a1dfc8d64e
The greedy pattern rewrite driver previously only deduplicated constant ops between iterations (via the operation folder). Structurally identical non-constant subexpressions remained distinct SSA values, blocking fold patterns that only fire when operands match. Reaching the true fixpoint required chaining an external `cse,canonicalize,...` pipeline. Add an opt-in `cseBetweenIterations` flag on `GreedyRewriteConfig` that runs full CSE on the scoped region after each pattern-application iteration, and surface it as a `cse-between-iterations` option on the canonicalizer pass. Off by default to preserve existing performance characteristics. Assisted-by: Claude Code
58 lines
1.9 KiB
C++
58 lines
1.9 KiB
C++
//===- CSE.cpp - Common Sub-expression Elimination ------------------------===//
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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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// This file implements the CSE pass. The actual CSE algorithm lives in
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// mlir/lib/Transforms/Utils/CSE.cpp so that it can be invoked from other
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// utilities (e.g. the greedy pattern rewrite driver).
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Transforms/CSE.h"
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#include "mlir/IR/Dominance.h"
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#include "mlir/IR/PatternMatch.h"
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#include "mlir/Pass/Pass.h"
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namespace mlir {
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#define GEN_PASS_DEF_CSEPASS
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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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/// CSE pass.
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struct CSE : public impl::CSEPassBase<CSE> {
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void runOnOperation() override;
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};
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} // namespace
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void CSE::runOnOperation() {
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IRRewriter rewriter(&getContext());
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auto &domInfo = getAnalysis<DominanceInfo>();
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bool changed = false;
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// `numCSE` / `numDCE` are `llvm::Statistic` objects, not raw `int64_t`, so
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// the public API's out-parameters cannot point at them directly.
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int64_t cseCount = 0;
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int64_t dceCount = 0;
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eliminateCommonSubExpressions(rewriter, domInfo, getOperation(), &changed,
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&cseCount, &dceCount);
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numCSE = cseCount;
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numDCE = dceCount;
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// If there was no change to the IR, we mark all analyses as preserved.
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if (!changed)
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return markAllAnalysesPreserved();
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// We only delete redundant operations without moving any operation to a
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// different block, so the dominance tree structure remains unchanged and
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// DominanceInfo/PostDominanceInfo can be safely preserved.
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markAnalysesPreserved<DominanceInfo, PostDominanceInfo>();
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}
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