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 6e50d3331df6b7e7383f3cbe97d57a4f855725e2..21f80385cf46940fe4b54c969ac6d9ce99eba9d0 100644 (file)
--- 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 aedd787ecf8d56ef000843e515d069bdf91b6dc3..a5e443fcf46b165b04c1f3d4ead8acdfc0dee345 100644 (file)
--- 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>()) {