Pirama Arumuga Nainar | f3ef533 | 2016-03-03 15:48:50 -0800 | [diff] [blame^] | 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 | OrderedBasicBlock::OrderedBasicBlock(const BasicBlock *BasicB) |
| 29 | : NextInstPos(0), BB(BasicB) { |
| 30 | LastInstFound = BB->end(); |
| 31 | } |
| 32 | |
| 33 | /// \brief 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 | bool OrderedBasicBlock::comesBefore(const Instruction *A, |
| 36 | const Instruction *B) { |
| 37 | const Instruction *Inst = nullptr; |
| 38 | assert(!(LastInstFound == BB->end() && NextInstPos != 0) && |
| 39 | "Instruction supposed to be in NumberedInsts"); |
| 40 | |
| 41 | // Start the search with the instruction found in the last lookup round. |
| 42 | auto II = BB->begin(); |
| 43 | auto IE = BB->end(); |
| 44 | if (LastInstFound != IE) |
| 45 | II = std::next(LastInstFound); |
| 46 | |
| 47 | // Number all instructions up to the point where we find 'A' or 'B'. |
| 48 | for (; II != IE; ++II) { |
| 49 | Inst = cast<Instruction>(II); |
| 50 | NumberedInsts[Inst] = NextInstPos++; |
| 51 | if (Inst == A || Inst == B) |
| 52 | break; |
| 53 | } |
| 54 | |
| 55 | assert(II != IE && "Instruction not found?"); |
| 56 | assert((Inst == A || Inst == B) && "Should find A or B"); |
| 57 | LastInstFound = II; |
| 58 | return Inst == A; |
| 59 | } |
| 60 | |
| 61 | /// \brief Find out whether \p A dominates \p B, meaning whether \p A |
| 62 | /// comes before \p B in \p BB. This is a simplification that considers |
| 63 | /// cached instruction positions and ignores other basic blocks, being |
| 64 | /// only relevant to compare relative instructions positions inside \p BB. |
| 65 | bool OrderedBasicBlock::dominates(const Instruction *A, const Instruction *B) { |
| 66 | assert(A->getParent() == B->getParent() && |
| 67 | "Instructions must be in the same basic block!"); |
| 68 | |
| 69 | // First we lookup the instructions. If they don't exist, lookup will give us |
| 70 | // back ::end(). If they both exist, we compare the numbers. Otherwise, if NA |
| 71 | // exists and NB doesn't, it means NA must come before NB because we would |
| 72 | // have numbered NB as well if it didn't. The same is true for NB. If it |
| 73 | // exists, but NA does not, NA must come after it. If neither exist, we need |
| 74 | // to number the block and cache the results (by calling comesBefore). |
| 75 | auto NAI = NumberedInsts.find(A); |
| 76 | auto NBI = NumberedInsts.find(B); |
| 77 | if (NAI != NumberedInsts.end() && NBI != NumberedInsts.end()) |
| 78 | return NAI->second < NBI->second; |
| 79 | if (NAI != NumberedInsts.end()) |
| 80 | return true; |
| 81 | if (NBI != NumberedInsts.end()) |
| 82 | return false; |
| 83 | |
| 84 | return comesBefore(A, B); |
| 85 | } |