From: Owen Anderson <resistor@mac.com>
Date: Sat, 12 Jul 2014 07:12:47 +0000 (+0000)
Subject: Fix an issue with the MergeBasicBlockIntoOnlyPred() helper function where it did
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=452bd5f9c6869cb2c9ca3201302e508e9b61bf77;p=oota-llvm.git

Fix an issue with the MergeBasicBlockIntoOnlyPred() helper function where it did
not properly handle the case where the predecessor block was the entry block to
the function.  The only in-tree client of this is JumpThreading, which worked
around the issue in its own code.  This patch moves the solution into the helper
so that JumpThreading (and other clients) do not have to replicate the same fix
everywhere.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212875 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 6e50d3331df..21f80385cf4 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -669,14 +669,9 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
       if (LoopHeaders.erase(SinglePred))
         LoopHeaders.insert(BB);
 
-      // 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();
       LVI->eraseBlock(SinglePred);
       MergeBasicBlockIntoOnlyPred(BB);
 
-      if (isEntry && BB != &BB->getParent()->getEntryBlock())
-        BB->moveBefore(&BB->getParent()->getEntryBlock());
       return true;
     }
   }
diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index aedd787ecf8..a5e443fcf46 100644
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -509,6 +509,11 @@ void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
   PredBB->getTerminator()->eraseFromParent();
   DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
 
+  // If the PredBB is the entry block of the function, move DestBB up to
+  // become the entry block after we erase PredBB.
+  if (PredBB == &DestBB->getParent()->getEntryBlock())
+    DestBB->moveAfter(PredBB);
+
   if (P) {
     if (DominatorTreeWrapperPass *DTWP =
             P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {