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       1             : //===- OrderedBasicBlock.cpp --------------------------------- -*- C++ -*-===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : //
      10             : // This file implements the OrderedBasicBlock class. OrderedBasicBlock
      11             : // maintains an interface where clients can query if one instruction comes
      12             : // before another in a BasicBlock. Since BasicBlock currently lacks a reliable
      13             : // way to query relative position between instructions one can use
      14             : // OrderedBasicBlock to do such queries. OrderedBasicBlock is lazily built on a
      15             : // source BasicBlock and maintains an internal Instruction -> Position map. A
      16             : // OrderedBasicBlock instance should be discarded whenever the source
      17             : // BasicBlock changes.
      18             : //
      19             : // It's currently used by the CaptureTracker in order to find relative
      20             : // positions of a pair of instructions inside a BasicBlock.
      21             : //
      22             : //===----------------------------------------------------------------------===//
      23             : 
      24             : #include "llvm/Analysis/OrderedBasicBlock.h"
      25             : #include "llvm/IR/Instruction.h"
      26             : using namespace llvm;
      27             : 
      28     5066230 : OrderedBasicBlock::OrderedBasicBlock(const BasicBlock *BasicB)
      29     5066230 :     : NextInstPos(0), BB(BasicB) {
      30     5066230 :   LastInstFound = BB->end();
      31     5066230 : }
      32             : 
      33             : /// Given no cached results, find if \p A comes before \p B in \p BB.
      34             : /// Cache and number out instruction while walking \p BB.
      35       87574 : bool OrderedBasicBlock::comesBefore(const Instruction *A,
      36             :                                     const Instruction *B) {
      37       87574 :   const Instruction *Inst = nullptr;
      38             :   assert(!(LastInstFound == BB->end() && NextInstPos != 0) &&
      39             :          "Instruction supposed to be in NumberedInsts");
      40             :   assert(A->getParent() == BB && "Instruction supposed to be in the block!");
      41             :   assert(B->getParent() == BB && "Instruction supposed to be in the block!");
      42             : 
      43             :   // Start the search with the instruction found in the last lookup round.
      44       87574 :   auto II = BB->begin();
      45             :   auto IE = BB->end();
      46       87574 :   if (LastInstFound != IE)
      47             :     II = std::next(LastInstFound);
      48             : 
      49             :   // Number all instructions up to the point where we find 'A' or 'B'.
      50     1266521 :   for (; II != IE; ++II) {
      51     1266521 :     Inst = cast<Instruction>(II);
      52     1266521 :     NumberedInsts[Inst] = NextInstPos++;
      53     1266521 :     if (Inst == A || Inst == B)
      54             :       break;
      55             :   }
      56             : 
      57             :   assert(II != IE && "Instruction not found?");
      58             :   assert((Inst == A || Inst == B) && "Should find A or B");
      59       87574 :   LastInstFound = II;
      60       87574 :   return Inst != B;
      61             : }
      62             : 
      63             : /// Find out whether \p A dominates \p B, meaning whether \p A
      64             : /// comes before \p B in \p BB. This is a simplification that considers
      65             : /// cached instruction positions and ignores other basic blocks, being
      66             : /// only relevant to compare relative instructions positions inside \p BB.
      67      123869 : bool OrderedBasicBlock::dominates(const Instruction *A, const Instruction *B) {
      68             :   assert(A->getParent() == B->getParent() &&
      69             :          "Instructions must be in the same basic block!");
      70             :   assert(A->getParent() == BB && "Instructions must be in the tracked block!");
      71             : 
      72             :   // First we lookup the instructions. If they don't exist, lookup will give us
      73             :   // back ::end(). If they both exist, we compare the numbers. Otherwise, if NA
      74             :   // exists and NB doesn't, it means NA must come before NB because we would
      75             :   // have numbered NB as well if it didn't. The same is true for NB. If it
      76             :   // exists, but NA does not, NA must come after it. If neither exist, we need
      77             :   // to number the block and cache the results (by calling comesBefore).
      78      123869 :   auto NAI = NumberedInsts.find(A);
      79      123869 :   auto NBI = NumberedInsts.find(B);
      80      123869 :   if (NAI != NumberedInsts.end() && NBI != NumberedInsts.end())
      81        8740 :     return NAI->second < NBI->second;
      82      115129 :   if (NAI != NumberedInsts.end())
      83             :     return true;
      84      108671 :   if (NBI != NumberedInsts.end())
      85             :     return false;
      86             : 
      87       87574 :   return comesBefore(A, B);
      88             : }