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SimplifyCFG: Enumerating all predecessors of a BB can be expensive (switches), avoid it if possible.

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No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164923 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2012-09-30 21:03:56 +00:00
parent 8bd5e35978
commit fdb96062b2
1 changed files with 7 additions and 3 deletions
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10
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -1173,10 +1173,14 @@ static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
// Check that BBEnd has two predecessors and the other predecessor ends with
// an unconditional branch.
SmallVector<BasicBlock*, 16> Preds(pred_begin(BBEnd), pred_end(BBEnd));
if (Preds.size() != 2)
pred_iterator PI = pred_begin(BBEnd), PE = pred_end(BBEnd);
BasicBlock *Pred0 = *PI++;
if (PI == PE) // Only one predecessor.
return false;
BasicBlock *BB2 = (Preds[0] == BB1) ? Preds[1] : Preds[0];
BasicBlock *Pred1 = *PI++;
if (PI != PE) // More than two predecessors.
return false;
BasicBlock *BB2 = (Pred0 == BB1) ? Pred1 : Pred0;
BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator());
if (!BI2 || !BI2->isUnconditional())
return false;