[llvm-commits] [llvm] r164923 - /llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp

[Benjamin Kramer]

Author: d0k
Date: Sun Sep 30 16:03:56 2012
New Revision: 164923

URL: http://llvm.org/viewvc/llvm-project?rev=164923&view=rev
Log:
SimplifyCFG: Enumerating all predecessors of a BB can be expensive (switches), avoid it if possible.

No functionality change.

Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=164923&r1=164922&r2=164923&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Sun Sep 30 16:03:56 2012
@@ -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;