RewriteInsertsPass.cpp

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//===- RewriteInsertsPass.cpp - MLIR conversion pass ----------------------===//
//
// 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 rewrite sequential chains of
// `spirv::CompositeInsert` operations into `spirv::CompositeConstruct`
// operations.
//
//===----------------------------------------------------------------------===//
 
#include "mlir/Dialect/SPIRV/Transforms/Passes.h"
 
#include "mlir/Dialect/SPIRV/IR/SPIRVOps.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinOps.h"
 
namespace mlir {
namespace spirv {
#define GEN_PASS_DEF_SPIRVREWRITEINSERTSPASS
#include "mlir/Dialect/SPIRV/Transforms/Passes.h.inc"
} // namespace spirv
} // namespace mlir
 
using namespace mlir;
 
namespace {
 
/// Replaces sequential chains of `spirv::CompositeInsertOp` operation into
/// `spirv::CompositeConstructOp` operation if possible.
class RewriteInsertsPass
    : public spirv::impl::SPIRVRewriteInsertsPassBase<RewriteInsertsPass> {
public:
  void runOnOperation() override;
 
private:
  /// Collects a sequential insertion chain by the given
  /// `spirv::CompositeInsertOp` operation, if the given operation is the last
  /// in the chain.
  LogicalResult
  collectInsertionChain(spirv::CompositeInsertOp op,
                        SmallVectorImpl<spirv::CompositeInsertOp> &insertions);
};
 
} // namespace
 
void RewriteInsertsPass::runOnOperation() {
  SmallVector<SmallVector<spirv::CompositeInsertOp, 4>, 4> workList;
  getOperation().walk([this, &workList](spirv::CompositeInsertOp op) {
    SmallVector<spirv::CompositeInsertOp, 4> insertions;
    if (succeeded(collectInsertionChain(op, insertions)))
      workList.push_back(insertions);
  });
 
  for (const auto &insertions : workList) {
    auto lastCompositeInsertOp = insertions.back();
    auto compositeType = lastCompositeInsertOp.getType();
    auto location = lastCompositeInsertOp.getLoc();
 
    SmallVector<Value, 4> operands;
    // Collect inserted objects.
    for (auto insertionOp : insertions)
      operands.push_back(insertionOp.getObject());
 
    OpBuilder builder(lastCompositeInsertOp);
    auto compositeConstructOp = builder.create<spirv::CompositeConstructOp>(
        location, compositeType, operands);
 
    lastCompositeInsertOp.replaceAllUsesWith(
        compositeConstructOp->getResult(0));
 
    // Erase ops.
    for (auto insertOp : llvm::reverse(insertions)) {
      auto *op = insertOp.getOperation();
      if (op->use_empty())
        insertOp.erase();
    }
  }
}
 
LogicalResult RewriteInsertsPass::collectInsertionChain(
    spirv::CompositeInsertOp op,
    SmallVectorImpl<spirv::CompositeInsertOp> &insertions) {
  auto indicesArrayAttr = cast<ArrayAttr>(op.getIndices());
  // TODO: handle nested composite object.
  if (indicesArrayAttr.size() == 1) {
    auto numElements = cast<spirv::CompositeType>(op.getComposite().getType())
                           .getNumElements();
 
    auto index = cast<IntegerAttr>(indicesArrayAttr[0]).getInt();
    // Need a last index to collect a sequential chain.
    if (index + 1 != numElements)
      return failure();
 
    insertions.resize(numElements);
    while (true) {
      insertions[index] = op;
 
      if (index == 0)
        return success();
 
      op = op.getComposite().getDefiningOp<spirv::CompositeInsertOp>();
      if (!op)
        return failure();
 
      --index;
      indicesArrayAttr = cast<ArrayAttr>(op.getIndices());
      if ((indicesArrayAttr.size() != 1) ||
          (cast<IntegerAttr>(indicesArrayAttr[0]).getInt() != index))
        return failure();
    }
  }
  return failure();
}