1 //===- IteratedDominanceFrontier.h - Calculate IDF --------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 /// Compute iterated dominance frontiers using a linear time algorithm.
12 /// The algorithm used here is based on:
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.
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.
22 //===----------------------------------------------------------------------===//
24 #ifndef LLVM_ANALYSIS_IDF_H
25 #define LLVM_ANALYSIS_IDF_H
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"
36 /// Determine the iterated dominance frontier, given a set of defining
37 /// blocks, and optionally, a set of live-in blocks.
39 /// In turn, the results can be used to place phi nodes.
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>
49 IDFCalculator(DominatorTreeBase<BasicBlock, IsPostDom> &DT)
50 : DT(DT), GD(nullptr), useLiveIn(false) {}
52 IDFCalculator(DominatorTreeBase<BasicBlock, IsPostDom> &DT,
53 const GraphDiff<BasicBlock *, IsPostDom> *GD)
54 : DT(DT), GD(GD), useLiveIn(false) {}
56 /// 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 /// calculating the IDF for (though later gets pruned based on liveness).
60 /// Note: This set *must* live for the entire lifetime of the IDF calculator.
61 void setDefiningBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
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.
69 /// Note: This set *must* live for the entire lifetime of the IDF calculator.
71 void setLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
72 LiveInBlocks = &Blocks;
76 /// Reset the live-in block set to be empty, and tell the IDF
77 /// calculator to not use liveness anymore.
78 void resetLiveInBlocks() {
79 LiveInBlocks = nullptr;
83 /// Calculate iterated dominance frontiers
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 /// set, to avoid computing the IDF for blocks where an inserted PHI node
89 void calculate(SmallVectorImpl<BasicBlock *> &IDFBlocks);
92 DominatorTreeBase<BasicBlock, IsPostDom> &DT;
93 const GraphDiff<BasicBlock *, IsPostDom> *GD;
95 const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
96 const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
98 typedef IDFCalculator<BasicBlock *, false> ForwardIDFCalculator;
99 typedef IDFCalculator<Inverse<BasicBlock *>, true> ReverseIDFCalculator;