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//=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This pass is used to evaluate branch probabilties on machine basic blocks.
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/Pass.h"
#include "llvm/Support/BranchProbability.h"
#include <climits>
#include <numeric>
namespace llvm {
class MachineBranchProbabilityInfo : public ImmutablePass {
virtual void anchor();
// Default weight value. Used when we don't have information about the edge.
// TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
// the successors have a weight yet. But it doesn't make sense when providing
// weight to an edge that may have siblings with non-zero weights. This can
// be handled various ways, but it's probably fine for an edge with unknown
// weight to just "inherit" the non-zero weight of an adjacent successor.
static const uint32_t DEFAULT_WEIGHT = 16;
static char ID;
MachineBranchProbabilityInfo() : ImmutablePass(ID) {
PassRegistry &Registry = *PassRegistry::getPassRegistry();
void getAnalysisUsage(AnalysisUsage &AU) const override {
// Return edge probability.
BranchProbability getEdgeProbability(const MachineBasicBlock *Src,
const MachineBasicBlock *Dst) const;
// Same as above, but using a const_succ_iterator from Src. This is faster
// when the iterator is already available.
getEdgeProbability(const MachineBasicBlock *Src,
MachineBasicBlock::const_succ_iterator Dst) const;
// A 'Hot' edge is an edge which probability is >= 80%.
bool isEdgeHot(const MachineBasicBlock *Src,
const MachineBasicBlock *Dst) const;
// Return a hot successor for the block BB or null if there isn't one.
// NB: This routine's complexity is linear on the number of successors.
MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) const;
// Print value between 0 (0% probability) and 1 (100% probability),
// however the value is never equal to 0, and can be 1 only iff SRC block
// has only one successor.
raw_ostream &printEdgeProbability(raw_ostream &OS,
const MachineBasicBlock *Src,
const MachineBasicBlock *Dst) const;