34a1888bea
Introduce a lightweight, targeted dead-op eliminator that complements the existing liveness-based runRegionDCE. The algorithm is O(ops): step 1 walks each op in reverse program order, erases it outright if trivially dead, or recurses into nested regions when recursive cleanup is enabled; step 2 drives a per-region worklist that only ever holds ops already verified dead, propagating new deadness by dropping each operand's use before re-checking isOpTriviallyDead on the defining op. Unlike runRegionDCE, this does not touch dead block arguments, dead successor operands, or dead use-def cycles. Use runRegionDCE when those are required. An includeNestedRegions parameter lets callers restrict simplification to the top-level region. Switch transform.apply_dce to use the new helper, dropping a custom worklist that had subtle invariants: SetVector dedup, linear search on every erase, and pre-order walk with skip. In general it is bad practice to implement complex custom logic in Transform ops apply methods: this should be an adaptor exposing MLIR transformations to the transform dialect; non-trivial logic deserves a public API for reusability and proper layering. Introduce a TrivialDeadCodeEliminationPass exposed as -trivial-dce. The pass removes trivially dead operations and, when removeBlocks is enabled, unreachable blocks. It does not run liveness analysis and does not remove dead use-def cycles. Add recursive and removeBlocks options, both defaulting to true, to control whether nested regions are visited and whether unreachable blocks are erased. Assisted-by: Claude Code
38 lines
1.2 KiB
C++
38 lines
1.2 KiB
C++
//===- TrivialDeadCodeElimination.cpp - Trivial DCE -----------------------===//
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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/IR/Operation.h"
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#include "mlir/Pass/Pass.h"
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#include "mlir/Transforms/Passes.h"
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#include "mlir/Transforms/RegionUtils.h"
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namespace mlir {
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#define GEN_PASS_DEF_TRIVIALDEADCODEELIMINATIONPASS
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#include "mlir/Transforms/Passes.h.inc"
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} // namespace mlir
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using namespace mlir;
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namespace {
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struct TrivialDeadCodeElimination
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: public impl::TrivialDeadCodeEliminationPassBase<
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TrivialDeadCodeElimination> {
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using impl::TrivialDeadCodeEliminationPassBase<
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TrivialDeadCodeElimination>::TrivialDeadCodeEliminationPassBase;
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void runOnOperation() override {
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Operation *target = getOperation();
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IRRewriter rewriter(target->getContext());
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if (removeBlocks)
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(void)eraseUnreachableBlocks(rewriter, target->getRegions(), recursive);
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for (Region ®ion : target->getRegions())
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eliminateTriviallyDeadOps(rewriter, region, recursive);
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}
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};
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} // namespace
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