LLVM  6.0.0svn
IteratedDominanceFrontier.h
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1 //===- IteratedDominanceFrontier.h - Calculate IDF --------------*- 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 /// \brief Compute iterated dominance frontiers using a linear time algorithm.
11 ///
12 /// The algorithm used here is based on:
13 ///
14 /// Sreedhar and Gao. A linear time algorithm for placing phi-nodes.
15 /// In Proceedings of the 22nd ACM SIGPLAN-SIGACT Symposium on Principles of
16 /// Programming Languages
17 /// POPL '95. ACM, New York, NY, 62-73.
18 ///
19 /// It has been modified to not explicitly use the DJ graph data structure and
20 /// to directly compute pruned SSA using per-variable liveness information.
21 //
22 //===----------------------------------------------------------------------===//
23 
24 #ifndef LLVM_ANALYSIS_IDF_H
25 #define LLVM_ANALYSIS_IDF_H
26 
27 #include "llvm/ADT/DenseMap.h"
28 #include "llvm/ADT/SmallPtrSet.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/IR/BasicBlock.h"
31 #include "llvm/IR/Dominators.h"
32 
33 namespace llvm {
34 
35 /// \brief Determine the iterated dominance frontier, given a set of defining
36 /// blocks, and optionally, a set of live-in blocks.
37 ///
38 /// In turn, the results can be used to place phi nodes.
39 ///
40 /// This algorithm is a linear time computation of Iterated Dominance Frontiers,
41 /// pruned using the live-in set.
42 /// By default, liveness is not used to prune the IDF computation.
43 /// The template parameters should be either BasicBlock* or Inverse<BasicBlock
44 /// *>, depending on if you want the forward or reverse IDF.
45 template <class NodeTy, bool IsPostDom>
47  public:
49  : DT(DT), useLiveIn(false) {}
50 
51  /// \brief Give the IDF calculator the set of blocks in which the value is
52  /// defined. This is equivalent to the set of starting blocks it should be
53  /// calculating the IDF for (though later gets pruned based on liveness).
54  ///
55  /// Note: This set *must* live for the entire lifetime of the IDF calculator.
57  DefBlocks = &Blocks;
58  }
59 
60  /// \brief Give the IDF calculator the set of blocks in which the value is
61  /// live on entry to the block. This is used to prune the IDF calculation to
62  /// not include blocks where any phi insertion would be dead.
63  ///
64  /// Note: This set *must* live for the entire lifetime of the IDF calculator.
65 
67  LiveInBlocks = &Blocks;
68  useLiveIn = true;
69  }
70 
71  /// \brief Reset the live-in block set to be empty, and tell the IDF
72  /// calculator to not use liveness anymore.
74  LiveInBlocks = nullptr;
75  useLiveIn = false;
76  }
77 
78  /// \brief Calculate iterated dominance frontiers
79  ///
80  /// This uses the linear-time phi algorithm based on DJ-graphs mentioned in
81  /// the file-level comment. It performs DF->IDF pruning using the live-in
82  /// set, to avoid computing the IDF for blocks where an inserted PHI node
83  /// would be dead.
85 
86 private:
88  bool useLiveIn;
89  const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
90  const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
91 };
94 }
95 #endif
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
IDFCalculator(DominatorTreeBase< BasicBlock, IsPostDom > &DT)
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
Definition: SmallPtrSet.h:344
void setDefiningBlocks(const SmallPtrSetImpl< BasicBlock *> &Blocks)
Give the IDF calculator the set of blocks in which the value is defined.
Core dominator tree base class.
Definition: LoopInfo.h:61
void resetLiveInBlocks()
Reset the live-in block set to be empty, and tell the IDF calculator to not use liveness anymore...
void setLiveInBlocks(const SmallPtrSetImpl< BasicBlock *> &Blocks)
Give the IDF calculator the set of blocks in which the value is live on entry to the block...
void calculate(SmallVectorImpl< BasicBlock *> &IDFBlocks)
Calculate iterated dominance frontiers.
IDFCalculator< BasicBlock *, false > ForwardIDFCalculator
IDFCalculator< Inverse< BasicBlock * >, true > ReverseIDFCalculator
Determine the iterated dominance frontier, given a set of defining blocks, and optionally, a set of live-in blocks.