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PGO branch weight: update edge weights in IfConverter.

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This commit only handles IfConvertTriangle. To update edge weights
of a successor, one interface is added to MachineBasicBlock:
/// Set successor weight of a given iterator.
setSuccWeight(succ_iterator I, uint32_t weight)

An existing testing case test/CodeGen/Thumb2/v8_IT_5.ll is updated,
since we now correctly update the edge weights, the cold block
is placed at the end of the function and we jump to the cold block.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200428 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren
2014-01-29 23:18:47 +00:00
parent 65a12969f9
commit ea120b6bb5
5 changed files with 101 additions and 1 deletions
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47
lib/CodeGen/IfConversion.cpp
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@ -1102,6 +1102,28 @@ bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
return true;
}
/// Scale down weights to fit into uint32_t. NewTrue is the new weight
/// for successor TrueBB, and NewFalse is the new weight for successor
/// FalseBB.
static void ScaleWeights(uint64_t NewTrue, uint64_t NewFalse,
MachineBasicBlock *MBB,
const MachineBasicBlock *TrueBB,
const MachineBasicBlock *FalseBB,
const MachineBranchProbabilityInfo *MBPI) {
uint64_t NewMax = (NewTrue > NewFalse) ? NewTrue : NewFalse;
uint32_t Scale = (NewMax / UINT32_MAX) + 1;
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
SE = MBB->succ_end();
SI != SE; ++SI) {
if (*SI == TrueBB)
MBB->setSuccWeight(SI, (uint32_t)(NewTrue / Scale));
else if (*SI == FalseBB)
MBB->setSuccWeight(SI, (uint32_t)(NewFalse / Scale));
else
MBB->setSuccWeight(SI, MBPI->getEdgeWeight(MBB, SI) / Scale);
}
}
/// IfConvertTriangle - If convert a triangle sub-CFG.
///
bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
@ -1158,6 +1180,14 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
DontKill.clear();
bool HasEarlyExit = CvtBBI->FalseBB != NULL;
uint64_t CvtNext = 0, CvtFalse = 0, SumWeight = 0;
uint32_t WeightScale = 0;
if (HasEarlyExit) {
// Get weights before modifying CvtBBI->BB.
CvtNext = MBPI->getEdgeWeight(CvtBBI->BB, NextBBI->BB);
CvtFalse = MBPI->getEdgeWeight(CvtBBI->BB, CvtBBI->FalseBB);
SumWeight = MBPI->getSumForBlock(CvtBBI->BB, WeightScale);
}
if (CvtBBI->BB->pred_size() > 1) {
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
// Copy instructions in the true block, predicate them, and add them to
@ -1185,6 +1215,23 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
llvm_unreachable("Unable to reverse branch condition!");
TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond, dl);
BBI.BB->addSuccessor(CvtBBI->FalseBB);
// Update the edge weight for both CvtBBI->FalseBB and NextBBI.
// New_Weight(BBI.BB, NextBBI->BB) =
// Weight(BBI.BB, NextBBI->BB) * getSumForBlock(CvtBBI->BB) +
// Weight(BBI.BB, CvtBBI->BB) * Weight(CvtBBI->BB, NextBBI->BB)
// New_Weight(BBI.BB, CvtBBI->FalseBB) =
// Weight(BBI.BB, CvtBBI->BB) * Weight(CvtBBI->BB, CvtBBI->FalseBB)
uint64_t BBNext = MBPI->getEdgeWeight(BBI.BB, NextBBI->BB);
uint64_t BBCvt = MBPI->getEdgeWeight(BBI.BB, CvtBBI->BB);
uint64_t NewNext = BBNext * SumWeight + (BBCvt * CvtNext) / WeightScale;
uint64_t NewFalse = (BBCvt * CvtFalse) / WeightScale;
// We need to scale down all weights of BBI.BB to fit uint32_t.
// Here BBI.BB is connected to CvtBBI->FalseBB and will fall through to
// the next block.
ScaleWeights(NewNext, NewFalse, BBI.BB, getNextBlock(BBI.BB),
CvtBBI->FalseBB, MBPI);
}
// Merge in the 'false' block if the 'false' block has no other