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//===- IteratedDominanceFrontier.h - Calculate IDF --------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \brief Compute iterated dominance frontiers using a linear time algorithm.
///
/// The algorithm used here is based on:
///
/// Sreedhar and Gao. A linear time algorithm for placing phi-nodes.
/// In Proceedings of the 22nd ACM SIGPLAN-SIGACT Symposium on Principles of
/// Programming Languages
/// POPL '95. ACM, New York, NY, 62-73.
///
/// It has been modified to not explicitly use the DJ graph data structure and
/// to directly compute pruned SSA using per-variable liveness information.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_IDF_H
#define LLVM_ANALYSIS_IDF_H
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
namespace llvm {
class BasicBlock;
template <class T> class DomTreeNodeBase;
typedef DomTreeNodeBase<BasicBlock> DomTreeNode;
class DominatorTree;
/// \brief Determine the iterated dominance frontier, given a set of defining
/// blocks, and optionally, a set of live-in blocks.
///
/// In turn, the results can be used to place phi nodes.
///
/// This algorithm is a linear time computation of Iterated Dominance Frontiers,
/// pruned using the live-in set.
/// By default, liveness is not used to prune the IDF computation.
class IDFCalculator {
public:
IDFCalculator(DominatorTree &DT) : DT(DT), useLiveIn(false) {}
/// \brief Give the IDF calculator the set of blocks in which the value is
/// defined. This is equivalent to the set of starting blocks it should be
/// calculating the IDF for (though later gets pruned based on liveness).
///
/// Note: This set *must* live for the entire lifetime of the IDF calculator.
void setDefiningBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
DefBlocks = &Blocks;
}
/// \brief Give the IDF calculator the set of blocks in which the value is
/// live on entry to the block. This is used to prune the IDF calculation to
/// not include blocks where any phi insertion would be dead.
///
/// Note: This set *must* live for the entire lifetime of the IDF calculator.
void setLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
LiveInBlocks = &Blocks;
useLiveIn = true;
}
/// \brief Reset the live-in block set to be empty, and tell the IDF
/// calculator to not use liveness anymore.
void resetLiveInBlocks() {
LiveInBlocks = nullptr;
useLiveIn = false;
}
/// \brief Calculate iterated dominance frontiers
///
/// This uses the linear-time phi algorithm based on DJ-graphs mentioned in
/// the file-level comment. It performs DF->IDF pruning using the live-in
/// set, to avoid computing the IDF for blocks where an inserted PHI node
/// would be dead.
void calculate(SmallVectorImpl<BasicBlock *> &IDFBlocks);
private:
DominatorTree &DT;
bool useLiveIn;
DenseMap<DomTreeNode *, unsigned> DomLevels;
const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
SmallVector<BasicBlock *, 32> PHIBlocks;
};
} // namespace llvm
#endif
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