• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
1 //===- llvm/Analysis/OrderedBasicBlock.h --------------------- -*- 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 defines the OrderedBasicBlock class. OrderedBasicBlock maintains
11 // an interface where clients can query if one instruction comes before another
12 // in a BasicBlock. Since BasicBlock currently lacks a reliable way to query
13 // relative position between instructions one can use OrderedBasicBlock to do
14 // such queries. OrderedBasicBlock is lazily built on a source BasicBlock and
15 // maintains an internal Instruction -> Position map. A OrderedBasicBlock
16 // instance should be discarded whenever the source BasicBlock changes.
17 //
18 // It's currently used by the CaptureTracker in order to find relative
19 // positions of a pair of instructions inside a BasicBlock.
20 //
21 //===----------------------------------------------------------------------===//
22 
23 #ifndef LLVM_ANALYSIS_ORDEREDBASICBLOCK_H
24 #define LLVM_ANALYSIS_ORDEREDBASICBLOCK_H
25 
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/IR/BasicBlock.h"
28 
29 namespace llvm {
30 
31 class Instruction;
32 class BasicBlock;
33 
34 class OrderedBasicBlock {
35 private:
36   /// \brief Map a instruction to its position in a BasicBlock.
37   SmallDenseMap<const Instruction *, unsigned, 32> NumberedInsts;
38 
39   /// \brief Keep track of last instruction inserted into \p NumberedInsts.
40   /// It speeds up queries for uncached instructions by providing a start point
41   /// for new queries in OrderedBasicBlock::comesBefore.
42   BasicBlock::const_iterator LastInstFound;
43 
44   /// \brief The position/number to tag the next instruction to be found.
45   unsigned NextInstPos;
46 
47   /// \brief The source BasicBlock to map.
48   const BasicBlock *BB;
49 
50   /// \brief Given no cached results, find if \p A comes before \p B in \p BB.
51   /// Cache and number out instruction while walking \p BB.
52   bool comesBefore(const Instruction *A, const Instruction *B);
53 
54 public:
55   OrderedBasicBlock(const BasicBlock *BasicB);
56 
57   /// \brief Find out whether \p A dominates \p B, meaning whether \p A
58   /// comes before \p B in \p BB. This is a simplification that considers
59   /// cached instruction positions and ignores other basic blocks, being
60   /// only relevant to compare relative instructions positions inside \p BB.
61   bool dominates(const Instruction *A, const Instruction *B);
62 };
63 
64 } // End llvm namespace
65 
66 #endif
67