From fdb96062b238aa0d751602c916c87f1e13bc59e6 Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Sun, 30 Sep 2012 21:03:56 +0000
Subject: [PATCH] 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
---
 lib/Transforms/Utils/SimplifyCFG.cpp | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 065325b7c25..a5e4d44b85e 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -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;