//
//===----------------------------------------------------------------------===//
-#include "llvm/Constants.h"
-#include "llvm/Function.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/ADT/PostOrderIterator.h"
-#include "llvm/Support/CFG.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"
using namespace llvm;
+#define DEBUG_TYPE "branch-prob"
+
INITIALIZE_PASS_BEGIN(BranchProbabilityInfo, "branch-prob",
"Branch Probability Analysis", false, true)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
/// 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;
return false;
}
- SmallPtrSet<BasicBlock *, 4> UnreachableEdges;
- SmallPtrSet<BasicBlock *, 4> ReachableEdges;
+ SmallVector<unsigned, 4> UnreachableEdges;
+ SmallVector<unsigned, 4> ReachableEdges;
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
if (PostDominatedByUnreachable.count(*I))
- UnreachableEdges.insert(*I);
+ UnreachableEdges.push_back(I.getSuccessorIndex());
else
- ReachableEdges.insert(*I);
+ ReachableEdges.push_back(I.getSuccessorIndex());
}
// If all successors are in the set of blocks post-dominated by unreachable,
return false;
uint32_t UnreachableWeight =
- std::max(UR_TAKEN_WEIGHT / UnreachableEdges.size(), MIN_WEIGHT);
- for (SmallPtrSet<BasicBlock *, 4>::iterator I = UnreachableEdges.begin(),
- E = UnreachableEdges.end();
+ std::max(UR_TAKEN_WEIGHT / (unsigned)UnreachableEdges.size(), MIN_WEIGHT);
+ for (SmallVectorImpl<unsigned>::iterator I = UnreachableEdges.begin(),
+ E = UnreachableEdges.end();
I != E; ++I)
setEdgeWeight(BB, *I, UnreachableWeight);
if (ReachableEdges.empty())
return true;
uint32_t ReachableWeight =
- std::max(UR_NONTAKEN_WEIGHT / ReachableEdges.size(), NORMAL_WEIGHT);
- for (SmallPtrSet<BasicBlock *, 4>::iterator I = ReachableEdges.begin(),
- E = ReachableEdges.end();
+ std::max(UR_NONTAKEN_WEIGHT / (unsigned)ReachableEdges.size(),
+ NORMAL_WEIGHT);
+ for (SmallVectorImpl<unsigned>::iterator I = ReachableEdges.begin(),
+ E = ReachableEdges.end();
I != E; ++I)
setEdgeWeight(BB, *I, ReachableWeight);
}
assert(Weights.size() == TI->getNumSuccessors() && "Checked above");
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
- setEdgeWeight(BB, TI->getSuccessor(i), Weights[i]);
+ setEdgeWeight(BB, i, Weights[i]);
+
+ return true;
+}
+
+/// \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;
+
+ // 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
+ 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;
+
+ uint32_t ColdWeight =
+ std::max(CC_TAKEN_WEIGHT / (unsigned) ColdEdges.size(), MIN_WEIGHT);
+ for (SmallVectorImpl<unsigned>::iterator I = ColdEdges.begin(),
+ E = ColdEdges.end();
+ I != E; ++I)
+ setEdgeWeight(BB, *I, ColdWeight);
+
+ if (NormalEdges.empty())
+ return true;
+ uint32_t NormalWeight = std::max(
+ CC_NONTAKEN_WEIGHT / (unsigned) NormalEdges.size(), NORMAL_WEIGHT);
+ for (SmallVectorImpl<unsigned>::iterator I = NormalEdges.begin(),
+ E = NormalEdges.end();
+ I != E; ++I)
+ setEdgeWeight(BB, *I, NormalWeight);
return true;
}
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;
+ unsigned TakenIdx = 0, NonTakenIdx = 1;
bool isProb = CI->getPredicate() == ICmpInst::ICMP_NE;
if (!isProb)
- std::swap(Taken, NonTaken);
+ std::swap(TakenIdx, NonTakenIdx);
- setEdgeWeight(BB, Taken, PH_TAKEN_WEIGHT);
- setEdgeWeight(BB, NonTaken, PH_NONTAKEN_WEIGHT);
+ setEdgeWeight(BB, TakenIdx, PH_TAKEN_WEIGHT);
+ setEdgeWeight(BB, NonTakenIdx, PH_NONTAKEN_WEIGHT);
return true;
}
if (!L)
return false;
- SmallPtrSet<BasicBlock *, 8> BackEdges;
- SmallPtrSet<BasicBlock *, 8> ExitingEdges;
- SmallPtrSet<BasicBlock *, 8> InEdges; // Edges from header to the loop.
+ 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) {
if (!L->contains(*I))
- ExitingEdges.insert(*I);
+ ExitingEdges.push_back(I.getSuccessorIndex());
else if (L->getHeader() == *I)
- BackEdges.insert(*I);
+ BackEdges.push_back(I.getSuccessorIndex());
else
- InEdges.insert(*I);
+ InEdges.push_back(I.getSuccessorIndex());
}
+ if (BackEdges.empty() && ExitingEdges.empty())
+ return false;
+
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(),
+ for (SmallVectorImpl<unsigned>::iterator EI = BackEdges.begin(),
EE = BackEdges.end(); EI != EE; ++EI) {
- BasicBlock *Back = *EI;
- setEdgeWeight(BB, Back, backWeight);
+ setEdgeWeight(BB, *EI, backWeight);
}
}
if (inWeight < NORMAL_WEIGHT)
inWeight = NORMAL_WEIGHT;
- for (SmallPtrSet<BasicBlock *, 8>::iterator EI = InEdges.begin(),
+ for (SmallVectorImpl<unsigned>::iterator EI = InEdges.begin(),
EE = InEdges.end(); EI != EE; ++EI) {
- BasicBlock *Back = *EI;
- setEdgeWeight(BB, Back, inWeight);
+ setEdgeWeight(BB, *EI, inWeight);
}
}
if (exitWeight < MIN_WEIGHT)
exitWeight = MIN_WEIGHT;
- for (SmallPtrSet<BasicBlock *, 8>::iterator EI = ExitingEdges.begin(),
+ for (SmallVectorImpl<unsigned>::iterator EI = ExitingEdges.begin(),
EE = ExitingEdges.end(); EI != EE; ++EI) {
- BasicBlock *Exiting = *EI;
- setEdgeWeight(BB, Exiting, exitWeight);
+ setEdgeWeight(BB, *EI, exitWeight);
}
}
// 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 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;
}
- BasicBlock *Taken = BI->getSuccessor(0);
- BasicBlock *NonTaken = BI->getSuccessor(1);
+ unsigned TakenIdx = 0, NonTakenIdx = 1;
if (!isProb)
- std::swap(Taken, NonTaken);
+ std::swap(TakenIdx, NonTakenIdx);
- setEdgeWeight(BB, Taken, ZH_TAKEN_WEIGHT);
- setEdgeWeight(BB, NonTaken, ZH_NONTAKEN_WEIGHT);
+ setEdgeWeight(BB, TakenIdx, ZH_TAKEN_WEIGHT);
+ setEdgeWeight(BB, NonTakenIdx, ZH_NONTAKEN_WEIGHT);
return true;
}
return false;
}
- BasicBlock *Taken = BI->getSuccessor(0);
- BasicBlock *NonTaken = BI->getSuccessor(1);
+ unsigned TakenIdx = 0, NonTakenIdx = 1;
if (!isProb)
- std::swap(Taken, NonTaken);
+ std::swap(TakenIdx, NonTakenIdx);
- setEdgeWeight(BB, Taken, FPH_TAKEN_WEIGHT);
- setEdgeWeight(BB, NonTaken, FPH_NONTAKEN_WEIGHT);
+ setEdgeWeight(BB, TakenIdx, FPH_TAKEN_WEIGHT);
+ setEdgeWeight(BB, NonTakenIdx, FPH_NONTAKEN_WEIGHT);
return true;
}
if (!II)
return false;
- BasicBlock *Normal = II->getNormalDest();
- BasicBlock *Unwind = II->getUnwindDest();
-
- setEdgeWeight(BB, Normal, IH_TAKEN_WEIGHT);
- setEdgeWeight(BB, Unwind, IH_NONTAKEN_WEIGHT);
+ setEdgeWeight(BB, 0/*Index for Normal*/, IH_TAKEN_WEIGHT);
+ setEdgeWeight(BB, 1/*Index for Unwind*/, IH_NONTAKEN_WEIGHT);
return true;
}
}
bool BranchProbabilityInfo::runOnFunction(Function &F) {
+ DEBUG(dbgs() << "---- Branch Probability Info : " << F.getName()
+ << " ----\n\n");
LastF = &F; // Store the last function we ran on for printing.
LI = &getAnalysis<LoopInfo>();
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.
continue;
if (calcMetadataWeights(*I))
continue;
+ if (calcColdCallHeuristics(*I))
+ continue;
if (calcLoopBranchHeuristics(*I))
continue;
if (calcPointerHeuristics(*I))
}
PostDominatedByUnreachable.clear();
+ PostDominatedByColdCall.clear();
return false;
}
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 Weight = getEdgeWeight(BB, I.getSuccessorIndex());
uint32_t PrevSum = Sum;
Sum += Weight;
BasicBlock *BranchProbabilityInfo::getHotSucc(BasicBlock *BB) const {
uint32_t Sum = 0;
uint32_t MaxWeight = 0;
- BasicBlock *MaxSucc = 0;
+ BasicBlock *MaxSucc = nullptr;
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
BasicBlock *Succ = *I;
if (BranchProbability(MaxWeight, Sum) > BranchProbability(4, 5))
return MaxSucc;
- return 0;
+ return nullptr;
}
-// Return edge's weight. If can't find it, return DEFAULT_WEIGHT value.
+/// Get the raw edge weight for the edge. If can't find it, return
+/// DEFAULT_WEIGHT value. Here an edge is specified using PredBlock and an index
+/// to the successors.
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);
+getEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors) const {
+ DenseMap<Edge, uint32_t>::const_iterator I =
+ Weights.find(std::make_pair(Src, IndexInSuccessors));
if (I != Weights.end())
return I->second;
return DEFAULT_WEIGHT;
}
+uint32_t BranchProbabilityInfo::getEdgeWeight(const BasicBlock *Src,
+ succ_const_iterator Dst) const {
+ return getEdgeWeight(Src, Dst.getSuccessorIndex());
+}
+
+/// Get the raw edge weight calculated for the block pair. This returns the sum
+/// of all raw edge weights from Src to Dst.
+uint32_t BranchProbabilityInfo::
+getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const {
+ uint32_t Weight = 0;
+ DenseMap<Edge, uint32_t>::const_iterator MapI;
+ for (succ_const_iterator I = succ_begin(Src), E = succ_end(Src); I != E; ++I)
+ if (*I == Dst) {
+ MapI = Weights.find(std::make_pair(Src, I.getSuccessorIndex()));
+ if (MapI != Weights.end())
+ Weight += MapI->second;
+ }
+ return (Weight == 0) ? DEFAULT_WEIGHT : Weight;
+}
+
+/// Set the edge weight for a given edge specified by PredBlock and an index
+/// to the successors.
void BranchProbabilityInfo::
-setEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst, uint32_t Weight) {
- Weights[std::make_pair(Src, Dst)] = Weight;
+setEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors,
+ uint32_t Weight) {
+ Weights[std::make_pair(Src, IndexInSuccessors)] = Weight;
DEBUG(dbgs() << "set edge " << Src->getName() << " -> "
- << Dst->getName() << " weight to " << Weight
- << (isEdgeHot(Src, Dst) ? " [is HOT now]\n" : "\n"));
+ << IndexInSuccessors << " successor weight to "
+ << Weight << "\n");
}
+/// Get an edge's probability, relative to other out-edges from Src.
+BranchProbability BranchProbabilityInfo::
+getEdgeProbability(const BasicBlock *Src, unsigned IndexInSuccessors) const {
+ uint32_t N = getEdgeWeight(Src, IndexInSuccessors);
+ uint32_t D = getSumForBlock(Src);
+
+ return BranchProbability(N, D);
+}
+/// Get the probability of going from Src to Dst. It returns the sum of all
+/// probabilities for edges from Src to Dst.
BranchProbability BranchProbabilityInfo::
getEdgeProbability(const BasicBlock *Src, const BasicBlock *Dst) const {