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29dbbd73de
Summary: MemorySSA uses this algorithm as well, and this enables us to reuse the code in both places. There are no actual algorithm or datastructure changes in here, just code movement. Reviewers: qcolombet, chandlerc Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D9118 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235406 91177308-0d34-0410-b5e6-96231b3b80d8
97 lines
3.3 KiB
C++
97 lines
3.3 KiB
C++
//===- IteratedDominanceFrontier.h - Calculate IDF --------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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/// \brief Compute iterated dominance frontiers using a linear time algorithm.
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///
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/// The algorithm used here is based on:
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///
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/// Sreedhar and Gao. A linear time algorithm for placing phi-nodes.
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/// In Proceedings of the 22nd ACM SIGPLAN-SIGACT Symposium on Principles of
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/// Programming Languages
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/// POPL '95. ACM, New York, NY, 62-73.
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///
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/// It has been modified to not explicitly use the DJ graph data structure and
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/// to directly compute pruned SSA using per-variable liveness information.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_IDF_H
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#define LLVM_ANALYSIS_IDF_H
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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namespace llvm {
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class BasicBlock;
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template <class T> class DomTreeNodeBase;
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typedef DomTreeNodeBase<BasicBlock> DomTreeNode;
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class DominatorTree;
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/// \brief Determine the iterated dominance frontier, given a set of defining
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/// blocks, and optionally, a set of live-in blocks.
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///
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/// In turn, the results can be used to place phi nodes.
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///
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/// This algorithm is a linear time computation of Iterated Dominance Frontiers,
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/// pruned using the live-in set.
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/// By default, liveness is not used to prune the IDF computation.
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class IDFCalculator {
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public:
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IDFCalculator(DominatorTree &DT) : DT(DT), useLiveIn(false) {}
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/// \brief Give the IDF calculator the set of blocks in which the value is
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/// defined. This is equivalent to the set of starting blocks it should be
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/// calculating the IDF for (though later gets pruned based on liveness).
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///
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/// Note: This set *must* live for the entire lifetime of the IDF calculator.
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void setDefiningBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
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DefBlocks = &Blocks;
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}
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/// \brief Give the IDF calculator the set of blocks in which the value is
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/// live on entry to the block. This is used to prune the IDF calculation to
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/// not include blocks where any phi insertion would be dead.
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///
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/// Note: This set *must* live for the entire lifetime of the IDF calculator.
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void setLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
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LiveInBlocks = &Blocks;
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useLiveIn = true;
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}
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/// \brief Reset the live-in block set to be empty, and tell the IDF
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/// calculator to not use liveness anymore.
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void resetLiveInBlocks() {
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LiveInBlocks = nullptr;
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useLiveIn = false;
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}
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/// \brief Calculate iterated dominance frontiers
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///
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/// This uses the linear-time phi algorithm based on DJ-graphs mentioned in
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/// the file-level comment. It performs DF->IDF pruning using the live-in
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/// set, to avoid computing the IDF for blocks where an inserted PHI node
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/// would be dead.
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void calculate(SmallVectorImpl<BasicBlock *> &IDFBlocks);
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private:
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DominatorTree &DT;
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bool useLiveIn;
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DenseMap<DomTreeNode *, unsigned> DomLevels;
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const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
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const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
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SmallVector<BasicBlock *, 32> PHIBlocks;
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};
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}
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#endif
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