5cc0f76d34
The pattern rewriter documentation states that "*all* IR mutations [...] are required to be performed via the `PatternRewriter`." This commit adds two functions that were missing from the rewriter API: `moveOpBefore` and `moveOpAfter`. After an operation was moved, the `notifyOperationInserted` callback is triggered. This allows listeners such as the greedy pattern rewrite driver to react to IR changes. This commit narrows the discrepancy between the kind of IR modification that can be performed and the kind of IR modifications that can be listened to.
123 lines
4.9 KiB
C++
123 lines
4.9 KiB
C++
//===- ForToWhile.cpp - scf.for to scf.while loop conversion --------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Transforms SCF.ForOp's into SCF.WhileOp's.
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Dialect/SCF/Transforms/Passes.h"
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#include "mlir/Dialect/Arith/IR/Arith.h"
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#include "mlir/Dialect/SCF/IR/SCF.h"
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#include "mlir/Dialect/SCF/Transforms/Transforms.h"
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#include "mlir/IR/PatternMatch.h"
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#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
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namespace mlir {
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#define GEN_PASS_DEF_SCFFORTOWHILELOOP
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#include "mlir/Dialect/SCF/Transforms/Passes.h.inc"
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} // namespace mlir
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using namespace llvm;
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using namespace mlir;
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using scf::ForOp;
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using scf::WhileOp;
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namespace {
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struct ForLoopLoweringPattern : public OpRewritePattern<ForOp> {
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using OpRewritePattern<ForOp>::OpRewritePattern;
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LogicalResult matchAndRewrite(ForOp forOp,
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PatternRewriter &rewriter) const override {
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// Generate type signature for the loop-carried values. The induction
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// variable is placed first, followed by the forOp.iterArgs.
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SmallVector<Type> lcvTypes;
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SmallVector<Location> lcvLocs;
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lcvTypes.push_back(forOp.getInductionVar().getType());
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lcvLocs.push_back(forOp.getInductionVar().getLoc());
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for (Value value : forOp.getInitArgs()) {
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lcvTypes.push_back(value.getType());
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lcvLocs.push_back(value.getLoc());
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}
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// Build scf.WhileOp
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SmallVector<Value> initArgs;
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initArgs.push_back(forOp.getLowerBound());
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llvm::append_range(initArgs, forOp.getInitArgs());
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auto whileOp = rewriter.create<WhileOp>(forOp.getLoc(), lcvTypes, initArgs,
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forOp->getAttrs());
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// 'before' region contains the loop condition and forwarding of iteration
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// arguments to the 'after' region.
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auto *beforeBlock = rewriter.createBlock(
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&whileOp.getBefore(), whileOp.getBefore().begin(), lcvTypes, lcvLocs);
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rewriter.setInsertionPointToStart(whileOp.getBeforeBody());
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auto cmpOp = rewriter.create<arith::CmpIOp>(
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whileOp.getLoc(), arith::CmpIPredicate::slt,
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beforeBlock->getArgument(0), forOp.getUpperBound());
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rewriter.create<scf::ConditionOp>(whileOp.getLoc(), cmpOp.getResult(),
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beforeBlock->getArguments());
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// Inline for-loop body into an executeRegion operation in the "after"
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// region. The return type of the execRegionOp does not contain the
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// iv - yields in the source for-loop contain only iterArgs.
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auto *afterBlock = rewriter.createBlock(
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&whileOp.getAfter(), whileOp.getAfter().begin(), lcvTypes, lcvLocs);
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// Add induction variable incrementation
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rewriter.setInsertionPointToEnd(afterBlock);
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auto ivIncOp = rewriter.create<arith::AddIOp>(
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whileOp.getLoc(), afterBlock->getArgument(0), forOp.getStep());
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// Rewrite uses of the for-loop block arguments to the new while-loop
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// "after" arguments
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for (const auto &barg : enumerate(forOp.getBody(0)->getArguments()))
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rewriter.replaceAllUsesWith(barg.value(),
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afterBlock->getArgument(barg.index()));
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// Inline for-loop body operations into 'after' region.
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for (auto &arg : llvm::make_early_inc_range(*forOp.getBody()))
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rewriter.moveOpBefore(&arg, afterBlock, afterBlock->end());
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// Add incremented IV to yield operations
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for (auto yieldOp : afterBlock->getOps<scf::YieldOp>()) {
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SmallVector<Value> yieldOperands = yieldOp.getOperands();
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yieldOperands.insert(yieldOperands.begin(), ivIncOp.getResult());
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rewriter.modifyOpInPlace(yieldOp,
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[&]() { yieldOp->setOperands(yieldOperands); });
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}
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// We cannot do a direct replacement of the forOp since the while op returns
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// an extra value (the induction variable escapes the loop through being
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// carried in the set of iterargs). Instead, rewrite uses of the forOp
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// results.
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for (const auto &arg : llvm::enumerate(forOp.getResults()))
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rewriter.replaceAllUsesWith(arg.value(),
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whileOp.getResult(arg.index() + 1));
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rewriter.eraseOp(forOp);
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return success();
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}
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};
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struct ForToWhileLoop : public impl::SCFForToWhileLoopBase<ForToWhileLoop> {
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void runOnOperation() override {
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auto *parentOp = getOperation();
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MLIRContext *ctx = parentOp->getContext();
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RewritePatternSet patterns(ctx);
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patterns.add<ForLoopLoweringPattern>(ctx);
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(void)applyPatternsAndFoldGreedily(parentOp, std::move(patterns));
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}
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};
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} // namespace
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std::unique_ptr<Pass> mlir::createForToWhileLoopPass() {
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return std::make_unique<ForToWhileLoop>();
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}
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