IFC @ r222830

1 files changed, 357 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..812fac0
--- /dev/null
+++ b/contrib/llvm/lib/Analysis/BranchProbabilityInfo.cpp
@@ -0,0 +1,357 @@
+//===-- 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/Instructions.h"
+#include "llvm/Analysis/BranchProbabilityInfo.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;
+
+
+// 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<BasicBlock *, 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 = 128)
+  //          V   |
+  //         BB2--+
+  //          |
+  //          | (Weight = 4)
+  //          V
+  //         BB3
+  //
+  // Probability of the edge BB2->BB1 = 128 / (128 + 4) = 0.9696..
+  // Probability of the edge BB2->BB3 = 4 / (128 + 4) = 0.0303..
+
+  static const uint32_t LBH_TAKEN_WEIGHT = 128;
+  static const uint32_t LBH_NONTAKEN_WEIGHT = 4;
+
+  // 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;
+  }
+
+  // Multiply Edge Weight by two.
+  void incEdgeWeight(BasicBlock *Src, BasicBlock *Dst) {
+    uint32_t Weight = BP->getEdgeWeight(Src, Dst);
+    uint32_t MaxWeight = getMaxWeightFor(Src);
+
+    if (Weight * 2 > MaxWeight)
+      BP->setEdgeWeight(Src, Dst, MaxWeight);
+    else
+      BP->setEdgeWeight(Src, Dst, Weight * 2);
+  }
+
+  // Divide Edge Weight by two.
+  void decEdgeWeight(BasicBlock *Src, BasicBlock *Dst) {
+    uint32_t Weight = BP->getEdgeWeight(Src, Dst);
+
+    assert(Weight > 0);
+    if (Weight / 2 < MIN_WEIGHT)
+      BP->setEdgeWeight(Src, Dst, MIN_WEIGHT);
+    else
+      BP->setEdgeWeight(Src, Dst, Weight / 2);
+  }
+
+
+  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) {
+  }
+
+  // Return Heuristics
+  void calcReturnHeuristics(BasicBlock *BB);
+
+  // Pointer Heuristics
+  void calcPointerHeuristics(BasicBlock *BB);
+
+  // Loop Branch Heuristics
+  void calcLoopBranchHeuristics(BasicBlock *BB);
+
+  bool runOnFunction(Function &F);
+};
+
+// Calculate Edge Weights using "Return Heuristics". Predict a successor which
+// leads directly to Return Instruction will not be taken.
+void BranchProbabilityAnalysis::calcReturnHeuristics(BasicBlock *BB){
+  if (BB->getTerminator()->getNumSuccessors() == 1)
+    return;
+
+  for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
+    BasicBlock *Succ = *I;
+    if (isReturningBlock(Succ)) {
+      decEdgeWeight(BB, Succ);
+    }
+  }
+}
+
+// Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
+// between two pointer or pointer and NULL will fail.
+void BranchProbabilityAnalysis::calcPointerHeuristics(BasicBlock *BB) {
+  BranchInst * BI = dyn_cast<BranchInst>(BB->getTerminator());
+  if (!BI || !BI->isConditional())
+    return;
+
+  Value *Cond = BI->getCondition();
+  ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
+  if (!CI)
+    return;
+
+  Value *LHS = CI->getOperand(0);
+
+  if (!LHS->getType()->isPointerTy())
+    return;
+
+  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->isEquality();
+  if (!isProb)
+    std::swap(Taken, NonTaken);
+
+  incEdgeWeight(BB, Taken);
+  decEdgeWeight(BB, NonTaken);
+}
+
+// Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
+// as taken, exiting edges as not-taken.
+void BranchProbabilityAnalysis::calcLoopBranchHeuristics(BasicBlock *BB) {
+  uint32_t numSuccs = BB->getTerminator()->getNumSuccessors();
+
+  Loop *L = LI->getLoopFor(BB);
+  if (!L)
+    return;
+
+  SmallVector<BasicBlock *, 8> BackEdges;
+  SmallVector<BasicBlock *, 8> ExitingEdges;
+
+  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.push_back(Succ);
+    else if (Succ == L->getHeader())
+      BackEdges.push_back(Succ);
+  }
+
+  if (uint32_t numBackEdges = BackEdges.size()) {
+    uint32_t backWeight = LBH_TAKEN_WEIGHT / numBackEdges;
+    if (backWeight < NORMAL_WEIGHT)
+      backWeight = NORMAL_WEIGHT;
+
+    for (SmallVector<BasicBlock *, 8>::iterator EI = BackEdges.begin(),
+         EE = BackEdges.end(); EI != EE; ++EI) {
+      BasicBlock *Back = *EI;
+      BP->setEdgeWeight(BB, Back, backWeight);
+    }
+  }
+
+  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 (SmallVector<BasicBlock *, 8>::iterator EI = ExitingEdges.begin(),
+         EE = ExitingEdges.end(); EI != EE; ++EI) {
+      BasicBlock *Exiting = *EI;
+      BP->setEdgeWeight(BB, Exiting, exitWeight);
+    }
+  }
+}
+
+bool BranchProbabilityAnalysis::runOnFunction(Function &F) {
+
+  for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
+    BasicBlock *BB = I++;
+
+    // Only LBH uses setEdgeWeight method.
+    calcLoopBranchHeuristics(BB);
+
+    // PH and RH use only incEdgeWeight and decEwdgeWeight methods to
+    // not efface LBH results.
+    calcPointerHeuristics(BB);
+    calcReturnHeuristics(BB);
+  }
+
+  return false;
+}
+
+
+bool BranchProbabilityInfo::runOnFunction(Function &F) {
+  LoopInfo &LI = getAnalysis<LoopInfo>();
+  BranchProbabilityAnalysis BPA(&Weights, this, &LI);
+  return BPA.runOnFunction(F);
+}
+
+uint32_t BranchProbabilityInfo::getSumForBlock(BasicBlock *BB) const {
+  uint32_t Sum = 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;
+  }
+
+  return Sum;
+}
+
+bool BranchProbabilityInfo::isEdgeHot(BasicBlock *Src, 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(BasicBlock *Src, 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(BasicBlock *Src, 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(BasicBlock *Src, 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 {
+  BranchProbability Prob = getEdgeProbability(Src, Dst);
+
+  OS << "edge " << Src->getNameStr() << " -> " << Dst->getNameStr()
+     << " probability is " << Prob
+     << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
+
+  return OS;
+}