Merge branch 'YosysHQ-main'

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -43,7 +43,7 @@ body:
     attributes:
       value: >
         When providing steps to reproduce the issue, please ensure that the issue
-        is reproducible in the current git master of Yosys. Also ensure to
+        is reproducible in the current git main of Yosys. Also ensure to
         provide all necessary source files needed.
 
 

.github/workflows/test-docs.yml

@@ -3,7 +3,7 @@ name: Build and test doc code samples
 on:
   pull_request:
     branches:
-    - master
+    - main
 
 jobs:
   test-docs:

Makefile

@@ -1,4 +1,4 @@
-
+# CONFIG := none
 # CONFIG := clang
 CONFIG := gcc
 # CONFIG := afl-gcc
@@ -141,7 +141,7 @@ LIBS += -lrt
 endif
 endif
 
-YOSYS_VER := 0.39+124
+YOSYS_VER := 0.39+147
 
 # Note: We arrange for .gitcommit to contain the (short) commit hash in
 # tarballs generated with git-archive(1) using .gitattributes. The git repo
@@ -217,7 +217,7 @@ endif
 ifeq ($(CONFIG),clang)
 CXX = clang++
 CXXFLAGS += -std=$(CXXSTD) -Os
-ABCMKARGS += ARCHFLAGS="-DABC_USE_STDINT_H -Wno-c++11-narrowing $(ABC_ARCHFLAGS)"
+ABCMKARGS += ARCHFLAGS="-DABC_USE_STDINT_H $(ABC_ARCHFLAGS)"
 
 ifneq ($(SANITIZER),)
 $(info [Clang Sanitizer] $(SANITIZER))
@@ -265,7 +265,7 @@ ABCMKARGS += ARCHFLAGS="-DABC_USE_STDINT_H"
 else ifeq ($(CONFIG),emcc)
 CXX = emcc
 CXXFLAGS := -std=$(CXXSTD) $(filter-out -fPIC -ggdb,$(CXXFLAGS))
-ABCMKARGS += ARCHFLAGS="-DABC_USE_STDINT_H -DABC_MEMALIGN=8 -Wno-c++11-narrowing"
+ABCMKARGS += ARCHFLAGS="-DABC_USE_STDINT_H -DABC_MEMALIGN=8"
 EMCC_CXXFLAGS := -Os -Wno-warn-absolute-paths
 EMCC_LINKFLAGS := --embed-file share
 EMCC_LINKFLAGS += -s NO_EXIT_RUNTIME=1
@@ -317,7 +317,7 @@ CXXFLAGS := $(WASIFLAGS) -std=$(CXXSTD) -Os -D_WASI_EMULATED_PROCESS_CLOCKS $(fi
 LINKFLAGS := $(WASIFLAGS) -Wl,-z,stack-size=1048576 $(filter-out -rdynamic,$(LINKFLAGS))
 LIBS := -lwasi-emulated-process-clocks $(filter-out -lrt,$(LIBS))
 ABCMKARGS += AR="$(AR)" RANLIB="$(RANLIB)"
-ABCMKARGS += ARCHFLAGS="$(WASIFLAGS) -D_WASI_EMULATED_PROCESS_CLOCKS -DABC_USE_STDINT_H -DABC_NO_DYNAMIC_LINKING -DABC_NO_RLIMIT -Wno-c++11-narrowing"
+ABCMKARGS += ARCHFLAGS="$(WASIFLAGS) -D_WASI_EMULATED_PROCESS_CLOCKS -DABC_USE_STDINT_H -DABC_NO_DYNAMIC_LINKING -DABC_NO_RLIMIT"
 ABCMKARGS += OPTFLAGS="-Os"
 EXE = .wasm
 
@@ -360,8 +360,12 @@ ABCMKARGS += ARCHFLAGS="-DABC_USE_STDINT_H -DWIN32_NO_DLL -DHAVE_STRUCT_TIMESPEC
 ABCMKARGS += LIBS="-lpthread -lshlwapi -s" ABC_USE_NO_READLINE=0 CC="x86_64-w64-mingw32-gcc" CXX="$(CXX)"
 EXE = .exe
 
-else ifneq ($(CONFIG),none)
-$(error Invalid CONFIG setting '$(CONFIG)'. Valid values: clang, gcc, emcc, mxe, msys2-32, msys2-64)
+else ifeq ($(CONFIG),none)
+CXXFLAGS += -std=$(CXXSTD) -Os
+ABCMKARGS += ARCHFLAGS="-DABC_USE_STDINT_H $(ABC_ARCHFLAGS)"
+
+else
+$(error Invalid CONFIG setting '$(CONFIG)'. Valid values: clang, gcc, emcc, mxe, msys2-32, msys2-64, none)
 endif
 
 ifeq ($(ENABLE_LIBYOSYS),1)
@@ -1127,6 +1131,9 @@ echo-git-rev:
 echo-abc-rev:
 	@echo "$(ABCREV)"
 
+echo-cxx:
+	@echo "$(CXX)"
+
 -include libs/*/*.d
 -include frontends/*/*.d
 -include passes/*/*.d

README.md

@@ -105,11 +105,17 @@ For Cygwin use the following command to install all prerequisites, or select the
 
 	setup-x86_64.exe -q --packages=bison,flex,gcc-core,gcc-g++,git,libffi-devel,libreadline-devel,make,pkg-config,python3,tcl-devel,boost-build,zlib-devel
 
-To configure the build system to use a specific compiler, use one of
+The environment variable `CXX` can be used to control the C++ compiler used, or
+run one of the following:
 
 	$ make config-clang
 	$ make config-gcc
 
+Note that these will result in `make` ignoring the `CXX` environment variable,
+unless `CXX` is assigned in the call to make, e.g.
+
+  $ make CXX=$CXX
+
 For other compilers and build configurations it might be
 necessary to make some changes to the config section of the
 Makefile.

backends/jny/jny.cc

@@ -124,7 +124,7 @@ struct JnyWriter
         design->sort();
 
         f << "{\n";
-        f << "  \"$schema\": \"https://raw.githubusercontent.com/YosysHQ/yosys/master/misc/jny.schema.json\",\n";
+        f << "  \"$schema\": \"https://raw.githubusercontent.com/YosysHQ/yosys/main/misc/jny.schema.json\",\n";
         f << stringf("  \"generator\": \"%s\",\n", escape_string(yosys_version_str).c_str());
         f << "  \"version\": \"0.0.1\",\n";
         f << "  \"invocation\": \"" << escape_string(invk) << "\",\n";
@@ -426,7 +426,7 @@ struct JnyBackend : public Backend {
         log("        Don't include property information in the netlist output.\n");
         log("\n");
         log("The JSON schema for JNY output files is located in the \"jny.schema.json\" file\n");
-        log("which is located at \"https://raw.githubusercontent.com/YosysHQ/yosys/master/misc/jny.schema.json\"\n");
+        log("which is located at \"https://raw.githubusercontent.com/YosysHQ/yosys/main/misc/jny.schema.json\"\n");
         log("\n");
     }
 

docs/source/getting_started/example_synth.rst

@@ -633,9 +633,9 @@ with the mapping to ``SB_RAM40_4K`` done by :cmd:ref:`techmap` using
 into flip flops (the ``logic fallback``) with :cmd:ref:`memory_map`.
 
 .. |techlibs/ice40/brams.txt| replace:: :file:`techlibs/ice40/brams.txt`
-.. _techlibs/ice40/brams.txt: https://github.com/YosysHQ/yosys/tree/master/techlibs/ice40/brams.txt
+.. _techlibs/ice40/brams.txt: https://github.com/YosysHQ/yosys/tree/main/techlibs/ice40/brams.txt
 .. |techlibs/ice40/brams_map.v| replace:: :file:`techlibs/ice40/brams_map.v`
-.. _techlibs/ice40/brams_map.v: https://github.com/YosysHQ/yosys/tree/master/techlibs/ice40/brams_map.v
+.. _techlibs/ice40/brams_map.v: https://github.com/YosysHQ/yosys/tree/main/techlibs/ice40/brams_map.v
 
 .. literalinclude:: /cmd/synth_ice40.rst
    :language: yoscrypt

docs/source/test_suites.rst

@@ -16,8 +16,8 @@ Automatic testing
 
 .. _Yosys Git repo: https://github.com/YosysHQ/yosys
 
-.. |test-linux| image:: https://github.com/YosysHQ/yosys/actions/workflows/test-linux.yml/badge.svg?branch=master
-.. |test-macos| image:: https://github.com/YosysHQ/yosys/actions/workflows/test-macos.yml/badge.svg?branch=master
+.. |test-linux| image:: https://github.com/YosysHQ/yosys/actions/workflows/test-linux.yml/badge.svg?branch=main
+.. |test-macos| image:: https://github.com/YosysHQ/yosys/actions/workflows/test-macos.yml/badge.svg?branch=main
 
 For up to date information, including OS versions, refer to `the git actions
 page`_.

docs/source/using_yosys/more_scripting/interactive_investigation.rst

@@ -18,7 +18,7 @@ in the circuit diagrams generated by it. The code used is included in the Yosys
 code base under |code_examples/show|_.
 
 .. |code_examples/show| replace:: :file:`docs/source/code_examples/show`
-.. _code_examples/show: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/show
+.. _code_examples/show: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/show
 
 A simple circuit
 ^^^^^^^^^^^^^^^^
@@ -337,7 +337,7 @@ The code used is included in the Yosys code base under
 |code_examples/scrambler|_.
 
 .. |code_examples/scrambler| replace:: :file:`docs/source/code_examples/scrambler`
-.. _code_examples/scrambler: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/scrambler
+.. _code_examples/scrambler: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/scrambler
 
 Changing design hierarchy
 ^^^^^^^^^^^^^^^^^^^^^^^^^

docs/source/using_yosys/more_scripting/model_checking.rst

@@ -29,7 +29,7 @@ Let's take a look at an example included in the Yosys code base under
 |code_examples/synth_flow|_:
 
 .. |code_examples/synth_flow| replace:: :file:`docs/source/code_examples/synth_flow`
-.. _code_examples/synth_flow: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/synth_flow
+.. _code_examples/synth_flow: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/synth_flow
 
 .. literalinclude:: /code_examples/synth_flow/techmap_01_map.v
    :language: verilog
@@ -81,7 +81,7 @@ The code used in this section is included in the Yosys code base under
 |code_examples/axis|_.
 
 .. |code_examples/axis| replace:: :file:`docs/source/code_examples/axis`
-.. _code_examples/axis: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/axis
+.. _code_examples/axis: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/axis
 
 The following AXI4 Stream Master has a bug. But the bug is not exposed if the
 slave keeps ``tready`` asserted all the time. (Something a test bench might do.)

docs/source/using_yosys/more_scripting/selections.rst

@@ -405,7 +405,7 @@ those cases selection variables must be used to capture more complex selections.
 Example code from |code_examples/selections|_:
 
 .. |code_examples/selections| replace:: :file:`docs/source/code_examples/selections`
-.. _code_examples/selections: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/selections
+.. _code_examples/selections: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/selections
 
 .. literalinclude:: /code_examples/selections/select.v
    :language: verilog

docs/source/using_yosys/synthesis/cell_libs.rst

@@ -21,7 +21,7 @@ detail in the :doc:`/getting_started/example_synth` document.
    
    To learn more about these commands, check out :ref:`interactive_show`.
 
-.. _example project: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/intro
+.. _example project: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/intro
 
 A simple counter
 ~~~~~~~~~~~~~~~~

docs/source/using_yosys/synthesis/extract.rst

@@ -15,7 +15,7 @@ The extract pass
 Example code can be found in |code_examples/macc|_.
 
 .. |code_examples/macc| replace:: :file:`docs/source/code_examples/macc`
-.. _code_examples/macc: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/macc
+.. _code_examples/macc: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/macc
 
 
 .. literalinclude:: /code_examples/macc/macc_simple_test.ys

docs/source/using_yosys/synthesis/memory.rst

@@ -36,7 +36,7 @@ Example
 |code_examples/synth_flow|_.
 
 .. |code_examples/synth_flow| replace:: :file:`docs/source/code_examples/synth_flow`
-.. _code_examples/synth_flow: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/synth_flow
+.. _code_examples/synth_flow: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/synth_flow
 
 .. figure:: /_images/code_examples/synth_flow/memory_01.*
    :class: width-helper
@@ -92,7 +92,7 @@ leftover memory cells unable to be converted are then picked up by
 
 For more on the lib format for :cmd:ref:`memory_libmap`, see
 `passes/memory/memlib.md
-<https://github.com/YosysHQ/yosys/blob/master/passes/memory/memlib.md>`_
+<https://github.com/YosysHQ/yosys/blob/main/passes/memory/memlib.md>`_
 
 Supported memory patterns
 ^^^^^^^^^^^^^^^^^^^^^^^^^

docs/source/using_yosys/synthesis/proc.rst

@@ -31,7 +31,7 @@ Example
 |code_examples/synth_flow|_.
 
 .. |code_examples/synth_flow| replace:: :file:`docs/source/code_examples/synth_flow`
-.. _code_examples/synth_flow: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/synth_flow
+.. _code_examples/synth_flow: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/synth_flow
 
 .. literalinclude:: /code_examples/synth_flow/proc_01.v
    :language: verilog

docs/source/yosys_internals/extending_yosys/extensions.rst

@@ -24,7 +24,7 @@ Code examples from this section are included in the
 |code_examples/extensions|_ directory of the Yosys source code.
 
 .. |code_examples/extensions| replace:: :file:`docs/source/code_examples/extensions`
-.. _code_examples/extensions: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/extensions
+.. _code_examples/extensions: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/extensions
 
 
 Program components and data formats
@@ -254,7 +254,7 @@ The following is the complete code of the "stubnets" example module. It is
 included in the Yosys source distribution under |code_examples/stubnets|_.
 
 .. |code_examples/stubnets| replace:: :file:`docs/source/code_examples/stubnets`
-.. _code_examples/stubnets: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/stubnets
+.. _code_examples/stubnets: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/stubnets
 
 .. literalinclude:: /code_examples/stubnets/stubnets.cc
     :language: c++

docs/source/yosys_internals/techmap.rst

@@ -16,7 +16,7 @@ Code examples used in this document are included in the Yosys code base under
 |code_examples/techmap|_.
 
 .. |code_examples/techmap| replace:: :file:`docs/source/code_examples/techmap`
-.. _code_examples/techmap: https://github.com/YosysHQ/yosys/tree/master/docs/source/code_examples/techmap
+.. _code_examples/techmap: https://github.com/YosysHQ/yosys/tree/main/docs/source/code_examples/techmap
 
 
 Mapping OR3X1

guidelines/Windows

@@ -44,7 +44,7 @@ Visual Studio builds are not directly supported by build scripts, but they are s
 
 1. Easy way
 
-  - Go to https://github.com/YosysHQ/yosys/actions/workflows/vs.yml?query=branch%3Amaster
+  - Go to https://github.com/YosysHQ/yosys/actions/workflows/vs.yml?query=branch%3Amain
   - Click on the most recent completed run
   - In Artifacts region find vcxsrc and click on it to download
   - Unpack downloaded ZIP file

kernel/celledges.cc

@@ -307,6 +307,87 @@ void shift_op(AbstractCellEdgesDatabase *db, RTLIL::Cell *cell)
 	}
 }
 
+void packed_mem_op(AbstractCellEdgesDatabase *db, RTLIL::Cell *cell)
+{
+	log_assert(cell->type == ID($mem_v2));
+	Const rd_clk_enable = cell->getParam(ID::RD_CLK_ENABLE);
+	int n_rd_ports = cell->getParam(ID::RD_PORTS).as_int();
+	int abits = cell->getParam(ID::ABITS).as_int();
+	int width = cell->getParam(ID::WIDTH).as_int();
+
+	for (int i = 0; i < n_rd_ports; i++) {
+		if (rd_clk_enable[i] != State::S0) {
+			for (int k = 0; k < width; k++)
+				db->add_edge(cell, ID::RD_ARST, i, ID::RD_DATA, i * width + k, -1);
+			continue;
+		}
+
+		for (int j = 0; j < abits; j++)
+			for (int k = 0; k < width; k++)
+				db->add_edge(cell, ID::RD_ADDR, i * abits + j,
+								   ID::RD_DATA, i * width + k, -1);
+	}
+}
+
+void memrd_op(AbstractCellEdgesDatabase *db, RTLIL::Cell *cell)
+{
+	log_assert(cell->type.in(ID($memrd), ID($memrd_v2)));
+	int abits = cell->getParam(ID::ABITS).as_int();
+	int width = cell->getParam(ID::WIDTH).as_int();
+
+	if (cell->getParam(ID::CLK_ENABLE).as_bool()) {
+		if (cell->type == ID($memrd_v2)) {
+			for (int k = 0; k < width; k++)
+				db->add_edge(cell, ID::ARST, 0, ID::DATA, k, -1);
+		}
+		return;
+	}
+
+	for (int j = 0; j < abits; j++)
+		for (int k = 0; k < width; k++)
+			db->add_edge(cell, ID::ADDR, j, ID::DATA, k, -1);
+}
+
+void mem_op(AbstractCellEdgesDatabase *db, RTLIL::Cell *cell)
+{
+	if (cell->type == ID($mem_v2))
+		packed_mem_op(db, cell);
+	else if (cell->type.in(ID($memrd), ID($memrd_v2)))
+		memrd_op(db, cell);
+	else if (cell->type.in(ID($memwr), ID($memwr_v2), ID($meminit)))
+		return; /* no edges here */
+	else
+		log_abort();
+}
+
+void ff_op(AbstractCellEdgesDatabase *db, RTLIL::Cell *cell)
+{
+	int width = cell->getPort(ID::Q).size();
+
+	if (cell->type.in(ID($dlatch), ID($adlatch), ID($dlatchsr))) {
+		for (int k = 0; k < width; k++) {
+			db->add_edge(cell, ID::D, k, ID::Q, k, -1);
+			db->add_edge(cell, ID::EN, 0, ID::Q, k, -1);
+		}
+	}
+
+	if (cell->hasPort(ID::CLR))
+		for (int k = 0; k < width; k++)
+			db->add_edge(cell, ID::CLR, 0, ID::Q, k, -1);
+	if (cell->hasPort(ID::SET))
+		for (int k = 0; k < width; k++)
+			db->add_edge(cell, ID::SET, 0, ID::Q, k, -1);
+	if (cell->hasPort(ID::ALOAD))
+		for (int k = 0; k < width; k++)
+			db->add_edge(cell, ID::ALOAD, 0, ID::Q, k, -1);
+	if (cell->hasPort(ID::AD))
+		for (int k = 0; k < width; k++)
+			db->add_edge(cell, ID::AD, k, ID::Q, k, -1);
+	if (cell->hasPort(ID::ARST))
+		for (int k = 0; k < width; k++)
+			db->add_edge(cell, ID::ARST, 0, ID::Q, k, -1);
+}
+
 PRIVATE_NAMESPACE_END
 
 bool YOSYS_NAMESPACE_PREFIX AbstractCellEdgesDatabase::add_edges_from_cell(RTLIL::Cell *cell)
@@ -361,6 +442,18 @@ bool YOSYS_NAMESPACE_PREFIX AbstractCellEdgesDatabase::add_edges_from_cell(RTLIL
 		return true;
 	}
 
+	if (cell->type.in(ID($mem_v2), ID($memrd), ID($memrd_v2), ID($memwr), ID($memwr_v2), ID($meminit))) {
+		mem_op(this, cell);
+		return true;
+	}
+
+	if (RTLIL::builtin_ff_cell_types().count(cell->type)) {
+		ff_op(this, cell);
+		return true;
+	}
+
+	// FIXME: $mul $div $mod $divfloor $modfloor $slice $concat
+	// FIXME: $lut $sop $alu $lcu $macc $fa
 	// FIXME: $mul $div $mod $divfloor $modfloor $pow $slice $concat $bweqx
 	// FIXME: $lut $sop $alu $lcu $macc $fa $logic_and $logic_or $bwmux
 

kernel/utils.h

@@ -149,7 +149,7 @@ template <typename T, typename C = std::less<T>, typename OPS = hash_ops<T>> cla
 	std::map<T, int, C> node_to_index;
 	std::vector<std::set<int, IndirectCmp>> edges;
 	std::vector<T> sorted;
-	std::set<std::set<T, C>> loops;
+	std::set<std::vector<T>> loops;
 
 	TopoSort() : indirect_cmp(nodes)
 	{
@@ -220,10 +220,10 @@ template <typename T, typename C = std::less<T>, typename OPS = hash_ops<T>> cla
 		if (active_cells[root_index]) {
 			found_loops = true;
 			if (analyze_loops) {
-				std::set<T, C> loop;
+				std::vector<T> loop;
 				for (int i = GetSize(active_stack) - 1; i >= 0; i--) {
 					const int index = active_stack[i];
-					loop.insert(nodes[index]);
+					loop.push_back(nodes[index]);
 					if (index == root_index)
 						break;
 				}

misc/create_vcxsrc.sh

@@ -46,7 +46,7 @@ Open "Git Bash" in this directory and run:
 	mv yosys yosys.bak
 	git clone https://github.com/YosysHQ/yosys.git yosys
 	cd yosys
-	git checkout -B master $(git rev-parse HEAD | cut -c1-10)
+	git checkout -B main $(git rev-parse HEAD | cut -c1-10)
 	unzip ../genfiles.zip
 EOT
 

misc/jny.schema.json

@@ -1,6 +1,6 @@
 {
 	"$schema": "https://json-schema.org/draft/2020-12/schema",
-	"$id": "https://raw.githubusercontent.com/YosysHQ/yosys/master/misc/jny.schema.json",
+	"$id": "https://raw.githubusercontent.com/YosysHQ/yosys/main/misc/jny.schema.json",
 	"title": "Yosys JSON Netlist metadata",
 	"description": "Yosys JSON Netlist",
 	"type": "object",

passes/cmds/check.cc

@@ -19,6 +19,7 @@
 
 #include "kernel/yosys.h"
 #include "kernel/sigtools.h"
+#include "kernel/celledges.h"
 #include "kernel/celltypes.h"
 #include "kernel/utils.h"
 
@@ -102,10 +103,10 @@ struct CheckPass : public Pass {
 
 			SigMap sigmap(module);
 			dict<SigBit, vector<string>> wire_drivers;
+			dict<SigBit, Cell *> driver_cells;
 			dict<SigBit, int> wire_drivers_count;
 			pool<SigBit> used_wires;
-			TopoSort<string> topo;
-
+			TopoSort<std::pair<RTLIL::IdString, int>> topo;
 			for (auto &proc_it : module->processes)
 			{
 				std::vector<RTLIL::CaseRule*> all_cases = {&proc_it.second->root_case};
@@ -150,6 +151,50 @@ struct CheckPass : public Pass {
 				}
 			}
 
+			struct CircuitEdgesDatabase : AbstractCellEdgesDatabase {
+				TopoSort<std::pair<RTLIL::IdString, int>> &topo;
+				SigMap sigmap;
+
+				CircuitEdgesDatabase(TopoSort<std::pair<RTLIL::IdString, int>> &topo, SigMap &sigmap)
+					: topo(topo), sigmap(sigmap) {}
+
+				void add_edge(RTLIL::Cell *cell, RTLIL::IdString from_port, int from_bit,
+							  RTLIL::IdString to_port, int to_bit, int) override {
+					SigSpec from_portsig = cell->getPort(from_port);
+					SigSpec to_portsig = cell->getPort(to_port);
+					log_assert(from_bit >= 0 && from_bit < from_portsig.size());
+					log_assert(to_bit >= 0 && to_bit < to_portsig.size());
+					SigBit from = sigmap(from_portsig[from_bit]);
+					SigBit to = sigmap(to_portsig[to_bit]);
+
+					if (from.wire && to.wire)
+						topo.edge(std::make_pair(from.wire->name, from.offset), std::make_pair(to.wire->name, to.offset));
+				}
+
+				bool add_edges_from_cell(Cell *cell) {
+					if (AbstractCellEdgesDatabase::add_edges_from_cell(cell))
+						return true;
+
+					// We don't have accurate cell edges, do the fallback of all input-output pairs
+					for (auto &conn : cell->connections()) {
+						if (cell->input(conn.first))
+						for (auto bit : sigmap(conn.second))
+						if (bit.wire)
+							topo.edge(std::make_pair(bit.wire->name, bit.offset),
+									  std::make_pair(cell->name, -1));
+
+						if (cell->output(conn.first))
+						for (auto bit : sigmap(conn.second))
+						if (bit.wire)
+							topo.edge(std::make_pair(cell->name, -1),
+									  std::make_pair(bit.wire->name, bit.offset));
+					}
+					return true;
+				}
+			};
+
+			CircuitEdgesDatabase edges_db(topo, sigmap);
+
 			for (auto cell : module->cells())
 			{
 				if (mapped && cell->type.begins_with("$") && design->module(cell->type) == nullptr) {
@@ -158,31 +203,30 @@ struct CheckPass : public Pass {
 					counter++;
 				cell_allowed:;
 				}
-				for (auto &conn : cell->connections()) {
-					SigSpec sig = sigmap(conn.second);
-					bool logic_cell = yosys_celltypes.cell_evaluable(cell->type);
-					if (cell->input(conn.first))
-						for (auto bit : sig)
-							if (bit.wire) {
-								if (logic_cell)
-									topo.edge(stringf("wire %s", log_signal(bit)),
-											stringf("cell %s (%s)", log_id(cell), log_id(cell->type)));
-								used_wires.insert(bit);
-							}
-					if (cell->output(conn.first))
-						for (int i = 0; i < GetSize(sig); i++) {
-							if (logic_cell)
-								topo.edge(stringf("cell %s (%s)", log_id(cell), log_id(cell->type)),
-										stringf("wire %s", log_signal(sig[i])));
 
-							if (sig[i].wire || !cell->input(conn.first))
-								wire_drivers[sig[i]].push_back(stringf("port %s[%d] of cell %s (%s)",
-										log_id(conn.first), i, log_id(cell), log_id(cell->type)));
-						}
-					if (!cell->input(conn.first) && cell->output(conn.first))
-						for (auto bit : sig)
-							if (bit.wire) wire_drivers_count[bit]++;
+				for (auto &conn : cell->connections()) {
+					bool input = cell->input(conn.first);
+					bool output = cell->output(conn.first);
+
+					SigSpec sig = sigmap(conn.second);
+					for (int i = 0; i < sig.size(); i++) {
+						SigBit bit = sig[i];
+
+						if (input && bit.wire)
+							used_wires.insert(bit);
+						if (output && !input && bit.wire)
+							wire_drivers_count[bit]++;
+						if (output && (bit.wire || !input))
+							wire_drivers[bit].push_back(stringf("port %s[%d] of cell %s (%s)", log_id(conn.first), i,
+																log_id(cell), log_id(cell->type)));
+						if (output)
+							driver_cells[bit] = cell;
+					}
 				}
+
+				if (yosys_celltypes.cell_evaluable(cell->type) || cell->type.in(ID($mem_v2), ID($memrd), ID($memrd_v2)) \
+						|| RTLIL::builtin_ff_cell_types().count(cell->type))
+					edges_db.add_edges_from_cell(cell);
 			}
 
 			pool<SigBit> init_bits;
@@ -239,8 +283,72 @@ struct CheckPass : public Pass {
 			topo.sort();
 			for (auto &loop : topo.loops) {
 				string message = stringf("found logic loop in module %s:\n", log_id(module));
-				for (auto &str : loop)
-					message += stringf("    %s\n", str.c_str());
+
+				// `loop` only contains wire bits, or an occassional special helper node for cells for
+				// which we have done the edges fallback. The cell and its ports that led to an edge is
+				// an information we need to recover now. For that we need to have the previous wire bit
+				// of the loop at hand.
+				SigBit prev;
+				for (auto it = loop.rbegin(); it != loop.rend(); it++)
+				if (it->second != -1) { // skip the fallback helper nodes
+					prev = SigBit(module->wire(it->first), it->second);
+					break;
+				}
+				log_assert(prev != SigBit());
+
+				for (auto &pair : loop) {
+					if (pair.second == -1)
+						continue; // helper node for edges fallback, we can ignore it
+
+					struct MatchingEdgePrinter : AbstractCellEdgesDatabase {
+						std::string &message;
+						SigMap &sigmap;
+						SigBit from, to;
+						int nhits;
+						const int HITS_LIMIT = 3;
+
+						MatchingEdgePrinter(std::string &message, SigMap &sigmap, SigBit from, SigBit to)
+							: message(message), sigmap(sigmap), from(from), to(to), nhits(0) {}
+
+						void add_edge(RTLIL::Cell *cell, RTLIL::IdString from_port, int from_bit,
+									  RTLIL::IdString to_port, int to_bit, int) override {
+							SigBit edge_from = sigmap(cell->getPort(from_port))[from_bit];
+							SigBit edge_to = sigmap(cell->getPort(to_port))[to_bit];
+
+							if (edge_from == from && edge_to == to && nhits++ < HITS_LIMIT)
+								message += stringf("        %s[%d] --> %s[%d]\n", log_id(from_port), from_bit,
+												   log_id(to_port), to_bit);
+							if (nhits == HITS_LIMIT)
+								message += "        ...\n";
+						}
+					};
+
+					Wire *wire = module->wire(pair.first);
+					log_assert(wire);
+					SigBit bit(module->wire(pair.first), pair.second);
+					log_assert(driver_cells.count(bit));
+					Cell *driver = driver_cells.at(bit);
+
+					std::string driver_src;
+					if (driver->has_attribute(ID::src)) {
+						std::string src_attr = driver->get_src_attribute();
+						driver_src = stringf(" source: %s", src_attr.c_str());
+					}
+					message += stringf("    cell %s (%s)%s\n", log_id(driver), log_id(driver->type), driver_src.c_str());
+					MatchingEdgePrinter printer(message, sigmap, prev, bit);
+					printer.add_edges_from_cell(driver);
+
+					if (wire->name.isPublic()) {
+						std::string wire_src;
+						if (wire->has_attribute(ID::src)) {
+							std::string src_attr = wire->get_src_attribute();
+							wire_src = stringf(" source: %s", src_attr.c_str());
+						}
+						message += stringf("    wire %s%s\n", log_signal(SigBit(wire, pair.second)), wire_src.c_str());						
+					}
+
+					prev = bit;
+				}
 				log_warning("%s", message.c_str());
 				counter++;
 			}

tests/opt/opt_dff_qd.ys

@@ -7,7 +7,7 @@ module top(...);
 input CLK;
 input EN;
 (* init = 24'h555555 *)
-output [19:0] Q;
+output [17:0] Q;
 input SRST;
 input ARST;
 input [1:0] CLR;
@@ -23,26 +23,20 @@ $sdffce #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b1), .SRST_POLARITY(1'b1), .SRST_V
 $dffsr #(.CLK_POLARITY(1'b1), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff7 (.CLK(CLK), .SET(SET), .CLR(CLR), .D(Q[15:14]), .Q(Q[15:14]));
 $dffsre #(.CLK_POLARITY(1'b1), .EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff8 (.CLK(CLK), .EN(EN), .SET(SET), .CLR(CLR), .D(Q[17:16]), .Q(Q[17:16]));
 
-$dlatch #(.EN_POLARITY(1'b1), .WIDTH(2)) ff9 (.EN(EN), .D(Q[19:18]), .Q(Q[19:18]));
-$adlatch #(.EN_POLARITY(1'b0), .ARST_POLARITY(1'b1), .ARST_VALUE(2'h2), .WIDTH(2)) ff10 (.EN(EN), .ARST(ARST), .D(Q[21:20]), .Q(Q[21:20]));
-$dlatchsr #(.EN_POLARITY(1'b0), .CLR_POLARITY(1'b1), .SET_POLARITY(1'b0), .WIDTH(2)) ff11 (.EN(EN), .SET(SET), .CLR(CLR), .D(Q[23:22]), .Q(Q[23:22]));
-
 endmodule
 
 EOT
 
 design -save orig
 
-# Equivalence check will fail for unmapped adlatch and dlatchsr due to negative hold hack.
-delete top/ff10 top/ff11
 equiv_opt -undef -assert -multiclock opt_dff -keepdc
 
 design -load orig
 opt_dff -keepdc
 select -assert-count 1 t:$and
 select -assert-count 3 t:$dffe
-select -assert-count 3 t:$dlatch
-select -assert-count 3 t:$sr
+select -assert-count 2 t:$dlatch
+select -assert-count 2 t:$sr
 select -assert-none t:$and t:$dffe t:$dlatch t:$sr %% %n t:* %i
 
 design -load orig
@@ -50,7 +44,7 @@ simplemap
 opt_dff -keepdc
 select -assert-count 2 t:$_AND_
 select -assert-count 6 t:$_DFFE_??_
-select -assert-count 6 t:$_DLATCH_?_
-select -assert-count 6 t:$_SR_??_
+select -assert-count 4 t:$_DLATCH_?_
+select -assert-count 4 t:$_SR_??_
 select -assert-none t:$_AND_ t:$_DFFE_??_ t:$_DLATCH_?_ t:$_SR_??_ %% %n t:* %i
 

tests/various/check.ys

@@ -0,0 +1,43 @@
+design -reset
+read -vlog2k <<EOF
+module top(input clk, input a, input b, output [9:0] x);
+	wire [9:0] ripple;
+	reg [9:0] prev_ripple = 9'b0;
+
+	always @(posedge clk) prev_ripple <= ripple;
+	assign ripple = {ripple[8:0], a} ^ prev_ripple; // only cyclic at the coarse-grain level
+	assign x = ripple[9] + b;
+endmodule
+EOF
+hierarchy -top top
+prep
+check -assert
+
+design -reset
+read -vlog2k <<EOF
+module top(clk, y, sideread_addr, sideread_data);
+	input wire clk;
+
+	reg [7:0] mem [255:0];
+	reg [8:0] i;
+	initial begin
+		for (i = 0; i < 256; i = i + 1)
+			mem[i] = i * 371;
+	end
+
+	output reg [7:0] y = 1;
+	always @(posedge clk)
+		y <= mem[y];
+
+	input wire [7:0] sideread_addr;
+	output wire [7:0] sideread_data;
+	assign sideread_data = mem[sideread_addr];
+endmodule
+EOF
+hierarchy -top top
+prep -rdff
+select -assert-count 1 t:$mem_v2
+check -assert
+memory_unpack
+select -assert-count 2 t:$memrd_v2
+check -assert

tests/various/check_2.ys

@@ -0,0 +1,17 @@
+# just so slightly adjust the example from check.ys to induce a loop
+design -reset
+read -vlog2k <<EOF
+module top(input clk, input a, input b, output [9:0] x);
+	wire [9:0] ripple;
+	reg [9:0] prev_ripple = 9'b0;
+
+	always @(posedge clk) prev_ripple <= ripple;
+	assign ripple = {ripple[8:1], a, ripple[0]} ^ prev_ripple;
+	assign x = ripple[9] + b;
+endmodule
+EOF
+hierarchy -top top
+prep
+logger -expect warning "found logic loop in module top:" 1
+logger -expect error "Found 1 problems in 'check -assert'" 1
+check -assert

tests/various/check_3.ys

@@ -0,0 +1,20 @@
+# loop involving asynchronous memory ports
+design -reset
+read -vlog2k <<EOF
+module pingpong(input wire [1:0] x, output wire [3:0] y1, output wire [3:0] y2);
+	reg [3:0] mem [15:0];
+	reg [5:0] i;
+	initial begin
+		for (i = 0; i < 16; i = i + 1)
+			mem[i] = i * 371;
+	end
+
+	assign y1 = mem[{y2[3:2], x}];
+	assign y2 = mem[y1];
+endmodule
+EOF
+hierarchy -top pingpong
+prep
+logger -nowarn "found logic loop in module pingpong:"
+logger -expect error "Found [0-9]+ problems in 'check -assert'" 1
+check -assert

tests/various/check_4.ys

@@ -0,0 +1,29 @@
+# loop involving the asynchronous reset on a memory port
+design -reset
+read -vlog2k <<EOF
+module top(input wire clk, input wire [3:0] addr, output reg [3:0] data);
+	reg [3:0] mem [15:0];
+	reg [5:0] i;
+	initial begin
+		for (i = 0; i < 16; i = i + 1)
+			mem[i] = i * 371;
+	end
+
+	wire arst = !data[0];
+
+	always @(posedge arst, posedge clk) begin
+		if (arst)		
+			data <= 4'hx;
+		else
+			data <= mem[addr];
+	end
+endmodule
+EOF
+hierarchy -top top
+proc
+opt -keepdc
+memory_dff
+opt_clean
+logger -nowarn "found logic loop in module pingpong:"
+logger -expect error "Found [0-9]+ problems in 'check -assert'" 1
+check -assert