Branch profiling: floating-point avoidance.
Patch by: Jakub Staszak!
Introduces BranchProbability. Changes unsigned to uint32_t all over and
uint64_t only when overflow is expected.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132867 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BranchProbabilityInfo.cpp b/lib/Analysis/BranchProbabilityInfo.cpp
index d69c012..812fac0 100644
--- a/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/lib/Analysis/BranchProbabilityInfo.cpp
@@ -13,7 +13,7 @@
#include "llvm/Instructions.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
-#include <climits>
+#include "llvm/Support/Debug.h"
using namespace llvm;
@@ -34,7 +34,7 @@
typedef std::pair<BasicBlock *, BasicBlock *> Edge;
- DenseMap<Edge, unsigned> *Weights;
+ DenseMap<Edge, uint32_t> *Weights;
BranchProbabilityInfo *BP;
@@ -62,15 +62,15 @@
// Probability of the edge BB2->BB1 = 128 / (128 + 4) = 0.9696..
// Probability of the edge BB2->BB3 = 4 / (128 + 4) = 0.0303..
- static const unsigned int LBH_TAKEN_WEIGHT = 128;
- static const unsigned int LBH_NONTAKEN_WEIGHT = 4;
+ 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 unsigned int NORMAL_WEIGHT = 16;
+ static const uint32_t NORMAL_WEIGHT = 16;
// Minimum weight of an edge. Please note, that weight is NEVER 0.
- static const unsigned int MIN_WEIGHT = 1;
+ static const uint32_t MIN_WEIGHT = 1;
// Return TRUE if BB leads directly to a Return Instruction.
static bool isReturningBlock(BasicBlock *BB) {
@@ -101,8 +101,8 @@
// Multiply Edge Weight by two.
void incEdgeWeight(BasicBlock *Src, BasicBlock *Dst) {
- unsigned Weight = BP->getEdgeWeight(Src, Dst);
- unsigned MaxWeight = getMaxWeightFor(Src);
+ uint32_t Weight = BP->getEdgeWeight(Src, Dst);
+ uint32_t MaxWeight = getMaxWeightFor(Src);
if (Weight * 2 > MaxWeight)
BP->setEdgeWeight(Src, Dst, MaxWeight);
@@ -112,7 +112,7 @@
// Divide Edge Weight by two.
void decEdgeWeight(BasicBlock *Src, BasicBlock *Dst) {
- unsigned Weight = BP->getEdgeWeight(Src, Dst);
+ uint32_t Weight = BP->getEdgeWeight(Src, Dst);
assert(Weight > 0);
if (Weight / 2 < MIN_WEIGHT)
@@ -122,12 +122,12 @@
}
- unsigned getMaxWeightFor(BasicBlock *BB) const {
- return UINT_MAX / BB->getTerminator()->getNumSuccessors();
+ uint32_t getMaxWeightFor(BasicBlock *BB) const {
+ return UINT32_MAX / BB->getTerminator()->getNumSuccessors();
}
public:
- BranchProbabilityAnalysis(DenseMap<Edge, unsigned> *W,
+ BranchProbabilityAnalysis(DenseMap<Edge, uint32_t> *W,
BranchProbabilityInfo *BP, LoopInfo *LI)
: Weights(W), BP(BP), LI(LI) {
}
@@ -195,7 +195,7 @@
// 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();
+ uint32_t numSuccs = BB->getTerminator()->getNumSuccessors();
Loop *L = LI->getLoopFor(BB);
if (!L)
@@ -213,8 +213,8 @@
BackEdges.push_back(Succ);
}
- if (unsigned numBackEdges = BackEdges.size()) {
- unsigned backWeight = LBH_TAKEN_WEIGHT / numBackEdges;
+ if (uint32_t numBackEdges = BackEdges.size()) {
+ uint32_t backWeight = LBH_TAKEN_WEIGHT / numBackEdges;
if (backWeight < NORMAL_WEIGHT)
backWeight = NORMAL_WEIGHT;
@@ -225,9 +225,9 @@
}
}
- unsigned numExitingEdges = ExitingEdges.size();
- if (unsigned numNonExitingEdges = numSuccs - numExitingEdges) {
- unsigned exitWeight = LBH_NONTAKEN_WEIGHT / numNonExitingEdges;
+ 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;
@@ -260,36 +260,43 @@
bool BranchProbabilityInfo::runOnFunction(Function &F) {
LoopInfo &LI = getAnalysis<LoopInfo>();
BranchProbabilityAnalysis BPA(&Weights, this, &LI);
- bool ret = BPA.runOnFunction(F);
- return ret;
+ return BPA.runOnFunction(F);
}
-// 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) {
+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;
- unsigned Weight = getEdgeWeight(Src, Succ);
- unsigned PrevSum = Sum;
+ uint32_t Weight = getEdgeWeight(BB, Succ);
+ uint32_t PrevSum = Sum;
Sum += Weight;
assert(Sum > PrevSum); (void) PrevSum;
}
- return getEdgeWeight(Src, Dst) * 5 > Sum * 4;
+ 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 {
- unsigned Sum = 0;
- unsigned MaxWeight = 0;
+ 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;
- unsigned Weight = getEdgeWeight(BB, Succ);
- unsigned PrevSum = Sum;
+ uint32_t Weight = getEdgeWeight(BB, Succ);
+ uint32_t PrevSum = Sum;
Sum += Weight;
assert(Sum > PrevSum); (void) PrevSum;
@@ -300,17 +307,18 @@
}
}
- if (MaxWeight * 5 > Sum * 4)
+ // 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.
-unsigned
+uint32_t
BranchProbabilityInfo::getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) const {
Edge E(Src, Dst);
- DenseMap<Edge, unsigned>::const_iterator I = Weights.find(E);
+ DenseMap<Edge, uint32_t>::const_iterator I = Weights.find(E);
if (I != Weights.end())
return I->second;
@@ -319,30 +327,31 @@
}
void BranchProbabilityInfo::setEdgeWeight(BasicBlock *Src, BasicBlock *Dst,
- unsigned Weight) {
+ uint32_t 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"));
+ 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 {
+ BasicBlock *Dst) const {
+ BranchProbability Prob = getEdgeProbability(Src, Dst);
- 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;
-
- Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
- }
-
- double Prob = (double)getEdgeWeight(Src, Dst) / Sum;
- OS << "probability (" << Src->getNameStr() << " --> " << Dst->getNameStr()
- << ") = " << Prob << "\n";
+ OS << "edge " << Src->getNameStr() << " -> " << Dst->getNameStr()
+ << " probability is " << Prob
+ << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
return OS;
}