[IfConversion] Add missing check in IfConversion/canFallThroughTo

Summary:
When trying to figure out if MBB could fallthrough to ToMBB (possibly by
falling through a bunch of other MBBs) we didn't actually check if there
was fallthrough between the last two blocks in the chain.

Reviewers: kparzysz, iteratee, MatzeB

Reviewed By: kparzysz, iteratee

Subscribers: javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D32996

llvm-svn: 302650

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/IfConversion.cpp b/llvm/lib/CodeGen/IfConversion.cpp
index 37fe4158233..46c3911b9d6 100644
--- a/llvm/lib/CodeGen/IfConversion.cpp
+++ b/llvm/lib/CodeGen/IfConversion.cpp
@@ -1318,7 +1318,8 @@ static bool canFallThroughTo(MachineBasicBlock &MBB, MachineBasicBlock &ToMBB) {
       return false;
     PI = I++;
   }
-  return true;
+  // Finally see if the last I is indeed a successor to PI.
+  return PI->isSuccessor(&*I);
 }
 
 /// Invalidate predecessor BB info so it would be re-analyzed to determine if it