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97 lines
3.5 KiB
C++
97 lines
3.5 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/DenseMap.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Dominators.h"
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namespace llvm {
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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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/// The template parameters should be either BasicBlock* or Inverse<BasicBlock
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/// *>, depending on if you want the forward or reverse IDF.
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template <class NodeTy>
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class IDFCalculator {
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public:
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IDFCalculator(DominatorTreeBase<BasicBlock> &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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DominatorTreeBase<BasicBlock> &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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};
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typedef IDFCalculator<BasicBlock *> ForwardIDFCalculator;
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typedef IDFCalculator<Inverse<BasicBlock *>> ReverseIDFCalculator;
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}
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#endif
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