mirror of
https://github.com/revng/revng
synced 2026-06-21 14:07:57 +00:00
Pietro Fezzardi
e9d84264ff
This commit does various things oriented at reducing the number of local variables emitted in C: - MarkAssignments now know that @Copy and @Assign involving @LocalVariable only have side effects that affect the local variable itself; this enables to reduce the number of times we're forced to emit a local variable due to interfering side effects - Drop the @AssignmentMarker FunctionTag; AddAssignmentMarkerPass now doesn't emit @AssignmentMarker anymore; instead it emits groups of @LocalVariable, @Copy, and @Assign, which benefit from the previous point - Drop 2 MarkAssignments::Reasons: HasManyUses and HasUsesOutsideOfBB; both these have now been aggregated into the AlwaysAssign reason for simplicity, representing all reasons non involving side effects - Update BeautifyGHAST and how it reasons about side effects when beautifying; before this commit it used @AssignmentMarker, now it looks at @Assign - Simplify ExitSSA; before this commit it was trying hard to be smart on where it emitted the store instructions representing the incoming values of the PHI that was being destroyed; this seemed smart when we originally did it but it generated C code that was not really better to read, so this useless complexity is finally gone
100 lines
2.7 KiB
C++
100 lines
2.7 KiB
C++
//
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// Copyright rev.ng Labs Srl. See LICENSE.md for details.
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//
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "revng/ADT/SmallMap.h"
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#include "revng/Support/Debug.h"
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#include "revng/Support/FunctionTags.h"
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#include "revng/Support/IRHelpers.h"
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using llvm::AllocaInst;
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using llvm::AnalysisUsage;
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using llvm::BasicBlock;
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using llvm::Function;
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using llvm::FunctionPass;
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using llvm::Instruction;
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using llvm::IRBuilder;
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using llvm::PHINode;
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using llvm::RegisterPass;
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using llvm::Value;
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static Logger<> Log{ "exit-ssa" };
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struct ExitSSAPass : public FunctionPass {
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public:
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static char ID;
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ExitSSAPass() : FunctionPass(ID) {}
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bool runOnFunction(Function &F) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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}
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};
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bool ExitSSAPass::runOnFunction(Function &F) {
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// Skip non-isolated functions
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if (not FunctionTags::Isolated.isTagOf(&F))
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return false;
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IRBuilder<> Builder(F.getContext());
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Builder.SetInsertPoint(&F.getEntryBlock().front());
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SmallMap<PHINode *, AllocaInst *, 8> PHIToAlloca;
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for (BasicBlock &BB : F)
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for (PHINode &PHI : BB.phis())
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PHIToAlloca[&PHI] = Builder.CreateAlloca(PHI.getType());
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if (PHIToAlloca.empty())
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return false;
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for (auto &[PHI, Alloca] : PHIToAlloca) {
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for (auto &IncomingUse : PHI->incoming_values()) {
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llvm::BasicBlock *BB = PHI->getIncomingBlock(IncomingUse);
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Builder.SetInsertPoint(BB->getTerminator());
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Value *Incoming = IncomingUse.get();
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BasicBlock *IncomingDefBB = &F.getEntryBlock();
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if (auto *I = dyn_cast<Instruction>(Incoming))
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IncomingDefBB = I->getParent();
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revng_assert(IncomingDefBB);
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revng_log(Log, "Incoming: " << dumpToString(Incoming));
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auto *S = Builder.CreateStore(Incoming, PHIToAlloca.at(PHI));
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revng_log(Log, dumpToString(S));
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}
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}
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for (auto &[PHI, Alloca] : PHIToAlloca) {
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Builder.SetInsertPoint(PHI);
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auto *Load = Builder.CreateLoad(Alloca);
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PHI->replaceAllUsesWith(Load);
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PHI->eraseFromParent();
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}
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for (BasicBlock &BB : F)
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for (Instruction &I : BB)
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revng_assert(not llvm::isa<PHINode>(I));
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return not PHIToAlloca.empty();
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}
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char ExitSSAPass::ID = 0;
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static RegisterPass<ExitSSAPass> X("exit-ssa",
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"Transformation pass that exits from Static "
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"Single Assignment form, promoting PHINodes "
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"to sets of Allocas, Load and Stores",
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false,
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false);
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