SimplifyCFG: Enumerating all predecessors of a BB can be expensive (switches), avoid it if possible.
No functionality change.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164923 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 065325b..a5e4d44 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1173,10 +1173,14 @@
// 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;