86 lines
3.5 KiB
C++
86 lines
3.5 KiB
C++
//===- OrderedBasicBlock.cpp --------------------------------- -*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the OrderedBasicBlock class. OrderedBasicBlock
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// maintains an interface where clients can query if one instruction comes
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// before another in a BasicBlock. Since BasicBlock currently lacks a reliable
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// way to query relative position between instructions one can use
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// OrderedBasicBlock to do such queries. OrderedBasicBlock is lazily built on a
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// source BasicBlock and maintains an internal Instruction -> Position map. A
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// OrderedBasicBlock instance should be discarded whenever the source
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// BasicBlock changes.
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//
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// It's currently used by the CaptureTracker in order to find relative
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// positions of a pair of instructions inside a BasicBlock.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/OrderedBasicBlock.h"
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#include "llvm/IR/Instruction.h"
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using namespace llvm;
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OrderedBasicBlock::OrderedBasicBlock(const BasicBlock *BasicB)
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: NextInstPos(0), BB(BasicB) {
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LastInstFound = BB->end();
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}
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/// \brief Given no cached results, find if \p A comes before \p B in \p BB.
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/// Cache and number out instruction while walking \p BB.
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bool OrderedBasicBlock::comesBefore(const Instruction *A,
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const Instruction *B) {
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const Instruction *Inst = nullptr;
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assert(!(LastInstFound == BB->end() && NextInstPos != 0) &&
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"Instruction supposed to be in NumberedInsts");
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// Start the search with the instruction found in the last lookup round.
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auto II = BB->begin();
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auto IE = BB->end();
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if (LastInstFound != IE)
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II = std::next(LastInstFound);
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// Number all instructions up to the point where we find 'A' or 'B'.
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for (; II != IE; ++II) {
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Inst = cast<Instruction>(II);
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NumberedInsts[Inst] = NextInstPos++;
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if (Inst == A || Inst == B)
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break;
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}
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assert(II != IE && "Instruction not found?");
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assert((Inst == A || Inst == B) && "Should find A or B");
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LastInstFound = II;
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return Inst == A;
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}
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/// \brief Find out whether \p A dominates \p B, meaning whether \p A
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/// comes before \p B in \p BB. This is a simplification that considers
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/// cached instruction positions and ignores other basic blocks, being
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/// only relevant to compare relative instructions positions inside \p BB.
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bool OrderedBasicBlock::dominates(const Instruction *A, const Instruction *B) {
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assert(A->getParent() == B->getParent() &&
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"Instructions must be in the same basic block!");
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// First we lookup the instructions. If they don't exist, lookup will give us
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// back ::end(). If they both exist, we compare the numbers. Otherwise, if NA
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// exists and NB doesn't, it means NA must come before NB because we would
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// have numbered NB as well if it didn't. The same is true for NB. If it
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// exists, but NA does not, NA must come after it. If neither exist, we need
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// to number the block and cache the results (by calling comesBefore).
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auto NAI = NumberedInsts.find(A);
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auto NBI = NumberedInsts.find(B);
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if (NAI != NumberedInsts.end() && NBI != NumberedInsts.end())
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return NAI->second < NBI->second;
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if (NAI != NumberedInsts.end())
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return true;
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if (NBI != NumberedInsts.end())
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return false;
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return comesBefore(A, B);
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}
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