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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 : /// 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/CFGDiff.h"
32 : #include "llvm/IR/Dominators.h"
33 :
34 : namespace llvm {
35 :
36 : /// Determine the iterated dominance frontier, given a set of defining
37 : /// blocks, and optionally, a set of live-in blocks.
38 : ///
39 : /// In turn, the results can be used to place phi nodes.
40 : ///
41 : /// This algorithm is a linear time computation of Iterated Dominance Frontiers,
42 : /// pruned using the live-in set.
43 : /// By default, liveness is not used to prune the IDF computation.
44 : /// The template parameters should be either BasicBlock* or Inverse<BasicBlock
45 : /// *>, depending on if you want the forward or reverse IDF.
46 : template <class NodeTy, bool IsPostDom>
47 : class IDFCalculator {
48 : public:
49 104248 : IDFCalculator(DominatorTreeBase<BasicBlock, IsPostDom> &DT)
50 104248 : : DT(DT), GD(nullptr), useLiveIn(false) {}
51 0 :
52 0 : IDFCalculator(DominatorTreeBase<BasicBlock, IsPostDom> &DT,
53 0 : const GraphDiff<BasicBlock *, IsPostDom> *GD)
54 0 : : DT(DT), GD(GD), useLiveIn(false) {}
55 :
56 0 : /// Give the IDF calculator the set of blocks in which the value is
57 : /// defined. This is equivalent to the set of starting blocks it should be
58 0 : /// calculating the IDF for (though later gets pruned based on liveness).
59 0 : ///
60 : /// Note: This set *must* live for the entire lifetime of the IDF calculator.
61 0 : void setDefiningBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
62 64248 : DefBlocks = &Blocks;
63 0 : }
64 0 :
65 : /// Give the IDF calculator the set of blocks in which the value is
66 : /// live on entry to the block. This is used to prune the IDF calculation to
67 : /// not include blocks where any phi insertion would be dead.
68 : ///
69 : /// Note: This set *must* live for the entire lifetime of the IDF calculator.
70 :
71 0 : void setLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
72 19478 : LiveInBlocks = &Blocks;
73 19478 : useLiveIn = true;
74 0 : }
75 0 :
76 0 : /// Reset the live-in block set to be empty, and tell the IDF
77 0 : /// calculator to not use liveness anymore.
78 0 : void resetLiveInBlocks() {
79 0 : LiveInBlocks = nullptr;
80 0 : useLiveIn = false;
81 0 : }
82 :
83 : /// Calculate iterated dominance frontiers
84 : ///
85 : /// This uses the linear-time phi algorithm based on DJ-graphs mentioned in
86 : /// the file-level comment. It performs DF->IDF pruning using the live-in
87 0 : /// set, to avoid computing the IDF for blocks where an inserted PHI node
88 0 : /// would be dead.
89 0 : void calculate(SmallVectorImpl<BasicBlock *> &IDFBlocks);
90 0 :
91 0 : private:
92 0 : DominatorTreeBase<BasicBlock, IsPostDom> &DT;
93 0 : const GraphDiff<BasicBlock *, IsPostDom> *GD;
94 0 : bool useLiveIn;
95 0 : const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
96 0 : const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
97 0 : };
98 0 : typedef IDFCalculator<BasicBlock *, false> ForwardIDFCalculator;
99 : typedef IDFCalculator<Inverse<BasicBlock *>, true> ReverseIDFCalculator;
100 : }
101 : #endif
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