fe3933da15
### Description This patch improves the folding efficiency of `vector.insert` and `vector.extract` operations by not returning early after successfully converting dynamic indices to static indices. This PR also renames the test pass `TestConstantFold` to `TestSingleFold` and adds comprehensive documentation explaining the single-pass folding behavior. ### Motivation Since the `OpBuilder::createOrFold` function only calls `fold` **once**, the current `fold` methods of `vector.insert` and `vector.extract` may leave the op in a state that can be folded further. For example, consider the following un-folded IR: ``` %v1 = vector.insert %e1, %v0 [0] : f32 into vector<128xf32> %c0 = arith.constant 0 : index %e2 = vector.extract %v1[%c0] : f32 from vector<128xf32> ``` If we use `createOrFold` to create the `vector.extract` op, then the result will be: ``` %v1 = vector.insert %e1, %v0 [127] : f32 into vector<128xf32> %e2 = vector.extract %v1[0] : f32 from vector<128xf32> ``` But this is not the optimal result. `createOrFold` should have returned `%e1`. The reason is that the execution of fold returns immediately after `extractInsertFoldConstantOp`, causing subsequent folding logics to be skipped. --------- Co-authored-by: Yang Bai <yangb@nvidia.com>
86 lines
3.1 KiB
C++
86 lines
3.1 KiB
C++
//===- TestSingleFold.cpp - Pass to test single-pass folding --------------===//
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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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#include "mlir/Pass/Pass.h"
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#include "mlir/Transforms/FoldUtils.h"
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using namespace mlir;
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namespace {
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/// Test pass for single-pass constant folding.
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///
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/// This pass tests the behavior of operations when folded exactly once. Unlike
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/// canonicalization passes that may apply multiple rounds of folding, this pass
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/// ensures that each operation is folded at most once, which is useful for
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/// testing scenarios where the fold implementation should handle complex cases
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/// without requiring multiple iterations.
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///
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/// The pass also removes dead constants after folding to clean up unused
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/// intermediate results.
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struct TestSingleFold : public PassWrapper<TestSingleFold, OperationPass<>>,
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public RewriterBase::Listener {
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MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(TestSingleFold)
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StringRef getArgument() const final { return "test-single-fold"; }
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StringRef getDescription() const final {
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return "Test single-pass operation folding and dead constant elimination";
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}
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// All constants in the operation post folding.
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SmallVector<Operation *> existingConstants;
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void foldOperation(Operation *op, OperationFolder &helper);
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void runOnOperation() override;
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void notifyOperationInserted(Operation *op,
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OpBuilder::InsertPoint previous) override {
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existingConstants.push_back(op);
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}
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void notifyOperationErased(Operation *op) override {
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auto *it = llvm::find(existingConstants, op);
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if (it != existingConstants.end())
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existingConstants.erase(it);
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}
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};
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} // namespace
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void TestSingleFold::foldOperation(Operation *op, OperationFolder &helper) {
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// Attempt to fold the specified operation, including handling unused or
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// duplicated constants.
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(void)helper.tryToFold(op);
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}
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void TestSingleFold::runOnOperation() {
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existingConstants.clear();
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// Collect and fold the operations within the operation.
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SmallVector<Operation *, 8> ops;
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getOperation()->walk<mlir::WalkOrder::PreOrder>(
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[&](Operation *op) { ops.push_back(op); });
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// Fold the constants in reverse so that the last generated constants from
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// folding are at the beginning. This creates somewhat of a linear ordering to
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// the newly generated constants that matches the operation order and improves
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// the readability of test cases.
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OperationFolder helper(&getContext(), /*listener=*/this);
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for (Operation *op : llvm::reverse(ops))
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foldOperation(op, helper);
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// By the time we are done, we may have simplified a bunch of code, leaving
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// around dead constants. Check for them now and remove them.
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for (auto *cst : existingConstants) {
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if (cst->use_empty())
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cst->erase();
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}
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}
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namespace mlir {
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namespace test {
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void registerTestSingleFold() { PassRegistration<TestSingleFold>(); }
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} // namespace test
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} // namespace mlir
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