llvm · cowardsa · Jul 25, 2025 · Jul 17, 2025 · Jul 18, 2025 · Jul 18, 2025
diff --git a/include/circt/Conversion/DatapathToComb.h b/include/circt/Conversion/DatapathToComb.h
@@ -0,0 +1,21 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_DATAPATHTOCOMB_H
+#define CIRCT_CONVERSION_DATAPATHTOCOMB_H
+
+#include "circt/Support/LLVM.h"
+
+namespace circt {
+
+#define GEN_PASS_DECL_CONVERTDATAPATHTOCOMB
+#include "circt/Conversion/Passes.h.inc"
+
+} // namespace circt
+
+#endif // CIRCT_CONVERSION_DATAPATHTOCOMB_H
diff --git a/include/circt/Conversion/Passes.h b/include/circt/Conversion/Passes.h
@@ -26,6 +26,7 @@
 #include "circt/Conversion/CombToSMT.h"
 #include "circt/Conversion/ConvertToArcs.h"
 #include "circt/Conversion/DCToHW.h"
+#include "circt/Conversion/DatapathToComb.h"
 #include "circt/Conversion/DatapathToSMT.h"
 #include "circt/Conversion/ExportChiselInterface.h"
 #include "circt/Conversion/ExportVerilog.h"

diff --git a/include/circt/Conversion/Passes.td b/include/circt/Conversion/Passes.td
@@ -871,4 +871,22 @@ def ConvertDatapathToSMT : Pass<"convert-datapath-to-smt"> {
   ];
 }
 
+//===----------------------------------------------------------------------===//
+// ConvertDatapathToComb
+//===----------------------------------------------------------------------===//
+
+def ConvertDatapathToComb : Pass<"convert-datapath-to-comb"> {
+  let summary = "Convert Datapath ops to Comb ops";
+    let dependentDialects = [
+    "circt::comb::CombDialect", "circt::datapath::DatapathDialect",
+    "circt::hw::HWDialect"
+  ];
+  let options = [
+    Option<"lowerCompressToAdd", "lower-compress-to-add", "bool", "false",
+           "Lower compress operators to variadic add.">,
+    Option<"forceBooth", "lower-partial-product-to-booth", "bool", "false",
+           "Force all partial products to be lowered to Booth arrays.">
+  ];
+}
+
 #endif // CIRCT_CONVERSION_PASSES_TD
@@ -23,6 +23,7 @@
 #include "mlir/Interfaces/InferIntRangeInterface.h"
 #include "mlir/Interfaces/InferTypeOpInterface.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"
+#include "mlir/Transforms/DialectConversion.h"
 
 namespace llvm {
 struct KnownBits;
@@ -85,6 +86,18 @@ Value createDynamicInject(OpBuilder &builder, Location loc, Value value,
 Value createInject(OpBuilder &builder, Location loc, Value value,
                    unsigned offset, Value replacement);
 
+/// Construct a full adder for three 1-bit inputs.
+std::pair<Value, Value> fullAdder(OpBuilder &builder, Location loc, Value a,
+                                  Value b, Value c);
+
+/// Perform Wallace tree reduction on partial products.
+/// See https://en.wikipedia.org/wiki/Wallace_tree
+/// \param targetAddends The number of addends to reduce to (2 for carry-save).
+/// \param inputAddends The rows of bits to be summed.
+SmallVector<Value> wallaceReduction(OpBuilder &builder, Location loc,
+                                    size_t width, size_t targetAddends,
+                                    SmallVector<SmallVector<Value>> &addends);
+
 } // namespace comb
 } // namespace circt
 

diff --git a/integration_test/circt-synth/datapath-lowering-lec.mlir b/integration_test/circt-synth/datapath-lowering-lec.mlir
@@ -0,0 +1,48 @@
+// REQUIRES: libz3
+// REQUIRES: circt-lec-jit
+
+// RUN: circt-opt %s --convert-datapath-to-comb -o %t.mlir
+// RUN: circt-lec %t.mlir %s -c1=partial_product_5 -c2=partial_product_5 --shared-libs=%libz3 | FileCheck %s --check-prefix=AND5
+// AND5: c1 == c2
+hw.module @partial_product_5(in %a : i5, in %b : i5, out sum : i5) {
+  %0:5 = datapath.partial_product %a, %b : (i5, i5) -> (i5, i5, i5, i5, i5)
+  %1 = comb.add bin %0#0, %0#1, %0#2, %0#3, %0#4 : i5
+  hw.output %1 : i5
+}
+
+// RUN: circt-lec %t.mlir %s -c1=partial_product_4 -c2=partial_product_4 --shared-libs=%libz3 | FileCheck %s --check-prefix=AND4
+// AND4: c1 == c2
+hw.module @partial_product_4(in %a : i4, in %b : i4, out sum : i4) {
+  %0:4 = datapath.partial_product %a, %b : (i4, i4) -> (i4, i4, i4, i4)
+  %1 = comb.add bin %0#0, %0#1, %0#2, %0#3 : i4
+  hw.output %1 : i4
+}
+
+// RUN: circt-lec %t.mlir %s -c1=compress_3 -c2=compress_3 --shared-libs=%libz3 | FileCheck %s --check-prefix=COMP3
+// COMP3: c1 == c2
+hw.module @compress_3(in %a : i4, in %b : i4, in %c : i4, out sum : i4) {
+  %0:2 = datapath.compress %a, %b, %c : i4 [3 -> 2]
+  %1 = comb.add bin %0#0, %0#1 : i4
+  hw.output %1 : i4
+}
+
+// RUN: circt-lec %t.mlir %s -c1=compress_6 -c2=compress_6 --shared-libs=%libz3 | FileCheck %s --check-prefix=COMP6
+// COMP6: c1 == c2
+hw.module @compress_6(in %a : i4, in %b : i4, in %c : i4, in %d : i4, in %e : i4, in %f : i4, out sum : i4) {
+  %0:3 = datapath.compress %a, %b, %c, %d, %e, %f : i4 [6 -> 3]
+  %1 = comb.add bin %0#0, %0#1, %0#2 : i4
+  hw.output %1 : i4
+}
+
+// RUN: circt-opt %s --pass-pipeline="builtin.module(hw.module(convert-datapath-to-comb{lower-partial-product-to-booth=true lower-compress-to-add=true}))" -o %t.mlir
+// RUN: circt-lec %t.mlir %s -c1=partial_product_5 -c2=partial_product_5 --shared-libs=%libz3 | FileCheck %s --check-prefix=BOOTH5
+// BOOTH5: c1 == c2
+
+// RUN: circt-lec %t.mlir %s -c1=partial_product_4 -c2=partial_product_4 --shared-libs=%libz3 | FileCheck %s --check-prefix=BOOTH4
+// BOOTH4: c1 == c2
+
+// RUN: circt-lec %t.mlir %s -c1=compress_3 -c2=compress_3 --shared-libs=%libz3 | FileCheck %s --check-prefix=COMPADD3
+// COMPADD3: c1 == c2
+
+// RUN: circt-lec %t.mlir %s -c1=compress_6 -c2=compress_6 --shared-libs=%libz3 | FileCheck %s --check-prefix=COMPADD6
+// COMPADD6: c1 == c2
diff --git a/lib/CAPI/Conversion/CMakeLists.txt b/lib/CAPI/Conversion/CMakeLists.txt
@@ -14,6 +14,7 @@ add_circt_public_c_api_library(CIRCTCAPIConversion
   CIRCTCombToLLVM
   CIRCTCombToSMT
   CIRCTConvertToArcs
+  CIRCTDatapathToComb
   CIRCTDatapathToSMT
   CIRCTDCToHW
   CIRCTExportChiselInterface

diff --git a/lib/Conversion/CMakeLists.txt b/lib/Conversion/CMakeLists.txt
@@ -9,6 +9,7 @@ add_subdirectory(CombToDatapath)
 add_subdirectory(CombToLLVM)
 add_subdirectory(CombToSMT)
 add_subdirectory(ConvertToArcs)
+add_subdirectory(DatapathToComb)
 add_subdirectory(DatapathToSMT)
 add_subdirectory(DCToHW)
 add_subdirectory(ExportAIGER)

diff --git a/lib/Conversion/CombToAIG/CombToAIG.cpp b/lib/Conversion/CombToAIG/CombToAIG.cpp
@@ -668,21 +668,6 @@ struct CombSubOpConversion : OpConversionPattern<SubOp> {
   }
 };
 
-// Construct a full adder for three 1-bit inputs.
-std::pair<Value, Value> fullAdder(ConversionPatternRewriter &rewriter,
-                                  Location loc, Value a, Value b, Value c) {
-  auto aXorB = rewriter.createOrFold<comb::XorOp>(loc, a, b, true);
-  Value sum = rewriter.createOrFold<comb::XorOp>(loc, aXorB, c, true);
-
-  auto carry = rewriter.createOrFold<comb::OrOp>(
-      loc,
-      ArrayRef<Value>{rewriter.createOrFold<comb::AndOp>(loc, a, b, true),
-                      rewriter.createOrFold<comb::AndOp>(loc, aXorB, c, true)},
-      true);
-
-  return {sum, carry};
-}
-
 struct CombMulOpConversion : OpConversionPattern<MulOp> {
   using OpConversionPattern<MulOp>::OpConversionPattern;
   using OpAdaptor = typename OpConversionPattern<MulOp>::OpAdaptor;
@@ -729,74 +714,14 @@ struct CombMulOpConversion : OpConversionPattern<MulOp> {
       return success();
     }
 
-    // Wallace tree reduction
-    replaceOpAndCopyNamehint(
-        rewriter, op,
-        wallaceReduction(falseValue, width, rewriter, loc, partialProducts));
+    // Wallace tree reduction - reduce to two addends.
+    auto addends =
+        comb::wallaceReduction(rewriter, loc, width, 2, partialProducts);
+    // Sum the two addends using a carry-propagate adder
+    auto newAdd = rewriter.create<comb::AddOp>(loc, addends, true);
+    replaceOpAndCopyNamehint(rewriter, op, newAdd);
     return success();
   }
-
-private:
-  // Perform Wallace tree reduction on partial products.
-  // See https://en.wikipedia.org/wiki/Wallace_tree
-  static Value
-  wallaceReduction(Value falseValue, size_t width,
-                   ConversionPatternRewriter &rewriter, Location loc,
-                   SmallVector<SmallVector<Value>> &partialProducts) {
-    SmallVector<SmallVector<Value>> newPartialProducts;
-    newPartialProducts.reserve(partialProducts.size());
-    // Continue reduction until we have only two rows. The length of
-    // `partialProducts` is reduced by 1/3 in each iteration.
-    while (partialProducts.size() > 2) {
-      newPartialProducts.clear();
-      // Take three rows at a time and reduce to two rows(sum and carry).
-      for (unsigned i = 0; i < partialProducts.size(); i += 3) {
-        if (i + 2 < partialProducts.size()) {
-          // We have three rows to reduce
-          auto &row1 = partialProducts[i];
-          auto &row2 = partialProducts[i + 1];
-          auto &row3 = partialProducts[i + 2];
-
-          assert(row1.size() == width && row2.size() == width &&
-                 row3.size() == width);
-
-          SmallVector<Value> sumRow, carryRow;
-          sumRow.reserve(width);
-          carryRow.reserve(width);
-          carryRow.push_back(falseValue);
-
-          // Process each bit position
-          for (unsigned j = 0; j < width; ++j) {
-            // Full adder logic
-            auto [sum, carry] =
-                fullAdder(rewriter, loc, row1[j], row2[j], row3[j]);
-            sumRow.push_back(sum);
-            if (j + 1 < width)
-              carryRow.push_back(carry);
-          }
-
-          newPartialProducts.push_back(std::move(sumRow));
-          newPartialProducts.push_back(std::move(carryRow));
-        } else {
-          // Add remaining rows as is
-          newPartialProducts.append(partialProducts.begin() + i,
-                                    partialProducts.end());
-        }
-      }
-
-      std::swap(newPartialProducts, partialProducts);
-    }
-
-    assert(partialProducts.size() == 2);
-    // Reverse the order of the bits
-    std::reverse(partialProducts[0].begin(), partialProducts[0].end());
-    std::reverse(partialProducts[1].begin(), partialProducts[1].end());
-    auto lhs = rewriter.create<comb::ConcatOp>(loc, partialProducts[0]);
-    auto rhs = rewriter.create<comb::ConcatOp>(loc, partialProducts[1]);
-
-    // Use comb.add for the final addition.
-    return rewriter.create<comb::AddOp>(loc, ArrayRef<Value>{lhs, rhs}, true);
-  }
 };
 
 template <typename OpTy>

diff --git a/lib/Conversion/DatapathToComb/CMakeLists.txt b/lib/Conversion/DatapathToComb/CMakeLists.txt
@@ -0,0 +1,15 @@
+add_circt_conversion_library(CIRCTDatapathToComb
+  DatapathToComb.cpp
+
+  DEPENDS
+  CIRCTConversionPassIncGen
+
+  LINK_LIBS PUBLIC
+  CIRCTComb
+  CIRCTDatapath
+  CIRCTHW
+  MLIRIR
+  MLIRPass
+  MLIRSupport
+  MLIRTransforms
+)