//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "branch-prob"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#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/CFG.h"
#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
using namespace llvm;
+#define DEBUG_TYPE "branch-prob"
+
INITIALIZE_PASS_BEGIN(BranchProbabilityInfo, "branch-prob",
"Branch Probability Analysis", false, true)
-INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_END(BranchProbabilityInfo, "branch-prob",
"Branch Probability Analysis", false, true)
// Minimum weight of an edge. Please note, that weight is NEVER 0.
static const uint32_t MIN_WEIGHT = 1;
-static uint32_t getMaxWeightFor(BasicBlock *BB) {
- return UINT32_MAX / BB->getTerminator()->getNumSuccessors();
-}
-
-
/// \brief Calculate edge weights for successors lead to unreachable.
///
/// Predict that a successor which leads necessarily to an
if (!WeightsNode)
return false;
+ // Check that the number of successors is manageable.
+ assert(TI->getNumSuccessors() < UINT32_MAX && "Too many successors");
+
// 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;
- // Build up the final weights that will be used in a temporary buffer, but
- // don't add them until all weihts are present. Each weight value is clamped
- // to [1, getMaxWeightFor(BB)].
- uint32_t WeightLimit = getMaxWeightFor(BB);
+ // 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 = dyn_cast<ConstantInt>(WeightsNode->getOperand(i));
+ ConstantInt *Weight =
+ mdconst::dyn_extract<ConstantInt>(WeightsNode->getOperand(i));
if (!Weight)
return false;
- Weights.push_back(
- std::max<uint32_t>(1, Weight->getLimitedValue(WeightLimit)));
+ 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");
- for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
- setEdgeWeight(BB, i, Weights[i]);
+
+ // 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;
+
+ WeightSum = 0;
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
+ uint32_t W = Weights[i] / ScalingFactor;
+ WeightSum += W;
+ setEdgeWeight(BB, i, W);
+ }
+ assert(WeightSum <= UINT32_MAX &&
+ "Expected weights to scale down to 32 bits");
return true;
}
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)
if (!CV)
return false;
+ // 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()) {
}
void BranchProbabilityInfo::getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<LoopInfo>();
+ AU.addRequired<LoopInfoWrapperPass>();
AU.setPreservesAll();
}
DEBUG(dbgs() << "---- Branch Probability Info : " << F.getName()
<< " ----\n\n");
LastF = &F; // Store the last function we ran on for printing.
- LI = &getAnalysis<LoopInfo>();
+ LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
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 (po_iterator<BasicBlock *> I = po_begin(&F.getEntryBlock()),
- E = po_end(&F.getEntryBlock());
- I != E; ++I) {
- DEBUG(dbgs() << "Computing probabilities for " << I->getName() << "\n");
- if (calcUnreachableHeuristics(*I))
+ for (auto BB : post_order(&F.getEntryBlock())) {
+ DEBUG(dbgs() << "Computing probabilities for " << BB->getName() << "\n");
+ if (calcUnreachableHeuristics(BB))
continue;
- if (calcMetadataWeights(*I))
+ if (calcMetadataWeights(BB))
continue;
- if (calcColdCallHeuristics(*I))
+ if (calcColdCallHeuristics(BB))
continue;
- if (calcLoopBranchHeuristics(*I))
+ if (calcLoopBranchHeuristics(BB))
continue;
- if (calcPointerHeuristics(*I))
+ if (calcPointerHeuristics(BB))
continue;
- if (calcZeroHeuristics(*I))
+ if (calcZeroHeuristics(BB))
continue;
- if (calcFloatingPointHeuristics(*I))
+ if (calcFloatingPointHeuristics(BB))
continue;
- calcInvokeHeuristics(*I);
+ calcInvokeHeuristics(BB);
}
PostDominatedByUnreachable.clear();
return false;
}
+void BranchProbabilityInfo::releaseMemory() {
+ Weights.clear();
+}
+
void BranchProbabilityInfo::print(raw_ostream &OS, const Module *) const {
OS << "---- Branch Probabilities ----\n";
// We print the probabilities from the last function the analysis ran over,
uint32_t PrevSum = Sum;
Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
+ assert(Sum >= PrevSum); (void) PrevSum;
}
return Sum;
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;
}
/// Get the raw edge weight for the edge. If can't find it, return
return DEFAULT_WEIGHT;
}
-uint32_t
-BranchProbabilityInfo::
-getEdgeWeight(const BasicBlock *Src, succ_const_iterator Dst) const {
- size_t index = std::distance(succ_begin(Src), Dst);
- return getEdgeWeight(Src, index);
+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
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())
+ if (MapI != Weights.end()) {
+ FoundWeight = true;
Weight += MapI->second;
+ }
}
- return (Weight == 0) ? DEFAULT_WEIGHT : Weight;
+ return (!FoundWeight) ? DEFAULT_WEIGHT : Weight;
}
/// Set the edge weight for a given edge specified by PredBlock and an index
projects / oota-llvm.git / blobdiff