711 lines
		
	
	
		
			24 KiB
		
	
	
	
		
			C++
		
	
	
	
			
		
		
	
	
			711 lines
		
	
	
		
			24 KiB
		
	
	
	
		
			C++
		
	
	
	
//===-- BranchProbabilityInfo.cpp - Branch Probability Analysis -----------===//
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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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// Loops should be simplified before this analysis.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/BranchProbabilityInfo.h"
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#include "llvm/ADT/PostOrderIterator.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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#define DEBUG_TYPE "branch-prob"
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INITIALIZE_PASS_BEGIN(BranchProbabilityInfoWrapperPass, "branch-prob",
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                      "Branch Probability Analysis", false, true)
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INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
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INITIALIZE_PASS_END(BranchProbabilityInfoWrapperPass, "branch-prob",
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                    "Branch Probability Analysis", false, true)
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char BranchProbabilityInfoWrapperPass::ID = 0;
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// Weights are for internal use only. They are used by heuristics to help to
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// estimate edges' probability. Example:
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//
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// Using "Loop Branch Heuristics" we predict weights of edges for the
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// block BB2.
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//         ...
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//          |
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//          V
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//         BB1<-+
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//          |   |
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//          |   | (Weight = 124)
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//          V   |
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//         BB2--+
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//          |
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//          | (Weight = 4)
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//          V
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//         BB3
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//
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// Probability of the edge BB2->BB1 = 124 / (124 + 4) = 0.96875
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// Probability of the edge BB2->BB3 = 4 / (124 + 4) = 0.03125
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static const uint32_t LBH_TAKEN_WEIGHT = 124;
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static const uint32_t LBH_NONTAKEN_WEIGHT = 4;
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/// \brief Unreachable-terminating branch taken weight.
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///
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/// This is the weight for a branch being taken to a block that terminates
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/// (eventually) in unreachable. These are predicted as unlikely as possible.
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static const uint32_t UR_TAKEN_WEIGHT = 1;
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/// \brief Unreachable-terminating branch not-taken weight.
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///
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/// This is the weight for a branch not being taken toward a block that
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/// terminates (eventually) in unreachable. Such a branch is essentially never
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/// taken. Set the weight to an absurdly high value so that nested loops don't
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/// easily subsume it.
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static const uint32_t UR_NONTAKEN_WEIGHT = 1024*1024 - 1;
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/// \brief Weight for a branch taken going into a cold block.
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///
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/// This is the weight for a branch taken toward a block marked
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/// cold.  A block is marked cold if it's postdominated by a
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/// block containing a call to a cold function.  Cold functions
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/// are those marked with attribute 'cold'.
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static const uint32_t CC_TAKEN_WEIGHT = 4;
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/// \brief Weight for a branch not-taken into a cold block.
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///
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/// This is the weight for a branch not taken toward a block marked
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/// cold.
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static const uint32_t CC_NONTAKEN_WEIGHT = 64;
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static const uint32_t PH_TAKEN_WEIGHT = 20;
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static const uint32_t PH_NONTAKEN_WEIGHT = 12;
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static const uint32_t ZH_TAKEN_WEIGHT = 20;
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static const uint32_t ZH_NONTAKEN_WEIGHT = 12;
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static const uint32_t FPH_TAKEN_WEIGHT = 20;
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static const uint32_t FPH_NONTAKEN_WEIGHT = 12;
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/// \brief Invoke-terminating normal branch taken weight
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///
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/// This is the weight for branching to the normal destination of an invoke
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/// instruction. We expect this to happen most of the time. Set the weight to an
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/// absurdly high value so that nested loops subsume it.
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static const uint32_t IH_TAKEN_WEIGHT = 1024 * 1024 - 1;
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/// \brief Invoke-terminating normal branch not-taken weight.
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///
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/// This is the weight for branching to the unwind destination of an invoke
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/// instruction. This is essentially never taken.
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static const uint32_t IH_NONTAKEN_WEIGHT = 1;
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/// \brief Calculate edge weights for successors lead to unreachable.
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///
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/// Predict that a successor which leads necessarily to an
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/// unreachable-terminated block as extremely unlikely.
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bool BranchProbabilityInfo::calcUnreachableHeuristics(const BasicBlock *BB) {
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  const TerminatorInst *TI = BB->getTerminator();
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  if (TI->getNumSuccessors() == 0) {
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    if (isa<UnreachableInst>(TI) ||
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        // If this block is terminated by a call to
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        // @llvm.experimental.deoptimize then treat it like an unreachable since
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        // the @llvm.experimental.deoptimize call is expected to practically
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        // never execute.
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        BB->getTerminatingDeoptimizeCall())
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      PostDominatedByUnreachable.insert(BB);
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    return false;
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  }
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  SmallVector<unsigned, 4> UnreachableEdges;
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  SmallVector<unsigned, 4> ReachableEdges;
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  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
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    if (PostDominatedByUnreachable.count(*I))
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      UnreachableEdges.push_back(I.getSuccessorIndex());
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    else
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      ReachableEdges.push_back(I.getSuccessorIndex());
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  }
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  // If all successors are in the set of blocks post-dominated by unreachable,
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  // this block is too.
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  if (UnreachableEdges.size() == TI->getNumSuccessors())
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    PostDominatedByUnreachable.insert(BB);
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  // Skip probabilities if this block has a single successor or if all were
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  // reachable.
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  if (TI->getNumSuccessors() == 1 || UnreachableEdges.empty())
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    return false;
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  // If the terminator is an InvokeInst, check only the normal destination block
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  // as the unwind edge of InvokeInst is also very unlikely taken.
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  if (auto *II = dyn_cast<InvokeInst>(TI))
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    if (PostDominatedByUnreachable.count(II->getNormalDest())) {
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      PostDominatedByUnreachable.insert(BB);
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      // Return false here so that edge weights for InvokeInst could be decided
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      // in calcInvokeHeuristics().
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      return false;
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    }
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  if (ReachableEdges.empty()) {
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    BranchProbability Prob(1, UnreachableEdges.size());
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    for (unsigned SuccIdx : UnreachableEdges)
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      setEdgeProbability(BB, SuccIdx, Prob);
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    return true;
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  }
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  BranchProbability UnreachableProb(UR_TAKEN_WEIGHT,
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                                    (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) *
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                                        UnreachableEdges.size());
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  BranchProbability ReachableProb(UR_NONTAKEN_WEIGHT,
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                                  (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) *
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                                      ReachableEdges.size());
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  for (unsigned SuccIdx : UnreachableEdges)
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    setEdgeProbability(BB, SuccIdx, UnreachableProb);
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  for (unsigned SuccIdx : ReachableEdges)
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    setEdgeProbability(BB, SuccIdx, ReachableProb);
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  return true;
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}
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// Propagate existing explicit probabilities from either profile data or
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// 'expect' intrinsic processing.
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bool BranchProbabilityInfo::calcMetadataWeights(const BasicBlock *BB) {
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  const TerminatorInst *TI = BB->getTerminator();
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  if (TI->getNumSuccessors() == 1)
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    return false;
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  if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
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    return false;
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  MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
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  if (!WeightsNode)
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    return false;
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  // Check that the number of successors is manageable.
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  assert(TI->getNumSuccessors() < UINT32_MAX && "Too many successors");
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  // Ensure there are weights for all of the successors. Note that the first
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  // operand to the metadata node is a name, not a weight.
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  if (WeightsNode->getNumOperands() != TI->getNumSuccessors() + 1)
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    return false;
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  // Build up the final weights that will be used in a temporary buffer.
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  // Compute the sum of all weights to later decide whether they need to
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  // be scaled to fit in 32 bits.
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  uint64_t WeightSum = 0;
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  SmallVector<uint32_t, 2> Weights;
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  Weights.reserve(TI->getNumSuccessors());
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  for (unsigned i = 1, e = WeightsNode->getNumOperands(); i != e; ++i) {
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    ConstantInt *Weight =
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        mdconst::dyn_extract<ConstantInt>(WeightsNode->getOperand(i));
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    if (!Weight)
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      return false;
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    assert(Weight->getValue().getActiveBits() <= 32 &&
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           "Too many bits for uint32_t");
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    Weights.push_back(Weight->getZExtValue());
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    WeightSum += Weights.back();
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  }
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  assert(Weights.size() == TI->getNumSuccessors() && "Checked above");
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  // If the sum of weights does not fit in 32 bits, scale every weight down
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  // accordingly.
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  uint64_t ScalingFactor =
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      (WeightSum > UINT32_MAX) ? WeightSum / UINT32_MAX + 1 : 1;
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  WeightSum = 0;
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  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
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    Weights[i] /= ScalingFactor;
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    WeightSum += Weights[i];
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  }
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  if (WeightSum == 0) {
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    for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
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      setEdgeProbability(BB, i, {1, e});
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  } else {
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    for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
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      setEdgeProbability(BB, i, {Weights[i], static_cast<uint32_t>(WeightSum)});
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  }
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  assert(WeightSum <= UINT32_MAX &&
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         "Expected weights to scale down to 32 bits");
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  return true;
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}
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/// \brief Calculate edge weights for edges leading to cold blocks.
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///
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/// A cold block is one post-dominated by  a block with a call to a
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/// cold function.  Those edges are unlikely to be taken, so we give
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/// them relatively low weight.
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///
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/// Return true if we could compute the weights for cold edges.
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/// Return false, otherwise.
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bool BranchProbabilityInfo::calcColdCallHeuristics(const BasicBlock *BB) {
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  const TerminatorInst *TI = BB->getTerminator();
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  if (TI->getNumSuccessors() == 0)
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    return false;
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  // Determine which successors are post-dominated by a cold block.
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  SmallVector<unsigned, 4> ColdEdges;
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  SmallVector<unsigned, 4> NormalEdges;
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  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
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    if (PostDominatedByColdCall.count(*I))
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      ColdEdges.push_back(I.getSuccessorIndex());
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    else
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      NormalEdges.push_back(I.getSuccessorIndex());
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  // If all successors are in the set of blocks post-dominated by cold calls,
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  // this block is in the set post-dominated by cold calls.
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  if (ColdEdges.size() == TI->getNumSuccessors())
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    PostDominatedByColdCall.insert(BB);
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  else {
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    // Otherwise, if the block itself contains a cold function, add it to the
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    // set of blocks postdominated by a cold call.
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    assert(!PostDominatedByColdCall.count(BB));
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    for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E; ++I)
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      if (const CallInst *CI = dyn_cast<CallInst>(I))
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        if (CI->hasFnAttr(Attribute::Cold)) {
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          PostDominatedByColdCall.insert(BB);
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          break;
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        }
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  }
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  // Skip probabilities if this block has a single successor.
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  if (TI->getNumSuccessors() == 1 || ColdEdges.empty())
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    return false;
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  if (NormalEdges.empty()) {
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    BranchProbability Prob(1, ColdEdges.size());
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    for (unsigned SuccIdx : ColdEdges)
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      setEdgeProbability(BB, SuccIdx, Prob);
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    return true;
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  }
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  BranchProbability ColdProb(CC_TAKEN_WEIGHT,
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                             (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) *
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                                 ColdEdges.size());
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  BranchProbability NormalProb(CC_NONTAKEN_WEIGHT,
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                               (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) *
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                                   NormalEdges.size());
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  for (unsigned SuccIdx : ColdEdges)
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    setEdgeProbability(BB, SuccIdx, ColdProb);
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  for (unsigned SuccIdx : NormalEdges)
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    setEdgeProbability(BB, SuccIdx, NormalProb);
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  return true;
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}
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// Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
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// between two pointer or pointer and NULL will fail.
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bool BranchProbabilityInfo::calcPointerHeuristics(const BasicBlock *BB) {
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  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
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  if (!BI || !BI->isConditional())
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    return false;
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  Value *Cond = BI->getCondition();
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  ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
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  if (!CI || !CI->isEquality())
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    return false;
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  Value *LHS = CI->getOperand(0);
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  if (!LHS->getType()->isPointerTy())
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    return false;
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  assert(CI->getOperand(1)->getType()->isPointerTy());
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  // p != 0   ->   isProb = true
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  // p == 0   ->   isProb = false
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  // p != q   ->   isProb = true
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  // p == q   ->   isProb = false;
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  unsigned TakenIdx = 0, NonTakenIdx = 1;
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  bool isProb = CI->getPredicate() == ICmpInst::ICMP_NE;
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  if (!isProb)
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    std::swap(TakenIdx, NonTakenIdx);
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  BranchProbability TakenProb(PH_TAKEN_WEIGHT,
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                              PH_TAKEN_WEIGHT + PH_NONTAKEN_WEIGHT);
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  setEdgeProbability(BB, TakenIdx, TakenProb);
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  setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
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  return true;
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}
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// Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
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// as taken, exiting edges as not-taken.
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bool BranchProbabilityInfo::calcLoopBranchHeuristics(const BasicBlock *BB,
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                                                     const LoopInfo &LI) {
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  Loop *L = LI.getLoopFor(BB);
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  if (!L)
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    return false;
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  SmallVector<unsigned, 8> BackEdges;
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  SmallVector<unsigned, 8> ExitingEdges;
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  SmallVector<unsigned, 8> InEdges; // Edges from header to the loop.
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  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
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    if (!L->contains(*I))
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      ExitingEdges.push_back(I.getSuccessorIndex());
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    else if (L->getHeader() == *I)
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      BackEdges.push_back(I.getSuccessorIndex());
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    else
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      InEdges.push_back(I.getSuccessorIndex());
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  }
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  if (BackEdges.empty() && ExitingEdges.empty())
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    return false;
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  // Collect the sum of probabilities of back-edges/in-edges/exiting-edges, and
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  // normalize them so that they sum up to one.
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  BranchProbability Probs[] = {BranchProbability::getZero(),
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                               BranchProbability::getZero(),
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                               BranchProbability::getZero()};
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  unsigned Denom = (BackEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
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                   (InEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
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                   (ExitingEdges.empty() ? 0 : LBH_NONTAKEN_WEIGHT);
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  if (!BackEdges.empty())
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    Probs[0] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
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  if (!InEdges.empty())
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    Probs[1] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
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  if (!ExitingEdges.empty())
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    Probs[2] = BranchProbability(LBH_NONTAKEN_WEIGHT, Denom);
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  if (uint32_t numBackEdges = BackEdges.size()) {
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    auto Prob = Probs[0] / numBackEdges;
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    for (unsigned SuccIdx : BackEdges)
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      setEdgeProbability(BB, SuccIdx, Prob);
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  }
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  if (uint32_t numInEdges = InEdges.size()) {
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    auto Prob = Probs[1] / numInEdges;
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    for (unsigned SuccIdx : InEdges)
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      setEdgeProbability(BB, SuccIdx, Prob);
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  }
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  if (uint32_t numExitingEdges = ExitingEdges.size()) {
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    auto Prob = Probs[2] / numExitingEdges;
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    for (unsigned SuccIdx : ExitingEdges)
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      setEdgeProbability(BB, SuccIdx, Prob);
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  }
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  return true;
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}
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bool BranchProbabilityInfo::calcZeroHeuristics(const BasicBlock *BB) {
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  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
 | 
						|
  if (!BI || !BI->isConditional())
 | 
						|
    return false;
 | 
						|
 | 
						|
  Value *Cond = BI->getCondition();
 | 
						|
  ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
 | 
						|
  if (!CI)
 | 
						|
    return false;
 | 
						|
 | 
						|
  Value *RHS = CI->getOperand(1);
 | 
						|
  ConstantInt *CV = dyn_cast<ConstantInt>(RHS);
 | 
						|
  if (!CV)
 | 
						|
    return false;
 | 
						|
 | 
						|
  // If the LHS is the result of AND'ing a value with a single bit bitmask,
 | 
						|
  // we don't have information about probabilities.
 | 
						|
  if (Instruction *LHS = dyn_cast<Instruction>(CI->getOperand(0)))
 | 
						|
    if (LHS->getOpcode() == Instruction::And)
 | 
						|
      if (ConstantInt *AndRHS = dyn_cast<ConstantInt>(LHS->getOperand(1)))
 | 
						|
        if (AndRHS->getUniqueInteger().isPowerOf2())
 | 
						|
          return false;
 | 
						|
 | 
						|
  bool isProb;
 | 
						|
  if (CV->isZero()) {
 | 
						|
    switch (CI->getPredicate()) {
 | 
						|
    case CmpInst::ICMP_EQ:
 | 
						|
      // X == 0   ->  Unlikely
 | 
						|
      isProb = false;
 | 
						|
      break;
 | 
						|
    case CmpInst::ICMP_NE:
 | 
						|
      // X != 0   ->  Likely
 | 
						|
      isProb = true;
 | 
						|
      break;
 | 
						|
    case CmpInst::ICMP_SLT:
 | 
						|
      // X < 0   ->  Unlikely
 | 
						|
      isProb = false;
 | 
						|
      break;
 | 
						|
    case CmpInst::ICMP_SGT:
 | 
						|
      // X > 0   ->  Likely
 | 
						|
      isProb = true;
 | 
						|
      break;
 | 
						|
    default:
 | 
						|
      return false;
 | 
						|
    }
 | 
						|
  } else if (CV->isOne() && CI->getPredicate() == CmpInst::ICMP_SLT) {
 | 
						|
    // InstCombine canonicalizes X <= 0 into X < 1.
 | 
						|
    // X <= 0   ->  Unlikely
 | 
						|
    isProb = false;
 | 
						|
  } else if (CV->isAllOnesValue()) {
 | 
						|
    switch (CI->getPredicate()) {
 | 
						|
    case CmpInst::ICMP_EQ:
 | 
						|
      // X == -1  ->  Unlikely
 | 
						|
      isProb = false;
 | 
						|
      break;
 | 
						|
    case CmpInst::ICMP_NE:
 | 
						|
      // X != -1  ->  Likely
 | 
						|
      isProb = true;
 | 
						|
      break;
 | 
						|
    case CmpInst::ICMP_SGT:
 | 
						|
      // InstCombine canonicalizes X >= 0 into X > -1.
 | 
						|
      // X >= 0   ->  Likely
 | 
						|
      isProb = true;
 | 
						|
      break;
 | 
						|
    default:
 | 
						|
      return false;
 | 
						|
    }
 | 
						|
  } else {
 | 
						|
    return false;
 | 
						|
  }
 | 
						|
 | 
						|
  unsigned TakenIdx = 0, NonTakenIdx = 1;
 | 
						|
 | 
						|
  if (!isProb)
 | 
						|
    std::swap(TakenIdx, NonTakenIdx);
 | 
						|
 | 
						|
  BranchProbability TakenProb(ZH_TAKEN_WEIGHT,
 | 
						|
                              ZH_TAKEN_WEIGHT + ZH_NONTAKEN_WEIGHT);
 | 
						|
  setEdgeProbability(BB, TakenIdx, TakenProb);
 | 
						|
  setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
 | 
						|
  return true;
 | 
						|
}
 | 
						|
 | 
						|
bool BranchProbabilityInfo::calcFloatingPointHeuristics(const BasicBlock *BB) {
 | 
						|
  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
 | 
						|
  if (!BI || !BI->isConditional())
 | 
						|
    return false;
 | 
						|
 | 
						|
  Value *Cond = BI->getCondition();
 | 
						|
  FCmpInst *FCmp = dyn_cast<FCmpInst>(Cond);
 | 
						|
  if (!FCmp)
 | 
						|
    return false;
 | 
						|
 | 
						|
  bool isProb;
 | 
						|
  if (FCmp->isEquality()) {
 | 
						|
    // f1 == f2 -> Unlikely
 | 
						|
    // f1 != f2 -> Likely
 | 
						|
    isProb = !FCmp->isTrueWhenEqual();
 | 
						|
  } else if (FCmp->getPredicate() == FCmpInst::FCMP_ORD) {
 | 
						|
    // !isnan -> Likely
 | 
						|
    isProb = true;
 | 
						|
  } else if (FCmp->getPredicate() == FCmpInst::FCMP_UNO) {
 | 
						|
    // isnan -> Unlikely
 | 
						|
    isProb = false;
 | 
						|
  } else {
 | 
						|
    return false;
 | 
						|
  }
 | 
						|
 | 
						|
  unsigned TakenIdx = 0, NonTakenIdx = 1;
 | 
						|
 | 
						|
  if (!isProb)
 | 
						|
    std::swap(TakenIdx, NonTakenIdx);
 | 
						|
 | 
						|
  BranchProbability TakenProb(FPH_TAKEN_WEIGHT,
 | 
						|
                              FPH_TAKEN_WEIGHT + FPH_NONTAKEN_WEIGHT);
 | 
						|
  setEdgeProbability(BB, TakenIdx, TakenProb);
 | 
						|
  setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
 | 
						|
  return true;
 | 
						|
}
 | 
						|
 | 
						|
bool BranchProbabilityInfo::calcInvokeHeuristics(const BasicBlock *BB) {
 | 
						|
  const InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator());
 | 
						|
  if (!II)
 | 
						|
    return false;
 | 
						|
 | 
						|
  BranchProbability TakenProb(IH_TAKEN_WEIGHT,
 | 
						|
                              IH_TAKEN_WEIGHT + IH_NONTAKEN_WEIGHT);
 | 
						|
  setEdgeProbability(BB, 0 /*Index for Normal*/, TakenProb);
 | 
						|
  setEdgeProbability(BB, 1 /*Index for Unwind*/, TakenProb.getCompl());
 | 
						|
  return true;
 | 
						|
}
 | 
						|
 | 
						|
void BranchProbabilityInfo::releaseMemory() {
 | 
						|
  Probs.clear();
 | 
						|
}
 | 
						|
 | 
						|
void BranchProbabilityInfo::print(raw_ostream &OS) const {
 | 
						|
  OS << "---- Branch Probabilities ----\n";
 | 
						|
  // We print the probabilities from the last function the analysis ran over,
 | 
						|
  // or the function it is currently running over.
 | 
						|
  assert(LastF && "Cannot print prior to running over a function");
 | 
						|
  for (const auto &BI : *LastF) {
 | 
						|
    for (succ_const_iterator SI = succ_begin(&BI), SE = succ_end(&BI); SI != SE;
 | 
						|
         ++SI) {
 | 
						|
      printEdgeProbability(OS << "  ", &BI, *SI);
 | 
						|
    }
 | 
						|
  }
 | 
						|
}
 | 
						|
 | 
						|
bool BranchProbabilityInfo::
 | 
						|
isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const {
 | 
						|
  // Hot probability is at least 4/5 = 80%
 | 
						|
  // FIXME: Compare against a static "hot" BranchProbability.
 | 
						|
  return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
 | 
						|
}
 | 
						|
 | 
						|
const BasicBlock *
 | 
						|
BranchProbabilityInfo::getHotSucc(const BasicBlock *BB) const {
 | 
						|
  auto MaxProb = BranchProbability::getZero();
 | 
						|
  const BasicBlock *MaxSucc = nullptr;
 | 
						|
 | 
						|
  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
 | 
						|
    const BasicBlock *Succ = *I;
 | 
						|
    auto Prob = getEdgeProbability(BB, Succ);
 | 
						|
    if (Prob > MaxProb) {
 | 
						|
      MaxProb = Prob;
 | 
						|
      MaxSucc = Succ;
 | 
						|
    }
 | 
						|
  }
 | 
						|
 | 
						|
  // Hot probability is at least 4/5 = 80%
 | 
						|
  if (MaxProb > BranchProbability(4, 5))
 | 
						|
    return MaxSucc;
 | 
						|
 | 
						|
  return nullptr;
 | 
						|
}
 | 
						|
 | 
						|
/// Get the raw edge probability for the edge. If can't find it, return a
 | 
						|
/// default probability 1/N where N is the number of successors. Here an edge is
 | 
						|
/// specified using PredBlock and an
 | 
						|
/// index to the successors.
 | 
						|
BranchProbability
 | 
						|
BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
 | 
						|
                                          unsigned IndexInSuccessors) const {
 | 
						|
  auto I = Probs.find(std::make_pair(Src, IndexInSuccessors));
 | 
						|
 | 
						|
  if (I != Probs.end())
 | 
						|
    return I->second;
 | 
						|
 | 
						|
  return {1,
 | 
						|
          static_cast<uint32_t>(std::distance(succ_begin(Src), succ_end(Src)))};
 | 
						|
}
 | 
						|
 | 
						|
BranchProbability
 | 
						|
BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
 | 
						|
                                          succ_const_iterator Dst) const {
 | 
						|
  return getEdgeProbability(Src, Dst.getSuccessorIndex());
 | 
						|
}
 | 
						|
 | 
						|
/// Get the raw edge probability calculated for the block pair. This returns the
 | 
						|
/// sum of all raw edge probabilities from Src to Dst.
 | 
						|
BranchProbability
 | 
						|
BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
 | 
						|
                                          const BasicBlock *Dst) const {
 | 
						|
  auto Prob = BranchProbability::getZero();
 | 
						|
  bool FoundProb = false;
 | 
						|
  for (succ_const_iterator I = succ_begin(Src), E = succ_end(Src); I != E; ++I)
 | 
						|
    if (*I == Dst) {
 | 
						|
      auto MapI = Probs.find(std::make_pair(Src, I.getSuccessorIndex()));
 | 
						|
      if (MapI != Probs.end()) {
 | 
						|
        FoundProb = true;
 | 
						|
        Prob += MapI->second;
 | 
						|
      }
 | 
						|
    }
 | 
						|
  uint32_t succ_num = std::distance(succ_begin(Src), succ_end(Src));
 | 
						|
  return FoundProb ? Prob : BranchProbability(1, succ_num);
 | 
						|
}
 | 
						|
 | 
						|
/// Set the edge probability for a given edge specified by PredBlock and an
 | 
						|
/// index to the successors.
 | 
						|
void BranchProbabilityInfo::setEdgeProbability(const BasicBlock *Src,
 | 
						|
                                               unsigned IndexInSuccessors,
 | 
						|
                                               BranchProbability Prob) {
 | 
						|
  Probs[std::make_pair(Src, IndexInSuccessors)] = Prob;
 | 
						|
  DEBUG(dbgs() << "set edge " << Src->getName() << " -> " << IndexInSuccessors
 | 
						|
               << " successor probability to " << Prob << "\n");
 | 
						|
}
 | 
						|
 | 
						|
raw_ostream &
 | 
						|
BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS,
 | 
						|
                                            const BasicBlock *Src,
 | 
						|
                                            const BasicBlock *Dst) const {
 | 
						|
 | 
						|
  const BranchProbability Prob = getEdgeProbability(Src, Dst);
 | 
						|
  OS << "edge " << Src->getName() << " -> " << Dst->getName()
 | 
						|
     << " probability is " << Prob
 | 
						|
     << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
 | 
						|
 | 
						|
  return OS;
 | 
						|
}
 | 
						|
 | 
						|
void BranchProbabilityInfo::calculate(const Function &F, const LoopInfo &LI) {
 | 
						|
  DEBUG(dbgs() << "---- Branch Probability Info : " << F.getName()
 | 
						|
               << " ----\n\n");
 | 
						|
  LastF = &F; // Store the last function we ran on for printing.
 | 
						|
  assert(PostDominatedByUnreachable.empty());
 | 
						|
  assert(PostDominatedByColdCall.empty());
 | 
						|
 | 
						|
  // Walk the basic blocks in post-order so that we can build up state about
 | 
						|
  // the successors of a block iteratively.
 | 
						|
  for (auto BB : post_order(&F.getEntryBlock())) {
 | 
						|
    DEBUG(dbgs() << "Computing probabilities for " << BB->getName() << "\n");
 | 
						|
    if (calcUnreachableHeuristics(BB))
 | 
						|
      continue;
 | 
						|
    if (calcMetadataWeights(BB))
 | 
						|
      continue;
 | 
						|
    if (calcColdCallHeuristics(BB))
 | 
						|
      continue;
 | 
						|
    if (calcLoopBranchHeuristics(BB, LI))
 | 
						|
      continue;
 | 
						|
    if (calcPointerHeuristics(BB))
 | 
						|
      continue;
 | 
						|
    if (calcZeroHeuristics(BB))
 | 
						|
      continue;
 | 
						|
    if (calcFloatingPointHeuristics(BB))
 | 
						|
      continue;
 | 
						|
    calcInvokeHeuristics(BB);
 | 
						|
  }
 | 
						|
 | 
						|
  PostDominatedByUnreachable.clear();
 | 
						|
  PostDominatedByColdCall.clear();
 | 
						|
}
 | 
						|
 | 
						|
void BranchProbabilityInfoWrapperPass::getAnalysisUsage(
 | 
						|
    AnalysisUsage &AU) const {
 | 
						|
  AU.addRequired<LoopInfoWrapperPass>();
 | 
						|
  AU.setPreservesAll();
 | 
						|
}
 | 
						|
 | 
						|
bool BranchProbabilityInfoWrapperPass::runOnFunction(Function &F) {
 | 
						|
  const LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
 | 
						|
  BPI.calculate(F, LI);
 | 
						|
  return false;
 | 
						|
}
 | 
						|
 | 
						|
void BranchProbabilityInfoWrapperPass::releaseMemory() { BPI.releaseMemory(); }
 | 
						|
 | 
						|
void BranchProbabilityInfoWrapperPass::print(raw_ostream &OS,
 | 
						|
                                             const Module *) const {
 | 
						|
  BPI.print(OS);
 | 
						|
}
 | 
						|
 | 
						|
char BranchProbabilityAnalysis::PassID;
 | 
						|
BranchProbabilityInfo
 | 
						|
BranchProbabilityAnalysis::run(Function &F, AnalysisManager<Function> &AM) {
 | 
						|
  BranchProbabilityInfo BPI;
 | 
						|
  BPI.calculate(F, AM.getResult<LoopAnalysis>(F));
 | 
						|
  return BPI;
 | 
						|
}
 | 
						|
 | 
						|
PreservedAnalyses
 | 
						|
BranchProbabilityPrinterPass::run(Function &F, AnalysisManager<Function> &AM) {
 | 
						|
  OS << "Printing analysis results of BPI for function "
 | 
						|
     << "'" << F.getName() << "':"
 | 
						|
     << "\n";
 | 
						|
  AM.getResult<BranchProbabilityAnalysis>(F).print(OS);
 | 
						|
  return PreservedAnalyses::all();
 | 
						|
}
 |