Revert a portion of Dan's change r71018 that I'm convinced is wrong.

Dan was trying to catch the case where a basic block ends with a conditional
branch to the fall-through block.  In this case, all the instructions have
been moved out of FromBBI, leaving it empty.  It cannot end with a
conditional branch.  As the existing comment indicates, it will always fall
through to the next block.  If the block already had the next block (NBB)
listed as a successor, the preceding loop has a check for that and does not
remove it.  Thus, we need to check and add the successor only when it is
not already listed.

With Dan's change, the empty block often ends up with the fall-through
successor listed twice.  This exposed the problem in pr4195, where
CodePlacementOpt did not handle the same predecessor listed more than once.
It is also at least partially responsible for pr4202 and probably a similar
issue with Thumb branches being out of range.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@71742 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/IfConversion.cpp b/lib/CodeGen/IfConversion.cpp
index 93e7ff6cfb65e1612ef6d276e4aa4c48675f9251..1d0887f843d8c663a8a8aeae3c2ac9e04c6e8fc7 100644 (file)
--- a/lib/CodeGen/IfConversion.cpp
+++ b/lib/CodeGen/IfConversion.cpp
@@ -1212,7 +1212,7 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
   }
 
   // Now FromBBI always falls through to the next block!
-  if (NBB)
+  if (NBB && !FromBBI.BB->isSuccessor(NBB))
     FromBBI.BB->addSuccessor(NBB);
 
   std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),