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[NFC][SimplifyCFG] PerformBranchToCommonDestFolding(): move instruction cloning to after CFG update 

This simplifies follow-up patch, and is NFC otherwise.
This commit is contained in:
Roman Lebedev 2021-01-22 23:35:30 +03:00
parent e838750005
commit eae1cc0de5
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GPG Key ID: 083C3EBB4A1689E0
1 changed files with 52 additions and 50 deletions
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102
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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@ -2831,6 +2831,58 @@ static bool PerformBranchToCommonDestFolding(BranchInst *BI, BranchInst *PBI,
// which will allow us to update live-out uses of bonus instructions.
AddPredecessorToBlock(UniqueSucc, PredBlock, BB, MSSAU);
// Try to update branch weights.
uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
if (extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
SuccTrueWeight, SuccFalseWeight)) {
SmallVector<uint64_t, 8> NewWeights;
if (PBI->getSuccessor(0) == BB) {
// PBI: br i1 %x, BB, FalseDest
// BI: br i1 %y, UniqueSucc, FalseDest
// TrueWeight is TrueWeight for PBI * TrueWeight for BI.
NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
// FalseWeight is FalseWeight for PBI * TotalWeight for BI +
// TrueWeight for PBI * FalseWeight for BI.
// We assume that total weights of a BranchInst can fit into 32 bits.
// Therefore, we will not have overflow using 64-bit arithmetic.
NewWeights.push_back(PredFalseWeight *
(SuccFalseWeight + SuccTrueWeight) +
PredTrueWeight * SuccFalseWeight);
} else {
// PBI: br i1 %x, TrueDest, BB
// BI: br i1 %y, TrueDest, UniqueSucc
// TrueWeight is TrueWeight for PBI * TotalWeight for BI +
// FalseWeight for PBI * TrueWeight for BI.
NewWeights.push_back(PredTrueWeight * (SuccFalseWeight + SuccTrueWeight) +
PredFalseWeight * SuccTrueWeight);
// FalseWeight is FalseWeight for PBI * FalseWeight for BI.
NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
}
// Halve the weights if any of them cannot fit in an uint32_t
FitWeights(NewWeights);
SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(), NewWeights.end());
setBranchWeights(PBI, MDWeights[0], MDWeights[1]);
// TODO: If BB is reachable from all paths through PredBlock, then we
// could replace PBI's branch probabilities with BI's.
} else
PBI->setMetadata(LLVMContext::MD_prof, nullptr);
// Now, update the CFG.
PBI->setSuccessor(PBI->getSuccessor(0) != BB, UniqueSucc);
if (DTU)
DTU->applyUpdates({{DominatorTree::Insert, PredBlock, UniqueSucc},
{DominatorTree::Delete, PredBlock, BB}});
// If BI was a loop latch, it may have had associated loop metadata.
// We need to copy it to the new latch, that is, PBI.
if (MDNode *LoopMD = BI->getMetadata(LLVMContext::MD_loop))
PBI->setMetadata(LLVMContext::MD_loop, LoopMD);
// If we have bonus instructions, clone them into the predecessor block.
// Note that there may be multiple predecessor blocks, so we cannot move
// bonus instructions to a predecessor block.
@ -2905,56 +2957,6 @@ static bool PerformBranchToCommonDestFolding(BranchInst *BI, BranchInst *PBI,
Opc, PBI->getCondition(), VMap[BI->getCondition()], "or.cond"));
PBI->setCondition(NewCond);
uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
if (extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
SuccTrueWeight, SuccFalseWeight)) {
SmallVector<uint64_t, 8> NewWeights;
if (PBI->getSuccessor(0) == BB) {
// PBI: br i1 %x, BB, FalseDest
// BI: br i1 %y, UniqueSucc, FalseDest
// TrueWeight is TrueWeight for PBI * TrueWeight for BI.
NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
// FalseWeight is FalseWeight for PBI * TotalWeight for BI +
// TrueWeight for PBI * FalseWeight for BI.
// We assume that total weights of a BranchInst can fit into 32 bits.
// Therefore, we will not have overflow using 64-bit arithmetic.
NewWeights.push_back(PredFalseWeight *
(SuccFalseWeight + SuccTrueWeight) +
PredTrueWeight * SuccFalseWeight);
} else {
// PBI: br i1 %x, TrueDest, BB
// BI: br i1 %y, TrueDest, UniqueSucc
// TrueWeight is TrueWeight for PBI * TotalWeight for BI +
// FalseWeight for PBI * TrueWeight for BI.
NewWeights.push_back(PredTrueWeight * (SuccFalseWeight + SuccTrueWeight) +
PredFalseWeight * SuccTrueWeight);
// FalseWeight is FalseWeight for PBI * FalseWeight for BI.
NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
}
// Halve the weights if any of them cannot fit in an uint32_t
FitWeights(NewWeights);
SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(), NewWeights.end());
setBranchWeights(PBI, MDWeights[0], MDWeights[1]);
// TODO: If BB is reachable from all paths through PredBlock, then we
// could replace PBI's branch probabilities with BI's.
} else
PBI->setMetadata(LLVMContext::MD_prof, nullptr);
PBI->setSuccessor(PBI->getSuccessor(0) != BB, UniqueSucc);
if (DTU)
DTU->applyUpdates({{DominatorTree::Insert, PredBlock, UniqueSucc},
{DominatorTree::Delete, PredBlock, BB}});
// If BI was a loop latch, it may have had associated loop metadata.
// We need to copy it to the new latch, that is, PBI.
if (MDNode *LoopMD = BI->getMetadata(LLVMContext::MD_loop))
PBI->setMetadata(LLVMContext::MD_loop, LoopMD);
// Copy any debug value intrinsics into the end of PredBlock.
for (Instruction &I : *BB) {
if (isa<DbgInfoIntrinsic>(I)) {