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[BPI] Replace weights by probabilities in BPI. 

This patch removes all weight-related interfaces from BPI and replace
them by probability versions. With this patch, we won't use edge weight
anymore in either IR or MC passes. Edge probabilitiy is a better
representation in terms of CFG update and validation.


Differential revision: http://reviews.llvm.org/D15519 

llvm-svn: 256263
This commit is contained in:
Cong Hou 2015-12-22 18:56:14 +00:00
parent 4e4f60ded0
commit e93b8e1539
8 changed files with 169 additions and 284 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
llvm/include/llvm/Analysis/BranchProbabilityInfo.h
View File

@ -84,36 +84,14 @@ public:
raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src,
const BasicBlock *Dst) const;
/// \brief Get the raw edge weight calculated for the edge.
/// \brief Set the raw edge probability for the given edge.
///
/// This returns the raw edge weight. It is guaranteed to fall between 1 and
/// UINT32_MAX. Note that the raw edge weight is not meaningful in isolation.
/// This interface should be very carefully, and primarily by routines that
/// are updating the analysis by later calling setEdgeWeight.
uint32_t getEdgeWeight(const BasicBlock *Src,
unsigned IndexInSuccessors) const;
/// \brief Get the raw edge weight calculated for the block pair.
///
/// This returns the sum of all raw edge weights from Src to Dst.
/// It is guaranteed to fall between 1 and UINT32_MAX.
uint32_t getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const;
uint32_t getEdgeWeight(const BasicBlock *Src,
succ_const_iterator Dst) const;
/// \brief Set the raw edge weight for a given edge.
///
/// This allows a pass to explicitly set the edge weight for an edge. It can
/// be used when updating the CFG to update and preserve the branch
/// This allows a pass to explicitly set the edge probability for an edge. It
/// can be used when updating the CFG to update and preserve the branch
/// probability information. Read the implementation of how these edge
/// weights are calculated carefully before using!
void setEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors,
uint32_t Weight);
static uint32_t getBranchWeightStackProtector(bool IsLikely) {
return IsLikely ? (1u << 20) - 1 : 1;
}
/// probabilities are calculated carefully before using!
void setEdgeProbability(const BasicBlock *Src, unsigned IndexInSuccessors,
BranchProbability Prob);
static BranchProbability getBranchProbStackProtector(bool IsLikely) {
static const BranchProbability LikelyProb((1u << 20) - 1, 1u << 20);
@ -135,7 +113,7 @@ private:
// weight to just "inherit" the non-zero weight of an adjacent successor.
static const uint32_t DEFAULT_WEIGHT = 16;
DenseMap<Edge, uint32_t> Weights;
DenseMap<Edge, BranchProbability> Probs;
/// \brief Track the last function we run over for printing.
Function *LastF;
@ -146,9 +124,6 @@ private:
/// \brief Track the set of blocks that always lead to a cold call.
SmallPtrSet<BasicBlock *, 16> PostDominatedByColdCall;
/// \brief Get sum of the block successors' weights.
uint32_t getSumForBlock(const BasicBlock *BB) const;
bool calcUnreachableHeuristics(BasicBlock *BB);
bool calcMetadataWeights(BasicBlock *BB);
bool calcColdCallHeuristics(BasicBlock *BB);

48
llvm/include/llvm/Support/BranchProbability.h
View File

@ -63,11 +63,6 @@ public:
static void normalizeProbabilities(ProbabilityIter Begin,
ProbabilityIter End);
// Normalize a list of weights by scaling them down so that the sum of them
// doesn't exceed UINT32_MAX.
template <class WeightListIter>
static void normalizeEdgeWeights(WeightListIter Begin, WeightListIter End);
uint32_t getNumerator() const { return N; }
static uint32_t getDenominator() { return D; }
@ -219,49 +214,6 @@ void BranchProbability::normalizeProbabilities(ProbabilityIter Begin,
I->N = (I->N * uint64_t(D) + Sum / 2) / Sum;
}
template <class WeightListIter>
void BranchProbability::normalizeEdgeWeights(WeightListIter Begin,
WeightListIter End) {
// First we compute the sum with 64-bits of precision.
uint64_t Sum = std::accumulate(Begin, End, uint64_t(0));
if (Sum > UINT32_MAX) {
// Compute the scale necessary to cause the weights to fit, and re-sum with
// that scale applied.
assert(Sum / UINT32_MAX < UINT32_MAX &&
"The sum of weights exceeds UINT32_MAX^2!");
uint32_t Scale = Sum / UINT32_MAX + 1;
for (auto I = Begin; I != End; ++I)
*I /= Scale;
Sum = std::accumulate(Begin, End, uint64_t(0));
}
// Eliminate zero weights.
auto ZeroWeightNum = std::count(Begin, End, 0u);
if (ZeroWeightNum > 0) {
// If all weights are zeros, replace them by 1.
if (Sum == 0)
std::fill(Begin, End, 1u);
else {
// We are converting zeros into ones, and here we need to make sure that
// after this the sum won't exceed UINT32_MAX.
if (Sum + ZeroWeightNum > UINT32_MAX) {
for (auto I = Begin; I != End; ++I)
*I /= 2;
ZeroWeightNum = std::count(Begin, End, 0u);
Sum = std::accumulate(Begin, End, uint64_t(0));
}
// Scale up non-zero weights and turn zero weights into ones.
uint64_t ScalingFactor = (UINT32_MAX - ZeroWeightNum) / Sum;
assert(ScalingFactor >= 1);
if (ScalingFactor > 1)
for (auto I = Begin; I != End; ++I)
*I *= ScalingFactor;
std::replace(Begin, End, 0u, 1u);
}
}
}
}
#endif

295
llvm/lib/Analysis/BranchProbabilityInfo.cpp
View File

@ -108,13 +108,6 @@ static const uint32_t IH_TAKEN_WEIGHT = 1024 * 1024 - 1;
/// instruction. This is essentially never taken.
static const uint32_t IH_NONTAKEN_WEIGHT = 1;
// 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;
/// \brief Calculate edge weights for successors lead to unreachable.
///
/// Predict that a successor which leads necessarily to an
@ -157,22 +150,24 @@ bool BranchProbabilityInfo::calcUnreachableHeuristics(BasicBlock *BB) {
return false;
}
uint32_t UnreachableWeight =
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())
if (ReachableEdges.empty()) {
BranchProbability Prob(1, UnreachableEdges.size());
for (unsigned SuccIdx : UnreachableEdges)
setEdgeProbability(BB, SuccIdx, Prob);
return true;
uint32_t ReachableWeight =
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);
}
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());
for (unsigned SuccIdx : UnreachableEdges)
setEdgeProbability(BB, SuccIdx, UnreachableProb);
for (unsigned SuccIdx : ReachableEdges)
setEdgeProbability(BB, SuccIdx, ReachableProb);
return true;
}
@ -223,10 +218,12 @@ bool BranchProbabilityInfo::calcMetadataWeights(BasicBlock *BB) {
WeightSum = 0;
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
uint32_t W = Weights[i] / ScalingFactor;
WeightSum += W;
setEdgeWeight(BB, i, W);
Weights[i] /= ScalingFactor;
WeightSum += Weights[i];
}
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
setEdgeProbability(BB, i, {Weights[i], static_cast<uint32_t>(WeightSum)});
assert(WeightSum <= UINT32_MAX &&
"Expected weights to scale down to 32 bits");
@ -275,21 +272,24 @@ bool BranchProbabilityInfo::calcColdCallHeuristics(BasicBlock *BB) {
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())
if (NormalEdges.empty()) {
BranchProbability Prob(1, ColdEdges.size());
for (unsigned SuccIdx : ColdEdges)
setEdgeProbability(BB, SuccIdx, Prob);
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);
}
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());
for (unsigned SuccIdx : ColdEdges)
setEdgeProbability(BB, SuccIdx, ColdProb);
for (unsigned SuccIdx : NormalEdges)
setEdgeProbability(BB, SuccIdx, NormalProb);
return true;
}
@ -322,8 +322,10 @@ bool BranchProbabilityInfo::calcPointerHeuristics(BasicBlock *BB) {
if (!isProb)
std::swap(TakenIdx, NonTakenIdx);
setEdgeWeight(BB, TakenIdx, PH_TAKEN_WEIGHT);
setEdgeWeight(BB, NonTakenIdx, PH_NONTAKEN_WEIGHT);
BranchProbability TakenProb(PH_TAKEN_WEIGHT,
PH_TAKEN_WEIGHT + PH_NONTAKEN_WEIGHT);
setEdgeProbability(BB, TakenIdx, TakenProb);
setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
return true;
}
@ -351,37 +353,35 @@ bool BranchProbabilityInfo::calcLoopBranchHeuristics(BasicBlock *BB,
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;
// 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);
for (SmallVectorImpl<unsigned>::iterator EI = BackEdges.begin(),
EE = BackEdges.end(); EI != EE; ++EI) {
setEdgeWeight(BB, *EI, backWeight);
}
if (uint32_t numBackEdges = BackEdges.size()) {
auto Prob = Probs[0] / numBackEdges;
for (unsigned SuccIdx : BackEdges)
setEdgeProbability(BB, SuccIdx, Prob);
}
if (uint32_t numInEdges = InEdges.size()) {
uint32_t inWeight = LBH_TAKEN_WEIGHT / numInEdges;
if (inWeight < NORMAL_WEIGHT)
inWeight = NORMAL_WEIGHT;
for (SmallVectorImpl<unsigned>::iterator EI = InEdges.begin(),
EE = InEdges.end(); EI != EE; ++EI) {
setEdgeWeight(BB, *EI, inWeight);
}
auto Prob = Probs[1] / numInEdges;
for (unsigned SuccIdx : InEdges)
setEdgeProbability(BB, SuccIdx, Prob);
}
if (uint32_t numExitingEdges = ExitingEdges.size()) {
uint32_t exitWeight = LBH_NONTAKEN_WEIGHT / numExitingEdges;
if (exitWeight < MIN_WEIGHT)
exitWeight = MIN_WEIGHT;
for (SmallVectorImpl<unsigned>::iterator EI = ExitingEdges.begin(),
EE = ExitingEdges.end(); EI != EE; ++EI) {
setEdgeWeight(BB, *EI, exitWeight);
}
auto Prob = Probs[2] / numExitingEdges;
for (unsigned SuccIdx : ExitingEdges)
setEdgeProbability(BB, SuccIdx, Prob);
}
return true;
@ -463,9 +463,10 @@ bool BranchProbabilityInfo::calcZeroHeuristics(BasicBlock *BB) {
if (!isProb)
std::swap(TakenIdx, NonTakenIdx);
setEdgeWeight(BB, TakenIdx, ZH_TAKEN_WEIGHT);
setEdgeWeight(BB, NonTakenIdx, ZH_NONTAKEN_WEIGHT);
BranchProbability TakenProb(ZH_TAKEN_WEIGHT,
ZH_TAKEN_WEIGHT + ZH_NONTAKEN_WEIGHT);
setEdgeProbability(BB, TakenIdx, TakenProb);
setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
return true;
}
@ -499,9 +500,10 @@ bool BranchProbabilityInfo::calcFloatingPointHeuristics(BasicBlock *BB) {
if (!isProb)
std::swap(TakenIdx, NonTakenIdx);
setEdgeWeight(BB, TakenIdx, FPH_TAKEN_WEIGHT);
setEdgeWeight(BB, NonTakenIdx, FPH_NONTAKEN_WEIGHT);
BranchProbability TakenProb(FPH_TAKEN_WEIGHT,
FPH_TAKEN_WEIGHT + FPH_NONTAKEN_WEIGHT);
setEdgeProbability(BB, TakenIdx, TakenProb);
setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
return true;
}
@ -510,13 +512,15 @@ bool BranchProbabilityInfo::calcInvokeHeuristics(BasicBlock *BB) {
if (!II)
return false;
setEdgeWeight(BB, 0/*Index for Normal*/, IH_TAKEN_WEIGHT);
setEdgeWeight(BB, 1/*Index for Unwind*/, IH_NONTAKEN_WEIGHT);
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() {
Weights.clear();
Probs.clear();
}
void BranchProbabilityInfo::print(raw_ostream &OS) const {
@ -532,20 +536,6 @@ void BranchProbabilityInfo::print(raw_ostream &OS) const {
}
}
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) {
uint32_t Weight = getEdgeWeight(BB, I.getSuccessorIndex());
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%
@ -554,107 +544,39 @@ isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const {
}
BasicBlock *BranchProbabilityInfo::getHotSucc(BasicBlock *BB) const {
uint32_t Sum = 0;
uint32_t MaxWeight = 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;
uint32_t Weight = getEdgeWeight(BB, Succ);
uint32_t 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;
}
}
// Hot probability is at least 4/5 = 80%
if (BranchProbability(MaxWeight, Sum) > BranchProbability(4, 5))
if (MaxProb > BranchProbability(4, 5))
return MaxSucc;
return nullptr;
}
/// 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, unsigned IndexInSuccessors) const {
DenseMap<Edge, uint32_t>::const_iterator I =
Weights.find(std::make_pair(Src, IndexInSuccessors));
/// 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;
}
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;
bool FoundWeight = false;
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()) {
FoundWeight = true;
Weight += MapI->second;
}
}
return (!FoundWeight) ? 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, unsigned IndexInSuccessors,
uint32_t Weight) {
Weights[std::make_pair(Src, IndexInSuccessors)] = Weight;
DEBUG(dbgs() << "set edge " << Src->getName() << " -> "
<< 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);
// It is possible that the edge weight on the only successor edge of Src is
// zero, in which case we return 100%.
if (N == 0 && D == 0)
return BranchProbability::getOne();
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 {
uint32_t N = getEdgeWeight(Src, Dst);
uint32_t D = getSumForBlock(Src);
// It is possible that the edge weight on the only successor edge of Src is
// zero, in which case we return 100%.
if (N == 0 && D == 0)
return BranchProbability::getOne();
return BranchProbability(N, D);
return {1,
static_cast<uint32_t>(std::distance(succ_begin(Src), succ_end(Src)))};
}
BranchProbability
@ -663,6 +585,35 @@ BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
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);
}
/// 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,
const BasicBlock *Src,

11
llvm/lib/CodeGen/StackProtector.cpp
View File

@ -453,12 +453,13 @@ bool StackProtector::InsertStackProtectors() {
LoadInst *LI1 = B.CreateLoad(StackGuardVar);
LoadInst *LI2 = B.CreateLoad(AI);
Value *Cmp = B.CreateICmpEQ(LI1, LI2);
unsigned SuccessWeight =
BranchProbabilityInfo::getBranchWeightStackProtector(true);
unsigned FailureWeight =
BranchProbabilityInfo::getBranchWeightStackProtector(false);
auto SuccessProb =
BranchProbabilityInfo::getBranchProbStackProtector(true);
auto FailureProb =
BranchProbabilityInfo::getBranchProbStackProtector(false);
MDNode *Weights = MDBuilder(F->getContext())
.createBranchWeights(SuccessWeight, FailureWeight);
.createBranchWeights(SuccessProb.getNumerator(),
FailureProb.getNumerator());
B.CreateCondBr(Cmp, NewBB, FailBB, Weights);
}
}

20
llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
View File

@ -414,8 +414,8 @@ static unsigned getBranchHint(unsigned PCC, FunctionLoweringInfo *FuncInfo,
const BasicBlock *TBB = BBTerm->getSuccessor(0);
const BasicBlock *FBB = BBTerm->getSuccessor(1);
uint32_t TWeight = FuncInfo->BPI->getEdgeWeight(BB, TBB);
uint32_t FWeight = FuncInfo->BPI->getEdgeWeight(BB, FBB);
auto TProb = FuncInfo->BPI->getEdgeProbability(BB, TBB);
auto FProb = FuncInfo->BPI->getEdgeProbability(BB, FBB);
// We only want to handle cases which are easy to predict at static time, e.g.
// C++ throw statement, that is very likely not taken, or calling never
@ -432,24 +432,22 @@ static unsigned getBranchHint(unsigned PCC, FunctionLoweringInfo *FuncInfo,
// 5. PH/ZH/FPH 20:12
const uint32_t Threshold = 10000;
// Minimal weight should be at least 1
if (std::max(TWeight, FWeight) /
std::max(1u, std::min(TWeight, FWeight)) < Threshold)
if (std::max(TProb, FProb) / Threshold < std::min(TProb, FProb))
return PPC::BR_NO_HINT;
DEBUG(dbgs() << "Use branch hint for '" << FuncInfo->Fn->getName() << "::"
<< BB->getName() << "'\n"
<< " -> " << TBB->getName() << ": " << TWeight << "\n"
<< " -> " << FBB->getName() << ": " << FWeight << "\n");
<< " -> " << TBB->getName() << ": " << TProb << "\n"
<< " -> " << FBB->getName() << ": " << FProb << "\n");
const BasicBlockSDNode *BBDN = cast<BasicBlockSDNode>(DestMBB);
// If Dest BasicBlock is False-BasicBlock (FBB), swap branch weight,
// because we want 'TWeight' stands for 'branch weight' to Dest BasicBlock
// If Dest BasicBlock is False-BasicBlock (FBB), swap branch probabilities,
// because we want 'TProb' stands for 'branch probability' to Dest BasicBlock
if (BBDN->getBasicBlock()->getBasicBlock() != TBB)
std::swap(TWeight, FWeight);
std::swap(TProb, FProb);
return (TWeight > FWeight) ? PPC::BR_TAKEN_HINT : PPC::BR_NONTAKEN_HINT;
return (TProb > FProb) ? PPC::BR_TAKEN_HINT : PPC::BR_NONTAKEN_HINT;
}
// isOpcWithIntImmediate - This method tests to see if the node is a specific

28
llvm/lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -1636,7 +1636,7 @@ void JumpThreading::UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB,
BFI->setBlockFreq(BB, BBNewFreq.getFrequency());
// Collect updated outgoing edges' frequencies from BB and use them to update
// edge weights.
// edge probabilities.
SmallVector<uint64_t, 4> BBSuccFreq;
for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
auto SuccFreq = (*I == SuccBB)
@ -1645,18 +1645,26 @@ void JumpThreading::UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB,
BBSuccFreq.push_back(SuccFreq.getFrequency());
}
// Normalize edge weights in Weights64 so that the sum of them can fit in
BranchProbability::normalizeEdgeWeights(BBSuccFreq.begin(), BBSuccFreq.end());
uint64_t MaxBBSuccFreq =
*std::max_element(BBSuccFreq.begin(), BBSuccFreq.end());
SmallVector<BranchProbability, 4> BBSuccProbs;
for (uint64_t Freq : BBSuccFreq)
BBSuccProbs.push_back(
BranchProbability::getBranchProbability(Freq, MaxBBSuccFreq));
SmallVector<uint32_t, 4> Weights;
for (auto Freq : BBSuccFreq)
Weights.push_back(static_cast<uint32_t>(Freq));
// Normalize edge probabilities so that they sum up to one.
BranchProbability::normalizeProbabilities(BBSuccProbs.begin(),
BBSuccProbs.end());
// Update edge weights in BPI.
for (int I = 0, E = Weights.size(); I < E; I++)
BPI->setEdgeWeight(BB, I, Weights[I]);
// Update edge probabilities in BPI.
for (int I = 0, E = BBSuccProbs.size(); I < E; I++)
BPI->setEdgeProbability(BB, I, BBSuccProbs[I]);
if (BBSuccProbs.size() >= 2) {
SmallVector<uint32_t, 4> Weights;
for (auto Prob : BBSuccProbs)
Weights.push_back(Prob.getNumerator());
if (Weights.size() >= 2) {
auto TI = BB->getTerminator();
TI->setMetadata(
LLVMContext::MD_prof,

10
llvm/test/Analysis/BranchProbabilityInfo/noreturn.ll
View File

@ -26,11 +26,11 @@ entry:
i32 2, label %case_b
i32 3, label %case_c
i32 4, label %case_d]
; CHECK: edge entry -> exit probability is 0x7fffe000 / 0x80000000 = 100.00% [HOT edge]
; CHECK: edge entry -> case_a probability is 0x00000800 / 0x80000000 = 0.00%
; CHECK: edge entry -> case_b probability is 0x00000800 / 0x80000000 = 0.00%
; CHECK: edge entry -> case_c probability is 0x00000800 / 0x80000000 = 0.00%
; CHECK: edge entry -> case_d probability is 0x00000800 / 0x80000000 = 0.00%
; CHECK: edge entry -> exit probability is 0x7ffff800 / 0x80000000 = 100.00% [HOT edge]
; CHECK: edge entry -> case_a probability is 0x00000200 / 0x80000000 = 0.00%
; CHECK: edge entry -> case_b probability is 0x00000200 / 0x80000000 = 0.00%
; CHECK: edge entry -> case_c probability is 0x00000200 / 0x80000000 = 0.00%
; CHECK: edge entry -> case_d probability is 0x00000200 / 0x80000000 = 0.00%
case_a:
br label %case_b

2
llvm/test/Transforms/JumpThreading/update-edge-weight.ll
View File

@ -2,7 +2,7 @@
; Test if edge weights are properly updated after jump threading.
; CHECK: !2 = !{!"branch_weights", i32 22, i32 7}
; CHECK: !2 = !{!"branch_weights", i32 1629125526, i32 518358122}
define void @foo(i32 %n) !prof !0 {
entry: