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84 lines
2.9 KiB
C++
84 lines
2.9 KiB
C++
//===--- BranchProbabilityInfo.h - Branch Probability Analysis --*- 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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// This pass is used to evaluate branch probabilties.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
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#define LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
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#include "llvm/InitializePasses.h"
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#include "llvm/Support/BranchProbability.h"
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#include "llvm/Analysis/LoopInfo.h"
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namespace llvm {
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class raw_ostream;
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class BranchProbabilityInfo : public FunctionPass {
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// Default weight value. Used when we don't have information about the edge.
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// TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
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// the successors have a weight yet. But it doesn't make sense when providing
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// weight to an edge that may have siblings with non-zero weights. This can
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// be handled various ways, but it's probably fine for an edge with unknown
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// weight to just "inherit" the non-zero weight of an adjacent successor.
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static const uint32_t DEFAULT_WEIGHT = 16;
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typedef std::pair<BasicBlock *, BasicBlock *> Edge;
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DenseMap<Edge, uint32_t> Weights;
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// Get sum of the block successors' weights.
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uint32_t getSumForBlock(BasicBlock *BB) const;
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public:
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static char ID;
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BranchProbabilityInfo() : FunctionPass(ID) {
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initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
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}
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void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<LoopInfo>();
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AU.setPreservesAll();
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}
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bool runOnFunction(Function &F);
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// Returned value is between 1 and UINT32_MAX. Look at
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// BranchProbabilityInfo.cpp for details.
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uint32_t getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) const;
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// Look at BranchProbabilityInfo.cpp for details. Use it with caution!
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void setEdgeWeight(BasicBlock *Src, BasicBlock *Dst, uint32_t Weight);
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// A 'Hot' edge is an edge which probability is >= 80%.
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bool isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const;
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// Return a hot successor for the block BB or null if there isn't one.
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BasicBlock *getHotSucc(BasicBlock *BB) const;
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// Return a probability as a fraction between 0 (0% probability) and
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// 1 (100% probability), however the value is never equal to 0, and can be 1
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// only iff SRC block has only one successor.
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BranchProbability getEdgeProbability(BasicBlock *Src, BasicBlock *Dst) const;
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// Print value between 0 (0% probability) and 1 (100% probability),
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// however the value is never equal to 0, and can be 1 only iff SRC block
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// has only one successor.
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raw_ostream &printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
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BasicBlock *Dst) const;
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};
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}
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#endif
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