[AMDGPU] fold memref.subview into amdgpu.gather_to_lds

Author: lialan

mlir/include/mlir/Dialect/AMDGPU/Transforms/Passes.h

@@ -22,8 +22,9 @@ class ConversionTarget;
 namespace amdgpu {
 
 #define GEN_PASS_DECL_AMDGPUEMULATEATOMICSPASS
-#define GEN_PASS_DECL_AMDGPURESOLVESTRIDEDMETADATAPASS
+#define GEN_PASS_DECL_AMDGPUFOLDSUBVIEWOPSPASS
 #define GEN_PASS_DECL_AMDGPUMASKEDLOADTOLOADPASS
+#define GEN_PASS_DECL_AMDGPURESOLVESTRIDEDMETADATAPASS
 #define GEN_PASS_REGISTRATION
 #include "mlir/Dialect/AMDGPU/Transforms/Passes.h.inc"
 
@@ -38,6 +39,9 @@ void populateAmdgpuResolveStridedMetadataPatterns(RewritePatternSet &patterns,
 void populateAmdgpuMaskedloadToLoadPatterns(RewritePatternSet &patterns,
                                             PatternBenefit benefit = 1);
 
+void populateAmdgpuFoldSubviewOpsPatterns(RewritePatternSet &patterns,
+                                          PatternBenefit benefit = 1);
+
 } // namespace amdgpu
 } // namespace mlir
 

mlir/include/mlir/Dialect/AMDGPU/Transforms/Passes.td

@@ -70,4 +70,16 @@ def AmdgpuMaskedloadToLoadPass : Pass<"amdgpu-maskedload-to-load"> {
     "memref::MemRefDialect"
   ];
 }
+
+def AmdgpuFoldSubviewOpsPass : Pass<"amdgpu-fold-subview-ops"> {
+  let summary = "Fold subview operations into their parent operations";
+  let description = [{
+    This pass identifies `memref.subview` source of `GatherToLDSOp` and
+    attempts to fold the source op, potentially simplifying the overall
+    operation and improving performance.
+  }];
+  let dependentDialects = [
+    "memref::MemRefDialect"
+  ];
+}
 #endif // MLIR_DIALECT_AMDGPU_TRANSFORMS_PASSES_TD_

mlir/lib/Dialect/AMDGPU/Transforms/CMakeLists.txt

@@ -1,7 +1,8 @@
 add_mlir_dialect_library(MLIRAMDGPUTransforms
   EmulateAtomics.cpp
-  ResolveStridedMetadata.cpp
+  FoldSubviewOps.cpp
   MaskedloadToLoad.cpp
+  ResolveStridedMetadata.cpp
 
   ADDITIONAL_HEADER_DIRS
   {$MLIR_MAIN_INCLUDE_DIR}/mlir/Dialect/AMDGPU/Transforms

mlir/lib/Dialect/AMDGPU/Transforms/FoldSubviewOps.cpp

@@ -0,0 +1,65 @@
+//===- FoldSubviewOps.cpp - AMDGPU fold subview ops ---------------------===//
+//
+// 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 "mlir/Dialect/AMDGPU/Transforms/Passes.h"
+
+#include "mlir/Dialect/AMDGPU/IR/AMDGPUDialect.h"
+#include "mlir/Dialect/Affine/ViewLikeInterfaceUtils.h"
+#include "mlir/Dialect/MemRef/IR/MemRef.h"
+#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
+
+namespace mlir::amdgpu {
+#define GEN_PASS_DEF_AMDGPUFOLDSUBVIEWOPSPASS
+#include "mlir/Dialect/AMDGPU/Transforms/Passes.h.inc"
+} // namespace mlir::amdgpu
+
+using namespace mlir;
+using namespace mlir::amdgpu;
+
+namespace {
+struct AmdgpuFoldSubviewOpsPass
+    : public amdgpu::impl::AmdgpuFoldSubviewOpsPassBase<
+          AmdgpuFoldSubviewOpsPass> {
+  void runOnOperation() override {
+    RewritePatternSet patterns(&getContext());
+    populateAmdgpuFoldSubviewOpsPatterns(patterns);
+    if (failed(applyPatternsGreedily(getOperation(), std::move(patterns))))
+      signalPassFailure();
+  }
+};
+
+struct FoldSubviewIntoGatherToLDSOp : public OpRewritePattern<GatherToLDSOp> {
+  using OpRewritePattern<GatherToLDSOp>::OpRewritePattern;
+  LogicalResult matchAndRewrite(GatherToLDSOp op,
+                                PatternRewriter &rewriter) const override {
+    Location loc = op.getLoc();
+
+    // Check if the source is a subview operation:
+    auto subviewOp = dyn_cast<memref::SubViewOp>(op.getSrc().getDefiningOp());
+    if (!subviewOp)
+      return rewriter.notifyMatchFailure(
+          loc, "GatherToLDSOp can only be folded if the source is a SubviewOp");
+
+    SmallVector<Value> sourceIndices;
+    mlir::affine::resolveIndicesIntoOpWithOffsetsAndStrides(
+        rewriter, loc, subviewOp.getMixedOffsets(), subviewOp.getMixedStrides(),
+        subviewOp.getDroppedDims(), op.getSrcIndices(), sourceIndices);
+
+    rewriter.replaceOpWithNewOp<GatherToLDSOp>(
+        op, subviewOp.getSource(), sourceIndices, op.getDst(),
+        op.getDstIndices(), op.getTransferType());
+
+    return success();
+  }
+};
+} // namespace
+
+void mlir::amdgpu::populateAmdgpuFoldSubviewOpsPatterns(
+    RewritePatternSet &patterns, PatternBenefit benefit) {
+  patterns.add<FoldSubviewIntoGatherToLDSOp>(patterns.getContext(), benefit);
+}

mlir/test/Dialect/AMDGPU/amdgpu-fold-subviews.mlir

@@ -0,0 +1,21 @@
+// RUN: mlir-opt -amdgpu-fold-subview-ops -split-input-file %s | FileCheck %s
+
+#gpu_lds_addrspace = 3
+
+// CHECK: func @test_memref
+// CHECK-SAME: %arg0: index, %arg1: index
+func.func @test_memref(%offset_i: index, %offset_j: index) {
+  // CHECK: %[[C0:.*]] = arith.constant 0 : index
+  // CHECK: %[[LOCAL:.*]] = memref.alloc() : memref<64x64xf16, 3>
+  // CHECK: %[[MEM:.*]] = memref.alloc() : memref<64x128xf16>
+  // CHECK:  %[[MEM]][%arg0, %arg1], %[[LOCAL]][%[[C0]], %[[C0]]]
+  // CHECK-SAME: vector<8xf16>, memref<64x128xf16>, memref<64x64xf16, 3>
+
+  %alloc = memref.alloc() : memref<64x64xf16, #gpu_lds_addrspace>
+  %mem = memref.alloc() : memref<64x128xf16>
+  %subview = memref.subview %mem[0, 0][32, 64][1, 1] : memref<64x128xf16> to memref<32x64xf16, strided<[128, 1]>>
+  %c0 = arith.constant 0 : index
+  amdgpu.gather_to_lds %subview[%offset_i, %offset_j], %alloc[%c0, %c0]
+    : vector<8xf16>, memref<32x64xf16, strided<[128, 1]>>, memref<64x64xf16, #gpu_lds_addrspace>
+  func.return
+}