#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.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",
+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:
// 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;
}
// Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
// as taken, exiting edges as not-taken.
-bool BranchProbabilityInfo::calcLoopBranchHeuristics(BasicBlock *BB) {
- Loop *L = LI->getLoopFor(BB);
+bool BranchProbabilityInfo::calcLoopBranchHeuristics(BasicBlock *BB,
+ const LoopInfo &LI) {
+ Loop *L = LI.getLoopFor(BB);
if (!L)
return false;
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()) {
return true;
}
-void BranchProbabilityInfo::getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<LoopInfo>();
- AU.setPreservesAll();
+void BranchProbabilityInfo::releaseMemory() {
+ Weights.clear();
}
-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.
- 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))
- continue;
- if (calcMetadataWeights(*I))
- continue;
- if (calcColdCallHeuristics(*I))
- continue;
- if (calcLoopBranchHeuristics(*I))
- continue;
- if (calcPointerHeuristics(*I))
- continue;
- if (calcZeroHeuristics(*I))
- continue;
- if (calcFloatingPointHeuristics(*I))
- continue;
- calcInvokeHeuristics(*I);
- }
-
- PostDominatedByUnreachable.clear();
- PostDominatedByColdCall.clear();
- return false;
-}
-
-void BranchProbabilityInfo::print(raw_ostream &OS, const Module *) const {
+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 BasicBlock &BB : *LastF)
- for (const BasicBlock *Succ : successors(&BB))
- printEdgeProbability(OS << " ", &BB, Succ);
+ for (Function::const_iterator BI = LastF->begin(), BE = LastF->end();
+ BI != BE; ++BI) {
+ for (succ_const_iterator SI = succ_begin(BI), SE = succ_end(BI);
+ SI != SE; ++SI) {
+ printEdgeProbability(OS << " ", BI, *SI);
+ }
+ }
}
uint32_t BranchProbabilityInfo::getSumForBlock(const BasicBlock *BB) const {
uint32_t PrevSum = Sum;
Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
+ assert(Sum >= PrevSum); (void) PrevSum;
}
return Sum;
uint32_t MaxWeight = 0;
BasicBlock *MaxSucc = nullptr;
- for (BasicBlock *Succ : successors(BB)) {
+ 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;
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
return OS;
}
+
+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);
+ }
+
+ PostDominatedByUnreachable.clear();
+ PostDominatedByColdCall.clear();
+}
+
+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);
+}
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