//
//===----------------------------------------------------------------------===//
+#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/LoopInfo.h"
// private methods are hidden in the .cpp file.
class BranchProbabilityAnalysis {
- typedef std::pair<BasicBlock *, BasicBlock *> Edge;
+ typedef std::pair<const BasicBlock *, const BasicBlock *> Edge;
DenseMap<Edge, uint32_t> *Weights;
// V
// BB1<-+
// | |
- // | | (Weight = 128)
+ // | | (Weight = 124)
// V |
// BB2--+
// |
// V
// BB3
//
- // Probability of the edge BB2->BB1 = 128 / (128 + 4) = 0.9696..
- // Probability of the edge BB2->BB3 = 4 / (128 + 4) = 0.0303..
+ // 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 = 128;
+ 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;
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();
}
}
// Return Heuristics
- void calcReturnHeuristics(BasicBlock *BB);
+ bool calcReturnHeuristics(BasicBlock *BB);
// Pointer Heuristics
- void calcPointerHeuristics(BasicBlock *BB);
+ bool calcPointerHeuristics(BasicBlock *BB);
// Loop Branch Heuristics
- void calcLoopBranchHeuristics(BasicBlock *BB);
+ bool calcLoopBranchHeuristics(BasicBlock *BB);
+
+ // Zero Heurestics
+ bool calcZeroHeuristics(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){
+bool BranchProbabilityAnalysis::calcReturnHeuristics(BasicBlock *BB){
if (BB->getTerminator()->getNumSuccessors() == 1)
- return;
+ 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)) {
- decEdgeWeight(BB, Succ);
+ 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.
-void BranchProbabilityAnalysis::calcPointerHeuristics(BasicBlock *BB) {
+bool BranchProbabilityAnalysis::calcPointerHeuristics(BasicBlock *BB) {
BranchInst * BI = dyn_cast<BranchInst>(BB->getTerminator());
if (!BI || !BI->isConditional())
- return;
+ return false;
Value *Cond = BI->getCondition();
ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
if (!CI || !CI->isEquality())
- return;
+ return false;
Value *LHS = CI->getOperand(0);
if (!LHS->getType()->isPointerTy())
- return;
+ return false;
assert(CI->getOperand(1)->getType()->isPointerTy());
if (!isProb)
std::swap(Taken, NonTaken);
- incEdgeWeight(BB, Taken);
- decEdgeWeight(BB, 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.
-void BranchProbabilityAnalysis::calcLoopBranchHeuristics(BasicBlock *BB) {
+bool BranchProbabilityAnalysis::calcLoopBranchHeuristics(BasicBlock *BB) {
uint32_t numSuccs = BB->getTerminator()->getNumSuccessors();
Loop *L = LI->getLoopFor(BB);
if (!L)
- return;
+ return false;
+
+ SmallPtrSet<BasicBlock *, 8> BackEdges;
+ SmallPtrSet<BasicBlock *, 8> ExitingEdges;
+ SmallPtrSet<BasicBlock *, 8> InEdges; // Edges from header to the loop.
- SmallVector<BasicBlock *, 8> BackEdges;
- SmallVector<BasicBlock *, 8> ExitingEdges;
+ 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.push_back(Succ);
+ ExitingEdges.insert(Succ);
else if (Succ == L->getHeader())
- BackEdges.push_back(Succ);
+ BackEdges.insert(Succ);
+ else if (isHeader)
+ InEdges.insert(Succ);
}
if (uint32_t numBackEdges = BackEdges.size()) {
if (backWeight < NORMAL_WEIGHT)
backWeight = NORMAL_WEIGHT;
- for (SmallVector<BasicBlock *, 8>::iterator EI = BackEdges.begin(),
+ 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 (SmallVector<BasicBlock *, 8>::iterator EI = ExitingEdges.begin(),
+ 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 || !CV->isZero())
+ return false;
+
+ bool isProb;
+ switch (CI->getPredicate()) {
+ case CmpInst::ICMP_EQ:
+ // Equal to zero is not expected to be taken.
+ isProb = false;
+ break;
+
+ case CmpInst::ICMP_NE:
+ // Not equal to zero is expected.
+ isProb = true;
+ break;
+
+ case CmpInst::ICMP_SLT:
+ // Less or equal to zero is not expected.
+ // X < 0 -> Unlikely
+ isProb = false;
+ break;
+
+ case CmpInst::ICMP_UGT:
+ case CmpInst::ICMP_SGT:
+ // Greater or equal to zero is expected.
+ // X > 0 -> Likely
+ isProb = true;
+ break;
+
+ default:
+ 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++;
- // Only LBH uses setEdgeWeight method.
- calcLoopBranchHeuristics(BB);
+ if (calcLoopBranchHeuristics(BB))
+ continue;
+
+ if (calcReturnHeuristics(BB))
+ continue;
- // PH and RH use only incEdgeWeight and decEwdgeWeight methods to
- // not efface LBH results.
- calcPointerHeuristics(BB);
- calcReturnHeuristics(BB);
+ if (calcPointerHeuristics(BB))
+ continue;
+
+ calcZeroHeuristics(BB);
}
return false;
return BPA.runOnFunction(F);
}
-uint32_t BranchProbabilityInfo::getSumForBlock(BasicBlock *BB) const {
+uint32_t BranchProbabilityInfo::getSumForBlock(const BasicBlock *BB) const {
uint32_t Sum = 0;
- for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
- BasicBlock *Succ = *I;
+ 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;
return Sum;
}
-bool BranchProbabilityInfo::isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const {
+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);
}
// Return edge's weight. If can't find it, return DEFAULT_WEIGHT value.
-uint32_t
-BranchProbabilityInfo::getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) const {
+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);
return DEFAULT_WEIGHT;
}
-void BranchProbabilityInfo::setEdgeWeight(BasicBlock *Src, BasicBlock *Dst,
- uint32_t 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
BranchProbability BranchProbabilityInfo::
-getEdgeProbability(BasicBlock *Src, BasicBlock *Dst) const {
+getEdgeProbability(const BasicBlock *Src, const BasicBlock *Dst) const {
uint32_t N = getEdgeWeight(Src, Dst);
uint32_t D = getSumForBlock(Src);
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