[Mlir-commits] [mlir] [MLIR][ArmSVE] Add initial lowering of vector.contract to SVE `*MMLA` instructions (PR #135636)
Kiran Chandramohan
llvmlistbot at llvm.org
Tue Jun 3 01:49:11 PDT 2025
================
@@ -0,0 +1,367 @@
+//===- LowerContractionToSMMLAPattern.cpp - Contract to SMMLA ---*- 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 file implements lowering patterns from vector.contract to operations
+// that map to instructions from the SVE FEAT_I8MM extension.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Dialect/Arith/IR/Arith.h"
+#include "mlir/Dialect/ArmSVE/IR/ArmSVEDialect.h"
+#include "mlir/Dialect/ArmSVE/Transforms/Transforms.h"
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
+#include "mlir/Dialect/Utils/IndexingUtils.h"
+#include "mlir/Dialect/Vector/IR/VectorOps.h"
+#include "mlir/IR/AffineMap.h"
+#include "mlir/IR/PatternMatch.h"
+#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
+
+#include "mlir/Dialect/UB/IR/UBOps.h"
+
+#define DEBUG_TYPE "lower-contract-to-arm-sve-i8mm"
+
+using namespace mlir;
+using namespace mlir::arm_sve;
+
+namespace {
+// Get the operand of a `vector.contract`. This function is intended to abstract
+// away from the particular way a value is extended before feeding it into the
+// `vector.contract` - via zero-extend or an explicit or implicit sign-extend
+// (for implicit sign-extension see `vector.contract` documentation).
+//
+// The template parameter `Op` indicates the extension operation (explicir or
+// implicit) for which we are checking.
+//
+// Return success only for extensions from `i8` to `i32`.
+template <typename Op>
+std::optional<Value> getExtOperand(Value v, Type i8Ty, Type i32Ty) {
+
+ static_assert(llvm::is_one_of<Op, arith::ExtSIOp, arith::ExtUIOp>::value,
+ "Must be instantiated with either sign- or zero- extension op");
+
+ // If the operand is not defined by an explicit extend operation of the
+ // accepted operation type allow for an implicit sign-extension.
+ auto extOp = dyn_cast_or_null<Op>(v.getDefiningOp());
+ if (!extOp) {
+ if constexpr (std::is_same<Op, arith::ExtSIOp>::value) {
+ auto vTy = cast<VectorType>(v.getType());
+ if (vTy.getElementType() != i8Ty)
+ return {};
+ return v;
+ }
+ return {};
+ }
+
+ // If the operand is defined by an explicit extend operation of the accepted
+ // operation type, check it's extented from `i8` to `i32`.
+ auto inOp = extOp.getIn();
+ auto inTy = dyn_cast<VectorType>(inOp.getType());
+ if (!inTy || inTy.getElementType() != i8Ty)
+ return {};
+
+ auto outTy = dyn_cast<VectorType>(extOp.getType());
+ if (!outTy || outTy.getElementType() != i32Ty)
+ return {};
+
+ return inOp;
+}
+
+// Designate the operation (resp. instruction) used to do sub-tile matrix
+// multiplications.
+enum class MMLA {
+ Signed, // smmla
+ Unsigned, // ummla
+ Mixed, // usmmla
+ MixedSwapped // usmmla with LHS and RHS swapped
+};
+
+// Create the matrix multply and accumulate operation according to `op`.
+Value createMMLA(PatternRewriter &rewriter, MMLA op, Location loc,
+ mlir::VectorType accType, Value acc, Value lhs, Value rhs) {
+ switch (op) {
+ case MMLA::Signed:
+ return rewriter.create<arm_sve::SmmlaOp>(loc, accType, acc, lhs, rhs);
+ case MMLA::Unsigned:
+ return rewriter.create<arm_sve::UmmlaOp>(loc, accType, acc, lhs, rhs);
+ case MMLA::Mixed:
+ return rewriter.create<arm_sve::UsmmlaOp>(loc, accType, acc, lhs, rhs);
+ case MMLA::MixedSwapped:
+ // The accumulator comes transposed and the result will be transposed
+ // later, so all we have to do here is swap the operands.
+ return rewriter.create<arm_sve::UsmmlaOp>(loc, accType, acc, rhs, lhs);
+ }
+}
+
+/// Lower a contraction operation that performs a matrix multiplication
+/// of two 8-bit integer matrix tiles with logical dimensions <Mx8> and <8x[N]>
+/// for the left-hand side and the right-hand side, respectively,
+/// yielding a <Mx[N]> 32-bit integer result.
+///
+/// The operands' shapes are such that the operands can be evenly split into
+/// sub-tiles with dimensions as expected by the targeted FEAT_I8MM
+/// instructions. The intent is that M and N are chosen (by higher level
+/// transforms) in such a way as to maximise register usage. The main use case
+/// we envision as of now is MMT4D, thus the RHS operand is expected
+/// pre-transposed.
+///
+/// The matrix multiplication is performed by unrolling the usual tiled matrix
+/// multiplication algorithm using sub-tiles with dimensions <2x8> for the LHS,
+/// <8x[2]> for the RHS, and <2x[2]> for the result and the input accumulator.
+///
+/// One way to illustrate the operation is as follows:
+///
+/// RHS<8x[N]>: <8x[2]> <8x[2]> ... <8x[2]>
+/// +-----------------------------
+/// LHS<Mx8>: <2x8> | <2x[2]> <2x[2]> ... <2x[2]>
+/// <2x8> | <2x[2]> <2x[2]> ... <2x[2]>
+/// ... | ... ... ... ...
+/// <2x8> | <2x[2]> <2x[2]> ... <2x[2]>
+///
+/// The RHS operand is unpacked into N/2 values, each representing a sequence of
+/// VSCALE number of sub-tiles with dimensions <8x2>.
+/// The LHS operand is initially unpacked into M/2 values, each representing a
+/// sub-tile with dimensions <2x8>, and then each such sub-tile is replicated
+/// VSCALE times.
+/// Multiplying thus replicated LHS sub-tile by the corresposponing RHS sub-tile
+/// correctly computes an entire result sub-tile.
+class LowerContractionToSVEI8MMPattern
+ : public OpRewritePattern<vector::ContractionOp> {
+public:
+ using OpRewritePattern::OpRewritePattern;
+ LogicalResult matchAndRewrite(vector::ContractionOp op,
+ PatternRewriter &rewriter) const override {
+
+ Location loc = op.getLoc();
+ mlir::VectorType lhsType = op.getLhsType();
+ mlir::VectorType rhsType = op.getRhsType();
+
+ // Check the rank the types so we can safely examine their dimensions.
+ if (lhsType.getRank() != 2 || rhsType.getRank() != 2)
+ return rewriter.notifyMatchFailure(op, "non-matching operand shape");
+
+ auto M = lhsType.getDimSize(0);
+ auto N = rhsType.getDimSize(0);
+ auto K = rhsType.getDimSize(1);
+
+ // Check the operands have the expected shape:
+ // * for LHS: fixed vector MxK
+ // * for RHS: scalable vector [N]xK
+ // * K == 8
+ // * M and N even and at least 2
+ if (lhsType.isScalable() || !rhsType.getScalableDims()[0] ||
+ rhsType.getScalableDims()[1] || lhsType.getDimSize(1) != K || K != 8 ||
+ M < 2 || M % 2 != 0 || N < 2 || N % 2 != 0 ||
+ !rhsType.getScalableDims()[0])
+ return rewriter.notifyMatchFailure(op, "non-matching operand shape");
+
+ // Check permutation maps. For now only accept
+ // lhs: (d0, d1, d2) -> (d0, d2)
+ // rhs: (d0, d1, d2) -> (d1, d2)
+ // acc: (d0, d1, d2) -> (d0, d1)
+ // This corresponds to matrix multiplication with transposed RHS.
+ if (op.getIndexingMapsArray()[0] !=
+ AffineMap::getMultiDimMapWithTargets(3, ArrayRef{0u, 2u},
+ op.getContext()) ||
+ op.getIndexingMapsArray()[1] !=
+ AffineMap::getMultiDimMapWithTargets(3, ArrayRef{1u, 2u},
+ op.getContext()) ||
+ op.getIndexingMapsArray()[2] !=
+ AffineMap::getMultiDimMapWithTargets(3, ArrayRef{0u, 1u},
+ op.getContext()))
+ return rewriter.notifyMatchFailure(op, "non-matching permutation maps");
+
+ // Check iterator types for matrix multiplication.
+ auto itTypes = op.getIteratorTypesArray();
+ if (itTypes.size() != 3 || itTypes[0] != vector::IteratorType::parallel ||
+ itTypes[1] != vector::IteratorType::parallel ||
+ itTypes[2] != vector::IteratorType::reduction)
+ return rewriter.notifyMatchFailure(
+ op, "iterator types do not correspond to matrix multiplication");
+
+ // Check the combining kind is addition.
+ if (op.getKind() != vector::CombiningKind::ADD)
+ return rewriter.notifyMatchFailure(op,
+ "combining kind is not an addition");
+
+ // Check the output is a vector of i32 elements.
+ auto outTy = dyn_cast<VectorType>(op.getResultType());
+ if (!outTy || outTy.getElementType() != rewriter.getI32Type())
+ return rewriter.notifyMatchFailure(op,
+ "output type is not a vector of i32");
+
+ // Check inputs are sign-/zero- extensions from i8 to i32. Get the values
+ // before the extension. All four signed/unsigned combinations for input
+ // operands are supported, but they are lowered to different operations.
+ // Determine which is the appropriate operation to lower to.
+ MMLA mmlaOp = MMLA::Signed;
+ auto maybeLhs = getExtOperand<arith::ExtSIOp>(
+ op.getLhs(), rewriter.getI8Type(), rewriter.getI32Type());
+ if (!maybeLhs) {
+ mmlaOp = MMLA::Unsigned;
+ maybeLhs = getExtOperand<arith::ExtUIOp>(
+ op.getLhs(), rewriter.getI8Type(), rewriter.getI32Type());
+ }
+ if (!maybeLhs)
+ return rewriter.notifyMatchFailure(
+ op, "LHS is not a sign- or zero- extended i8");
+
+ auto maybeRhs = getExtOperand<arith::ExtSIOp>(
+ op.getRhs(), rewriter.getI8Type(), rewriter.getI32Type());
+ if (maybeRhs) {
+ if (mmlaOp == MMLA::Unsigned)
+ mmlaOp = MMLA::Mixed;
+ } else {
+ if (mmlaOp == MMLA::Signed)
+ mmlaOp = MMLA::MixedSwapped;
+ maybeRhs = getExtOperand<arith::ExtUIOp>(
+ op.getRhs(), rewriter.getI8Type(), rewriter.getI32Type());
+ }
+ if (!maybeRhs)
+ return rewriter.notifyMatchFailure(
+ op, "RHS is not a sign- or zero- extended i8");
+
+ // One-dimensional vector types for arm_sve.*mmla
+ auto nxv16i8 = VectorType::get(/*shape=*/16, rewriter.getI8Type(),
+ /*scalableDims=*/{true});
+ auto nxv4i32 = VectorType::get(/*shape=*/4, rewriter.getI32Type(),
+ /*scalableDims=*/{true});
+
+ // Extract LHS sub-tiles with logicall shape <2x8>.
+ SmallVector<Value> lhsTile;
+ for (int64_t i = 0; i < M; i += 2) {
+ // Exract two consective rows of the LHS tile.
----------------
kiranchandramohan wrote:
```suggestion
//Extract two consecutive rows of the LHS tile.
```
https://github.com/llvm/llvm-project/pull/135636
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