LLVM  6.0.0svn
OrderedBasicBlock.cpp
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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 
25 #include "llvm/IR/Instruction.h"
26 using namespace llvm;
27 
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 != B;
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.
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 }
OrderedBasicBlock(const BasicBlock *BasicB)
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
bool dominates(const Instruction *A, const Instruction *B)
Find out whether A dominates B, meaning whether A comes before B in BB.
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:252
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
* if(!EatIfPresent(lltok::kw_thread_local)) return false
ParseOptionalThreadLocal := /*empty.
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
iterator end()
Definition: BasicBlock.h:254
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
const BasicBlock * getParent() const
Definition: Instruction.h:66