1 files changed, 511 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Analysis/BranchProbabilityInfo.cpp b/contrib/llvm/lib/Analysis/BranchProbabilityInfo.cpp
new file mode 100644
index 0000000..bde3b76
--- /dev/null
+++ b/contrib/llvm/lib/Analysis/BranchProbabilityInfo.cpp
@@ -0,0 +1,511 @@
+//===-- BranchProbabilityInfo.cpp - Branch Probability Analysis -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Loops should be simplified before this analysis.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/LLVMContext.h"
+#include "llvm/Metadata.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+INITIALIZE_PASS_BEGIN(BranchProbabilityInfo, "branch-prob",
+                      "Branch Probability Analysis", false, true)
+INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_END(BranchProbabilityInfo, "branch-prob",
+                    "Branch Probability Analysis", false, true)
+
+char BranchProbabilityInfo::ID = 0;
+
+namespace {
+// Please note that BranchProbabilityAnalysis is not a FunctionPass.
+// It is created by BranchProbabilityInfo (which is a FunctionPass), which
+// provides a clear interface. Thanks to that, all heuristics and other
+// private methods are hidden in the .cpp file.
+class BranchProbabilityAnalysis {
+
+  typedef std::pair<const BasicBlock *, const BasicBlock *> Edge;
+
+  DenseMap<Edge, uint32_t> *Weights;
+
+  BranchProbabilityInfo *BP;
+
+  LoopInfo *LI;
+
+
+  // Weights are for internal use only. They are used by heuristics to help to
+  // estimate edges' probability. Example:
+  //
+  // Using "Loop Branch Heuristics" we predict weights of edges for the
+  // block BB2.
+  //         ...
+  //          |
+  //          V
+  //         BB1<-+
+  //          |   |
+  //          |   | (Weight = 124)
+  //          V   |
+  //         BB2--+
+  //          |
+  //          | (Weight = 4)
+  //          V
+  //         BB3
+  //
+  // Probability of the edge BB2->BB1 = 124 / (124 + 4) = 0.96875
+  // Probability of the edge BB2->BB3 = 4 / (124 + 4) = 0.03125
+
+  static const uint32_t LBH_TAKEN_WEIGHT = 124;
+  static const uint32_t LBH_NONTAKEN_WEIGHT = 4;
+
+  static const uint32_t RH_TAKEN_WEIGHT = 24;
+  static const uint32_t RH_NONTAKEN_WEIGHT = 8;
+
+  static const uint32_t PH_TAKEN_WEIGHT = 20;
+  static const uint32_t PH_NONTAKEN_WEIGHT = 12;
+
+  static const uint32_t ZH_TAKEN_WEIGHT = 20;
+  static const uint32_t ZH_NONTAKEN_WEIGHT = 12;
+
+  // Standard weight value. Used when none of the heuristics set weight for
+  // the edge.
+  static const uint32_t NORMAL_WEIGHT = 16;
+
+  // Minimum weight of an edge. Please note, that weight is NEVER 0.
+  static const uint32_t MIN_WEIGHT = 1;
+
+  // Return TRUE if BB leads directly to a Return Instruction.
+  static bool isReturningBlock(BasicBlock *BB) {
+    SmallPtrSet<BasicBlock *, 8> Visited;
+
+    while (true) {
+      TerminatorInst *TI = BB->getTerminator();
+      if (isa<ReturnInst>(TI))
+        return true;
+
+      if (TI->getNumSuccessors() > 1)
+        break;
+
+      // It is unreachable block which we can consider as a return instruction.
+      if (TI->getNumSuccessors() == 0)
+        return true;
+
+      Visited.insert(BB);
+      BB = TI->getSuccessor(0);
+
+      // Stop if cycle is detected.
+      if (Visited.count(BB))
+        return false;
+    }
+
+    return false;
+  }
+
+  uint32_t getMaxWeightFor(BasicBlock *BB) const {
+    return UINT32_MAX / BB->getTerminator()->getNumSuccessors();
+  }
+
+public:
+  BranchProbabilityAnalysis(DenseMap<Edge, uint32_t> *W,
+                            BranchProbabilityInfo *BP, LoopInfo *LI)
+    : Weights(W), BP(BP), LI(LI) {
+  }
+
+  // Metadata Weights
+  bool calcMetadataWeights(BasicBlock *BB);
+
+  // Return Heuristics
+  bool calcReturnHeuristics(BasicBlock *BB);
+
+  // Pointer Heuristics
+  bool calcPointerHeuristics(BasicBlock *BB);
+
+  // Loop Branch Heuristics
+  bool calcLoopBranchHeuristics(BasicBlock *BB);
+
+  // Zero Heurestics
+  bool calcZeroHeuristics(BasicBlock *BB);
+
+  bool runOnFunction(Function &F);
+};
+} // end anonymous namespace
+
+// Propagate existing explicit probabilities from either profile data or
+// 'expect' intrinsic processing.
+bool BranchProbabilityAnalysis::calcMetadataWeights(BasicBlock *BB) {
+  TerminatorInst *TI = BB->getTerminator();
+  if (TI->getNumSuccessors() == 1)
+    return false;
+  if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
+    return false;
+
+  MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
+  if (!WeightsNode)
+    return false;
+
+  // Ensure there are weights for all of the successors. Note that the first
+  // operand to the metadata node is a name, not a weight.
+  if (WeightsNode->getNumOperands() != TI->getNumSuccessors() + 1)
+    return false;
+
+  // Build up the final weights that will be used in a temporary buffer, but
+  // don't add them until all weihts are present. Each weight value is clamped
+  // to [1, getMaxWeightFor(BB)].
+  uint32_t WeightLimit = getMaxWeightFor(BB);
+  SmallVector<uint32_t, 2> Weights;
+  Weights.reserve(TI->getNumSuccessors());
+  for (unsigned i = 1, e = WeightsNode->getNumOperands(); i != e; ++i) {
+    ConstantInt *Weight = dyn_cast<ConstantInt>(WeightsNode->getOperand(i));
+    if (!Weight)
+      return false;
+    Weights.push_back(
+      std::max<uint32_t>(1, Weight->getLimitedValue(WeightLimit)));
+  }
+  assert(Weights.size() == TI->getNumSuccessors() && "Checked above");
+  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+    BP->setEdgeWeight(BB, TI->getSuccessor(i), Weights[i]);
+
+  return true;
+}
+
+// Calculate Edge Weights using "Return Heuristics". Predict a successor which
+// leads directly to Return Instruction will not be taken.
+bool BranchProbabilityAnalysis::calcReturnHeuristics(BasicBlock *BB){
+  if (BB->getTerminator()->getNumSuccessors() == 1)
+    return false;
+
+  SmallPtrSet<BasicBlock *, 4> ReturningEdges;
+  SmallPtrSet<BasicBlock *, 4> StayEdges;
+
+  for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
+    BasicBlock *Succ = *I;
+    if (isReturningBlock(Succ))
+      ReturningEdges.insert(Succ);
+    else
+      StayEdges.insert(Succ);
+  }
+
+  if (uint32_t numStayEdges = StayEdges.size()) {
+    uint32_t stayWeight = RH_TAKEN_WEIGHT / numStayEdges;
+    if (stayWeight < NORMAL_WEIGHT)
+      stayWeight = NORMAL_WEIGHT;
+
+    for (SmallPtrSet<BasicBlock *, 4>::iterator I = StayEdges.begin(),
+         E = StayEdges.end(); I != E; ++I)
+      BP->setEdgeWeight(BB, *I, stayWeight);
+  }
+
+  if (uint32_t numRetEdges = ReturningEdges.size()) {
+    uint32_t retWeight = RH_NONTAKEN_WEIGHT / numRetEdges;
+    if (retWeight < MIN_WEIGHT)
+      retWeight = MIN_WEIGHT;
+    for (SmallPtrSet<BasicBlock *, 4>::iterator I = ReturningEdges.begin(),
+         E = ReturningEdges.end(); I != E; ++I) {
+      BP->setEdgeWeight(BB, *I, retWeight);
+    }
+  }
+
+  return ReturningEdges.size() > 0;
+}
+
+// Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
+// between two pointer or pointer and NULL will fail.
+bool BranchProbabilityAnalysis::calcPointerHeuristics(BasicBlock *BB) {
+  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 || !CI->isEquality())
+    return false;
+
+  Value *LHS = CI->getOperand(0);
+
+  if (!LHS->getType()->isPointerTy())
+    return false;
+
+  assert(CI->getOperand(1)->getType()->isPointerTy());
+
+  BasicBlock *Taken = BI->getSuccessor(0);
+  BasicBlock *NonTaken = BI->getSuccessor(1);
+
+  // p != 0   ->   isProb = true
+  // p == 0   ->   isProb = false
+  // p != q   ->   isProb = true
+  // p == q   ->   isProb = false;
+  bool isProb = CI->getPredicate() == ICmpInst::ICMP_NE;
+  if (!isProb)
+    std::swap(Taken, NonTaken);
+
+  BP->setEdgeWeight(BB, Taken, PH_TAKEN_WEIGHT);
+  BP->setEdgeWeight(BB, NonTaken, PH_NONTAKEN_WEIGHT);
+  return true;
+}
+
+// Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
+// as taken, exiting edges as not-taken.
+bool BranchProbabilityAnalysis::calcLoopBranchHeuristics(BasicBlock *BB) {
+  uint32_t numSuccs = BB->getTerminator()->getNumSuccessors();
+
+  Loop *L = LI->getLoopFor(BB);
+  if (!L)
+    return false;
+
+  SmallPtrSet<BasicBlock *, 8> BackEdges;
+  SmallPtrSet<BasicBlock *, 8> ExitingEdges;
+  SmallPtrSet<BasicBlock *, 8> InEdges; // Edges from header to the loop.
+
+  bool isHeader = BB == L->getHeader();
+
+  for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
+    BasicBlock *Succ = *I;
+    Loop *SuccL = LI->getLoopFor(Succ);
+    if (SuccL != L)
+      ExitingEdges.insert(Succ);
+    else if (Succ == L->getHeader())
+      BackEdges.insert(Succ);
+    else if (isHeader)
+      InEdges.insert(Succ);
+  }
+
+  if (uint32_t numBackEdges = BackEdges.size()) {
+    uint32_t backWeight = LBH_TAKEN_WEIGHT / numBackEdges;
+    if (backWeight < NORMAL_WEIGHT)
+      backWeight = NORMAL_WEIGHT;
+
+    for (SmallPtrSet<BasicBlock *, 8>::iterator EI = BackEdges.begin(),
+         EE = BackEdges.end(); EI != EE; ++EI) {
+      BasicBlock *Back = *EI;
+      BP->setEdgeWeight(BB, Back, backWeight);
+    }
+  }
+
+  if (uint32_t numInEdges = InEdges.size()) {
+    uint32_t inWeight = LBH_TAKEN_WEIGHT / numInEdges;
+    if (inWeight < NORMAL_WEIGHT)
+      inWeight = NORMAL_WEIGHT;
+
+    for (SmallPtrSet<BasicBlock *, 8>::iterator EI = InEdges.begin(),
+         EE = InEdges.end(); EI != EE; ++EI) {
+      BasicBlock *Back = *EI;
+      BP->setEdgeWeight(BB, Back, inWeight);
+    }
+  }
+
+  uint32_t numExitingEdges = ExitingEdges.size();
+  if (uint32_t numNonExitingEdges = numSuccs - numExitingEdges) {
+    uint32_t exitWeight = LBH_NONTAKEN_WEIGHT / numNonExitingEdges;
+    if (exitWeight < MIN_WEIGHT)
+      exitWeight = MIN_WEIGHT;
+
+    for (SmallPtrSet<BasicBlock *, 8>::iterator EI = ExitingEdges.begin(),
+         EE = ExitingEdges.end(); EI != EE; ++EI) {
+      BasicBlock *Exiting = *EI;
+      BP->setEdgeWeight(BB, Exiting, exitWeight);
+    }
+  }
+
+  return true;
+}
+
+bool BranchProbabilityAnalysis::calcZeroHeuristics(BasicBlock *BB) {
+  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;
+
+  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() && CI->getPredicate() == CmpInst::ICMP_SGT) {
+    // InstCombine canonicalizes X >= 0 into X > -1.
+    // X >= 0   ->  Likely
+    isProb = true;
+  } else {
+    return false;
+  }
+
+  BasicBlock *Taken = BI->getSuccessor(0);
+  BasicBlock *NonTaken = BI->getSuccessor(1);
+
+  if (!isProb)
+    std::swap(Taken, NonTaken);
+
+  BP->setEdgeWeight(BB, Taken, ZH_TAKEN_WEIGHT);
+  BP->setEdgeWeight(BB, NonTaken, ZH_NONTAKEN_WEIGHT);
+
+  return true;
+}
+
+
+bool BranchProbabilityAnalysis::runOnFunction(Function &F) {
+
+  for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
+    BasicBlock *BB = I++;
+
+    if (calcMetadataWeights(BB))
+      continue;
+
+    if (calcLoopBranchHeuristics(BB))
+      continue;
+
+    if (calcReturnHeuristics(BB))
+      continue;
+
+    if (calcPointerHeuristics(BB))
+      continue;
+
+    calcZeroHeuristics(BB);
+  }
+
+  return false;
+}
+
+void BranchProbabilityInfo::getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.addRequired<LoopInfo>();
+    AU.setPreservesAll();
+}
+
+bool BranchProbabilityInfo::runOnFunction(Function &F) {
+  LoopInfo &LI = getAnalysis<LoopInfo>();
+  BranchProbabilityAnalysis BPA(&Weights, this, &LI);
+  return BPA.runOnFunction(F);
+}
+
+uint32_t BranchProbabilityInfo::getSumForBlock(const BasicBlock *BB) const {
+  uint32_t Sum = 0;
+
+  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
+    const BasicBlock *Succ = *I;
+    uint32_t Weight = getEdgeWeight(BB, Succ);
+    uint32_t PrevSum = Sum;
+
+    Sum += Weight;
+    assert(Sum > PrevSum); (void) PrevSum;
+  }
+
+  return Sum;
+}
+
+bool BranchProbabilityInfo::
+isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const {
+  // Hot probability is at least 4/5 = 80%
+  uint32_t Weight = getEdgeWeight(Src, Dst);
+  uint32_t Sum = getSumForBlock(Src);
+
+  // FIXME: Implement BranchProbability::compare then change this code to
+  // compare this BranchProbability against a static "hot" BranchProbability.
+  return (uint64_t)Weight * 5 > (uint64_t)Sum * 4;
+}
+
+BasicBlock *BranchProbabilityInfo::getHotSucc(BasicBlock *BB) const {
+  uint32_t Sum = 0;
+  uint32_t MaxWeight = 0;
+  BasicBlock *MaxSucc = 0;
+
+  for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
+    BasicBlock *Succ = *I;
+    uint32_t Weight = getEdgeWeight(BB, Succ);
+    uint32_t PrevSum = Sum;
+
+    Sum += Weight;
+    assert(Sum > PrevSum); (void) PrevSum;
+
+    if (Weight > MaxWeight) {
+      MaxWeight = Weight;
+      MaxSucc = Succ;
+    }
+  }
+
+  // FIXME: Use BranchProbability::compare.
+  if ((uint64_t)MaxWeight * 5 > (uint64_t)Sum * 4)
+    return MaxSucc;
+
+  return 0;
+}
+
+// Return edge's weight. If can't find it, return DEFAULT_WEIGHT value.
+uint32_t BranchProbabilityInfo::
+getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const {
+  Edge E(Src, Dst);
+  DenseMap<Edge, uint32_t>::const_iterator I = Weights.find(E);
+
+  if (I != Weights.end())
+    return I->second;
+
+  return DEFAULT_WEIGHT;
+}
+
+void BranchProbabilityInfo::
+setEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst, uint32_t Weight) {
+  Weights[std::make_pair(Src, Dst)] = Weight;
+  DEBUG(dbgs() << "set edge " << Src->getNameStr() << " -> "
+               << Dst->getNameStr() << " weight to " << Weight
+               << (isEdgeHot(Src, Dst) ? " [is HOT now]\n" : "\n"));
+}
+
+
+BranchProbability BranchProbabilityInfo::
+getEdgeProbability(const BasicBlock *Src, const BasicBlock *Dst) const {
+
+  uint32_t N = getEdgeWeight(Src, Dst);
+  uint32_t D = getSumForBlock(Src);
+
+  return BranchProbability(N, D);
+}
+
+raw_ostream &
+BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
+                                            BasicBlock *Dst) const {
+
+  const BranchProbability Prob = getEdgeProbability(Src, Dst);
+  OS << "edge " << Src->getNameStr() << " -> " << Dst->getNameStr()
+     << " probability is " << Prob
+     << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
+
+  return OS;
+}