[Mlir-commits] [mlir] [SCFToAffine] Add a pass to raise scf to affine ops. (PR #152925)
Ming Yan
llvmlistbot at llvm.org
Sun Aug 24 22:54:36 PDT 2025
https://github.com/NexMing updated https://github.com/llvm/llvm-project/pull/152925
>From 48dad4a635baad85a353a3371084cbee9a72c0d4 Mon Sep 17 00:00:00 2001
From: Ming Yan <nexming7 at gmail.com>
Date: Mon, 11 Aug 2025 00:14:47 +0800
Subject: [PATCH 1/2] [SCFToAffine] Add a pass to raise scf to affine ops.
This patch supports the conversion from `scf.for` to `affine.for`.
---
mlir/include/mlir/Conversion/Passes.h | 1 +
mlir/include/mlir/Conversion/Passes.td | 12 ++
.../mlir/Conversion/SCFToAffine/SCFToAffine.h | 26 ++++
mlir/lib/Conversion/CMakeLists.txt | 1 +
.../lib/Conversion/SCFToAffine/CMakeLists.txt | 17 +++
.../Conversion/SCFToAffine/SCFToAffine.cpp | 136 ++++++++++++++++++
.../Conversion/SCFToAffine/scf-to-affine.mlir | 57 ++++++++
7 files changed, 250 insertions(+)
create mode 100644 mlir/include/mlir/Conversion/SCFToAffine/SCFToAffine.h
create mode 100644 mlir/lib/Conversion/SCFToAffine/CMakeLists.txt
create mode 100644 mlir/lib/Conversion/SCFToAffine/SCFToAffine.cpp
create mode 100644 mlir/test/Conversion/SCFToAffine/scf-to-affine.mlir
diff --git a/mlir/include/mlir/Conversion/Passes.h b/mlir/include/mlir/Conversion/Passes.h
index 91b2ecf8922a3..f6df794685484 100644
--- a/mlir/include/mlir/Conversion/Passes.h
+++ b/mlir/include/mlir/Conversion/Passes.h
@@ -58,6 +58,7 @@
#include "mlir/Conversion/OpenMPToLLVM/ConvertOpenMPToLLVM.h"
#include "mlir/Conversion/PDLToPDLInterp/PDLToPDLInterp.h"
#include "mlir/Conversion/ReconcileUnrealizedCasts/ReconcileUnrealizedCasts.h"
+#include "mlir/Conversion/SCFToAffine/SCFToAffine.h"
#include "mlir/Conversion/SCFToControlFlow/SCFToControlFlow.h"
#include "mlir/Conversion/SCFToEmitC/SCFToEmitC.h"
#include "mlir/Conversion/SCFToGPU/SCFToGPUPass.h"
diff --git a/mlir/include/mlir/Conversion/Passes.td b/mlir/include/mlir/Conversion/Passes.td
index 2058aba7f9e37..57f726356cbbf 100644
--- a/mlir/include/mlir/Conversion/Passes.td
+++ b/mlir/include/mlir/Conversion/Passes.td
@@ -1027,6 +1027,18 @@ def ReconcileUnrealizedCastsPass : Pass<"reconcile-unrealized-casts"> {
}];
}
+//===----------------------------------------------------------------------===//
+// SCFToAffine
+//===----------------------------------------------------------------------===//
+
+def RaiseSCFToAffinePass : Pass<"raise-scf-to-affine"> {
+ let summary = "Raise SCF to affine ops";
+ let dependentDialects = [
+ "affine::AffineDialect",
+ "scf::SCFDialect",
+ ];
+}
+
//===----------------------------------------------------------------------===//
// SCFToControlFlow
//===----------------------------------------------------------------------===//
diff --git a/mlir/include/mlir/Conversion/SCFToAffine/SCFToAffine.h b/mlir/include/mlir/Conversion/SCFToAffine/SCFToAffine.h
new file mode 100644
index 0000000000000..4f87ef8e6c6e4
--- /dev/null
+++ b/mlir/include/mlir/Conversion/SCFToAffine/SCFToAffine.h
@@ -0,0 +1,26 @@
+//===- SCFToAffine.h - SCF to Affine Pass entrypoint ------------*- 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 MLIR_CONVERSION_SCFTOAFFINE_SCFTOAFFINE_H_
+#define MLIR_CONVERSION_SCFTOAFFINE_SCFTOAFFINE_H_
+
+#include <memory>
+
+namespace mlir {
+class Pass;
+class RewritePatternSet;
+
+#define GEN_PASS_DECL_RAISESCFTOAFFINEPASS
+#include "mlir/Conversion/Passes.h.inc"
+
+/// Collect a set of patterns to convert SCF operations to Affine operations.
+void populateSCFToAffineConversionPatterns(RewritePatternSet &patterns);
+
+} // namespace mlir
+
+#endif // MLIR_CONVERSION_SCFTOAFFINE_SCFTOAFFINE_H_
diff --git a/mlir/lib/Conversion/CMakeLists.txt b/mlir/lib/Conversion/CMakeLists.txt
index 171f7169fd41d..da4e8704ef5a5 100644
--- a/mlir/lib/Conversion/CMakeLists.txt
+++ b/mlir/lib/Conversion/CMakeLists.txt
@@ -51,6 +51,7 @@ add_subdirectory(OpenACCToSCF)
add_subdirectory(OpenMPToLLVM)
add_subdirectory(PDLToPDLInterp)
add_subdirectory(ReconcileUnrealizedCasts)
+add_subdirectory(SCFToAffine)
add_subdirectory(SCFToControlFlow)
add_subdirectory(SCFToEmitC)
add_subdirectory(SCFToGPU)
diff --git a/mlir/lib/Conversion/SCFToAffine/CMakeLists.txt b/mlir/lib/Conversion/SCFToAffine/CMakeLists.txt
new file mode 100644
index 0000000000000..bf1494d6f3cf0
--- /dev/null
+++ b/mlir/lib/Conversion/SCFToAffine/CMakeLists.txt
@@ -0,0 +1,17 @@
+add_mlir_conversion_library(MLIRSCFToAffine
+ SCFToAffine.cpp
+
+ ADDITIONAL_HEADER_DIRS
+ ${MLIR_MAIN_INCLUDE_DIR}/mlir/Conversion/SCFToAffine
+
+ DEPENDS
+ MLIRConversionPassIncGen
+
+ LINK_LIBS PUBLIC
+ MLIRArithDialect
+ MLIRAffineDialect
+ MLIRLLVMDialect
+ MLIRSCFDialect
+ MLIRSCFTransforms
+ MLIRTransforms
+ )
diff --git a/mlir/lib/Conversion/SCFToAffine/SCFToAffine.cpp b/mlir/lib/Conversion/SCFToAffine/SCFToAffine.cpp
new file mode 100644
index 0000000000000..35e662d88b488
--- /dev/null
+++ b/mlir/lib/Conversion/SCFToAffine/SCFToAffine.cpp
@@ -0,0 +1,136 @@
+//===- SCFToAffine.cpp - SCF to Affine conversion -------------------------===//
+//
+// 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 a pass to raise scf.for, scf.if and loop.terminator
+// ops into affine ops.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Conversion/SCFToAffine/SCFToAffine.h"
+#include "mlir/Dialect/Affine/IR/AffineOps.h"
+#include "mlir/Dialect/SCF/IR/SCF.h"
+#include "mlir/IR/Verifier.h"
+#include "mlir/Transforms/DialectConversion.h"
+#include "mlir/Transforms/Passes.h"
+
+namespace mlir {
+#define GEN_PASS_DEF_RAISESCFTOAFFINEPASS
+#include "mlir/Conversion/Passes.h.inc"
+} // namespace mlir
+
+using namespace mlir;
+
+namespace {
+
+struct SCFToAffinePass
+ : public impl::RaiseSCFToAffinePassBase<SCFToAffinePass> {
+ void runOnOperation() override;
+};
+
+bool canRaiseToAffine(scf::ForOp op) {
+ return affine::isValidDim(op.getLowerBound()) &&
+ affine::isValidDim(op.getUpperBound()) &&
+ affine::isValidSymbol(op.getStep());
+}
+
+struct ForOpRewrite : public OpRewritePattern<scf::ForOp> {
+ using OpRewritePattern<scf::ForOp>::OpRewritePattern;
+
+ std::pair<affine::AffineForOp, Value>
+ createAffineFor(scf::ForOp op, PatternRewriter &rewriter) const {
+ if (auto constantStep = op.getStep().getDefiningOp<arith::ConstantOp>()) {
+ int64_t step = cast<IntegerAttr>(constantStep.getValue()).getInt();
+ if (step > 0)
+ return positiveConstantStep(op, step, rewriter);
+ }
+ return genericBounds(op, rewriter);
+ }
+
+ std::pair<affine::AffineForOp, Value>
+ positiveConstantStep(scf::ForOp op, int64_t step,
+ PatternRewriter &rewriter) const {
+ auto affineFor = affine::AffineForOp::create(
+ rewriter, op.getLoc(), ValueRange(op.getLowerBound()),
+ AffineMap::get(1, 0, rewriter.getAffineDimExpr(0)),
+ ValueRange(op.getUpperBound()),
+ AffineMap::get(1, 0, rewriter.getAffineDimExpr(0)), step,
+ op.getInits());
+ return std::make_pair(affineFor, affineFor.getInductionVar());
+ }
+
+ std::pair<affine::AffineForOp, Value>
+ genericBounds(scf::ForOp op, PatternRewriter &rewriter) const {
+ Value lower = op.getLowerBound();
+ Value upper = op.getUpperBound();
+ Value step = op.getStep();
+ AffineExpr lowerExpr = rewriter.getAffineDimExpr(0);
+ AffineExpr upperExpr = rewriter.getAffineDimExpr(1);
+ AffineExpr stepExpr = rewriter.getAffineSymbolExpr(0);
+ auto affineFor = affine::AffineForOp::create(
+ rewriter, op.getLoc(), ValueRange(), rewriter.getConstantAffineMap(0),
+ ValueRange({lower, upper, step}),
+ AffineMap::get(
+ 2, 1, (upperExpr - lowerExpr + stepExpr - 1).floorDiv(stepExpr)),
+ 1, op.getInits());
+
+ rewriter.setInsertionPointToStart(affineFor.getBody());
+ auto actualIndexMap = AffineMap::get(
+ 2, 1, lowerExpr + rewriter.getAffineDimExpr(1) * stepExpr);
+ auto actualIndex = affine::AffineApplyOp::create(
+ rewriter, op.getLoc(), actualIndexMap,
+ ValueRange({lower, affineFor.getInductionVar(), step}));
+ return std::make_pair(affineFor, actualIndex.getResult());
+ }
+
+ LogicalResult matchAndRewrite(scf::ForOp op,
+ PatternRewriter &rewriter) const override {
+ if (!canRaiseToAffine(op))
+ return failure();
+
+ auto [affineFor, actualIndex] = createAffineFor(op, rewriter);
+ Block *affineBody = affineFor.getBody();
+
+ if (affineBody->mightHaveTerminator())
+ rewriter.eraseOp(affineBody->getTerminator());
+
+ SmallVector<Value> argValues;
+ argValues.push_back(actualIndex);
+ llvm::append_range(argValues, affineFor.getRegionIterArgs());
+ rewriter.inlineBlockBefore(op.getBody(), affineBody, affineBody->end(),
+ argValues);
+
+ auto scfYieldOp = cast<scf::YieldOp>(affineBody->getTerminator());
+ rewriter.setInsertionPointToEnd(affineBody);
+ rewriter.replaceOpWithNewOp<affine::AffineYieldOp>(
+ scfYieldOp, scfYieldOp->getOperands());
+
+ rewriter.replaceOp(op, affineFor);
+ return success();
+ }
+};
+
+} // namespace
+
+void mlir::populateSCFToAffineConversionPatterns(RewritePatternSet &patterns) {
+ patterns.add<ForOpRewrite>(patterns.getContext());
+}
+
+void SCFToAffinePass::runOnOperation() {
+ MLIRContext &ctx = getContext();
+ RewritePatternSet patterns(&ctx);
+ populateSCFToAffineConversionPatterns(patterns);
+
+ // Configure conversion to raise SCF operations.
+ ConversionTarget target(ctx);
+ target.addDynamicallyLegalOp<scf::ForOp>(
+ [](scf::ForOp op) { return !canRaiseToAffine(op); });
+ target.markUnknownOpDynamicallyLegal([](Operation *) { return true; });
+ if (failed(
+ applyPartialConversion(getOperation(), target, std::move(patterns))))
+ signalPassFailure();
+}
diff --git a/mlir/test/Conversion/SCFToAffine/scf-to-affine.mlir b/mlir/test/Conversion/SCFToAffine/scf-to-affine.mlir
new file mode 100644
index 0000000000000..2e2649ed8ef1c
--- /dev/null
+++ b/mlir/test/Conversion/SCFToAffine/scf-to-affine.mlir
@@ -0,0 +1,57 @@
+// RUN: mlir-opt -raise-scf-to-affine -split-input-file %s | FileCheck %s
+
+// CHECK: #[[$ATTR_0:.+]] = affine_map<(d0, d1)[s0] -> ((d1 - d0 + s0 - 1) floordiv s0)>
+// CHECK: #[[$ATTR_1:.+]] = affine_map<(d0, d1)[s0] -> (d0 + d1 * s0)>
+// CHECK: #[[$ATTR_2:.+]] = affine_map<(d0) -> (d0)>
+// CHECK-LABEL: func.func @simple_loop(
+// CHECK-SAME: %[[ARG0:.*]]: memref<?xi32>,
+// CHECK-SAME: %[[ARG1:.*]]: memref<3xindex>) {
+// CHECK: %[[VAL_0:.*]] = arith.constant 0 : i32
+// CHECK: %[[VAL_1:.*]] = arith.constant 0 : index
+// CHECK: %[[VAL_2:.*]] = arith.constant 1 : index
+// CHECK: %[[VAL_3:.*]] = arith.constant 2 : index
+// CHECK: %[[VAL_4:.*]] = memref.load %[[ARG1]]{{\[}}%[[VAL_1]]] : memref<3xindex>
+// CHECK: %[[VAL_5:.*]] = memref.load %[[ARG1]]{{\[}}%[[VAL_2]]] : memref<3xindex>
+// CHECK: %[[VAL_6:.*]] = memref.load %[[ARG1]]{{\[}}%[[VAL_3]]] : memref<3xindex>
+// CHECK: affine.for %[[VAL_7:.*]] = 0 to #[[$ATTR_0]](%[[VAL_4]], %[[VAL_5]]){{\[}}%[[VAL_6]]] {
+// CHECK: %[[VAL_8:.*]] = affine.apply #[[$ATTR_1]](%[[VAL_4]], %[[VAL_7]]){{\[}}%[[VAL_6]]]
+// CHECK: memref.store %[[VAL_0]], %[[ARG0]]{{\[}}%[[VAL_8]]] : memref<?xi32>
+// CHECK: }
+// CHECK: return
+// CHECK: }
+
+func.func @simple_loop(%arg0: memref<?xi32>, %arg1: memref<3xindex>) {
+ %c0_i32 = arith.constant 0 : i32
+ %c0 = arith.constant 0 : index
+ %c1 = arith.constant 1 : index
+ %c2 = arith.constant 2 : index
+ %0 = memref.load %arg1[%c0] : memref<3xindex>
+ %1 = memref.load %arg1[%c1] : memref<3xindex>
+ %2 = memref.load %arg1[%c2] : memref<3xindex>
+ scf.for %arg2 = %0 to %1 step %2 {
+ memref.store %c0_i32, %arg0[%arg2] : memref<?xi32>
+ }
+ return
+}
+
+// CHECK-LABEL: func.func @loop_with_constant_step(
+// CHECK-SAME: %[[ARG0:.*]]: memref<?xi32>,
+// CHECK-SAME: %[[ARG1:.*]]: index,
+// CHECK-SAME: %[[ARG2:.*]]: index) {
+// CHECK: %[[VAL_0:.*]] = arith.constant 0 : i32
+// CHECK: %[[VAL_1:.*]] = arith.constant 3 : index
+// CHECK: affine.for %[[VAL_2:.*]] = #[[$ATTR_2]](%[[ARG1]]) to #[[$ATTR_2]](%[[ARG2]]) step 3 {
+// CHECK: memref.store %[[VAL_0]], %[[ARG0]]{{\[}}%[[VAL_2]]] : memref<?xi32>
+// CHECK: }
+// CHECK: return
+// CHECK: }
+
+func.func @loop_with_constant_step(%arg0: memref<?xi32>, %arg1: index, %arg2: index) {
+ %c0_i32 = arith.constant 0 : i32
+ %c3 = arith.constant 3 : index
+ scf.for %arg3 = %arg1 to %arg2 step %c3 {
+ memref.store %c0_i32, %arg0[%arg3] : memref<?xi32>
+ }
+ return
+}
+
>From fe9698eccf94d64ceeca0f1d2d0bfb90e07a4ff5 Mon Sep 17 00:00:00 2001
From: yanming <ming.yan at terapines.com>
Date: Mon, 25 Aug 2025 13:53:06 +0800
Subject: [PATCH 2/2] Use `walkAndApplyPatterns` instead of
`applyPartialConversion`
---
mlir/lib/Conversion/SCFToAffine/SCFToAffine.cpp | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)
diff --git a/mlir/lib/Conversion/SCFToAffine/SCFToAffine.cpp b/mlir/lib/Conversion/SCFToAffine/SCFToAffine.cpp
index 35e662d88b488..c8d250ab6e447 100644
--- a/mlir/lib/Conversion/SCFToAffine/SCFToAffine.cpp
+++ b/mlir/lib/Conversion/SCFToAffine/SCFToAffine.cpp
@@ -15,8 +15,8 @@
#include "mlir/Dialect/Affine/IR/AffineOps.h"
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/IR/Verifier.h"
-#include "mlir/Transforms/DialectConversion.h"
#include "mlir/Transforms/Passes.h"
+#include "mlir/Transforms/WalkPatternRewriteDriver.h"
namespace mlir {
#define GEN_PASS_DEF_RAISESCFTOAFFINEPASS
@@ -124,13 +124,5 @@ void SCFToAffinePass::runOnOperation() {
MLIRContext &ctx = getContext();
RewritePatternSet patterns(&ctx);
populateSCFToAffineConversionPatterns(patterns);
-
- // Configure conversion to raise SCF operations.
- ConversionTarget target(ctx);
- target.addDynamicallyLegalOp<scf::ForOp>(
- [](scf::ForOp op) { return !canRaiseToAffine(op); });
- target.markUnknownOpDynamicallyLegal([](Operation *) { return true; });
- if (failed(
- applyPartialConversion(getOperation(), target, std::move(patterns))))
- signalPassFailure();
+ walkAndApplyPatterns(getOperation(), std::move(patterns));
}
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