SplitVectorLoadUpsChains.cpp

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//===- SplitVectorLoadUpsChains.cpp - Split Load+UPS Chains ----*- C++ -*-===//
//
// This file is licensed 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
//
// (c) Copyright 2025 Advanced Micro Devices Inc.
//
//===----------------------------------------------------------------------===//
// This pass optimizes chains of vector.load followed by aievec.ups operations
// for AIE2p targets. Instead of loading a 1024-bit vector and then shuffling
// it into two halves for separate UPS operations (3 shuffles total), it splits
// both the load and UPS into two 512-bit halves, requiring only 1 shuffle for
// concatenation.
//===----------------------------------------------------------------------===//
 
#include "aie/Dialect/AIEVec/IR/AIEVecOps.h"
#include "aie/Dialect/AIEVec/Pipelines/Passes.h"
#include "mlir/Dialect/Affine/IR/AffineOps.h"
#include "mlir/Dialect/Arith/IR/Arith.h"
#include "mlir/Dialect/MemRef/IR/MemRef.h"
#include "mlir/Dialect/Vector/IR/VectorOps.h"
#include "mlir/IR/PatternMatch.h"
#include "mlir/Pass/Pass.h"
#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
 
#define DEBUG_TYPE "aievec-split-load-ups-chains"
 
using namespace mlir;
using namespace xilinx::aievec;
 
namespace {
 
/// Pattern to optimize vector.load + aievec.ups chains by splitting them.
///
/// This pattern detects cases where a 1024-bit vector is loaded and then
/// passed to an aievec.ups operation that produces a 2048-bit result.
/// Instead of the inefficient approach of:
///   1. Load 1024 bits
///   2. Shuffle to split into 2×512 bits
///   3. Apply 2× UPS operations
///   4. Shuffle to concatenate results
///
/// It transforms to:
///   1. Load 2×512 bits directly
///   2. Apply 2× UPS operations immediately
///   3. Shuffle once to concatenate results
///
/// This reduces shuffle operations from 3 to 1.
struct SplitVectorLoadUpsChainPattern : public OpRewritePattern<UPSOp> {
  using OpRewritePattern<UPSOp>::OpRewritePattern;
 
  LogicalResult matchAndRewrite(UPSOp upsOp,
                                PatternRewriter &rewriter) const override {
    // Get source value and its type
    Value source = upsOp.getSource();
    auto srcVecTy = dyn_cast<VectorType>(source.getType());
    if (!srcVecTy)
      return failure();
 
    // Get result type
    auto resultVecTy = dyn_cast<VectorType>(upsOp.getResult().getType());
    if (!resultVecTy)
      return failure();
 
    // Check if this is a 1024-bit -> 2048-bit integer UPS
    Type srcElemTy = srcVecTy.getElementType();
    Type resultElemTy = resultVecTy.getElementType();
 
    if (!srcElemTy.isInteger() || !resultElemTy.isInteger())
      return failure();
 
    unsigned srcBitWidth = srcElemTy.getIntOrFloatBitWidth();
    unsigned resultBitWidth = resultElemTy.getIntOrFloatBitWidth();
    int64_t srcLanes = srcVecTy.getNumElements();
    int64_t resultLanes = resultVecTy.getNumElements();
 
    int64_t srcVectorSize = srcBitWidth * srcLanes;
    int64_t resultVectorSize = resultBitWidth * resultLanes;
 
    // Only optimize the 1024-bit -> 2048-bit case
    // (e.g., v64int16 -> v64acc32)
    if (srcVectorSize != 1024 || resultVectorSize != 2048)
      return failure();
 
    // Check that the UPS result width is 32 and source width is 16
    if (resultBitWidth != 32 || srcBitWidth != 16)
      return failure();
 
    // Check if source is directly from a vector.load
    auto loadOp = source.getDefiningOp<vector::LoadOp>();
    if (!loadOp)
      return failure();
 
    // Ensure the load is only used by this UPS operation
    if (!loadOp.getResult().hasOneUse())
      return failure();
 
    Location loc = upsOp.getLoc();
 
    // Get load operation details
    Value memRef = loadOp.getBase();
    ValueRange indices = loadOp.getIndices();
 
    // Create element type for half-sized vector (v32int16)
    int64_t halfLanes = srcLanes / 2;
    auto halfSrcVecTy = VectorType::get({halfLanes}, srcElemTy);
    auto halfResultVecTy = VectorType::get({halfLanes}, resultElemTy);
 
    // Calculate offset for second half load
    // For v64int16, we need to offset by 32 elements (64 bytes for i16)
    int64_t elementOffset = halfLanes;
 
    // Create indices for first half load (same as original)
    SmallVector<Value> firstHalfIndices(indices.begin(), indices.end());
 
    // Create indices for second half load
    SmallVector<Value> secondHalfIndices(indices.begin(), indices.end());
 
    // Adjust the last index by the element offset
    if (!indices.empty()) {
      Value lastIdx = indices.back();
      Value offsetVal =
          arith::ConstantIndexOp::create(rewriter, loc, elementOffset);
      Value newLastIdx =
          arith::AddIOp::create(rewriter, loc, lastIdx, offsetVal);
      secondHalfIndices.back() = newLastIdx;
    }
 
    // Create first half load
    auto loadHalf0 = vector::LoadOp::create(rewriter, loc, halfSrcVecTy, memRef,
                                            firstHalfIndices);
 
    // Create second half load
    auto loadHalf1 = vector::LoadOp::create(rewriter, loc, halfSrcVecTy, memRef,
                                            secondHalfIndices);
 
    // Create UPS for first half
    auto upsHalf0 = UPSOp::create(rewriter, loc, halfResultVecTy,
                                  loadHalf0.getResult(), upsOp.getShift());
 
    // Create UPS for second half
    auto upsHalf1 = UPSOp::create(rewriter, loc, halfResultVecTy,
                                  loadHalf1.getResult(), upsOp.getShift());
 
    // Concatenate the two halves using vector.shuffle
    // The mask is sequential from 0 to 63 to concatenate [half0; half1]
    SmallVector<int64_t> concatMask;
    for (int64_t i = 0; i < resultLanes; ++i) {
      concatMask.push_back(i);
    }
 
    auto concatOp = vector::ShuffleOp::create(
        rewriter, loc, upsHalf0.getResult(), upsHalf1.getResult(), concatMask);
 
    // Replace the original UPS operation with the concatenated result
    rewriter.replaceOp(upsOp, concatOp.getResult());
 
    // The original load will be removed by dead code elimination
    // since it no longer has any uses
 
    return success();
  }
};
 
/// Pattern to optimize aievec.srs + vector.store chains by splitting them.
///
/// This pattern detects cases where a 2048-bit vector is passed to an
/// aievec.srs operation that produces a 1024-bit result, which is then stored.
/// Instead of the inefficient approach of:
///   1. Shuffle to split 2048-bit into 2×1024 bits
///   2. Apply 2× SRS operations
///   3. Shuffle to concatenate results
///   4. Store 1024 bits
///
/// It transforms to:
///   1. Split source via shuffle into 2×1024 bits (for SRS input)
///   2. Apply 2× SRS operations to get 2×512 bits
///   3. Store 2×512 bits directly
///
/// This reduces shuffle operations from 3 to 1.
struct SplitVectorSrsStoreChainPattern
    : public OpRewritePattern<vector::StoreOp> {
  using OpRewritePattern<vector::StoreOp>::OpRewritePattern;
 
  LogicalResult matchAndRewrite(vector::StoreOp storeOp,
                                PatternRewriter &rewriter) const override {
    // Get the value being stored and its type
    Value valueToStore = storeOp.getValueToStore();
    auto storeVecTy = dyn_cast<VectorType>(valueToStore.getType());
    if (!storeVecTy)
      return failure();
 
    // Check if the value comes from an aievec.srs operation
    auto srsOp = valueToStore.getDefiningOp<SRSOp>();
    if (!srsOp)
      return failure();
 
    // Ensure the SRS is only used by this store operation
    if (!srsOp.getResult().hasOneUse())
      return failure();
 
    // Get source and result types of SRS
    Value srsSource = srsOp.getSource();
    auto srcVecTy = dyn_cast<VectorType>(srsSource.getType());
    if (!srcVecTy)
      return failure();
 
    Type srcElemTy = srcVecTy.getElementType();
    Type resultElemTy = storeVecTy.getElementType();
 
    if (!srcElemTy.isInteger() || !resultElemTy.isInteger())
      return failure();
 
    unsigned srcBitWidth = srcElemTy.getIntOrFloatBitWidth();
    unsigned resultBitWidth = resultElemTy.getIntOrFloatBitWidth();
    int64_t srcLanes = srcVecTy.getNumElements();
    int64_t resultLanes = storeVecTy.getNumElements();
 
    int64_t srcVectorSize = srcBitWidth * srcLanes;
    int64_t resultVectorSize = resultBitWidth * resultLanes;
 
    // Only optimize the 2048-bit -> 1024-bit case
    // (e.g., v64acc32 -> v64int16)
    if (srcVectorSize != 2048 || resultVectorSize != 1024)
      return failure();
 
    // Check that the SRS source width is 32 and result width is 16
    if (srcBitWidth != 32 || resultBitWidth != 16)
      return failure();
 
    Location loc = storeOp.getLoc();
 
    // Get store operation details
    Value memRef = storeOp.getBase();
    ValueRange indices = storeOp.getIndices();
 
    // Create element types for half-sized vectors
    int64_t halfSrcLanes = srcLanes / 2;
    int64_t halfResultLanes = resultLanes / 2;
    auto halfResultVecTy = VectorType::get({halfResultLanes}, resultElemTy);
 
    // Split the SRS source into two halves using shuffle
    SmallVector<int64_t> firstHalfMask, secondHalfMask;
    for (int64_t i = 0; i < halfSrcLanes; ++i) {
      firstHalfMask.push_back(i);
      secondHalfMask.push_back(halfSrcLanes + i);
    }
 
    auto srcHalf0 = vector::ShuffleOp::create(rewriter, loc, srsSource,
                                              srsSource, firstHalfMask);
    auto srcHalf1 = vector::ShuffleOp::create(rewriter, loc, srsSource,
                                              srsSource, secondHalfMask);
 
    // Create SRS for first half
    auto srsHalf0 = SRSOp::create(rewriter, loc, halfResultVecTy,
                                  srcHalf0.getResult(), srsOp.getShift());
 
    // Create SRS for second half
    auto srsHalf1 = SRSOp::create(rewriter, loc, halfResultVecTy,
                                  srcHalf1.getResult(), srsOp.getShift());
 
    // Calculate offset for second half store
    int64_t elementOffset = halfResultLanes;
 
    // Create indices for first half store (same as original)
    SmallVector<Value> firstHalfIndices(indices.begin(), indices.end());
 
    // Create indices for second half store
    SmallVector<Value> secondHalfIndices(indices.begin(), indices.end());
 
    // Adjust the last index by the element offset
    if (!indices.empty()) {
      Value lastIdx = indices.back();
      Value offsetVal =
          arith::ConstantIndexOp::create(rewriter, loc, elementOffset);
      Value newLastIdx =
          arith::AddIOp::create(rewriter, loc, lastIdx, offsetVal);
      secondHalfIndices.back() = newLastIdx;
    }
 
    // Create first half store
    vector::StoreOp::create(rewriter, loc, srsHalf0.getResult(), memRef,
                            firstHalfIndices);
 
    // Create second half store
    vector::StoreOp::create(rewriter, loc, srsHalf1.getResult(), memRef,
                            secondHalfIndices);
 
    // Erase the original store operation
    rewriter.eraseOp(storeOp);
 
    // The original SRS will be removed by dead code elimination
    // since it no longer has any uses
 
    return success();
  }
};
 
/// Pass to split vector.load + aievec.ups chains for better performance
struct SplitVectorLoadUpsChainsPass
    : public PassWrapper<SplitVectorLoadUpsChainsPass, OperationPass<>> {
  MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(SplitVectorLoadUpsChainsPass)
 
  StringRef getArgument() const final { return "aievec-split-load-ups-chains"; }
 
  StringRef getDescription() const final {
    return "Split vector.load + aievec.ups chains to reduce shuffle operations";
  }
 
  void getDependentDialects(DialectRegistry &registry) const override {
    registry.insert<vector::VectorDialect, arith::ArithDialect,
                    memref::MemRefDialect, affine::AffineDialect,
                    xilinx::aievec::AIEVecDialect>();
  }
 
  void runOnOperation() override {
    Operation *op = getOperation();
    MLIRContext *context = &getContext();
    RewritePatternSet patterns(context);
 
    patterns
        .add<SplitVectorLoadUpsChainPattern, SplitVectorSrsStoreChainPattern>(
            context);
 
    if (failed(applyPatternsGreedily(op, std::move(patterns)))) {
      signalPassFailure();
    }
  }
};
 
} // namespace
 
namespace xilinx {
namespace aievec {
 
std::unique_ptr<::mlir::Pass> createSplitVectorLoadUpsChainsPass() {
  return std::make_unique<SplitVectorLoadUpsChainsPass>();
}
 
} // namespace aievec
} // namespace xilinx