From: Chris Lattner <sabre@nondot.org>
Date: Thu, 27 Nov 2008 19:29:14 +0000 (+0000)
Subject: defensive patch: if CGP is merging a block with the entry block, make sure
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=9918fb5631974f2201a640384b7ebe672c749e43;p=oota-llvm.git

defensive patch: if CGP is merging a block with the entry block, make sure
it ends up being the entry block.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60180 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index caf60c8c7af..9bf39911b6c 100644
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -204,8 +204,15 @@ void CodeGenPrepare::EliminateMostlyEmptyBlock(BasicBlock *BB) {
 
   // If the destination block has a single pred, then this is a trivial edge,
   // just collapse it.
-  if (DestBB->getSinglePredecessor()) {
+  if (BasicBlock *SinglePred = DestBB->getSinglePredecessor()) {
+    // Remember if SinglePred was the entry block of the function.  If so, we
+    // will need to move BB back to the entry position.
+    bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
     MergeBasicBlockIntoOnlyPred(DestBB);
+
+    if (isEntry && BB != &BB->getParent()->getEntryBlock())
+      BB->moveBefore(&BB->getParent()->getEntryBlock());
+    
     DOUT << "AFTER:\n" << *DestBB << "\n\n\n";
     return;
   }