mirror of
https://github.com/revng/revng
synced 2026-06-21 14:07:57 +00:00
Lauri Vasama
ddcaa1fad2
* Discover deferrable allocas in a separate pass before applying changes in order to avoid double work. * Defer allocas to just before the first user or the terminator, if no user exists in the target block. * Move allocas when the target block is the same as the original block.
91 lines
2.8 KiB
C++
91 lines
2.8 KiB
C++
//
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// This file is distributed under the MIT License. See LICENSE.md for details.
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//
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/Pass.h"
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#include "revng/LocalVariables/LocalVariableHelpers.h"
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namespace {
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struct DeferAllocasPass : public llvm::FunctionPass {
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public:
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static char ID;
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DeferAllocasPass() : FunctionPass(ID) {}
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bool runOnFunction(llvm::Function &F) override;
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};
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char DeferAllocasPass::ID = 0;
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static llvm::BasicBlock *findUseDominator(const llvm::DominatorTree &DT,
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llvm::Value *Value) {
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llvm::BasicBlock *Dominator = nullptr;
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for (llvm::User *User : Value->users()) {
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llvm::BasicBlock *BB = llvm::cast<llvm::Instruction>(User)->getParent();
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Dominator = Dominator == nullptr ?
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BB :
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DT.findNearestCommonDominator(Dominator, BB);
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}
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return Dominator;
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}
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static llvm::Instruction *findFirstUserInBlock(llvm::Value *Value,
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llvm::BasicBlock *BB) {
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llvm::Instruction *FirstUser = nullptr;
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for (llvm::User *User : Value->users()) {
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llvm::Instruction *I = llvm::cast<llvm::Instruction>(User);
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if (I->getParent() == BB) {
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if (FirstUser == nullptr or I->comesBefore(FirstUser))
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FirstUser = I;
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}
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}
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return FirstUser;
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}
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bool DeferAllocasPass::runOnFunction(llvm::Function &F) {
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llvm::DominatorTree DT;
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DT.recalculate(F);
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using DeferrableAlloca = std::tuple<llvm::AllocaInst *, //
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llvm::BasicBlock *,
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llvm::BasicBlock::iterator>;
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llvm::SmallVector<DeferrableAlloca> DeferrableAllocas;
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for (llvm::BasicBlock &BB : F) {
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for (llvm::Instruction &I : BB) {
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auto Alloca = llvm::dyn_cast<llvm::AllocaInst>(&I);
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if (not Alloca or hasStackFrameMetadata(Alloca))
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continue;
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llvm::BasicBlock *NewBB = findUseDominator(DT, Alloca);
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if (NewBB != nullptr) {
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llvm::Instruction *FirstUser = findFirstUserInBlock(Alloca, NewBB);
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if (FirstUser == nullptr)
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FirstUser = NewBB->getTerminator();
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llvm::BasicBlock::iterator NewPos = FirstUser->getIterator();
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if (NewBB != &BB or NewPos != std::next(Alloca->getIterator()))
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DeferrableAllocas.emplace_back(Alloca, NewBB, NewPos);
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}
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}
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}
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for (auto [Alloca, NewBB, NewPos] : DeferrableAllocas)
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Alloca->moveBefore(*NewBB, NewPos);
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return not DeferrableAllocas.empty();
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}
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static llvm::RegisterPass<DeferAllocasPass> X("defer-allocas",
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"Transformation pass which moves "
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"alloca instructions to the "
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"basic block dominating all uses "
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"of the alloca value.");
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} // namespace
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