91 lines
3.3 KiB
C++
91 lines
3.3 KiB
C++
//===- InferAlignment.cpp -------------------------------------------------===//
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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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// Infer alignment for load, stores and other memory operations based on
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// trailing zero known bits information.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar/InferAlignment.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Support/KnownBits.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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static bool tryToImproveAlign(
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const DataLayout &DL, Instruction *I,
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function_ref<Align(Value *PtrOp, Align OldAlign, Align PrefAlign)> Fn) {
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if (auto *LI = dyn_cast<LoadInst>(I)) {
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Value *PtrOp = LI->getPointerOperand();
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Align OldAlign = LI->getAlign();
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Align NewAlign = Fn(PtrOp, OldAlign, DL.getPrefTypeAlign(LI->getType()));
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if (NewAlign > OldAlign) {
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LI->setAlignment(NewAlign);
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return true;
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}
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} else if (auto *SI = dyn_cast<StoreInst>(I)) {
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Value *PtrOp = SI->getPointerOperand();
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Value *ValOp = SI->getValueOperand();
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Align OldAlign = SI->getAlign();
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Align NewAlign = Fn(PtrOp, OldAlign, DL.getPrefTypeAlign(ValOp->getType()));
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if (NewAlign > OldAlign) {
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SI->setAlignment(NewAlign);
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return true;
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}
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}
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// TODO: Also handle memory intrinsics.
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return false;
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}
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bool inferAlignment(Function &F, AssumptionCache &AC, DominatorTree &DT) {
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const DataLayout &DL = F.getParent()->getDataLayout();
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bool Changed = false;
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// Enforce preferred type alignment if possible. We do this as a separate
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// pass first, because it may improve the alignments we infer below.
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for (BasicBlock &BB : F) {
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for (Instruction &I : BB) {
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Changed |= tryToImproveAlign(
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DL, &I, [&](Value *PtrOp, Align OldAlign, Align PrefAlign) {
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if (PrefAlign > OldAlign)
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return std::max(OldAlign,
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tryEnforceAlignment(PtrOp, PrefAlign, DL));
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return OldAlign;
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});
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}
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}
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// Compute alignment from known bits.
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for (BasicBlock &BB : F) {
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for (Instruction &I : BB) {
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Changed |= tryToImproveAlign(
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DL, &I, [&](Value *PtrOp, Align OldAlign, Align PrefAlign) {
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KnownBits Known = computeKnownBits(PtrOp, DL, 0, &AC, &I, &DT);
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unsigned TrailZ = std::min(Known.countMinTrailingZeros(),
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+Value::MaxAlignmentExponent);
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return Align(1ull << std::min(Known.getBitWidth() - 1, TrailZ));
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});
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}
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}
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return Changed;
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}
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PreservedAnalyses InferAlignmentPass::run(Function &F,
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FunctionAnalysisManager &AM) {
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AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
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DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F);
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inferAlignment(F, AC, DT);
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// Changes to alignment shouldn't invalidated analyses.
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return PreservedAnalyses::all();
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}
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