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 /// \brief 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/ArrayRef.h"
28 #include "llvm/ADT/DenseMap.h"
29 #include "llvm/ADT/SmallPtrSet.h"
30 #include "llvm/ADT/SmallVector.h"
35 template <class T> class DomTreeNodeBase;
36 typedef DomTreeNodeBase<BasicBlock> DomTreeNode;
39 /// \brief Determine the iterated dominance frontier, given a set of defining
40 /// blocks, and optionally, a set of live-in blocks.
42 /// In turn, the results can be used to place phi nodes.
44 /// This algorithm is a linear time computation of Iterated Dominance Frontiers,
45 /// pruned using the live-in set.
46 /// By default, liveness is not used to prune the IDF computation.
50 IDFCalculator(DominatorTree &DT) : DT(DT), useLiveIn(false) {}
52 /// \brief Give the IDF calculator the set of blocks in which the value is
53 /// defined. This is equivalent to the set of starting blocks it should be
54 /// calculating the IDF for (though later gets pruned based on liveness).
56 /// Note: This set *must* live for the entire lifetime of the IDF calculator.
57 void setDefiningBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
61 /// \brief Give the IDF calculator the set of blocks in which the value is
62 /// live on entry to the block. This is used to prune the IDF calculation to
63 /// not include blocks where any phi insertion would be dead.
65 /// Note: This set *must* live for the entire lifetime of the IDF calculator.
67 void setLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
68 LiveInBlocks = &Blocks;
72 /// \brief Reset the live-in block set to be empty, and tell the IDF
73 /// calculator to not use liveness anymore.
74 void resetLiveInBlocks() {
75 LiveInBlocks = nullptr;
79 /// \brief Calculate iterated dominance frontiers
81 /// This uses the linear-time phi algorithm based on DJ-graphs mentioned in
82 /// the file-level comment. It performs DF->IDF pruning using the live-in
83 /// set, to avoid computing the IDF for blocks where an inserted PHI node
85 void calculate(SmallVectorImpl<BasicBlock *> &IDFBlocks);
90 DenseMap<DomTreeNode *, unsigned> DomLevels;
91 const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
92 const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
93 SmallVector<BasicBlock *, 32> PHIBlocks;