[AIGToComb] [circt-synth] Add a AIG to Comb conversion pass

This adds a conversion pass from AIG dialect to Comb dialect.
AndInverterOp can be easily converted into comb.and + comb.xor
+ hw.constant.

This enables us to utilize core dialects tools for synthesis
results without any addition. Primarly use case is running LEC
on IR before and after synthesis.

include/circt/Conversion/AIGToComb.h

@@ -0,0 +1,22 @@
+//===- AIGToComb.h - AIG to Comb dialect conversion -------------*- C++ -*-===//
+//
+// 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_CONVERSION_AIGTOCOMB_H
+#define CIRCT_CONVERSION_AIGTOCOMB_H
+
+#include "circt/Support/LLVM.h"
+#include <memory>
+
+namespace circt {
+
+#define GEN_PASS_DECL_CONVERTAIGTOCOMB
+#include "circt/Conversion/Passes.h.inc"
+
+} // namespace circt
+
+#endif // CIRCT_CONVERSION_AIGTOCOMB_H

include/circt/Conversion/Passes.h

@@ -13,6 +13,7 @@
 #ifndef CIRCT_CONVERSION_PASSES_H
 #define CIRCT_CONVERSION_PASSES_H
 
+#include "circt/Conversion/AIGToComb.h"
 #include "circt/Conversion/AffineToLoopSchedule.h"
 #include "circt/Conversion/ArcToLLVM.h"
 #include "circt/Conversion/CFToHandshake.h"

include/circt/Conversion/Passes.td

@@ -808,4 +808,20 @@ def ConvertCombToAIG: Pass<"convert-comb-to-aig",  "hw::HWModuleOp"> {
   ];
 }
 
+//===----------------------------------------------------------------------===//
+// ConvertAIGToComb
+//===----------------------------------------------------------------------===//
+
+def ConvertAIGToComb: Pass<"convert-aig-to-comb", "hw::HWModuleOp"> {
+  let summary = "Lower AIG ops to Comb ops.";
+  let description = [{
+    This pass converts AIG operations to Comb operations. This is mostly
+    used for verifying post-synthesis results.
+  }];
+  let dependentDialects = [
+    "circt::comb::CombDialect", "circt::hw::HWDialect"
+  ];
+}
+
+
 #endif // CIRCT_CONVERSION_PASSES_TD

lib/CAPI/Conversion/CMakeLists.txt

@@ -3,6 +3,7 @@ add_circt_public_c_api_library(CIRCTCAPIConversion
 
   LINK_LIBS PUBLIC
   CIRCTAffineToLoopSchedule
+  CIRCTAIGToComb
   CIRCTArcToLLVM
   CIRCTCalyxToFSM
   CIRCTCalyxToHW

lib/Conversion/AIGToComb/AIGToComb.cpp

@@ -0,0 +1,86 @@
+//===- AIGToComb.cpp - AIG to Comb Conversion Pass --------------*- C++ -*-===//
+//
+// 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 is the main AIG to Comb Conversion Pass Implementation.
+//
+//===----------------------------------------------------------------------===//
+
+#include "circt/Conversion/AIGToComb.h"
+#include "circt/Dialect/AIG/AIGOps.h"
+#include "circt/Dialect/Comb/CombOps.h"
+#include "circt/Dialect/HW/HWOps.h"
+#include "mlir/Pass/Pass.h"
+#include "mlir/Transforms/DialectConversion.h"
+
+namespace circt {
+#define GEN_PASS_DEF_CONVERTAIGTOCOMB
+#include "circt/Conversion/Passes.h.inc"
+} // namespace circt
+
+using namespace circt;
+using namespace comb;
+
+//===----------------------------------------------------------------------===//
+// Conversion patterns
+//===----------------------------------------------------------------------===//
+
+namespace {
+
+struct AIGAndInverterOpConversion : OpConversionPattern<aig::AndInverterOp> {
+  using OpConversionPattern<aig::AndInverterOp>::OpConversionPattern;
+  LogicalResult
+  matchAndRewrite(aig::AndInverterOp op, OpAdaptor adaptor,
+                  ConversionPatternRewriter &rewriter) const override {
+    // Convert to comb.and + comb.xor + hw.constant
+    auto width = op.getResult().getType().getIntOrFloatBitWidth();
+    auto allOnes =
+        rewriter.create<hw::ConstantOp>(op.getLoc(), APInt::getAllOnes(width));
+    SmallVector<Value> operands;
+    operands.reserve(op.getNumOperands());
+    for (auto [input, inverted] : llvm::zip(op.getOperands(), op.getInverted()))
+      operands.push_back(inverted ? rewriter.createOrFold<comb::XorOp>(
+                                        op.getLoc(), input, allOnes, true)
+                                  : input);
+    // NOTE: Use createOrFold to avoid creating a new operation if possible.
+    rewriter.replaceOp(
+        op, rewriter.createOrFold<comb::AndOp>(op.getLoc(), operands, true));
+    return success();
+  }
+};
+
+} // namespace
+
+//===----------------------------------------------------------------------===//
+// Convert AIG to Comb pass
+//===----------------------------------------------------------------------===//
+
+namespace {
+struct ConvertAIGToCombPass
+    : public impl::ConvertAIGToCombBase<ConvertAIGToCombPass> {
+
+  void runOnOperation() override;
+  using ConvertAIGToCombBase<ConvertAIGToCombPass>::ConvertAIGToCombBase;
+};
+} // namespace
+
+static void populateAIGToCombConversionPatterns(RewritePatternSet &patterns) {
+  patterns.add<AIGAndInverterOpConversion>(patterns.getContext());
+}
+
+void ConvertAIGToCombPass::runOnOperation() {
+  ConversionTarget target(getContext());
+  target.addLegalDialect<comb::CombDialect, hw::HWDialect>();
+  target.addIllegalDialect<aig::AIGDialect>();
+
+  RewritePatternSet patterns(&getContext());
+  populateAIGToCombConversionPatterns(patterns);
+
+  if (failed(mlir::applyPartialConversion(getOperation(), target,
+                                          std::move(patterns))))
+    return signalPassFailure();
+}

lib/Conversion/AIGToComb/CMakeLists.txt

@@ -0,0 +1,15 @@
+add_circt_conversion_library(CIRCTAIGToComb
+  AIGToComb.cpp
+
+  DEPENDS
+  CIRCTConversionPassIncGen
+
+  LINK_LIBS PUBLIC
+  CIRCTAIG
+  CIRCTHW
+  CIRCTComb
+  MLIRIR
+  MLIRPass
+  MLIRSupport
+  MLIRTransforms
+)

lib/Conversion/CMakeLists.txt

@@ -1,4 +1,5 @@
 add_subdirectory(AffineToLoopSchedule)
+add_subdirectory(AIGToComb)
 add_subdirectory(ArcToLLVM)
 add_subdirectory(CalyxToFSM)
 add_subdirectory(CalyxToHW)

test/Conversion/AIGToComb/aig-to-comb.mlir

@@ -0,0 +1,12 @@
+// RUN: circt-opt %s --convert-aig-to-comb | FileCheck %s
+
+// CHECK-LABEL: @test
+hw.module @test(in %a: i32, in %b: i32, in %c: i32, in %d: i32, out out0: i32) {
+  // CHECK: %c-1_i32 = hw.constant -1 : i32
+  // CHECK: %[[NOT_A:.+]] = comb.xor bin %a, %c-1_i32 : i32
+  // CHECK: %[[NOT_C:.+]] = comb.xor bin %c, %c-1_i32 : i32
+  // CHECK: %[[RESULT:.+]] = comb.and bin %[[NOT_A]], %b, %[[NOT_C]], %d : i32
+  // CHECK: hw.output %[[RESULT]] : i32
+  %0 = aig.and_inv not %a, %b, not %c, %d : i32
+  hw.output %0 : i32
+}

test/circt-synth/basic.mlir

@@ -1,10 +1,11 @@
 // RUN: circt-synth %s | FileCheck %s
 // RUN: circt-synth %s --until-before aig-lowering | FileCheck %s --check-prefix=AIG
+// RUN: circt-synth %s --until-before aig-lowering --convert-to-comb | FileCheck %s --check-prefix=COMB
 
 // AIG-LABEL: @and
 // CHECK-LABEL: @and
+// COMB-LABEL: @and
 hw.module @and(in %a: i2, in %b: i2, in %c: i2, out and: i2) {
-  %0 = comb.and %a, %b, %c : i2
   // AIG-NEXT:  %[[AND_INV:.+]] = aig.and_inv %a, %b, %c : i2
   // AIG-NEXT: hw.output %[[AND_INV]] : i2
   // CHECK-DAG: %[[B_1:.+]] = comb.extract %b from 1 : (i2) -> i1
@@ -19,5 +20,7 @@ hw.module @and(in %a: i2, in %b: i2, in %c: i2, out and: i2) {
   // CHECK-DAG: %[[AND_INV_3:.+]] = aig.and_inv %[[A_0]], %[[AND_INV_1]] : i1
   // CHECK-DAG: %[[CONCAT:.+]] = comb.concat %[[AND_INV_2]], %[[AND_INV_3]] : i1, i1
   // CHECK-NEXT: hw.output %[[CONCAT]] : i2
+  // COMB-NOT: aig.and_inv
+  %0 = comb.and %a, %b, %c : i2
   hw.output %0 : i2
 }

tools/circt-synth/CMakeLists.txt

@@ -2,6 +2,7 @@ add_circt_tool(circt-synth circt-synth.cpp)
 target_link_libraries(circt-synth
   PRIVATE
   CIRCTAIG
+  CIRCTAIGToComb
   CIRCTAIGTransforms
   CIRCTComb
   CIRCTCombToAIG

tools/circt-synth/circt-synth.cpp

@@ -11,6 +11,7 @@
 ///
 //===----------------------------------------------------------------------===//
 
+#include "circt/Conversion/AIGToComb.h"
 #include "circt/Conversion/CombToAIG.h"
 #include "circt/Dialect/AIG/AIGDialect.h"
 #include "circt/Dialect/AIG/AIGPasses.h"
@@ -26,6 +27,7 @@
 #include "mlir/Support/FileUtilities.h"
 #include "mlir/Support/LogicalResult.h"
 #include "mlir/Transforms/Passes.h"
+#include "llvm/ADT/ScopeExit.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/PrettyStackTrace.h"
@@ -77,6 +79,11 @@ static llvm::cl::opt<Until> runUntilAfter(
     "until-after", llvm::cl::desc("Stop pipeline after a specified point"),
     runUntilValues, llvm::cl::init(UntilEnd), llvm::cl::cat(mainCategory));
 
+static cl::opt<bool>
+    convertToComb("convert-to-comb",
+                  cl::desc("Convert AIG to Comb at the end of the pipeline"),
+                  cl::init(false), cl::cat(mainCategory));
+
 //===----------------------------------------------------------------------===//
 // Main Tool Logic
 //===----------------------------------------------------------------------===//
@@ -90,6 +97,15 @@ static bool untilReached(Until until) {
 //===----------------------------------------------------------------------===//
 
 static void populateSynthesisPipeline(PassManager &pm) {
+  // Add the AIG to Comb at the scope exit if requested.
+  auto addAIGToComb = llvm::make_scope_exit([&]() {
+    if (convertToComb) {
+      auto &mpm = pm.nest<hw::HWModuleOp>();
+      mpm.addPass(circt::createConvertAIGToComb());
+      mpm.addPass(createCSEPass());
+    }
+  });
+
   auto &mpm = pm.nest<hw::HWModuleOp>();
   mpm.addPass(circt::createConvertCombToAIG());
   mpm.addPass(createCSEPass());