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77 lines
2.8 KiB
C++
77 lines
2.8 KiB
C++
//=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass is used to evaluate branch probabilties on machine basic blocks.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
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#define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/BranchProbability.h"
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#include <climits>
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#include <numeric>
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namespace llvm {
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class MachineBranchProbabilityInfo : public ImmutablePass {
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virtual void anchor();
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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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public:
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static char ID;
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MachineBranchProbabilityInfo() : ImmutablePass(ID) {
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PassRegistry &Registry = *PassRegistry::getPassRegistry();
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initializeMachineBranchProbabilityInfoPass(Registry);
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesAll();
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}
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// Return edge probability.
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BranchProbability getEdgeProbability(const MachineBasicBlock *Src,
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const MachineBasicBlock *Dst) const;
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// Same as above, but using a const_succ_iterator from Src. This is faster
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// when the iterator is already available.
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BranchProbability
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getEdgeProbability(const MachineBasicBlock *Src,
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MachineBasicBlock::const_succ_iterator Dst) const;
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// A 'Hot' edge is an edge which probability is >= 80%.
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bool isEdgeHot(const MachineBasicBlock *Src,
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const MachineBasicBlock *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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// NB: This routine's complexity is linear on the number of successors.
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MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) 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,
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const MachineBasicBlock *Src,
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const MachineBasicBlock *Dst) const;
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};
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}
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#endif
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