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We have several bug reports that could be characterized as "reducing scalarization", and this topic was also raised on llvm-dev recently: http://lists.llvm.org/pipermail/llvm-dev/2020-January/138157.html ...so I'm proposing that we deal with these patterns in a new, lightweight IR vector pass that runs before/after other vectorization passes. There are 4 alternate options that I can think of to deal with this kind of problem (and we've seen various attempts at all of these), but they all have flaws: InstCombine - can't happen without TTI, but we don't want target-specific folds there. SDAG - too late to assist other vectorization passes; TLI is not equipped for these kind of cost queries; limited to a single basic block. CGP - too late to assist other vectorization passes; would need to re-implement basic cleanups like CSE/instcombine. SLP - doesn't fit with existing transforms; limited to a single basic block. This initial patch/transform is based on existing code in AggressiveInstCombine: we walk backwards through the function looking for a pattern match. But we diverge from that cost-independent IR canonicalization pass by using TTI to decide if the vector alternative is profitable. We probably have at least 10 similar bug reports/patterns (binops, constants, inserts, cheap shuffles, etc) that would fit in this pass as follow-up enhancements. It's possible that we could iterate on a worklist to fix-point like InstCombine does, but it's safer to start with a most basic case and evolve from there, so I didn't try to do anything fancy with this initial implementation. Differential Revision: https://reviews.llvm.org/D73480
31 lines
1.0 KiB
C++
31 lines
1.0 KiB
C++
//===-------- VectorCombine.h - Optimize partial vector operations --------===//
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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 pass optimizes scalar/vector interactions using target cost models. The
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// transforms implemented here may not fit in traditional loop-based or SLP
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// vectorization passes.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_VECTOR_VECTORCOMBINE_H
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#define LLVM_TRANSFORMS_VECTOR_VECTORCOMBINE_H
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#include "llvm/IR/PassManager.h"
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namespace llvm {
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/// Optimize scalar/vector interactions in IR using target cost models.
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struct VectorCombinePass : public PassInfoMixin<VectorCombinePass> {
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public:
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PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
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};
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}
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#endif // LLVM_TRANSFORMS_VECTOR_VECTORCOMBINE_H
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