-//===-- BranchProbabilityInfo.cpp - Branch Probability Analysis -*- C++ -*-===//
+//===-- BranchProbabilityInfo.cpp - Branch Probability Analysis -----------===//
//
// The LLVM Compiler Infrastructure
//
//
//===----------------------------------------------------------------------===//
-#include "llvm/Instructions.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
-#include <climits>
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
using namespace llvm;
-INITIALIZE_PASS_BEGIN(BranchProbabilityInfo, "branch-prob",
+#define DEBUG_TYPE "branch-prob"
+
+INITIALIZE_PASS_BEGIN(BranchProbabilityInfoWrapperPass, "branch-prob",
"Branch Probability Analysis", false, true)
-INITIALIZE_PASS_DEPENDENCY(LoopInfo)
-INITIALIZE_PASS_END(BranchProbabilityInfo, "branch-prob",
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_END(BranchProbabilityInfoWrapperPass, "branch-prob",
"Branch Probability Analysis", false, true)
-char BranchProbabilityInfo::ID = 0;
+char BranchProbabilityInfoWrapperPass::ID = 0;
+// 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;
+
+/// \brief Unreachable-terminating branch taken weight.
+///
+/// This is the weight for a branch being taken to a block that terminates
+/// (eventually) in unreachable. These are predicted as unlikely as possible.
+static const uint32_t UR_TAKEN_WEIGHT = 1;
+
+/// \brief Unreachable-terminating branch not-taken weight.
+///
+/// This is the weight for a branch not being taken toward a block that
+/// terminates (eventually) in unreachable. Such a branch is essentially never
+/// taken. Set the weight to an absurdly high value so that nested loops don't
+/// easily subsume it.
+static const uint32_t UR_NONTAKEN_WEIGHT = 1024*1024 - 1;
+
+/// \brief Weight for a branch taken going into a cold block.
+///
+/// This is the weight for a branch taken toward a block marked
+/// cold. A block is marked cold if it's postdominated by a
+/// block containing a call to a cold function. Cold functions
+/// are those marked with attribute 'cold'.
+static const uint32_t CC_TAKEN_WEIGHT = 4;
+
+/// \brief Weight for a branch not-taken into a cold block.
+///
+/// This is the weight for a branch not taken toward a block marked
+/// cold.
+static const uint32_t CC_NONTAKEN_WEIGHT = 64;
+
+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;
+
+static const uint32_t FPH_TAKEN_WEIGHT = 20;
+static const uint32_t FPH_NONTAKEN_WEIGHT = 12;
+
+/// \brief Invoke-terminating normal branch taken weight
+///
+/// This is the weight for branching to the normal destination of an invoke
+/// instruction. We expect this to happen most of the time. Set the weight to an
+/// absurdly high value so that nested loops subsume it.
+static const uint32_t IH_TAKEN_WEIGHT = 1024 * 1024 - 1;
+
+/// \brief Invoke-terminating normal branch not-taken weight.
+///
+/// This is the weight for branching to the unwind destination of an invoke
+/// instruction. This is essentially never taken.
+static const uint32_t IH_NONTAKEN_WEIGHT = 1;
+
+/// \brief Calculate edge weights for successors lead to unreachable.
+///
+/// Predict that a successor which leads necessarily to an
+/// unreachable-terminated block as extremely unlikely.
+bool BranchProbabilityInfo::calcUnreachableHeuristics(BasicBlock *BB) {
+ TerminatorInst *TI = BB->getTerminator();
+ if (TI->getNumSuccessors() == 0) {
+ if (isa<UnreachableInst>(TI))
+ PostDominatedByUnreachable.insert(BB);
+ return false;
+ }
-// 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 {
+ SmallVector<unsigned, 4> UnreachableEdges;
+ SmallVector<unsigned, 4> ReachableEdges;
- typedef std::pair<BasicBlock *, BasicBlock *> Edge;
+ for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
+ if (PostDominatedByUnreachable.count(*I))
+ UnreachableEdges.push_back(I.getSuccessorIndex());
+ else
+ ReachableEdges.push_back(I.getSuccessorIndex());
+ }
- DenseMap<Edge, unsigned> *Weights;
+ // If all successors are in the set of blocks post-dominated by unreachable,
+ // this block is too.
+ if (UnreachableEdges.size() == TI->getNumSuccessors())
+ PostDominatedByUnreachable.insert(BB);
- BranchProbabilityInfo *BP;
+ // Skip probabilities if this block has a single successor or if all were
+ // reachable.
+ if (TI->getNumSuccessors() == 1 || UnreachableEdges.empty())
+ return false;
- LoopInfo *LI;
+ // If the terminator is an InvokeInst, check only the normal destination block
+ // as the unwind edge of InvokeInst is also very unlikely taken.
+ if (auto *II = dyn_cast<InvokeInst>(TI))
+ if (PostDominatedByUnreachable.count(II->getNormalDest())) {
+ PostDominatedByUnreachable.insert(BB);
+ // Return false here so that edge weights for InvokeInst could be decided
+ // in calcInvokeHeuristics().
+ return false;
+ }
+ if (ReachableEdges.empty()) {
+ BranchProbability Prob(1, UnreachableEdges.size());
+ for (unsigned SuccIdx : UnreachableEdges)
+ setEdgeProbability(BB, SuccIdx, Prob);
+ return true;
+ }
- // 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..
+ BranchProbability UnreachableProb(UR_TAKEN_WEIGHT,
+ (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) *
+ UnreachableEdges.size());
+ BranchProbability ReachableProb(UR_NONTAKEN_WEIGHT,
+ (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) *
+ ReachableEdges.size());
- static const unsigned int LBH_TAKEN_WEIGHT = 128;
- static const unsigned int LBH_NONTAKEN_WEIGHT = 4;
+ for (unsigned SuccIdx : UnreachableEdges)
+ setEdgeProbability(BB, SuccIdx, UnreachableProb);
+ for (unsigned SuccIdx : ReachableEdges)
+ setEdgeProbability(BB, SuccIdx, ReachableProb);
- // Standard weight value. Used when none of the heuristics set weight for
- // the edge.
- static const unsigned int NORMAL_WEIGHT = 16;
+ return true;
+}
- // Minimum weight of an edge. Please note, that weight is NEVER 0.
- static const unsigned int MIN_WEIGHT = 1;
+// Propagate existing explicit probabilities from either profile data or
+// 'expect' intrinsic processing.
+bool BranchProbabilityInfo::calcMetadataWeights(BasicBlock *BB) {
+ TerminatorInst *TI = BB->getTerminator();
+ if (TI->getNumSuccessors() == 1)
+ return false;
+ if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
+ return false;
- // Return TRUE if BB leads directly to a Return Instruction.
- static bool isReturningBlock(BasicBlock *BB) {
- SmallPtrSet<BasicBlock *, 8> Visited;
+ MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
+ if (!WeightsNode)
+ return false;
- while (true) {
- TerminatorInst *TI = BB->getTerminator();
- if (isa<ReturnInst>(TI))
- return true;
+ // Check that the number of successors is manageable.
+ assert(TI->getNumSuccessors() < UINT32_MAX && "Too many successors");
- if (TI->getNumSuccessors() > 1)
- break;
+ // 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;
- // It is unreachable block which we can consider as a return instruction.
- if (TI->getNumSuccessors() == 0)
- return true;
+ // Build up the final weights that will be used in a temporary buffer.
+ // Compute the sum of all weights to later decide whether they need to
+ // be scaled to fit in 32 bits.
+ uint64_t WeightSum = 0;
+ SmallVector<uint32_t, 2> Weights;
+ Weights.reserve(TI->getNumSuccessors());
+ for (unsigned i = 1, e = WeightsNode->getNumOperands(); i != e; ++i) {
+ ConstantInt *Weight =
+ mdconst::dyn_extract<ConstantInt>(WeightsNode->getOperand(i));
+ if (!Weight)
+ return false;
+ assert(Weight->getValue().getActiveBits() <= 32 &&
+ "Too many bits for uint32_t");
+ Weights.push_back(Weight->getZExtValue());
+ WeightSum += Weights.back();
+ }
+ assert(Weights.size() == TI->getNumSuccessors() && "Checked above");
- Visited.insert(BB);
- BB = TI->getSuccessor(0);
+ // If the sum of weights does not fit in 32 bits, scale every weight down
+ // accordingly.
+ uint64_t ScalingFactor =
+ (WeightSum > UINT32_MAX) ? WeightSum / UINT32_MAX + 1 : 1;
- // Stop if cycle is detected.
- if (Visited.count(BB))
- return false;
- }
+ WeightSum = 0;
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
+ Weights[i] /= ScalingFactor;
+ WeightSum += Weights[i];
+ }
- return false;
+ if (WeightSum == 0) {
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+ setEdgeProbability(BB, i, {1, e});
+ } else {
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+ setEdgeProbability(BB, i, {Weights[i], static_cast<uint32_t>(WeightSum)});
}
- // Multiply Edge Weight by two.
- void incEdgeWeight(BasicBlock *Src, BasicBlock *Dst) {
- unsigned Weight = BP->getEdgeWeight(Src, Dst);
- unsigned MaxWeight = getMaxWeightFor(Src);
+ assert(WeightSum <= UINT32_MAX &&
+ "Expected weights to scale down to 32 bits");
- if (Weight * 2 > MaxWeight)
- BP->setEdgeWeight(Src, Dst, MaxWeight);
- else
- BP->setEdgeWeight(Src, Dst, Weight * 2);
- }
+ return true;
+}
- // Divide Edge Weight by two.
- void decEdgeWeight(BasicBlock *Src, BasicBlock *Dst) {
- unsigned Weight = BP->getEdgeWeight(Src, Dst);
+/// \brief Calculate edge weights for edges leading to cold blocks.
+///
+/// A cold block is one post-dominated by a block with a call to a
+/// cold function. Those edges are unlikely to be taken, so we give
+/// them relatively low weight.
+///
+/// Return true if we could compute the weights for cold edges.
+/// Return false, otherwise.
+bool BranchProbabilityInfo::calcColdCallHeuristics(BasicBlock *BB) {
+ TerminatorInst *TI = BB->getTerminator();
+ if (TI->getNumSuccessors() == 0)
+ return false;
- assert(Weight > 0);
- if (Weight / 2 < MIN_WEIGHT)
- BP->setEdgeWeight(Src, Dst, MIN_WEIGHT);
+ // Determine which successors are post-dominated by a cold block.
+ SmallVector<unsigned, 4> ColdEdges;
+ SmallVector<unsigned, 4> NormalEdges;
+ for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
+ if (PostDominatedByColdCall.count(*I))
+ ColdEdges.push_back(I.getSuccessorIndex());
else
- BP->setEdgeWeight(Src, Dst, Weight / 2);
+ NormalEdges.push_back(I.getSuccessorIndex());
+
+ // If all successors are in the set of blocks post-dominated by cold calls,
+ // this block is in the set post-dominated by cold calls.
+ if (ColdEdges.size() == TI->getNumSuccessors())
+ PostDominatedByColdCall.insert(BB);
+ else {
+ // Otherwise, if the block itself contains a cold function, add it to the
+ // set of blocks postdominated by a cold call.
+ assert(!PostDominatedByColdCall.count(BB));
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (CallInst *CI = dyn_cast<CallInst>(I))
+ if (CI->hasFnAttr(Attribute::Cold)) {
+ PostDominatedByColdCall.insert(BB);
+ break;
+ }
}
+ // Skip probabilities if this block has a single successor.
+ if (TI->getNumSuccessors() == 1 || ColdEdges.empty())
+ return false;
- unsigned getMaxWeightFor(BasicBlock *BB) const {
- return UINT_MAX / BB->getTerminator()->getNumSuccessors();
- }
-
-public:
- BranchProbabilityAnalysis(DenseMap<Edge, unsigned> *W,
- BranchProbabilityInfo *BP, LoopInfo *LI)
- : Weights(W), BP(BP), LI(LI) {
+ if (NormalEdges.empty()) {
+ BranchProbability Prob(1, ColdEdges.size());
+ for (unsigned SuccIdx : ColdEdges)
+ setEdgeProbability(BB, SuccIdx, Prob);
+ return true;
}
- // Return Heuristics
- void calcReturnHeuristics(BasicBlock *BB);
-
- // Pointer Heuristics
- void calcPointerHeuristics(BasicBlock *BB);
-
- // Loop Branch Heuristics
- void calcLoopBranchHeuristics(BasicBlock *BB);
-
- bool runOnFunction(Function &F);
-};
+ BranchProbability ColdProb(CC_TAKEN_WEIGHT,
+ (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) *
+ ColdEdges.size());
+ BranchProbability NormalProb(CC_NONTAKEN_WEIGHT,
+ (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) *
+ NormalEdges.size());
-// 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 (unsigned SuccIdx : ColdEdges)
+ setEdgeProbability(BB, SuccIdx, ColdProb);
+ for (unsigned SuccIdx : NormalEdges)
+ setEdgeProbability(BB, SuccIdx, NormalProb);
- for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
- BasicBlock *Succ = *I;
- if (isReturningBlock(Succ)) {
- decEdgeWeight(BB, Succ);
- }
- }
+ return true;
}
// Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
// between two pointer or pointer and NULL will fail.
-void BranchProbabilityAnalysis::calcPointerHeuristics(BasicBlock *BB) {
+bool BranchProbabilityInfo::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)
- return;
+ if (!CI || !CI->isEquality())
+ return false;
Value *LHS = CI->getOperand(0);
if (!LHS->getType()->isPointerTy())
- return;
+ 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->isEquality();
+ unsigned TakenIdx = 0, NonTakenIdx = 1;
+ bool isProb = CI->getPredicate() == ICmpInst::ICMP_NE;
if (!isProb)
- std::swap(Taken, NonTaken);
+ std::swap(TakenIdx, NonTakenIdx);
- incEdgeWeight(BB, Taken);
- decEdgeWeight(BB, NonTaken);
+ BranchProbability TakenProb(PH_TAKEN_WEIGHT,
+ PH_TAKEN_WEIGHT + PH_NONTAKEN_WEIGHT);
+ setEdgeProbability(BB, TakenIdx, TakenProb);
+ setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
+ return true;
}
// Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
// as taken, exiting edges as not-taken.
-void BranchProbabilityAnalysis::calcLoopBranchHeuristics(BasicBlock *BB) {
- unsigned numSuccs = BB->getTerminator()->getNumSuccessors();
-
- Loop *L = LI->getLoopFor(BB);
+bool BranchProbabilityInfo::calcLoopBranchHeuristics(BasicBlock *BB,
+ const LoopInfo &LI) {
+ Loop *L = LI.getLoopFor(BB);
if (!L)
- return;
+ return false;
- SmallVector<BasicBlock *, 8> BackEdges;
- SmallVector<BasicBlock *, 8> ExitingEdges;
+ SmallVector<unsigned, 8> BackEdges;
+ SmallVector<unsigned, 8> ExitingEdges;
+ SmallVector<unsigned, 8> InEdges; // Edges from header to the loop.
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 (!L->contains(*I))
+ ExitingEdges.push_back(I.getSuccessorIndex());
+ else if (L->getHeader() == *I)
+ BackEdges.push_back(I.getSuccessorIndex());
+ else
+ InEdges.push_back(I.getSuccessorIndex());
}
- if (unsigned numBackEdges = BackEdges.size()) {
- unsigned backWeight = LBH_TAKEN_WEIGHT / numBackEdges;
- if (backWeight < NORMAL_WEIGHT)
- backWeight = NORMAL_WEIGHT;
+ if (BackEdges.empty() && ExitingEdges.empty())
+ return false;
- for (SmallVector<BasicBlock *, 8>::iterator EI = BackEdges.begin(),
- EE = BackEdges.end(); EI != EE; ++EI) {
- BasicBlock *Back = *EI;
- BP->setEdgeWeight(BB, Back, backWeight);
- }
+ // Collect the sum of probabilities of back-edges/in-edges/exiting-edges, and
+ // normalize them so that they sum up to one.
+ SmallVector<BranchProbability, 4> Probs(3, BranchProbability::getZero());
+ unsigned Denom = (BackEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
+ (InEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
+ (ExitingEdges.empty() ? 0 : LBH_NONTAKEN_WEIGHT);
+ if (!BackEdges.empty())
+ Probs[0] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
+ if (!InEdges.empty())
+ Probs[1] = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
+ if (!ExitingEdges.empty())
+ Probs[2] = BranchProbability(LBH_NONTAKEN_WEIGHT, Denom);
+
+ if (uint32_t numBackEdges = BackEdges.size()) {
+ auto Prob = Probs[0] / numBackEdges;
+ for (unsigned SuccIdx : BackEdges)
+ setEdgeProbability(BB, SuccIdx, Prob);
}
- unsigned numExitingEdges = ExitingEdges.size();
- if (unsigned numNonExitingEdges = numSuccs - numExitingEdges) {
- unsigned exitWeight = LBH_NONTAKEN_WEIGHT / numNonExitingEdges;
- if (exitWeight < MIN_WEIGHT)
- exitWeight = MIN_WEIGHT;
+ if (uint32_t numInEdges = InEdges.size()) {
+ auto Prob = Probs[1] / numInEdges;
+ for (unsigned SuccIdx : InEdges)
+ setEdgeProbability(BB, SuccIdx, Prob);
+ }
- for (SmallVector<BasicBlock *, 8>::iterator EI = ExitingEdges.begin(),
- EE = ExitingEdges.end(); EI != EE; ++EI) {
- BasicBlock *Exiting = *EI;
- BP->setEdgeWeight(BB, Exiting, exitWeight);
- }
+ if (uint32_t numExitingEdges = ExitingEdges.size()) {
+ auto Prob = Probs[2] / numExitingEdges;
+ for (unsigned SuccIdx : ExitingEdges)
+ setEdgeProbability(BB, SuccIdx, Prob);
}
+
+ return true;
}
-bool BranchProbabilityAnalysis::runOnFunction(Function &F) {
+bool BranchProbabilityInfo::calcZeroHeuristics(BasicBlock *BB) {
+ BranchInst * BI = dyn_cast<BranchInst>(BB->getTerminator());
+ if (!BI || !BI->isConditional())
+ return false;
- for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
- BasicBlock *BB = I++;
+ Value *Cond = BI->getCondition();
+ ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
+ if (!CI)
+ return false;
- // Only LBH uses setEdgeWeight method.
- calcLoopBranchHeuristics(BB);
+ Value *RHS = CI->getOperand(1);
+ ConstantInt *CV = dyn_cast<ConstantInt>(RHS);
+ if (!CV)
+ return false;
- // PH and RH use only incEdgeWeight and decEwdgeWeight methods to
- // not efface LBH results.
- calcPointerHeuristics(BB);
- calcReturnHeuristics(BB);
+ // 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;
}
- 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(BasicBlock *BB) {
+ 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);
-bool BranchProbabilityInfo::runOnFunction(Function &F) {
- LoopInfo &LI = getAnalysis<LoopInfo>();
- BranchProbabilityAnalysis BPA(&Weights, this, &LI);
- bool ret = BPA.runOnFunction(F);
- return ret;
+ BranchProbability TakenProb(FPH_TAKEN_WEIGHT,
+ FPH_TAKEN_WEIGHT + FPH_NONTAKEN_WEIGHT);
+ setEdgeProbability(BB, TakenIdx, TakenProb);
+ setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
+ return true;
}
-// TODO: This currently hardcodes 80% as a fraction 4/5. We will soon add a
-// BranchProbability class to encapsulate the fractional probability and
-// define a few static instances of the class for use as predefined thresholds.
-bool BranchProbabilityInfo::isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const {
- unsigned Sum = 0;
- for (succ_iterator I = succ_begin(Src), E = succ_end(Src); I != E; ++I) {
- BasicBlock *Succ = *I;
- unsigned Weight = getEdgeWeight(Src, Succ);
- unsigned PrevSum = Sum;
+bool BranchProbabilityInfo::calcInvokeHeuristics(BasicBlock *BB) {
+ InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator());
+ if (!II)
+ return false;
- Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
+ 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);
+ }
}
+}
- return getEdgeWeight(Src, Dst) * 5 > Sum * 4;
+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);
}
BasicBlock *BranchProbabilityInfo::getHotSucc(BasicBlock *BB) const {
- unsigned Sum = 0;
- unsigned MaxWeight = 0;
- BasicBlock *MaxSucc = 0;
+ auto MaxProb = BranchProbability::getZero();
+ BasicBlock *MaxSucc = nullptr;
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
BasicBlock *Succ = *I;
- unsigned Weight = getEdgeWeight(BB, Succ);
- unsigned PrevSum = Sum;
-
- Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
-
- if (Weight > MaxWeight) {
- MaxWeight = Weight;
+ auto Prob = getEdgeProbability(BB, Succ);
+ if (Prob > MaxProb) {
+ MaxProb = Prob;
MaxSucc = Succ;
}
}
- if (MaxWeight * 5 > Sum * 4)
+ // Hot probability is at least 4/5 = 80%
+ if (MaxProb > BranchProbability(4, 5))
return MaxSucc;
- return 0;
+ return nullptr;
}
-// Return edge's weight. If can't find it, return DEFAULT_WEIGHT value.
-unsigned
-BranchProbabilityInfo::getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) const {
- Edge E(Src, Dst);
- DenseMap<Edge, unsigned>::const_iterator I = Weights.find(E);
+/// 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 != Weights.end())
+ if (I != Probs.end())
return I->second;
- return DEFAULT_WEIGHT;
+ 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);
}
-void BranchProbabilityInfo::setEdgeWeight(BasicBlock *Src, BasicBlock *Dst,
- unsigned Weight) {
- Weights[std::make_pair(Src, Dst)] = Weight;
- DEBUG(dbgs() << "setEdgeWeight: " << Src->getNameStr() << " -> "
- << Dst->getNameStr() << " to " << Weight
- << (isEdgeHot(Src, Dst) ? " [is HOT now]\n" : "\n"));
+/// 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, BasicBlock *Src,
- BasicBlock *Dst) const {
+BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS,
+ const BasicBlock *Src,
+ const BasicBlock *Dst) const {
- unsigned Sum = 0;
- for (succ_iterator I = succ_begin(Src), E = succ_end(Src); I != E; ++I) {
- BasicBlock *Succ = *I;
- unsigned Weight = getEdgeWeight(Src, Succ);
- unsigned PrevSum = Sum;
+ const BranchProbability Prob = getEdgeProbability(Src, Dst);
+ OS << "edge " << Src->getName() << " -> " << Dst->getName()
+ << " probability is " << Prob
+ << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
+
+ return OS;
+}
- Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
+void BranchProbabilityInfo::calculate(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);
}
- double Prob = (double)getEdgeWeight(Src, Dst) / Sum;
- OS << "probability (" << Src->getNameStr() << " --> " << Dst->getNameStr()
- << ") = " << Prob << "\n";
+ PostDominatedByUnreachable.clear();
+ PostDominatedByColdCall.clear();
+}
- return OS;
+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);
}
projects / oota-llvm.git / blobdiff