/// \brief Generate branch weight metadata for all branches in \p F.
///
/// For every branch instruction B in \p F, we compute the weight of the
/// target block for each of the edges out of B. This is the weight
/// that we associate with that branch.
///
/// TODO - This weight assignment will most likely be wrong if the
/// target branch has more than two predecessors. This needs to be done
/// using some form of flow propagation.
///
/// Once all the branch weights are computed, we emit the MD_prof
/// metadata on B using the computed values.
///
/// \param F The function to query.
bool SampleProfile::emitAnnotations(Function &F) {
bool Changed = false;
FunctionProfile &FProfile = Profiles[F.getName()];
unsigned FirstLineno = inst_begin(F)->getDebugLoc().getLine();
MDBuilder MDB(F.getContext());
// Clear the block weights cache.
FProfile.BlockWeights.clear();
// When we find a branch instruction: For each edge E out of the branch,
// the weight of E is the weight of the target block.
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
BasicBlock *B = I;
TerminatorInst *TI = B->getTerminator();
if (TI->getNumSuccessors() == 1)
continue;
if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
continue;
SmallVector<uint32_t, 4> Weights;
unsigned NSuccs = TI->getNumSuccessors();
for (unsigned I = 0; I < NSuccs; ++I) {
BasicBlock *Succ = TI->getSuccessor(I);
uint32_t Weight =
computeBlockWeight(Succ, FirstLineno, FProfile.BodySamples);
Weights.push_back(Weight);
}
TI->setMetadata(llvm::LLVMContext::MD_prof,
MDB.createBranchWeights(Weights));
Changed = true;
}
return Changed;
}
void Loop::setLoopID(MDNode *LoopID) const {
assert(LoopID && "Loop ID should not be null");
assert(LoopID->getNumOperands() > 0 && "Loop ID needs at least one operand");
assert(LoopID->getOperand(0) == LoopID && "Loop ID should refer to itself");
if (isLoopSimplifyForm()) {
getLoopLatch()->getTerminator()->setMetadata(LoopMDName, LoopID);
return;
}
BasicBlock *H = getHeader();
for (block_iterator I = block_begin(), IE = block_end(); I != IE; ++I) {
TerminatorInst *TI = (*I)->getTerminator();
for (unsigned i = 0, ie = TI->getNumSuccessors(); i != ie; ++i) {
if (TI->getSuccessor(i) == H)
TI->setMetadata(LoopMDName, LoopID);
}
}
}
void Loop::setLoopID(MDNode *LoopID) const {
assert(LoopID && "Loop ID should not be null");
assert(LoopID->getNumOperands() > 0 && "Loop ID needs at least one operand");
assert(LoopID->getOperand(0) == LoopID && "Loop ID should refer to itself");
if (isLoopSimplifyForm()) {
getLoopLatch()->getTerminator()->setMetadata(LLVMContext::MD_loop, LoopID);
return;
}
BasicBlock *H = getHeader();
for (BasicBlock *BB : this->blocks()) {
TerminatorInst *TI = BB->getTerminator();
for (BasicBlock *Successor : TI->successors()) {
if (Successor == H)
TI->setMetadata(LLVMContext::MD_loop, LoopID);
}
}
}
/// setBranchWeightMetadata - Translate the counter values associated with each
/// edge into branch weights for each conditional branch (a branch with 2 or
/// more desinations).
void ProfileMetadataLoaderPass::setBranchWeightMetadata(Module &M,
ProfileData &PB) {
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
if (F->isDeclaration()) continue;
DEBUG(dbgs() << "Setting branch metadata in '" << F->getName() << "'\n");
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
TerminatorInst *TI = BB->getTerminator();
unsigned NumSuccessors = TI->getNumSuccessors();
// If there is only one successor then we can not set a branch
// probability as the target is certain.
if (NumSuccessors < 2) continue;
// Load the weights of all edges leading from this terminator.
DEBUG(dbgs() << "-- Terminator with " << NumSuccessors
<< " successors:\n");
SmallVector<uint32_t, 4> Weights(NumSuccessors);
for (unsigned s = 0 ; s < NumSuccessors ; ++s) {
ProfileData::Edge edge = PB.getEdge(BB, TI->getSuccessor(s));
Weights[s] = (uint32_t)PB.getEdgeWeight(edge);
DEBUG(dbgs() << "---- Edge '" << edge << "' has weight "
<< Weights[s] << "\n");
}
// Set branch weight metadata. This will set branch probabilities of
// 100%/0% if that is true of the dynamic execution.
// BranchProbabilityInfo can account for this when it loads this metadata
// (it gives the unexectuted branch a weight of 1 for the purposes of
// probability calculations).
MDBuilder MDB(TI->getContext());
MDNode *Node = MDB.createBranchWeights(Weights);
TI->setMetadata(LLVMContext::MD_prof, Node);
NumTermsAnnotated++;
}
}
}
