LLVM  9.0.0svn
IteratedDominanceFrontier.h
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1 //===- IteratedDominanceFrontier.h - Calculate IDF --------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 /// \file
9 /// Compute iterated dominance frontiers using a linear time algorithm.
10 ///
11 /// The algorithm used here is based on:
12 ///
13 /// Sreedhar and Gao. A linear time algorithm for placing phi-nodes.
14 /// In Proceedings of the 22nd ACM SIGPLAN-SIGACT Symposium on Principles of
15 /// Programming Languages
16 /// POPL '95. ACM, New York, NY, 62-73.
17 ///
18 /// It has been modified to not explicitly use the DJ graph data structure and
19 /// to directly compute pruned SSA using per-variable liveness information.
20 //
21 //===----------------------------------------------------------------------===//
22 
23 #ifndef LLVM_ANALYSIS_IDF_H
24 #define LLVM_ANALYSIS_IDF_H
25 
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/ADT/SmallPtrSet.h"
28 #include "llvm/ADT/SmallVector.h"
29 #include "llvm/IR/BasicBlock.h"
30 #include "llvm/IR/CFGDiff.h"
31 #include "llvm/IR/Dominators.h"
32 
33 namespace llvm {
34 
35 /// 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), GD(nullptr), useLiveIn(false) {}
50 
53  : DT(DT), GD(GD), useLiveIn(false) {}
54 
55  /// Give the IDF calculator the set of blocks in which the value is
56  /// defined. This is equivalent to the set of starting blocks it should be
57  /// calculating the IDF for (though later gets pruned based on liveness).
58  ///
59  /// Note: This set *must* live for the entire lifetime of the IDF calculator.
61  DefBlocks = &Blocks;
62  }
63 
64  /// Give the IDF calculator the set of blocks in which the value is
65  /// live on entry to the block. This is used to prune the IDF calculation to
66  /// not include blocks where any phi insertion would be dead.
67  ///
68  /// Note: This set *must* live for the entire lifetime of the IDF calculator.
69 
71  LiveInBlocks = &Blocks;
72  useLiveIn = true;
73  }
74 
75  /// Reset the live-in block set to be empty, and tell the IDF
76  /// calculator to not use liveness anymore.
78  LiveInBlocks = nullptr;
79  useLiveIn = false;
80  }
81 
82  /// Calculate iterated dominance frontiers
83  ///
84  /// This uses the linear-time phi algorithm based on DJ-graphs mentioned in
85  /// the file-level comment. It performs DF->IDF pruning using the live-in
86  /// set, to avoid computing the IDF for blocks where an inserted PHI node
87  /// would be dead.
89 
90 private:
93  bool useLiveIn;
94  const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
95  const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
96 };
99 }
100 #endif
This class represents lattice values for constants.
Definition: AllocatorList.h:23
IDFCalculator(DominatorTreeBase< BasicBlock, IsPostDom > &DT)
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
Definition: SmallPtrSet.h:343
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:63
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.
IDFCalculator(DominatorTreeBase< BasicBlock, IsPostDom > &DT, const GraphDiff< BasicBlock *, IsPostDom > *GD)