mirror of
https://github.com/revng/revng
synced 2026-06-21 14:07:57 +00:00
Alessandro Di Federico
77 lines
2.3 KiB
C++
77 lines
2.3 KiB
C++
#ifndef _SIMPLIFYCOMPARISON_H
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#define _SIMPLIFYCOMPARISON_H
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//
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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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// Standard includes
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#include <unordered_map>
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// LLVM includes
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#include "llvm/Pass.h"
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// Local includes
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#include "reachingdefinitions.h"
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/// \brief Look for sophisticated comparisons that can be simplified
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/// This pass looks for comparisons checkin for the sign of a value, and, if
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/// possible, tries to build the boolean expression used to compute that value.
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/// If all the expression depends only on the operands of a subtraction
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/// operation, the table of truth of that boolean expressions is built, and is
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/// matched against a known list. In case it corresponds to a known expression,
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/// it is replaced with associated, simpler comparison.
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/// This is particularly useful on ARM.
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class SimplifyComparisonsPass : public llvm::FunctionPass {
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public:
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static char ID;
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public:
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struct Comparison {
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Comparison() { }
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Comparison(llvm::CmpInst *Cmp) :
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Predicate(Cmp->getPredicate()),
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LHS(Cmp->getOperand(0)),
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RHS(Cmp->getOperand(1)) { }
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llvm::CmpInst::Predicate Predicate;
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llvm::Value *LHS;
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llvm::Value *RHS;
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};
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public:
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SimplifyComparisonsPass() : llvm::FunctionPass(ID) { }
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void getAnalysisUsage(llvm::AnalysisUsage &AU) const override {
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AU.setPreservesAll();
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AU.addRequired<ReachingDefinitionsPass>();
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}
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// TODO: this pass ignores function calls, and in particular calls to newpc,
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// which could lead to a corrupted IR in case of split between the
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// instruction generating the condition (e.g. ARM's cmp) and its user
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// (e.g. blt instruction).
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bool runOnFunction(llvm::Function &F) override;
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llvm::Value *findOldest(llvm::Value *V);
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Comparison getComparison(llvm::CmpInst *Cmp) {
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auto It = SimplifiedComparisons.find(Cmp);
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if (It != SimplifiedComparisons.end())
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return It->second;
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else
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return Comparison(Cmp);
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}
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virtual void releaseMemory() override {
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DBG("release", { dbg << "SimplifyComparisonsPass is releasing memory\n"; });
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freeContainer(SimplifiedComparisons);
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}
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private:
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ReachingDefinitionsPass *RDP;
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std::unordered_map<llvm::CmpInst *, Comparison> SimplifiedComparisons;
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};
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#endif // _SIMPLIFYCOMPARISON_H
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