[llvm] r212875 - Fix an issue with the MergeBasicBlockIntoOnlyPred() helper function where it did

[Owen Anderson]

Author: resistor
Date: Sat Jul 12 02:12:47 2014
New Revision: 212875

URL: http://llvm.org/viewvc/llvm-project?rev=212875&view=rev
Log:
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.

Modified:
    llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
    llvm/trunk/lib/Transforms/Utils/Local.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=212875&r1=212874&r2=212875&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Sat Jul 12 02:12:47 2014
@@ -669,14 +669,9 @@ bool JumpThreading::ProcessBlock(BasicBl
       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;
     }
   }

Modified: llvm/trunk/lib/Transforms/Utils/Local.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/Local.cpp?rev=212875&r1=212874&r2=212875&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/Local.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/Local.cpp Sat Jul 12 02:12:47 2014
@@ -509,6 +509,11 @@ void llvm::MergeBasicBlockIntoOnlyPred(B
   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>()) {