprEnum::from)),
             ExprEnum::BoolLiteral(expr) => Ok(expr.run_pass(pass_args)?.map(ExprEnum::from)),
+            ExprEnum::PhantomConst(expr) => Ok(expr.run_pass(pass_args)?.map(ExprEnum::from)),
             ExprEnum::BundleLiteral(expr) => Ok(expr.run_pass(pass_args)?.map(ExprEnum::from)),
             ExprEnum::ArrayLiteral(expr) => Ok(expr.run_pass(pass_args)?.map(ExprEnum::from)),
             ExprEnum::EnumLiteral(expr) => Ok(expr.run_pass(pass_args)?.map(ExprEnum::from)),
@@ -1670,7 +1675,8 @@ impl RunPassDispatch for AnyReg {
                 | CanonicalType::Enum(_)
                 | CanonicalType::Bundle(_)
                 | CanonicalType::Reset(_)
-                | CanonicalType::Clock(_) => unreachable!(),
+                | CanonicalType::Clock(_)
+                | CanonicalType::PhantomConst(_) => unreachable!(),
             }
         })
     }
@@ -1769,6 +1775,7 @@ impl_run_pass_copy!([] SVAttributeAnnotation);
 impl_run_pass_copy!([] UInt);
 impl_run_pass_copy!([] usize);
 impl_run_pass_copy!([] FormalKind);
+impl_run_pass_copy!([] PhantomConst);
 
 macro_rules! impl_run_pass_for_struct {
     (
diff --git a/crates/fayalite/src/module/transform/simplify_enums.rs b/crates/fayalite/src/module/transform/simplify_enums.rs
index 4eb0d0c..e8b6168 100644
--- a/crates/fayalite/src/module/transform/simplify_enums.rs
+++ b/crates/fayalite/src/module/transform/simplify_enums.rs
@@ -69,7 +69,8 @@ fn contains_any_enum_types(ty: CanonicalType) -> bool {
                 | CanonicalType::AsyncReset(_)
                 | CanonicalType::SyncReset(_)
                 | CanonicalType::Reset(_)
-                | CanonicalType::Clock(_) => false,
+                | CanonicalType::Clock(_)
+                | CanonicalType::PhantomConst(_) => false,
             }
         }
     }
@@ -512,7 +513,8 @@ impl State {
             | CanonicalType::AsyncReset(_)
             | CanonicalType::SyncReset(_)
             | CanonicalType::Reset(_)
-            | CanonicalType::Clock(_) => unreachable!(),
+            | CanonicalType::Clock(_)
+            | CanonicalType::PhantomConst(_) => unreachable!(),
         }
     }
 }
@@ -577,7 +579,8 @@ fn connect_port(
         | (CanonicalType::Clock(_), _)
         | (CanonicalType::AsyncReset(_), _)
         | (CanonicalType::SyncReset(_), _)
-        | (CanonicalType::Reset(_), _) => unreachable!(
+        | (CanonicalType::Reset(_), _)
+        | (CanonicalType::PhantomConst(_), _) => unreachable!(
             "trying to connect memory ports:\n{:?}\n{:?}",
             Expr::ty(lhs),
             Expr::ty(rhs),
@@ -665,6 +668,7 @@ impl Folder for State {
             ExprEnum::UIntLiteral(_)
             | ExprEnum::SIntLiteral(_)
             | ExprEnum::BoolLiteral(_)
+            | ExprEnum::PhantomConst(_)
             | ExprEnum::BundleLiteral(_)
             | ExprEnum::ArrayLiteral(_)
             | ExprEnum::Uninit(_)
@@ -923,7 +927,8 @@ impl Folder for State {
             | CanonicalType::Clock(_)
             | CanonicalType::AsyncReset(_)
             | CanonicalType::SyncReset(_)
-            | CanonicalType::Reset(_) => canonical_type.default_fold(self),
+            | CanonicalType::Reset(_)
+            | CanonicalType::PhantomConst(_) => canonical_type.default_fold(self),
         }
     }
 
diff --git a/crates/fayalite/src/module/transform/simplify_memories.rs b/crates/fayalite/src/module/transform/simplify_memories.rs
index e8f9cbf..101385e 100644
--- a/crates/fayalite/src/module/transform/simplify_memories.rs
+++ b/crates/fayalite/src/module/transform/simplify_memories.rs
@@ -62,6 +62,7 @@ enum MemSplit {
     Bundle {
         fields: Rc<[MemSplit]>,
     },
+    PhantomConst,
     Single {
         output_mem: Option<Mem>,
         element_type: SingleType,
@@ -76,6 +77,7 @@ impl MemSplit {
     fn mark_changed_element_type(self) -> Self {
         match self {
             MemSplit::Bundle { fields: _ } => self,
+            MemSplit::PhantomConst => self,
             MemSplit::Single {
                 output_mem,
                 element_type,
@@ -97,6 +99,7 @@ impl MemSplit {
                     .map(|field| Self::new(field.ty).mark_changed_element_type())
                     .collect(),
             },
+            CanonicalType::PhantomConst(_) => MemSplit::PhantomConst,
             CanonicalType::Array(ty) => {
                 let element = MemSplit::new(ty.element());
                 if let Self::Single {
@@ -339,6 +342,7 @@ impl SplitMemState<'_, '_> {
                     self.split_state_stack.pop();
                 }
             }
+            MemSplit::PhantomConst => {}
             MemSplit::Single {
                 output_mem,
                 element_type: single_type,
@@ -538,7 +542,12 @@ impl ModuleState {
             };
         loop {
             match input_element_type {
-                CanonicalType::Bundle(_) => unreachable!("bundle types are always split"),
+                CanonicalType::Bundle(_) => {
+                    unreachable!("bundle types are always split")
+                }
+                CanonicalType::PhantomConst(_) => {
+                    unreachable!("PhantomConst are always removed")
+                }
                 CanonicalType::Enum(_)
                     if input_array_types
                         .first()
@@ -743,7 +752,8 @@ impl ModuleState {
                 ..
             }
             | MemSplit::Bundle { .. }
-            | MemSplit::Array { .. } => {
+            | MemSplit::Array { .. }
+            | MemSplit::PhantomConst => {
                 let mut replacement_ports = Vec::with_capacity(input_mem.ports().len());
                 let mut wire_port_rdata = Vec::with_capacity(input_mem.ports().len());
                 let mut wire_port_wdata = Vec::with_capacity(input_mem.ports().len());
diff --git a/crates/fayalite/src/module/transform/visit.rs b/crates/fayalite/src/module/transform/visit.rs
index 97de4fc..662a578 100644
--- a/crates/fayalite/src/module/transform/visit.rs
+++ b/crates/fayalite/src/module/transform/visit.rs
@@ -28,6 +28,7 @@ use crate::{
         NormalModuleBody, ScopedNameId, Stmt, StmtConnect, StmtDeclaration, StmtFormal, StmtIf,
         StmtInstance, StmtMatch, StmtReg, StmtWire,
     },
+    phantom_const::PhantomConst,
     reg::Reg,
     reset::{AsyncReset, Reset, ResetType, SyncReset},
     source_location::SourceLocation,
diff --git a/crates/fayalite/src/phantom_const.rs b/crates/fayalite/src/phantom_const.rs
new file mode 100644
index 0000000..dd6cff6
--- /dev/null
+++ b/crates/fayalite/src/phantom_const.rs
@@ -0,0 +1,313 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// See Notices.txt for copyright information
+
+use serde::{de::DeserializeOwned, Deserialize, Serialize};
+
+use crate::{
+    expr::{
+        ops::{ExprPartialEq, ExprPartialOrd},
+        Expr, ToExpr,
+    },
+    int::Bool,
+    intern::{Intern, Interned, InternedCompare, LazyInterned, Memoize},
+    source_location::SourceLocation,
+    ty::{impl_match_variant_as_self, CanonicalType, StaticType, Type, TypeProperties},
+};
+use std::{
+    any::Any,
+    fmt,
+    hash::{Hash, Hasher},
+    marker::PhantomData,
+};
+
+#[derive(Clone)]
+pub struct PhantomConstCanonicalValue {
+    parsed: serde_json::Value,
+    serialized: Interned<str>,
+}
+
+impl PhantomConstCanonicalValue {
+    pub fn from_json_value(parsed: serde_json::Value) -> Self {
+        let serialized = Intern::intern_owned(
+            serde_json::to_string(&parsed)
+                .expect("conversion from json value to text shouldn't fail"),
+        );
+        Self { parsed, serialized }
+    }
+    pub fn as_json_value(&self) -> &serde_json::Value {
+        &self.parsed
+    }
+    pub fn as_str(&self) -> Interned<str> {
+        self.serialized
+    }
+}
+
+impl fmt::Debug for PhantomConstCanonicalValue {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.serialized)
+    }
+}
+
+impl fmt::Display for PhantomConstCanonicalValue {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.serialized)
+    }
+}
+
+impl PartialEq for PhantomConstCanonicalValue {
+    fn eq(&self, other: &Self) -> bool {
+        self.serialized == other.serialized
+    }
+}
+
+impl Eq for PhantomConstCanonicalValue {}
+
+impl Hash for PhantomConstCanonicalValue {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.serialized.hash(state);
+    }
+}
+
+impl Serialize for PhantomConstCanonicalValue {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        self.parsed.serialize(serializer)
+    }
+}
+
+impl<'de> Deserialize<'de> for PhantomConstCanonicalValue {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        Ok(Self::from_json_value(serde_json::Value::deserialize(
+            deserializer,
+        )?))
+    }
+}
+
+pub trait PhantomConstValue: Intern + InternedCompare + Serialize + fmt::Debug {
+    fn deserialize_value<'de, D>(deserializer: D) -> Result<Interned<Self>, D::Error>
+    where
+        D: serde::Deserializer<'de>;
+}
+
+impl<T> PhantomConstValue for T
+where
+    T: ?Sized + Intern + InternedCompare + Serialize + fmt::Debug,
+    Interned<T>: DeserializeOwned,
+{
+    fn deserialize_value<'de, D>(deserializer: D) -> Result<Interned<Self>, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        <Interned<T> as Deserialize<'de>>::deserialize(deserializer)
+    }
+}
+
+/// Wrapper type that allows any Rust value to be smuggled as a HDL [`Type`].
+/// This only works for values that can be [serialized][Serialize] to and [deserialized][Deserialize] from [JSON][serde_json].
+pub struct PhantomConst<T: ?Sized + PhantomConstValue = PhantomConstCanonicalValue> {
+    value: LazyInterned<T>,
+}
+
+impl<T: ?Sized + PhantomConstValue> fmt::Debug for PhantomConst<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("PhantomConst").field(&self.get()).finish()
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> Clone for PhantomConst<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> Copy for PhantomConst<T> {}
+
+impl<T: ?Sized + PhantomConstValue> PartialEq for PhantomConst<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.get() == other.get()
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> Eq for PhantomConst<T> {}
+
+impl<T: ?Sized + PhantomConstValue> Hash for PhantomConst<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.get().hash(state);
+    }
+}
+
+struct PhantomConstCanonicalMemoize<T: ?Sized, const IS_FROM_CANONICAL: bool>(PhantomData<T>);
+
+impl<T: ?Sized, const IS_FROM_CANONICAL: bool> Copy
+    for PhantomConstCanonicalMemoize<T, IS_FROM_CANONICAL>
+{
+}
+
+impl<T: ?Sized, const IS_FROM_CANONICAL: bool> Clone
+    for PhantomConstCanonicalMemoize<T, IS_FROM_CANONICAL>
+{
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T: ?Sized, const IS_FROM_CANONICAL: bool> Eq
+    for PhantomConstCanonicalMemoize<T, IS_FROM_CANONICAL>
+{
+}
+
+impl<T: ?Sized, const IS_FROM_CANONICAL: bool> PartialEq
+    for PhantomConstCanonicalMemoize<T, IS_FROM_CANONICAL>
+{
+    fn eq(&self, _other: &Self) -> bool {
+        true
+    }
+}
+
+impl<T: ?Sized, const IS_FROM_CANONICAL: bool> Hash
+    for PhantomConstCanonicalMemoize<T, IS_FROM_CANONICAL>
+{
+    fn hash<H: Hasher>(&self, _state: &mut H) {}
+}
+
+impl<T: ?Sized + PhantomConstValue> Memoize for PhantomConstCanonicalMemoize<T, false> {
+    type Input = Interned<T>;
+    type InputOwned = Interned<T>;
+    type Output = Interned<PhantomConstCanonicalValue>;
+
+    fn inner(self, input: &Self::Input) -> Self::Output {
+        Intern::intern_sized(PhantomConstCanonicalValue::from_json_value(
+            serde_json::to_value(input)
+                .expect("serialization failed when constructing a canonical PhantomConst"),
+        ))
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> Memoize for PhantomConstCanonicalMemoize<T, true> {
+    type Input = Interned<PhantomConstCanonicalValue>;
+    type InputOwned = Interned<PhantomConstCanonicalValue>;
+    type Output = Interned<T>;
+
+    fn inner(self, input: &Self::Input) -> Self::Output {
+        PhantomConstValue::deserialize_value(input.as_json_value())
+            .expect("deserialization failed ")
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> PhantomConst<T>
+where
+    Interned<T>: Default,
+{
+    pub const fn default() -> Self {
+        PhantomConst {
+            value: LazyInterned::new_lazy(&Interned::<T>::default),
+        }
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> PhantomConst<T> {
+    pub fn new(value: Interned<T>) -> Self {
+        Self {
+            value: LazyInterned::Interned(value),
+        }
+    }
+    pub fn get(self) -> Interned<T> {
+        self.value.interned()
+    }
+    pub fn type_properties(self) -> TypeProperties {
+        <()>::TYPE_PROPERTIES
+    }
+    pub fn can_connect(self, other: Self) -> bool {
+        self == other
+    }
+    pub fn canonical_phantom_const(self) -> PhantomConst {
+        if let Some(&retval) = <dyn Any>::downcast_ref::<PhantomConst>(&self) {
+            return retval;
+        }
+        <PhantomConst>::new(
+            PhantomConstCanonicalMemoize::<T, false>(PhantomData).get_owned(self.get()),
+        )
+    }
+    pub fn from_canonical_phantom_const(canonical_type: PhantomConst) -> Self {
+        if let Some(&retval) = <dyn Any>::downcast_ref::<Self>(&canonical_type) {
+            return retval;
+        }
+        Self::new(
+            PhantomConstCanonicalMemoize::<T, true>(PhantomData).get_owned(canonical_type.get()),
+        )
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> Type for PhantomConst<T> {
+    type BaseType = PhantomConst;
+    type MaskType = ();
+    impl_match_variant_as_self!();
+
+    fn mask_type(&self) -> Self::MaskType {
+        ()
+    }
+
+    fn canonical(&self) -> CanonicalType {
+        CanonicalType::PhantomConst(self.canonical_phantom_const())
+    }
+
+    fn from_canonical(canonical_type: CanonicalType) -> Self {
+        let CanonicalType::PhantomConst(phantom_const) = canonical_type else {
+            panic!("expected PhantomConst");
+        };
+        Self::from_canonical_phantom_const(phantom_const)
+    }
+
+    fn source_location() -> SourceLocation {
+        SourceLocation::builtin()
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> StaticType for PhantomConst<T>
+where
+    Interned<T>: Default,
+{
+    const TYPE: Self = Self::default();
+    const MASK_TYPE: Self::MaskType = ();
+    const TYPE_PROPERTIES: TypeProperties = <()>::TYPE_PROPERTIES;
+    const MASK_TYPE_PROPERTIES: TypeProperties = <()>::TYPE_PROPERTIES;
+}
+
+impl<T: ?Sized + PhantomConstValue> ExprPartialEq<Self> for PhantomConst<T> {
+    fn cmp_eq(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
+        true.to_expr()
+    }
+
+    fn cmp_ne(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
+        false.to_expr()
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> ExprPartialOrd<Self> for PhantomConst<T> {
+    fn cmp_lt(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
+        false.to_expr()
+    }
+
+    fn cmp_le(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
+        true.to_expr()
+    }
+
+    fn cmp_gt(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
+        false.to_expr()
+    }
+
+    fn cmp_ge(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
+        true.to_expr()
+    }
+}
diff --git a/crates/fayalite/src/prelude.rs b/crates/fayalite/src/prelude.rs
index 9e7a85e..39fa143 100644
--- a/crates/fayalite/src/prelude.rs
+++ b/crates/fayalite/src/prelude.rs
@@ -26,6 +26,7 @@ pub use crate::{
         annotate, connect, connect_any, incomplete_wire, instance, memory, memory_array,
         memory_with_init, reg_builder, wire, Instance, Module, ModuleBuilder,
     },
+    phantom_const::PhantomConst,
     reg::Reg,
     reset::{AsyncReset, Reset, SyncReset, ToAsyncReset, ToReset, ToSyncReset},
     source_location::SourceLocation,
diff --git a/crates/fayalite/src/sim.rs b/crates/fayalite/src/sim.rs
index f630f5a..96f6dd9 100644
--- a/crates/fayalite/src/sim.rs
+++ b/crates/fayalite/src/sim.rs
@@ -167,6 +167,14 @@ impl<T: Type> CompiledTypeLayout<T> {
                             body: CompiledTypeLayoutBody::Array { element },
                         }
                     }
+                    CanonicalType::PhantomConst(_) => {
+                        let unit_layout = CompiledTypeLayout::get(());
+                        CompiledTypeLayout {
+                            ty: *input,
+                            layout: unit_layout.layout,
+                            body: unit_layout.body,
+                        }
+                    }
                     CanonicalType::Bundle(bundle) => {
                         let mut layout = TypeLayout::empty();
                         let fields = bundle
@@ -1792,7 +1800,7 @@ impl Compiler {
                 }
                 .into()
             }
-            CanonicalType::Bundle(_) => unreachable!(),
+            CanonicalType::Bundle(_) | CanonicalType::PhantomConst(_) => unreachable!(),
             CanonicalType::AsyncReset(_) => TraceAsyncReset {
                 location: self.make_trace_scalar_helper(
                     instantiated_module,
@@ -2009,6 +2017,13 @@ impl Compiler {
             | CanonicalType::Clock(_) => {
                 self.make_trace_scalar(instantiated_module, target, name, source_location)
             }
+            CanonicalType::PhantomConst(_) => TraceBundle {
+                name,
+                fields: Interned::default(),
+                ty: Bundle::new(Interned::default()),
+                flow: target.flow(),
+            }
+            .into(),
         }
     }
     fn make_trace_decl(
@@ -2469,6 +2484,9 @@ impl Compiler {
                     Expr::field(Expr::<Bundle>::from_canonical(expr.arg()), &field.name)
                 }),
             ),
+            CanonicalType::PhantomConst(_) => {
+                self.compile_cast_aggregate_to_bits(instantiated_module, [])
+            }
         }
     }
     fn compile_cast_bits_to(
@@ -2518,6 +2536,10 @@ impl Compiler {
             CanonicalType::SyncReset(ty) => Expr::canonical(expr.arg().cast_to(ty)),
             CanonicalType::Reset(_) => unreachable!(),
             CanonicalType::Clock(ty) => Expr::canonical(expr.arg().cast_to(ty)),
+            CanonicalType::PhantomConst(ty) => {
+                let _ = self.compile_expr(instantiated_module, Expr::canonical(expr.arg()));
+                Expr::canonical(ty.to_expr())
+            }
         };
         let retval = self.compile_expr(instantiated_module, Expr::canonical(retval));
         self.compiled_expr_to_value(retval, instantiated_module.leaf_module().source_location())
@@ -2567,6 +2589,7 @@ impl Compiler {
                 CanonicalType::SyncReset(_) => false,
                 CanonicalType::Reset(_) => false,
                 CanonicalType::Clock(_) => false,
+                CanonicalType::PhantomConst(_) => unreachable!(),
             };
             let dest_signed = match Expr::ty(expr) {
                 CanonicalType::UInt(_) => false,
@@ -2579,6 +2602,7 @@ impl Compiler {
                 CanonicalType::SyncReset(_) => false,
                 CanonicalType::Reset(_) => false,
                 CanonicalType::Clock(_) => false,
+                CanonicalType::PhantomConst(_) => unreachable!(),
             };
             self.simple_nary_big_expr(instantiated_module, Expr::ty(expr), [arg], |dest, [src]| {
                 match (src_signed, dest_signed) {
@@ -2634,6 +2658,9 @@ impl Compiler {
                     }]
                 })
                 .into(),
+            ExprEnum::PhantomConst(_) => self
+                .compile_aggregate_literal(instantiated_module, Expr::ty(expr), Interned::default())
+                .into(),
             ExprEnum::BundleLiteral(literal) => self
                 .compile_aggregate_literal(
                     instantiated_module,
@@ -3537,6 +3564,7 @@ impl Compiler {
                 CanonicalType::SyncReset(_) => unreachable!(),
                 CanonicalType::Reset(_) => unreachable!(),
                 CanonicalType::Clock(_) => unreachable!(),
+                CanonicalType::PhantomConst(_) => unreachable!("PhantomConst mismatch"),
             }
         }
         let Some(target) = lhs.target() else {
@@ -3901,6 +3929,7 @@ impl Compiler {
                     CanonicalType::SyncReset(_) => false,
                     CanonicalType::Reset(_) => false,
                     CanonicalType::Clock(_) => false,
+                    CanonicalType::PhantomConst(_) => unreachable!(),
                 };
                 let width = data_layout.ty.bit_width();
                 if let Some(MemoryPortReadInsns {
@@ -5909,6 +5938,7 @@ impl SimValue<CanonicalType> {
             CanonicalType::Clock(ty) => {
                 Expr::canonical(Bool::bits_to_expr(Cow::Borrowed(bits)).cast_to(ty))
             }
+            CanonicalType::PhantomConst(ty) => Expr::canonical(ty.to_expr()),
         }
     }
 }
@@ -6312,7 +6342,8 @@ impl ToSimValue<CanonicalType> for bool {
             | CanonicalType::SInt(_)
             | CanonicalType::Array(_)
             | CanonicalType::Enum(_)
-            | CanonicalType::Bundle(_) => {
+            | CanonicalType::Bundle(_)
+            | CanonicalType::PhantomConst(_) => {
                 panic!("can't create SimValue from bool: expected value of type: {ty:?}");
             }
             CanonicalType::Bool(_)
@@ -6977,6 +7008,7 @@ impl SimulationImpl {
                     CanonicalType::SyncReset(_) => false,
                     CanonicalType::Reset(_) => false,
                     CanonicalType::Clock(_) => false,
+                    CanonicalType::PhantomConst(_) => unreachable!(),
                 };
                 match compiled_value.range.len() {
                     TypeLen::A_SMALL_SLOT => read_write_small_scalar(
diff --git a/crates/fayalite/src/ty.rs b/crates/fayalite/src/ty.rs
index 69080c9..2786782 100644
--- a/crates/fayalite/src/ty.rs
+++ b/crates/fayalite/src/ty.rs
@@ -9,8 +9,10 @@ use crate::{
     expr::Expr,
     int::{Bool, SInt, UInt},
     intern::{Intern, Interned},
+    phantom_const::PhantomConst,
     reset::{AsyncReset, Reset, SyncReset},
     source_location::SourceLocation,
+    util::ConstUsize,
 };
 use std::{fmt, hash::Hash, iter::FusedIterator, ops::Index};
 
@@ -35,6 +37,7 @@ pub enum CanonicalType {
     SyncReset(SyncReset),
     Reset(Reset),
     Clock(Clock),
+    PhantomConst(PhantomConst),
 }
 
 impl fmt::Debug for CanonicalType {
@@ -50,6 +53,7 @@ impl fmt::Debug for CanonicalType {
             Self::SyncReset(v) => v.fmt(f),
             Self::Reset(v) => v.fmt(f),
             Self::Clock(v) => v.fmt(f),
+            Self::PhantomConst(v) => v.fmt(f),
         }
     }
 }
@@ -67,6 +71,7 @@ impl CanonicalType {
             CanonicalType::SyncReset(v) => v.type_properties(),
             CanonicalType::Reset(v) => v.type_properties(),
             CanonicalType::Clock(v) => v.type_properties(),
+            CanonicalType::PhantomConst(v) => v.type_properties(),
         }
     }
     pub fn is_passive(self) -> bool {
@@ -143,6 +148,12 @@ impl CanonicalType {
                 };
                 lhs.can_connect(rhs)
             }
+            CanonicalType::PhantomConst(lhs) => {
+                let CanonicalType::PhantomConst(rhs) = rhs else {
+                    return false;
+                };
+                lhs.can_connect(rhs)
+            }
         }
     }
 }
@@ -166,7 +177,7 @@ impl<T: 'static + Send + Sync> MatchVariantAndInactiveScope for MatchVariantWith
 }
 
 pub trait FillInDefaultedGenerics {
-    type Type: Type;
+    type Type;
     fn fill_in_defaulted_generics(self) -> Self::Type;
 }
 
@@ -178,6 +189,22 @@ impl<T: Type> FillInDefaultedGenerics for T {
     }
 }
 
+impl FillInDefaultedGenerics for usize {
+    type Type = usize;
+
+    fn fill_in_defaulted_generics(self) -> Self::Type {
+        self
+    }
+}
+
+impl<const V: usize> FillInDefaultedGenerics for ConstUsize<V> {
+    type Type = ConstUsize<V>;
+
+    fn fill_in_defaulted_generics(self) -> Self::Type {
+        self
+    }
+}
+
 mod sealed {
     pub trait TypeOrDefaultSealed {}
     pub trait BaseTypeSealed {}
@@ -205,6 +232,7 @@ impl_base_type!(AsyncReset);
 impl_base_type!(SyncReset);
 impl_base_type!(Reset);
 impl_base_type!(Clock);
+impl_base_type!(PhantomConst);
 
 impl sealed::BaseTypeSealed for CanonicalType {}
 
@@ -299,6 +327,7 @@ impl Type for CanonicalType {
             CanonicalType::SyncReset(v) => v.mask_type().canonical(),
             CanonicalType::Reset(v) => v.mask_type().canonical(),
             CanonicalType::Clock(v) => v.mask_type().canonical(),
+            CanonicalType::PhantomConst(v) => v.mask_type().canonical(),
         }
     }
     fn canonical(&self) -> CanonicalType {
diff --git a/crates/fayalite/src/util.rs b/crates/fayalite/src/util.rs
index fadc7af..66fc921 100644
--- a/crates/fayalite/src/util.rs
+++ b/crates/fayalite/src/util.rs
@@ -29,4 +29,5 @@ pub use misc::{
 };
 
 pub mod job_server;
+pub mod prefix_sum;
 pub mod ready_valid;
diff --git a/crates/fayalite/src/util/prefix_sum.rs b/crates/fayalite/src/util/prefix_sum.rs
new file mode 100644
index 0000000..758d89c
--- /dev/null
+++ b/crates/fayalite/src/util/prefix_sum.rs
@@ -0,0 +1,839 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// See Notices.txt for copyright information
+
+// code derived from:
+// https://web.archive.org/web/20250303054010/https://git.libre-soc.org/?p=nmutil.git;a=blob;f=src/nmutil/prefix_sum.py;hb=effeb28e5848392adddcdad1f6e7a098f2a44c9c
+
+use crate::intern::{Intern, Interned, Memoize};
+use std::{borrow::Cow, num::NonZeroUsize};
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub struct PrefixSumOp {
+    pub lhs_index: usize,
+    pub rhs_and_dest_index: NonZeroUsize,
+    pub row: u32,
+}
+
+#[derive(Clone, PartialEq, Eq, Hash, Debug)]
+#[non_exhaustive]
+pub struct DiagramConfig {
+    pub space: Cow<'static, str>,
+    pub vertical_bar: Cow<'static, str>,
+    pub plus: Cow<'static, str>,
+    pub slant: Cow<'static, str>,
+    pub connect: Cow<'static, str>,
+    pub no_connect: Cow<'static, str>,
+    pub padding: usize,
+}
+
+impl DiagramConfig {
+    pub const fn new() -> Self {
+        Self {
+            space: Cow::Borrowed(" "),
+            vertical_bar: Cow::Borrowed("|"),
+            plus: Cow::Borrowed("\u{2295}"), // ⊕
+            slant: Cow::Borrowed(r"\"),
+            connect: Cow::Borrowed("\u{25CF}"), // ●
+            no_connect: Cow::Borrowed("X"),
+            padding: 1,
+        }
+    }
+    pub fn draw(self, ops: impl IntoIterator<Item = PrefixSumOp>, item_count: usize) -> String {
+        #[derive(Copy, Clone, Debug)]
+        struct DiagramCell {
+            slant: bool,
+            plus: bool,
+            tee: bool,
+        }
+        let mut ops_by_row: Vec<Vec<PrefixSumOp>> = Vec::new();
+        let mut last_row = 0;
+        ops.into_iter().for_each(|op| {
+            assert!(
+                op.lhs_index < op.rhs_and_dest_index.get(),
+                "invalid PrefixSumOp! lhs_index must be less \
+                than rhs_and_dest_index: {op:?}",
+            );
+            assert!(
+                op.row >= last_row,
+                "invalid PrefixSumOp! row must \
+                not decrease (row last was: {last_row}): {op:?}",
+            );
+            let ops = if op.row > last_row || ops_by_row.is_empty() {
+                ops_by_row.push(vec![]);
+                ops_by_row.last_mut().expect("just pushed")
+            } else {
+                ops_by_row
+                    .last_mut()
+                    .expect("just checked if ops_by_row is empty")
+            };
+            if let Some(last) = ops.last() {
+                assert!(
+                    op.rhs_and_dest_index < last.rhs_and_dest_index,
+                    "invalid PrefixSumOp! rhs_and_dest_index must strictly \
+                    decrease in a row:\nthis op: {op:?}\nlast op: {last:?}",
+                );
+            }
+            ops.push(op);
+            last_row = op.row;
+        });
+        let blank_row = || {
+            vec![
+                DiagramCell {
+                    slant: false,
+                    plus: false,
+                    tee: false
+                };
+                item_count
+            ]
+        };
+        let mut cells = vec![blank_row()];
+        for ops in ops_by_row {
+            let max_distance = ops
+                .iter()
+                .map(
+                    |&PrefixSumOp {
+                         lhs_index,
+                         rhs_and_dest_index,
+                         ..
+                     }| { rhs_and_dest_index.get() - lhs_index },
+                )
+                .max()
+                .expect("ops is known to be non-empty");
+            cells.extend((0..max_distance).map(|_| blank_row()));
+            for op in ops {
+                let mut y = cells.len() - 1;
+                assert!(
+                    op.rhs_and_dest_index.get() < item_count,
+                    "invalid PrefixSumOp! rhs_and_dest_index must be \
+                    less than item_count ({item_count}): {op:?}",
+                );
+                let mut x = op.rhs_and_dest_index.get();
+                cells[y][x].plus = true;
+                x -= 1;
+                y -= 1;
+                while op.lhs_index < x {
+                    cells[y][x].slant = true;
+                    x -= 1;
+                    y -= 1;
+                }
+                cells[y][x].tee = true;
+            }
+        }
+        let mut retval = String::new();
+        let mut row_text = vec![String::new(); 2 * self.padding + 1];
+        for cells_row in cells {
+            for cell in cells_row {
+                // top padding
+                for y in 0..self.padding {
+                    // top left padding
+                    for x in 0..self.padding {
+                        row_text[y] += if x == y && (cell.plus || cell.slant) {
+                            &self.slant
+                        } else {
+                            &self.space
+                        };
+                    }
+                    // top vertical bar
+                    row_text[y] += &self.vertical_bar;
+                    // top right padding
+                    for _ in 0..self.padding {
+                        row_text[y] += &self.space;
+                    }
+                }
+                // center left padding
+                for _ in 0..self.padding {
+                    row_text[self.padding] += &self.space;
+                }
+                // center
+                row_text[self.padding] += if cell.plus {
+                    &self.plus
+                } else if cell.tee {
+                    &self.connect
+                } else if cell.slant {
+                    &self.no_connect
+                } else {
+                    &self.vertical_bar
+                };
+                // center right padding
+                for _ in 0..self.padding {
+                    row_text[self.padding] += &self.space;
+                }
+                let bottom_padding_start = self.padding + 1;
+                let bottom_padding_last = self.padding * 2;
+                // bottom padding
+                for y in bottom_padding_start..=bottom_padding_last {
+                    // bottom left padding
+                    for _ in 0..self.padding {
+                        row_text[y] += &self.space;
+                    }
+                    // bottom vertical bar
+                    row_text[y] += &self.vertical_bar;
+                    // bottom right padding
+                    for x in bottom_padding_start..=bottom_padding_last {
+                        row_text[y] += if x == y && (cell.tee || cell.slant) {
+                            &self.slant
+                        } else {
+                            &self.space
+                        };
+                    }
+                }
+            }
+            for line in &mut row_text {
+                retval += line.trim_end();
+                retval += "\n";
+                line.clear();
+            }
+        }
+        retval
+    }
+}
+
+impl Default for DiagramConfig {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl PrefixSumOp {
+    pub fn diagram(ops: impl IntoIterator<Item = Self>, item_count: usize) -> String {
+        Self::diagram_with_config(ops, item_count, DiagramConfig::new())
+    }
+    pub fn diagram_with_config(
+        ops: impl IntoIterator<Item = Self>,
+        item_count: usize,
+        config: DiagramConfig,
+    ) -> String {
+        config.draw(ops, item_count)
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+pub enum PrefixSumAlgorithm {
+    /// Uses the algorithm from:
+    /// https://en.wikipedia.org/wiki/Prefix_sum#Algorithm_1:_Shorter_span,_more_parallel
+    LowLatency,
+    /// Uses the algorithm from:
+    /// https://en.wikipedia.org/wiki/Prefix_sum#Algorithm_2:_Work-efficient
+    WorkEfficient,
+}
+
+impl PrefixSumAlgorithm {
+    fn ops_impl(self, item_count: usize) -> Vec<PrefixSumOp> {
+        let mut retval = Vec::new();
+        let mut distance = 1;
+        let mut row = 0;
+        while distance < item_count {
+            let double_distance = distance
+                .checked_mul(2)
+                .expect("prefix-sum item_count is too big");
+            let (start, step) = match self {
+                Self::LowLatency => (distance, 1),
+                Self::WorkEfficient => (double_distance - 1, double_distance),
+            };
+            for rhs_and_dest_index in (start..item_count).step_by(step).rev() {
+                let Some(rhs_and_dest_index) = NonZeroUsize::new(rhs_and_dest_index) else {
+                    unreachable!();
+                };
+                let lhs_index = rhs_and_dest_index.get() - distance;
+                retval.push(PrefixSumOp {
+                    lhs_index,
+                    rhs_and_dest_index,
+                    row,
+                });
+            }
+            distance = double_distance;
+            row += 1;
+        }
+        match self {
+            Self::LowLatency => {}
+            Self::WorkEfficient => {
+                distance /= 2;
+                while distance >= 1 {
+                    let start = distance
+                        .checked_mul(3)
+                        .expect("prefix-sum item_count is too big")
+                        - 1;
+                    for rhs_and_dest_index in (start..item_count).step_by(distance * 2).rev() {
+                        let Some(rhs_and_dest_index) = NonZeroUsize::new(rhs_and_dest_index) else {
+                            unreachable!();
+                        };
+                        let lhs_index = rhs_and_dest_index.get() - distance;
+                        retval.push(PrefixSumOp {
+                            lhs_index,
+                            rhs_and_dest_index,
+                            row,
+                        });
+                    }
+                    row += 1;
+                    distance /= 2;
+                }
+            }
+        }
+        retval
+    }
+    pub fn ops(self, item_count: usize) -> Interned<[PrefixSumOp]> {
+        #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+        struct MyMemoize(PrefixSumAlgorithm);
+        impl Memoize for MyMemoize {
+            type Input = usize;
+            type InputOwned = usize;
+            type Output = Interned<[PrefixSumOp]>;
+
+            fn inner(self, item_count: &Self::Input) -> Self::Output {
+                Intern::intern_owned(self.0.ops_impl(*item_count))
+            }
+        }
+        MyMemoize(self).get_owned(item_count)
+    }
+    pub fn run<T>(self, items: impl IntoIterator<Item = T>, f: impl FnMut(&T, &T) -> T) -> Vec<T> {
+        let mut items = Vec::from_iter(items);
+        self.run_on_slice(&mut items, f);
+        items
+    }
+    pub fn run_on_slice<T>(self, items: &mut [T], mut f: impl FnMut(&T, &T) -> T) -> &mut [T] {
+        self.ops(items.len()).into_iter().for_each(
+            |PrefixSumOp {
+                 lhs_index,
+                 rhs_and_dest_index,
+                 row: _,
+             }| {
+                items[rhs_and_dest_index.get()] =
+                    f(&items[lhs_index], &items[rhs_and_dest_index.get()]);
+            },
+        );
+        items
+    }
+    pub fn filtered_ops(
+        self,
+        item_live_out_flags: impl IntoIterator<Item = bool>,
+    ) -> Vec<PrefixSumOp> {
+        let mut item_live_out_flags = Vec::from_iter(item_live_out_flags);
+        let prefix_sum_ops = self.ops(item_live_out_flags.len());
+        let mut ops_live_flags = vec![false; prefix_sum_ops.len()];
+        for (
+            op_index,
+            &PrefixSumOp {
+                lhs_index,
+                rhs_and_dest_index,
+                row: _,
+            },
+        ) in prefix_sum_ops.iter().enumerate().rev()
+        {
+            let live = item_live_out_flags[rhs_and_dest_index.get()];
+            item_live_out_flags[lhs_index] |= live;
+            ops_live_flags[op_index] = live;
+        }
+        prefix_sum_ops
+            .into_iter()
+            .zip(ops_live_flags)
+            .filter_map(|(op, live)| live.then_some(op))
+            .collect()
+    }
+    pub fn reduce_ops(self, item_count: usize) -> Interned<[PrefixSumOp]> {
+        #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+        struct MyMemoize(PrefixSumAlgorithm);
+        impl Memoize for MyMemoize {
+            type Input = usize;
+            type InputOwned = usize;
+            type Output = Interned<[PrefixSumOp]>;
+
+            fn inner(self, item_count: &Self::Input) -> Self::Output {
+                let mut item_live_out_flags = vec![false; *item_count];
+                let Some(last_item_live_out_flag) = item_live_out_flags.last_mut() else {
+                    return Interned::default();
+                };
+                *last_item_live_out_flag = true;
+                Intern::intern_owned(self.0.filtered_ops(item_live_out_flags))
+            }
+        }
+        MyMemoize(self).get_owned(item_count)
+    }
+}
+
+pub fn reduce_ops(item_count: usize) -> Interned<[PrefixSumOp]> {
+    PrefixSumAlgorithm::LowLatency.reduce_ops(item_count)
+}
+
+pub fn reduce<T>(items: impl IntoIterator<Item = T>, mut f: impl FnMut(T, T) -> T) -> Option<T> {
+    let mut items: Vec<_> = items.into_iter().map(Some).collect();
+    for op in reduce_ops(items.len()) {
+        let (Some(lhs), Some(rhs)) = (
+            items[op.lhs_index].take(),
+            items[op.rhs_and_dest_index.get()].take(),
+        ) else {
+            unreachable!();
+        };
+        items[op.rhs_and_dest_index.get()] = Some(f(lhs, rhs));
+    }
+    items.last_mut().and_then(Option::take)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn input_strings() -> [String; 9] {
+        std::array::from_fn(|i| String::from_utf8(vec![b'a' + i as u8]).unwrap())
+    }
+
+    #[test]
+    fn test_prefix_sum_strings() {
+        let input = input_strings();
+        let expected: Vec<String> = input
+            .iter()
+            .scan(String::new(), |l, r| {
+                *l += r;
+                Some(l.clone())
+            })
+            .collect();
+        println!("expected: {expected:?}");
+        assert_eq!(
+            *PrefixSumAlgorithm::WorkEfficient
+                .run_on_slice(&mut input.clone(), |l, r| l.to_string() + r),
+            *expected
+        );
+        assert_eq!(
+            *PrefixSumAlgorithm::LowLatency
+                .run_on_slice(&mut input.clone(), |l, r| l.to_string() + r),
+            *expected
+        );
+    }
+
+    #[test]
+    fn test_reduce_string() {
+        let input = input_strings();
+        let expected = input.clone().into_iter().reduce(|l, r| l + &r);
+        assert_eq!(reduce(input, |l, r| l + &r), expected);
+    }
+
+    fn op(lhs_index: usize, rhs_and_dest_index: usize, row: u32) -> PrefixSumOp {
+        PrefixSumOp {
+            lhs_index,
+            rhs_and_dest_index: NonZeroUsize::new(rhs_and_dest_index).expect("should be non-zero"),
+            row,
+        }
+    }
+
+    #[test]
+    fn test_reduce_ops_9() {
+        let expected = vec![
+            op(7, 8, 0),
+            op(5, 6, 0),
+            op(3, 4, 0),
+            op(1, 2, 0),
+            op(6, 8, 1),
+            op(2, 4, 1),
+            op(4, 8, 2),
+            op(0, 8, 3),
+        ];
+        println!("expected: {expected:#?}");
+        let ops = reduce_ops(9);
+        println!("ops: {ops:#?}");
+        assert_eq!(*ops, *expected);
+    }
+
+    #[test]
+    fn test_reduce_ops_8() {
+        let expected = vec![
+            op(6, 7, 0),
+            op(4, 5, 0),
+            op(2, 3, 0),
+            op(0, 1, 0),
+            op(5, 7, 1),
+            op(1, 3, 1),
+            op(3, 7, 2),
+        ];
+        println!("expected: {expected:#?}");
+        let ops = reduce_ops(8);
+        println!("ops: {ops:#?}");
+        assert_eq!(*ops, *expected);
+    }
+
+    #[test]
+    fn test_count_ones() {
+        for width in 0..=10u32 {
+            for v in 0..1u32 << width {
+                let expected = v.count_ones();
+                assert_eq!(
+                    reduce((0..width).map(|i| (v >> i) & 1), |l, r| l + r).unwrap_or(0),
+                    expected,
+                    "v={v:#X}"
+                );
+            }
+        }
+    }
+
+    #[track_caller]
+    fn test_diagram(ops: impl IntoIterator<Item = PrefixSumOp>, item_count: usize, expected: &str) {
+        let text = PrefixSumOp::diagram_with_config(
+            ops,
+            item_count,
+            DiagramConfig {
+                plus: Cow::Borrowed("@"),
+                ..Default::default()
+            },
+        );
+        println!("text:\n{text}\n");
+        assert_eq!(text, expected);
+    }
+
+    #[test]
+    fn test_work_efficient_diagram_16() {
+        let item_count = 16;
+        test_diagram(
+            PrefixSumAlgorithm::WorkEfficient.ops(item_count),
+            item_count,
+            &r"
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
+ ●  |  ●  |  ●  |  ●  |  ●  |  ●  |  ●  |  ●  |
+ |\ |  |\ |  |\ |  |\ |  |\ |  |\ |  |\ |  |\ |
+ | \|  | \|  | \|  | \|  | \|  | \|  | \|  | \|
+ |  @  |  @  |  @  |  @  |  @  |  @  |  @  |  @
+ |  |\ |  |  |  |\ |  |  |  |\ |  |  |  |\ |  |
+ |  | \|  |  |  | \|  |  |  | \|  |  |  | \|  |
+ |  |  X  |  |  |  X  |  |  |  X  |  |  |  X  |
+ |  |  |\ |  |  |  |\ |  |  |  |\ |  |  |  |\ |
+ |  |  | \|  |  |  | \|  |  |  | \|  |  |  | \|
+ |  |  |  @  |  |  |  @  |  |  |  @  |  |  |  @
+ |  |  |  |\ |  |  |  |  |  |  |  |\ |  |  |  |
+ |  |  |  | \|  |  |  |  |  |  |  | \|  |  |  |
+ |  |  |  |  X  |  |  |  |  |  |  |  X  |  |  |
+ |  |  |  |  |\ |  |  |  |  |  |  |  |\ |  |  |
+ |  |  |  |  | \|  |  |  |  |  |  |  | \|  |  |
+ |  |  |  |  |  X  |  |  |  |  |  |  |  X  |  |
+ |  |  |  |  |  |\ |  |  |  |  |  |  |  |\ |  |
+ |  |  |  |  |  | \|  |  |  |  |  |  |  | \|  |
+ |  |  |  |  |  |  X  |  |  |  |  |  |  |  X  |
+ |  |  |  |  |  |  |\ |  |  |  |  |  |  |  |\ |
+ |  |  |  |  |  |  | \|  |  |  |  |  |  |  | \|
+ |  |  |  |  |  |  |  @  |  |  |  |  |  |  |  @
+ |  |  |  |  |  |  |  |\ |  |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  | \|  |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  X  |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |\ |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  | \|  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  X  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |\ |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  | \|  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  X  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |\ |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  | \|  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  X  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |\ |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  | \|  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  X  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |\ |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  | \|  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  X  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |\ |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  | \|  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  X  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |\ |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | \|
+ |  |  |  |  |  |  |  ●  |  |  |  |  |  |  |  @
+ |  |  |  |  |  |  |  |\ |  |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  | \|  |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  X  |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |\ |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  | \|  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  X  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |\ |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  | \|  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  X  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |\ |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  | \|  |  |  |  |
+ |  |  |  ●  |  |  |  ●  |  |  |  @  |  |  |  |
+ |  |  |  |\ |  |  |  |\ |  |  |  |\ |  |  |  |
+ |  |  |  | \|  |  |  | \|  |  |  | \|  |  |  |
+ |  |  |  |  X  |  |  |  X  |  |  |  X  |  |  |
+ |  |  |  |  |\ |  |  |  |\ |  |  |  |\ |  |  |
+ |  |  |  |  | \|  |  |  | \|  |  |  | \|  |  |
+ |  ●  |  ●  |  @  |  ●  |  @  |  ●  |  @  |  |
+ |  |\ |  |\ |  |\ |  |\ |  |\ |  |\ |  |\ |  |
+ |  | \|  | \|  | \|  | \|  | \|  | \|  | \|  |
+ |  |  @  |  @  |  @  |  @  |  @  |  @  |  @  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
+"[1..], // trim newline at start
+        );
+    }
+
+    #[test]
+    fn test_low_latency_diagram_16() {
+        let item_count = 16;
+        test_diagram(
+            PrefixSumAlgorithm::LowLatency.ops(item_count),
+            item_count,
+            &r"
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
+ ●  ●  ●  ●  ●  ●  ●  ●  ●  ●  ●  ●  ●  ●  ●  |
+ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |
+ | \| \| \| \| \| \| \| \| \| \| \| \| \| \| \|
+ ●  @  @  @  @  @  @  @  @  @  @  @  @  @  @  @
+ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |  |
+ | \| \| \| \| \| \| \| \| \| \| \| \| \| \|  |
+ |  X  X  X  X  X  X  X  X  X  X  X  X  X  X  |
+ |  |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |
+ |  | \| \| \| \| \| \| \| \| \| \| \| \| \| \|
+ ●  ●  @  @  @  @  @  @  @  @  @  @  @  @  @  @
+ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |  |  |  |
+ | \| \| \| \| \| \| \| \| \| \| \| \|  |  |  |
+ |  X  X  X  X  X  X  X  X  X  X  X  X  |  |  |
+ |  |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |  |  |
+ |  | \| \| \| \| \| \| \| \| \| \| \| \|  |  |
+ |  |  X  X  X  X  X  X  X  X  X  X  X  X  |  |
+ |  |  |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |  |
+ |  |  | \| \| \| \| \| \| \| \| \| \| \| \|  |
+ |  |  |  X  X  X  X  X  X  X  X  X  X  X  X  |
+ |  |  |  |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |\ |
+ |  |  |  | \| \| \| \| \| \| \| \| \| \| \| \|
+ ●  ●  ●  ●  @  @  @  @  @  @  @  @  @  @  @  @
+ |\ |\ |\ |\ |\ |\ |\ |\ |  |  |  |  |  |  |  |
+ | \| \| \| \| \| \| \| \|  |  |  |  |  |  |  |
+ |  X  X  X  X  X  X  X  X  |  |  |  |  |  |  |
+ |  |\ |\ |\ |\ |\ |\ |\ |\ |  |  |  |  |  |  |
+ |  | \| \| \| \| \| \| \| \|  |  |  |  |  |  |
+ |  |  X  X  X  X  X  X  X  X  |  |  |  |  |  |
+ |  |  |\ |\ |\ |\ |\ |\ |\ |\ |  |  |  |  |  |
+ |  |  | \| \| \| \| \| \| \| \|  |  |  |  |  |
+ |  |  |  X  X  X  X  X  X  X  X  |  |  |  |  |
+ |  |  |  |\ |\ |\ |\ |\ |\ |\ |\ |  |  |  |  |
+ |  |  |  | \| \| \| \| \| \| \| \|  |  |  |  |
+ |  |  |  |  X  X  X  X  X  X  X  X  |  |  |  |
+ |  |  |  |  |\ |\ |\ |\ |\ |\ |\ |\ |  |  |  |
+ |  |  |  |  | \| \| \| \| \| \| \| \|  |  |  |
+ |  |  |  |  |  X  X  X  X  X  X  X  X  |  |  |
+ |  |  |  |  |  |\ |\ |\ |\ |\ |\ |\ |\ |  |  |
+ |  |  |  |  |  | \| \| \| \| \| \| \| \|  |  |
+ |  |  |  |  |  |  X  X  X  X  X  X  X  X  |  |
+ |  |  |  |  |  |  |\ |\ |\ |\ |\ |\ |\ |\ |  |
+ |  |  |  |  |  |  | \| \| \| \| \| \| \| \|  |
+ |  |  |  |  |  |  |  X  X  X  X  X  X  X  X  |
+ |  |  |  |  |  |  |  |\ |\ |\ |\ |\ |\ |\ |\ |
+ |  |  |  |  |  |  |  | \| \| \| \| \| \| \| \|
+ |  |  |  |  |  |  |  |  @  @  @  @  @  @  @  @
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
+"[1..], // trim newline at start
+        );
+    }
+
+    #[test]
+    fn test_work_efficient_diagram_9() {
+        let item_count = 9;
+        test_diagram(
+            PrefixSumAlgorithm::WorkEfficient.ops(item_count),
+            item_count,
+            &r"
+ |  |  |  |  |  |  |  |  |
+ ●  |  ●  |  ●  |  ●  |  |
+ |\ |  |\ |  |\ |  |\ |  |
+ | \|  | \|  | \|  | \|  |
+ |  @  |  @  |  @  |  @  |
+ |  |\ |  |  |  |\ |  |  |
+ |  | \|  |  |  | \|  |  |
+ |  |  X  |  |  |  X  |  |
+ |  |  |\ |  |  |  |\ |  |
+ |  |  | \|  |  |  | \|  |
+ |  |  |  @  |  |  |  @  |
+ |  |  |  |\ |  |  |  |  |
+ |  |  |  | \|  |  |  |  |
+ |  |  |  |  X  |  |  |  |
+ |  |  |  |  |\ |  |  |  |
+ |  |  |  |  | \|  |  |  |
+ |  |  |  |  |  X  |  |  |
+ |  |  |  |  |  |\ |  |  |
+ |  |  |  |  |  | \|  |  |
+ |  |  |  |  |  |  X  |  |
+ |  |  |  |  |  |  |\ |  |
+ |  |  |  |  |  |  | \|  |
+ |  |  |  ●  |  |  |  @  |
+ |  |  |  |\ |  |  |  |  |
+ |  |  |  | \|  |  |  |  |
+ |  |  |  |  X  |  |  |  |
+ |  |  |  |  |\ |  |  |  |
+ |  |  |  |  | \|  |  |  |
+ |  ●  |  ●  |  @  |  ●  |
+ |  |\ |  |\ |  |\ |  |\ |
+ |  | \|  | \|  | \|  | \|
+ |  |  @  |  @  |  @  |  @
+ |  |  |  |  |  |  |  |  |
+"[1..], // trim newline at start
+        );
+    }
+
+    #[test]
+    fn test_low_latency_diagram_9() {
+        let item_count = 9;
+        test_diagram(
+            PrefixSumAlgorithm::LowLatency.ops(item_count),
+            item_count,
+            &r"
+ |  |  |  |  |  |  |  |  |
+ ●  ●  ●  ●  ●  ●  ●  ●  |
+ |\ |\ |\ |\ |\ |\ |\ |\ |
+ | \| \| \| \| \| \| \| \|
+ ●  @  @  @  @  @  @  @  @
+ |\ |\ |\ |\ |\ |\ |\ |  |
+ | \| \| \| \| \| \| \|  |
+ |  X  X  X  X  X  X  X  |
+ |  |\ |\ |\ |\ |\ |\ |\ |
+ |  | \| \| \| \| \| \| \|
+ ●  ●  @  @  @  @  @  @  @
+ |\ |\ |\ |\ |\ |  |  |  |
+ | \| \| \| \| \|  |  |  |
+ |  X  X  X  X  X  |  |  |
+ |  |\ |\ |\ |\ |\ |  |  |
+ |  | \| \| \| \| \|  |  |
+ |  |  X  X  X  X  X  |  |
+ |  |  |\ |\ |\ |\ |\ |  |
+ |  |  | \| \| \| \| \|  |
+ |  |  |  X  X  X  X  X  |
+ |  |  |  |\ |\ |\ |\ |\ |
+ |  |  |  | \| \| \| \| \|
+ ●  |  |  |  @  @  @  @  @
+ |\ |  |  |  |  |  |  |  |
+ | \|  |  |  |  |  |  |  |
+ |  X  |  |  |  |  |  |  |
+ |  |\ |  |  |  |  |  |  |
+ |  | \|  |  |  |  |  |  |
+ |  |  X  |  |  |  |  |  |
+ |  |  |\ |  |  |  |  |  |
+ |  |  | \|  |  |  |  |  |
+ |  |  |  X  |  |  |  |  |
+ |  |  |  |\ |  |  |  |  |
+ |  |  |  | \|  |  |  |  |
+ |  |  |  |  X  |  |  |  |
+ |  |  |  |  |\ |  |  |  |
+ |  |  |  |  | \|  |  |  |
+ |  |  |  |  |  X  |  |  |
+ |  |  |  |  |  |\ |  |  |
+ |  |  |  |  |  | \|  |  |
+ |  |  |  |  |  |  X  |  |
+ |  |  |  |  |  |  |\ |  |
+ |  |  |  |  |  |  | \|  |
+ |  |  |  |  |  |  |  X  |
+ |  |  |  |  |  |  |  |\ |
+ |  |  |  |  |  |  |  | \|
+ |  |  |  |  |  |  |  |  @
+ |  |  |  |  |  |  |  |  |
+"[1..], // trim newline at start
+        );
+    }
+
+    #[test]
+    fn test_reduce_diagram_16() {
+        let item_count = 16;
+        test_diagram(
+            reduce_ops(item_count),
+            item_count,
+            &r"
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
+ ●  |  ●  |  ●  |  ●  |  ●  |  ●  |  ●  |  ●  |
+ |\ |  |\ |  |\ |  |\ |  |\ |  |\ |  |\ |  |\ |
+ | \|  | \|  | \|  | \|  | \|  | \|  | \|  | \|
+ |  @  |  @  |  @  |  @  |  @  |  @  |  @  |  @
+ |  |\ |  |  |  |\ |  |  |  |\ |  |  |  |\ |  |
+ |  | \|  |  |  | \|  |  |  | \|  |  |  | \|  |
+ |  |  X  |  |  |  X  |  |  |  X  |  |  |  X  |
+ |  |  |\ |  |  |  |\ |  |  |  |\ |  |  |  |\ |
+ |  |  | \|  |  |  | \|  |  |  | \|  |  |  | \|
+ |  |  |  @  |  |  |  @  |  |  |  @  |  |  |  @
+ |  |  |  |\ |  |  |  |  |  |  |  |\ |  |  |  |
+ |  |  |  | \|  |  |  |  |  |  |  | \|  |  |  |
+ |  |  |  |  X  |  |  |  |  |  |  |  X  |  |  |
+ |  |  |  |  |\ |  |  |  |  |  |  |  |\ |  |  |
+ |  |  |  |  | \|  |  |  |  |  |  |  | \|  |  |
+ |  |  |  |  |  X  |  |  |  |  |  |  |  X  |  |
+ |  |  |  |  |  |\ |  |  |  |  |  |  |  |\ |  |
+ |  |  |  |  |  | \|  |  |  |  |  |  |  | \|  |
+ |  |  |  |  |  |  X  |  |  |  |  |  |  |  X  |
+ |  |  |  |  |  |  |\ |  |  |  |  |  |  |  |\ |
+ |  |  |  |  |  |  | \|  |  |  |  |  |  |  | \|
+ |  |  |  |  |  |  |  @  |  |  |  |  |  |  |  @
+ |  |  |  |  |  |  |  |\ |  |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  | \|  |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  X  |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |\ |  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  | \|  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  X  |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |\ |  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  | \|  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  X  |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |\ |  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  | \|  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  X  |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |\ |  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  | \|  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  X  |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |\ |  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  | \|  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  X  |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |\ |  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  | \|  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  X  |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |\ |
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | \|
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  @
+ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
+"[1..], // trim newline at start
+        );
+    }
+
+    #[test]
+    fn test_reduce_diagram_9() {
+        let item_count = 9;
+        test_diagram(
+            reduce_ops(item_count),
+            item_count,
+            &r"
+ |  |  |  |  |  |  |  |  |
+ |  ●  |  ●  |  ●  |  ●  |
+ |  |\ |  |\ |  |\ |  |\ |
+ |  | \|  | \|  | \|  | \|
+ |  |  @  |  @  |  @  |  @
+ |  |  |\ |  |  |  |\ |  |
+ |  |  | \|  |  |  | \|  |
+ |  |  |  X  |  |  |  X  |
+ |  |  |  |\ |  |  |  |\ |
+ |  |  |  | \|  |  |  | \|
+ |  |  |  |  @  |  |  |  @
+ |  |  |  |  |\ |  |  |  |
+ |  |  |  |  | \|  |  |  |
+ |  |  |  |  |  X  |  |  |
+ |  |  |  |  |  |\ |  |  |
+ |  |  |  |  |  | \|  |  |
+ |  |  |  |  |  |  X  |  |
+ |  |  |  |  |  |  |\ |  |
+ |  |  |  |  |  |  | \|  |
+ |  |  |  |  |  |  |  X  |
+ |  |  |  |  |  |  |  |\ |
+ |  |  |  |  |  |  |  | \|
+ ●  |  |  |  |  |  |  |  @
+ |\ |  |  |  |  |  |  |  |
+ | \|  |  |  |  |  |  |  |
+ |  X  |  |  |  |  |  |  |
+ |  |\ |  |  |  |  |  |  |
+ |  | \|  |  |  |  |  |  |
+ |  |  X  |  |  |  |  |  |
+ |  |  |\ |  |  |  |  |  |
+ |  |  | \|  |  |  |  |  |
+ |  |  |  X  |  |  |  |  |
+ |  |  |  |\ |  |  |  |  |
+ |  |  |  | \|  |  |  |  |
+ |  |  |  |  X  |  |  |  |
+ |  |  |  |  |\ |  |  |  |
+ |  |  |  |  | \|  |  |  |
+ |  |  |  |  |  X  |  |  |
+ |  |  |  |  |  |\ |  |  |
+ |  |  |  |  |  | \|  |  |
+ |  |  |  |  |  |  X  |  |
+ |  |  |  |  |  |  |\ |  |
+ |  |  |  |  |  |  | \|  |
+ |  |  |  |  |  |  |  X  |
+ |  |  |  |  |  |  |  |\ |
+ |  |  |  |  |  |  |  | \|
+ |  |  |  |  |  |  |  |  @
+ |  |  |  |  |  |  |  |  |
+"[1..], // trim newline at start
+        );
+    }
+}
diff --git a/crates/fayalite/tests/module.rs b/crates/fayalite/tests/module.rs
index 49f5689..49b226a 100644
--- a/crates/fayalite/tests/module.rs
+++ b/crates/fayalite/tests/module.rs
@@ -191,10 +191,14 @@ circuit check_array_repeat:
     };
 }
 
+pub trait UnknownTrait {}
+
+impl<T: ?Sized> UnknownTrait for T {}
+
 #[hdl_module(outline_generated)]
 pub fn check_skipped_generics<T, #[hdl(skip)] U, const N: usize, #[hdl(skip)] const M: usize>(v: U)
 where
-    T: StaticType,
+    T: StaticType + UnknownTrait,
     ConstUsize<N>: KnownSize,
     U: std::fmt::Display,
 {
@@ -376,18 +380,18 @@ circuit check_written_inside_both_if_else:
     };
 }
 
-#[hdl(outline_generated)]
+#[hdl(outline_generated, cmp_eq)]
 pub struct TestStruct<T> {
     pub a: T,
     pub b: UInt<8>,
 }
 
-#[hdl(outline_generated)]
+#[hdl(outline_generated, cmp_eq)]
 pub struct TestStruct2 {
     pub v: UInt<8>,
 }
 
-#[hdl(outline_generated)]
+#[hdl(outline_generated, cmp_eq)]
 pub struct TestStruct3 {}
 
 #[hdl_module(outline_generated)]
@@ -4421,3 +4425,125 @@ circuit check_let_patterns:
 ",
     };
 }
+
+#[hdl_module(outline_generated)]
+pub fn check_struct_cmp_eq() {
+    #[hdl]
+    let tuple_lhs: (UInt<1>, SInt<1>, Bool) = m.input();
+    #[hdl]
+    let tuple_rhs: (UInt<1>, SInt<1>, Bool) = m.input();
+    #[hdl]
+    let tuple_cmp_eq: Bool = m.output();
+    connect(tuple_cmp_eq, tuple_lhs.cmp_eq(tuple_rhs));
+    #[hdl]
+    let tuple_cmp_ne: Bool = m.output();
+    connect(tuple_cmp_ne, tuple_lhs.cmp_ne(tuple_rhs));
+
+    #[hdl]
+    let test_struct_lhs: TestStruct<SInt<8>> = m.input();
+    #[hdl]
+    let test_struct_rhs: TestStruct<SInt<8>> = m.input();
+    #[hdl]
+    let test_struct_cmp_eq: Bool = m.output();
+    connect(test_struct_cmp_eq, test_struct_lhs.cmp_eq(test_struct_rhs));
+    #[hdl]
+    let test_struct_cmp_ne: Bool = m.output();
+    connect(test_struct_cmp_ne, test_struct_lhs.cmp_ne(test_struct_rhs));
+
+    #[hdl]
+    let test_struct_2_lhs: TestStruct2 = m.input();
+    #[hdl]
+    let test_struct_2_rhs: TestStruct2 = m.input();
+    #[hdl]
+    let test_struct_2_cmp_eq: Bool = m.output();
+    connect(
+        test_struct_2_cmp_eq,
+        test_struct_2_lhs.cmp_eq(test_struct_2_rhs),
+    );
+    #[hdl]
+    let test_struct_2_cmp_ne: Bool = m.output();
+    connect(
+        test_struct_2_cmp_ne,
+        test_struct_2_lhs.cmp_ne(test_struct_2_rhs),
+    );
+
+    #[hdl]
+    let test_struct_3_lhs: TestStruct3 = m.input();
+    #[hdl]
+    let test_struct_3_rhs: TestStruct3 = m.input();
+    #[hdl]
+    let test_struct_3_cmp_eq: Bool = m.output();
+    connect(
+        test_struct_3_cmp_eq,
+        test_struct_3_lhs.cmp_eq(test_struct_3_rhs),
+    );
+    #[hdl]
+    let test_struct_3_cmp_ne: Bool = m.output();
+    connect(
+        test_struct_3_cmp_ne,
+        test_struct_3_lhs.cmp_ne(test_struct_3_rhs),
+    );
+}
+
+#[test]
+fn test_struct_cmp_eq() {
+    let _n = SourceLocation::normalize_files_for_tests();
+    let m = check_struct_cmp_eq();
+    dbg!(m);
+    #[rustfmt::skip] // work around https://github.com/rust-lang/rustfmt/issues/6161
+    assert_export_firrtl! {
+        m =>
+        "/test/check_struct_cmp_eq.fir": r"FIRRTL version 3.2.0
+circuit check_struct_cmp_eq:
+    type Ty0 = {`0`: UInt<1>, `1`: SInt<1>, `2`: UInt<1>}
+    type Ty1 = {a: SInt<8>, b: UInt<8>}
+    type Ty2 = {v: UInt<8>}
+    type Ty3 = {}
+    module check_struct_cmp_eq: @[module-XXXXXXXXXX.rs 1:1]
+        input tuple_lhs: Ty0 @[module-XXXXXXXXXX.rs 2:1]
+        input tuple_rhs: Ty0 @[module-XXXXXXXXXX.rs 3:1]
+        output tuple_cmp_eq: UInt<1> @[module-XXXXXXXXXX.rs 4:1]
+        output tuple_cmp_ne: UInt<1> @[module-XXXXXXXXXX.rs 6:1]
+        input test_struct_lhs: Ty1 @[module-XXXXXXXXXX.rs 8:1]
+        input test_struct_rhs: Ty1 @[module-XXXXXXXXXX.rs 9:1]
+        output test_struct_cmp_eq: UInt<1> @[module-XXXXXXXXXX.rs 10:1]
+        output test_struct_cmp_ne: UInt<1> @[module-XXXXXXXXXX.rs 12:1]
+        input test_struct_2_lhs: Ty2 @[module-XXXXXXXXXX.rs 14:1]
+        input test_struct_2_rhs: Ty2 @[module-XXXXXXXXXX.rs 15:1]
+        output test_struct_2_cmp_eq: UInt<1> @[module-XXXXXXXXXX.rs 16:1]
+        output test_struct_2_cmp_ne: UInt<1> @[module-XXXXXXXXXX.rs 18:1]
+        input test_struct_3_lhs: Ty3 @[module-XXXXXXXXXX.rs 20:1]
+        input test_struct_3_rhs: Ty3 @[module-XXXXXXXXXX.rs 21:1]
+        output test_struct_3_cmp_eq: UInt<1> @[module-XXXXXXXXXX.rs 22:1]
+        output test_struct_3_cmp_ne: UInt<1> @[module-XXXXXXXXXX.rs 24:1]
+        wire _array_literal_expr: UInt<1>[3]
+        connect _array_literal_expr[0], eq(tuple_lhs.`0`, tuple_rhs.`0`)
+        connect _array_literal_expr[1], eq(tuple_lhs.`1`, tuple_rhs.`1`)
+        connect _array_literal_expr[2], eq(tuple_lhs.`2`, tuple_rhs.`2`)
+        wire _cast_array_to_bits_expr: UInt<1>[3]
+        connect _cast_array_to_bits_expr[0], _array_literal_expr[0]
+        connect _cast_array_to_bits_expr[1], _array_literal_expr[1]
+        connect _cast_array_to_bits_expr[2], _array_literal_expr[2]
+        wire _cast_to_bits_expr: UInt<3>
+        connect _cast_to_bits_expr, cat(_cast_array_to_bits_expr[2], cat(_cast_array_to_bits_expr[1], _cast_array_to_bits_expr[0]))
+        connect tuple_cmp_eq, andr(_cast_to_bits_expr) @[module-XXXXXXXXXX.rs 5:1]
+        wire _array_literal_expr_1: UInt<1>[3]
+        connect _array_literal_expr_1[0], neq(tuple_lhs.`0`, tuple_rhs.`0`)
+        connect _array_literal_expr_1[1], neq(tuple_lhs.`1`, tuple_rhs.`1`)
+        connect _array_literal_expr_1[2], neq(tuple_lhs.`2`, tuple_rhs.`2`)
+        wire _cast_array_to_bits_expr_1: UInt<1>[3]
+        connect _cast_array_to_bits_expr_1[0], _array_literal_expr_1[0]
+        connect _cast_array_to_bits_expr_1[1], _array_literal_expr_1[1]
+        connect _cast_array_to_bits_expr_1[2], _array_literal_expr_1[2]
+        wire _cast_to_bits_expr_1: UInt<3>
+        connect _cast_to_bits_expr_1, cat(_cast_array_to_bits_expr_1[2], cat(_cast_array_to_bits_expr_1[1], _cast_array_to_bits_expr_1[0]))
+        connect tuple_cmp_ne, orr(_cast_to_bits_expr_1) @[module-XXXXXXXXXX.rs 7:1]
+        connect test_struct_cmp_eq, and(eq(test_struct_lhs.a, test_struct_rhs.a), eq(test_struct_lhs.b, test_struct_rhs.b)) @[module-XXXXXXXXXX.rs 11:1]
+        connect test_struct_cmp_ne, or(neq(test_struct_lhs.a, test_struct_rhs.a), neq(test_struct_lhs.b, test_struct_rhs.b)) @[module-XXXXXXXXXX.rs 13:1]
+        connect test_struct_2_cmp_eq, eq(test_struct_2_lhs.v, test_struct_2_rhs.v) @[module-XXXXXXXXXX.rs 17:1]
+        connect test_struct_2_cmp_ne, neq(test_struct_2_lhs.v, test_struct_2_rhs.v) @[module-XXXXXXXXXX.rs 19:1]
+        connect test_struct_3_cmp_eq, UInt<1>(0h1) @[module-XXXXXXXXXX.rs 23:1]
+        connect test_struct_3_cmp_ne, UInt<1>(0h0) @[module-XXXXXXXXXX.rs 25:1]
+",
+    };
+}
diff --git a/crates/fayalite/visit_types.json b/crates/fayalite/visit_types.json
index 3eff1f5..b284372 100644
--- a/crates/fayalite/visit_types.json
+++ b/crates/fayalite/visit_types.json
@@ -49,7 +49,8 @@
                 "AsyncReset": "Visible",
                 "SyncReset": "Visible",
                 "Reset": "Visible",
-                "Clock": "Visible"
+                "Clock": "Visible",
+                "PhantomConst": "Visible"
             }
         },
         "Bundle": {
@@ -1262,6 +1263,12 @@
                 "ArrayElement": "Visible",
                 "DynArrayElement": "Visible"
             }
+        },
+        "PhantomConst": {
+            "data": {
+                "$kind": "Opaque"
+            },
+            "generics": "<T: ?Sized + crate::phantom_const::PhantomConstValue>"
         }
     }
 }
\ No newline at end of file