From 7d3e56523bf93fb3c63fc19de843278f38e43012 Mon Sep 17 00:00:00 2001
From: nella <simontupy64@gmail.com>
Date: Wed, 13 May 2026 16:25:15 +0200
Subject: [PATCH] Preserve param signedness across overrides.

---
 kernel/rtlil.cc               |  9 +++++++++
 kernel/rtlil.h                |  2 ++
 passes/cmds/setattr.cc        |  1 +
 passes/hierarchy/hierarchy.cc |  8 ++++++--
 tests/verilog/issue5745.ys    | 18 ++++++++++++++++++
 5 files changed, 36 insertions(+), 2 deletions(-)
 create mode 100644 tests/verilog/issue5745.ys

diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index a99f0803e..1a7dc6b41 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -615,6 +615,15 @@ int RTLIL::Const::as_int_saturating(bool is_signed) const
 	return as_int(is_signed);
 }
 
+void RTLIL::Const::tag_bare_integer_const(const std::string &value)
+{
+	if (value.empty() || value.find('\'') != std::string::npos)
+		return;
+	size_t start = (value[0] == '-' || value[0] == '+') ? 1 : 0;
+	if (start < value.size() && std::all_of(value.begin() + start, value.end(), ::isdigit))
+		flags |= RTLIL::CONST_FLAG_SIGNED;
+}
+
 int RTLIL::Const::get_min_size(bool is_signed) const
 {
 	if (empty()) return 0;
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index b32f9ea76..e55caf35a 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -1091,6 +1091,8 @@ public:
 	// over/underflow, otherwise the max/min value for int depending on the sign.
 	int as_int_saturating(bool is_signed = false) const;
 
+	void tag_bare_integer_const(const std::string &value);
+
 	std::string as_string(const char* any = "-") const;
 	static Const from_string(const std::string &str);
 	std::vector<RTLIL::State> to_bits() const;
diff --git a/passes/cmds/setattr.cc b/passes/cmds/setattr.cc
index 25d8fd34c..ef9bd0d34 100644
--- a/passes/cmds/setattr.cc
+++ b/passes/cmds/setattr.cc
@@ -41,6 +41,7 @@ struct setunset_t
 			if (!RTLIL::SigSpec::parse(sig_value, nullptr, set_value))
 				log_cmd_error("Can't decode value '%s'!\n", set_value);
 			value = sig_value.as_const();
+			value.tag_bare_integer_const(set_value);
 		}
 	}
 };
diff --git a/passes/hierarchy/hierarchy.cc b/passes/hierarchy/hierarchy.cc
index 416997bee..34cedfd34 100644
--- a/passes/hierarchy/hierarchy.cc
+++ b/passes/hierarchy/hierarchy.cc
@@ -985,7 +985,9 @@ struct HierarchyPass : public Pass {
 					SigSpec sig_value;
 					if (!RTLIL::SigSpec::parse(sig_value, NULL, para.second))
 						log_cmd_error("Can't decode value '%s'!\n", para.second);
-					top_parameters[RTLIL::escape_id(para.first)] = sig_value.as_const();
+					RTLIL::Const c = sig_value.as_const();
+					c.tag_bare_integer_const(para.second);
+					top_parameters[RTLIL::escape_id(para.first)] = c;
 				}
 			}
 
@@ -1073,7 +1075,9 @@ struct HierarchyPass : public Pass {
 				SigSpec sig_value;
 				if (!RTLIL::SigSpec::parse(sig_value, NULL, para.second))
 					log_cmd_error("Can't decode value '%s'!\n", para.second);
-				top_parameters[RTLIL::escape_id(para.first)] = sig_value.as_const();
+				RTLIL::Const c = sig_value.as_const();
+				c.tag_bare_integer_const(para.second);
+				top_parameters[RTLIL::escape_id(para.first)] = c;
 			}
 
 			top_mod = design->module(top_mod->derive(design, top_parameters));
diff --git a/tests/verilog/issue5745.ys b/tests/verilog/issue5745.ys
new file mode 100644
index 000000000..938ead63a
--- /dev/null
+++ b/tests/verilog/issue5745.ys
@@ -0,0 +1,18 @@
+# Issue #5745: chparam values are unsigned when using read_verilog frontend
+#
+# When chparam overrides a parameter value, the signed attribute is lost,
+# causing signed comparisons to silently use unsigned logic.
+#
+# m = -32 (signed 9-bit), p2 = 11. Correct signed semantics: -32 < 11, so k = 1.
+# Bug: chparam strips the signed attribute from p2. The $lt cell gets A_SIGNED=0,
+# B_SIGNED=0, so the comparison treats m as unsigned (480 > 11), giving k = 0.
+
+read_verilog <<EOT
+module mod #(parameter p2=11) (output k);
+  wire signed [8:0] m = -32;
+  assign k = m < p2;
+endmodule
+EOT
+chparam -set p2 11
+hierarchy -top mod
+sat -prove k 1 -verify
\ No newline at end of file