[circt-synth] [Synthesis] Add synthesis pipeline and refactor the lib structure (#8681)

This commit introduces a standardized synthesis pipeline and restructures the codebase:

* Creates a new SynthesisPipeline class to define the default synthesis pipeline. This pipeline serves both circt-synth and is exposed through the C API for Python bindings.
* Added a dedicated Synthesis directory under `lib/` to house synthesis-related code. This architectural change is aimed to promote synthesis capabilities to a first-class component within CIRCT rather than limiting it to the circt-synth tool.

include/circt-c/Synthesis.h

@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef CIRCT_C_SYNTHESIS_H
+#define CIRCT_C_SYNTHESIS_H
+
+#include "mlir-c/IR.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+MLIR_CAPI_EXPORTED void registerSynthesisPipeline(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // CIRCT_C_SYNTHESIS_H

include/circt/Synthesis/SynthesisPipeline.h

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the default synthesis pipeline.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LIB_SYNTHESIS_SYNTHESISPIPELINE_H
+#define LIB_SYNTHESIS_SYNTHESISPIPELINE_H
+
+#include "circt-c/Synthesis.h"
+#include "mlir/Pass/PassManager.h"
+#include "mlir/Pass/PassOptions.h"
+#include <string>
+#include <vector>
+
+//===----------------------------------------------------------------------===//
+// Pipeline Options
+//===----------------------------------------------------------------------===//
+namespace circt {
+namespace synthesis {
+
+/// Options for the aig optimization pipeline.
+struct AIGOptimizationPipelineOptions
+    : public mlir::PassPipelineOptions<AIGOptimizationPipelineOptions> {
+  PassOptions::ListOption<std::string> abcCommands{
+      *this, "abc-commands", llvm::cl::desc("ABC passes to run")};
+
+  PassOptions::Option<std::string> abcPath{
+      *this, "abc-path", llvm::cl::desc("Path to ABC"), llvm::cl::init("abc")};
+
+  PassOptions::Option<bool> ignoreAbcFailures{
+      *this, "ignore-abc-failures",
+      llvm::cl::desc("Continue on ABC failure instead of aborting"),
+      llvm::cl::init(false)};
+};
+
+//===----------------------------------------------------------------------===//
+// Pipeline Functions
+//===----------------------------------------------------------------------===//
+
+/// Populate the synthesis pipelines.
+void buildAIGLoweringPipeline(mlir::OpPassManager &pm);
+void buildAIGOptimizationPipeline(
+    mlir::OpPassManager &pm, const AIGOptimizationPipelineOptions &options);
+
+/// Register the synthesis pipelines.
+void registerSynthesisPipeline();
+
+} // namespace synthesis
+} // namespace circt
+
+#endif // LIB_SYNTHESIS_SYNTHESISPIPELINE_H

integration_test/Bindings/Python/synthesis.py

@@ -0,0 +1,36 @@
+# REQUIRES: bindings_python
+# RUN: %PYTHON% %s | FileCheck %s
+
+import circt
+from circt.dialects import hw, comb
+from circt.ir import Context, Location, Module, InsertionPoint, IntegerType
+from circt.passmanager import PassManager
+
+with Context() as ctx, Location.unknown():
+  circt.register_dialects(ctx)
+
+  m = Module.create()
+  with InsertionPoint(m.body):
+    i4 = IntegerType.get_signless(4)
+
+    # Create a module with comb.mul
+    def build_module(module):
+      a, b = module.entry_block.arguments
+      hw.OutputOp([comb.mul([a, b])])
+
+    hw.HWModuleOp(
+        name="foo",
+        input_ports=[("a", i4), ("b", i4)],
+        output_ports=[("out", i4)],
+        body_builder=build_module,
+    )
+
+  # Check that the synthesis pipeline is registered.
+  pm = PassManager.parse(
+      "builtin.module(hw.module(synthesis-aig-lowering-pipeline, "
+      "synthesis-aig-optimization-pipeline))")
+  pm.run(m.operation)
+  # CHECK: hw.module @foo(
+  # CHECK-NOT: comb.mul
+  # CHECK: aig.and_inv
+  print(m.operation)

lib/Bindings/Python/CIRCTModule.cpp

@@ -26,6 +26,7 @@
 #include "circt-c/Dialect/OM.h"
 #include "circt-c/Dialect/Pipeline.h"
 #include "circt-c/Dialect/RTG.h"
+#include "circt-c/Synthesis.h"
 #include "circt-c/Transforms.h"
 #ifdef CIRCT_INCLUDE_TESTS
 #include "circt-c/Dialect/RTGTest.h"
@@ -63,6 +64,7 @@ static void registerPasses() {
   registerHandshakePasses();
   registerKanagawaPasses();
   registerPipelinePasses();
+  registerSynthesisPipeline();
   mlirRegisterCIRCTConversionPasses();
   mlirRegisterCIRCTTransformsPasses();
   mlirRegisterTransformsCSE();

lib/Bindings/Python/CMakeLists.txt

@@ -55,6 +55,7 @@ set(PYTHON_BINDINGS_LINK_LIBS
   CIRCTCAPISV
   CIRCTCAPIVerif
   CIRCTCAPITransforms
+  CIRCTCAPISynthesis
   MLIRCAPIIndex
   MLIRCAPISMT
   MLIRCAPIExportSMTLIB

lib/CAPI/CMakeLists.txt

@@ -4,4 +4,5 @@ add_subdirectory(ExportVerilog)
 add_subdirectory(Dialect)
 add_subdirectory(Firtool)
 add_subdirectory(RtgTool)
+add_subdirectory(Synthesis)
 add_subdirectory(Transforms)

lib/CAPI/Synthesis/CMakeLists.txt

@@ -0,0 +1,7 @@
+add_circt_public_c_api_library(CIRCTCAPISynthesis
+  SynthesisPipeline.cpp
+
+  LINK_LIBS PUBLIC
+  CIRCTSynthesis
+  MLIRCAPIIR
+)

lib/CAPI/Synthesis/SynthesisPipeline.cpp

@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "circt-c/Synthesis.h"
+
+#include "circt/Synthesis/SynthesisPipeline.h"
+
+void registerSynthesisPipeline() {
+  circt::synthesis::registerSynthesisPipeline();
+}

lib/CMakeLists.txt

@@ -11,6 +11,7 @@ add_subdirectory(Firtool)
 add_subdirectory(Reduce)
 add_subdirectory(Scheduling)
 add_subdirectory(Support)
+add_subdirectory(Synthesis)
 add_subdirectory(Target)
 add_subdirectory(Tools)
 add_subdirectory(Transforms)

lib/Synthesis/CMakeLists.txt

@@ -0,0 +1,13 @@
+add_circt_library(CIRCTSynthesis
+  SynthesisPipeline.cpp
+
+  LINK_LIBS PUBLIC
+  CIRCTAIGTransforms
+  CIRCTCombToAIG
+  CIRCTHWTransforms
+  CIRCTSupport
+
+  MLIRIR
+  MLIRSupport
+  MLIRTransforms
+)

lib/Synthesis/SynthesisPipeline.cpp

@@ -0,0 +1,95 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the default synthesis pipeline from core dialect to AIG.
+//
+//===----------------------------------------------------------------------===//
+
+#include "circt/Synthesis/SynthesisPipeline.h"
+#include "circt/Conversion/CombToAIG.h"
+#include "circt/Dialect/AIG/AIGPasses.h"
+#include "circt/Dialect/Comb/CombOps.h"
+#include "circt/Dialect/HW/HWOps.h"
+#include "circt/Dialect/HW/HWPasses.h"
+#include "circt/Support/Passes.h"
+#include "circt/Transforms/Passes.h"
+#include "mlir/Pass/PassManager.h"
+#include "mlir/Transforms/Passes.h"
+#include "llvm/ADT/SmallVector.h"
+
+using namespace mlir;
+using namespace circt;
+using namespace circt::synthesis;
+
+//===----------------------------------------------------------------------===//
+// Pipeline Implementation
+//===----------------------------------------------------------------------===//
+
+/// Helper function to populate additional legal ops for partial legalization.
+template <typename... AllowedOpTy>
+static void partiallyLegalizeCombToAIG(SmallVectorImpl<std::string> &ops) {
+  (ops.push_back(AllowedOpTy::getOperationName().str()), ...);
+}
+
+void circt::synthesis::buildAIGLoweringPipeline(OpPassManager &pm) {
+  {
+    // Partially legalize Comb to AIG, run CSE and canonicalization.
+    circt::ConvertCombToAIGOptions convOptions;
+    partiallyLegalizeCombToAIG<comb::AndOp, comb::OrOp, comb::XorOp,
+                               comb::MuxOp, comb::ICmpOp, hw::ArrayGetOp,
+                               hw::ArraySliceOp, hw::ArrayCreateOp,
+                               hw::ArrayConcatOp, hw::AggregateConstantOp>(
+        convOptions.additionalLegalOps);
+    pm.addPass(circt::createConvertCombToAIG(convOptions));
+  }
+  pm.addPass(createCSEPass());
+  pm.addPass(createSimpleCanonicalizerPass());
+
+  pm.addPass(circt::hw::createHWAggregateToCombPass());
+  pm.addPass(circt::createConvertCombToAIG());
+  pm.addPass(createCSEPass());
+  pm.addPass(createSimpleCanonicalizerPass());
+  pm.addPass(createCSEPass());
+}
+
+void circt::synthesis::buildAIGOptimizationPipeline(
+    OpPassManager &pm, const AIGOptimizationPipelineOptions &options) {
+
+  pm.addPass(aig::createLowerVariadic());
+
+  // TODO: LowerWordToBits is not scalable for large designs. Change to
+  // conditionally enable the pass once the rest of the pipeline was able
+  // to handle multibit operands properly.
+  pm.addPass(aig::createLowerWordToBits());
+  pm.addPass(createCSEPass());
+  pm.addPass(createSimpleCanonicalizerPass());
+
+  if (!options.abcCommands.empty()) {
+    aig::ABCRunnerOptions abcOptions;
+    abcOptions.abcPath = options.abcPath;
+    abcOptions.abcCommands.assign(options.abcCommands.begin(),
+                                  options.abcCommands.end());
+    abcOptions.continueOnFailure = options.ignoreAbcFailures;
+    pm.addPass(aig::createABCRunner(abcOptions));
+  }
+  // TODO: Add balancing, rewriting, FRAIG conversion, etc.
+}
+
+//===----------------------------------------------------------------------===//
+// Pipeline Registration
+//===----------------------------------------------------------------------===//
+
+void circt::synthesis::registerSynthesisPipeline() {
+  PassPipelineRegistration<EmptyPipelineOptions>(
+      "synthesis-aig-lowering-pipeline",
+      "The default pipeline for until AIG lowering", buildAIGLoweringPipeline);
+  PassPipelineRegistration<AIGOptimizationPipelineOptions>(
+      "synthesis-aig-optimization-pipeline",
+      "The default pipeline for AIG optimization pipeline",
+      buildAIGOptimizationPipeline);
+}

tools/circt-synth/CMakeLists.txt

@@ -3,20 +3,17 @@ target_link_libraries(circt-synth
   PRIVATE
   CIRCTAIG
   CIRCTAIGToComb
-  CIRCTAIGTransforms
   CIRCTAIGAnalysis
   CIRCTComb
-  CIRCTCombToAIG
   CIRCTDebug
   CIRCTEmit
   CIRCTHW
-  CIRCTHWTransforms
   CIRCTLTL
   CIRCTOM
   CIRCTSeq
   CIRCTSim
-  CIRCTSupport
   CIRCTSV
+  CIRCTSynthesis
   CIRCTTransforms
   CIRCTVerif
   MLIRBytecodeWriter

tools/circt-synth/circt-synth.cpp

@@ -12,7 +12,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "circt/Conversion/AIGToComb.h"
-#include "circt/Conversion/CombToAIG.h"
 #include "circt/Dialect/AIG/AIGDialect.h"
 #include "circt/Dialect/AIG/AIGPasses.h"
 #include "circt/Dialect/AIG/Analysis/LongestPathAnalysis.h"
@@ -22,7 +21,6 @@
 #include "circt/Dialect/Emit/EmitDialect.h"
 #include "circt/Dialect/HW/HWDialect.h"
 #include "circt/Dialect/HW/HWOps.h"
-#include "circt/Dialect/HW/HWPasses.h"
 #include "circt/Dialect/LTL/LTLDialect.h"
 #include "circt/Dialect/OM/OMDialect.h"
 #include "circt/Dialect/SV/SVDialect.h"
@@ -31,12 +29,14 @@
 #include "circt/Dialect/Verif/VerifDialect.h"
 #include "circt/Support/Passes.h"
 #include "circt/Support/Version.h"
+#include "circt/Synthesis/SynthesisPipeline.h"
 #include "circt/Transforms/Passes.h"
 #include "mlir/Bytecode/BytecodeWriter.h"
 #include "mlir/IR/Diagnostics.h"
 #include "mlir/IR/OwningOpRef.h"
 #include "mlir/Parser/Parser.h"
 #include "mlir/Pass/PassManager.h"
+#include "mlir/Pass/PassRegistry.h"
 #include "mlir/Support/FileUtilities.h"
 #include "mlir/Support/LogicalResult.h"
 #include "mlir/Transforms/Passes.h"
@@ -51,6 +51,7 @@ namespace cl = llvm::cl;
 
 using namespace mlir;
 using namespace circt;
+using namespace synthesis;
 
 //===----------------------------------------------------------------------===//
 // Command-line options declaration
@@ -90,7 +91,6 @@ static cl::opt<bool>
                               cl::desc("Allow unknown dialects in the input"),
                               cl::init(false), cl::cat(mainCategory));
 
-// Options to control early-out from pipeline.
 enum Until { UntilAIGLowering, UntilEnd };
 
 static auto runUntilValues = llvm::cl::values(
@@ -140,7 +140,7 @@ static cl::opt<std::string> abcPath("abc-path", cl::desc("Path to ABC"),
                                     cl::cat(mainCategory));
 
 static cl::opt<bool>
-    continueOnFailure("ignore-abc-failures",
+    ignoreAbcFailures("ignore-abc-failures",
                       cl::desc("Continue on ABC failure instead of aborting"),
                       cl::init(false), cl::cat(mainCategory));
 
@@ -152,6 +152,17 @@ static bool untilReached(Until until) {
   return until >= runUntilBefore || until > runUntilAfter;
 }
 
+static void
+nestOrAddToHierarchicalRunner(OpPassManager &pm,
+                              std::function<void(OpPassManager &pm)> pipeline,
+                              const std::string &topName) {
+  if (topName.empty()) {
+    pipeline(pm.nest<hw::HWModuleOp>());
+  } else {
+    pm.addPass(circt::createHierarchicalRunner(topName, pipeline));
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // Tool implementation
 //===----------------------------------------------------------------------===//
@@ -161,60 +172,24 @@ static void partiallyLegalizeCombToAIG(SmallVectorImpl<std::string> &ops) {
   (ops.push_back(AllowedOpTy::getOperationName().str()), ...);
 }
 
-static void populateSynthesisPipeline(PassManager &pm) {
+// Add a default synthesis pipeline and analysis.
-  auto pipeline = [](OpPassManager &mpm) {
+static void populateCIRCTSynthPipeline(PassManager &pm) {
-    // Add the AIG to Comb at the scope exit if requested.
+  auto pipeline = [](OpPassManager &pm) {
-    auto addAIGToComb = llvm::make_scope_exit([&]() {
+    circt::synthesis::buildAIGLoweringPipeline(pm);
-      if (convertToComb) {
-        mpm.addPass(circt::createConvertAIGToComb());
-        mpm.addPass(createCSEPass());
-      }
-    });
-    {
-      // Partially legalize Comb to AIG, run CSE and canonicalization.
-      circt::ConvertCombToAIGOptions options;
-      partiallyLegalizeCombToAIG<comb::AndOp, comb::OrOp, comb::XorOp,
-                                 comb::MuxOp, comb::ICmpOp, hw::ArrayGetOp,
-                                 hw::ArraySliceOp, hw::ArrayCreateOp,
-                                 hw::ArrayConcatOp, hw::AggregateConstantOp>(
-          options.additionalLegalOps);
-      mpm.addPass(circt::createConvertCombToAIG(options));
-    }
-    mpm.addPass(createCSEPass());
-    mpm.addPass(createSimpleCanonicalizerPass());
-
-    mpm.addPass(circt::hw::createHWAggregateToCombPass());
-    mpm.addPass(circt::createConvertCombToAIG());
-    mpm.addPass(createCSEPass());
     if (untilReached(UntilAIGLowering))
       return;
-    mpm.addPass(createSimpleCanonicalizerPass());
+
-    mpm.addPass(createCSEPass());
+    circt::synthesis::AIGOptimizationPipelineOptions options;
-    mpm.addPass(aig::createLowerVariadic());
+    options.abcCommands = abcCommands;
-    // TODO: LowerWordToBits is not scalable for large designs. Change to
+    options.abcPath.setValue(abcPath);
-    // conditionally enable the pass once the rest of the pipeline was able
+    options.ignoreAbcFailures.setValue(ignoreAbcFailures);
-    // to handle multibit operands properly.
+
-    mpm.addPass(aig::createLowerWordToBits());
+    circt::synthesis::buildAIGOptimizationPipeline(pm, options);
-    mpm.addPass(createCSEPass());
-    mpm.addPass(createSimpleCanonicalizerPass());
-    if (!abcCommands.empty()) {
-      aig::ABCRunnerOptions options;
-      options.abcPath = abcPath;
-      options.abcCommands.assign(abcCommands.begin(), abcCommands.end());
-      options.continueOnFailure = continueOnFailure;
-      mpm.addPass(aig::createABCRunner(options));
-    }
-    // TODO: Add balancing, rewriting, FRAIG conversion, etc.
-    if (untilReached(UntilEnd))
-      return;
   };
 
-  if (topName.empty()) {
+  nestOrAddToHierarchicalRunner(pm, pipeline, topName);
-    pipeline(pm.nest<hw::HWModuleOp>());
-  } else {
-    pm.addPass(circt::createHierarchicalRunner(topName, pipeline));
-  }
 
+  // Run analysis if requested.
   if (!outputLongestPath.empty()) {
     circt::aig::PrintLongestPathAnalysisOptions options;
     options.outputFile = outputLongestPath;
@@ -223,7 +198,14 @@ static void populateSynthesisPipeline(PassManager &pm) {
     pm.addPass(circt::aig::createPrintLongestPathAnalysis(options));
   }
 
-  // TODO: Add LUT mapping, etc.
+  if (convertToComb)
+    nestOrAddToHierarchicalRunner(
+        pm,
+        [&](OpPassManager &pm) {
+          pm.addPass(circt::createConvertAIGToComb());
+          pm.addPass(createCSEPass());
+        },
+        topName);
 }
 
 /// Check output stream before writing bytecode to it.
@@ -285,7 +267,7 @@ static LogicalResult executeSynthesis(MLIRContext &context) {
     pm.addInstrumentation(
         std::make_unique<VerbosePassInstrumentation<mlir::ModuleOp>>(
             "circt-synth"));
-  populateSynthesisPipeline(pm);
+  populateCIRCTSynthPipeline(pm);
 
   if (!topName.empty()) {
     // Set a top module name for the longest path analysis.
@@ -320,6 +302,7 @@ int main(int argc, char **argv) {
   registerPassManagerCLOptions();
   registerDefaultTimingManagerCLOptions();
   registerAsmPrinterCLOptions();
+
   cl::AddExtraVersionPrinter(
       [](llvm::raw_ostream &os) { os << circt::getCirctVersion() << '\n'; });