[TailDuplication] Enable tail duplication of fallthrough BBs

Signed-off-by: Vladimir Radosavljevic <[email protected]>

llvm/lib/CodeGen/TailDuplicator.cpp

@@ -559,8 +559,6 @@ bool TailDuplicator::shouldTailDuplicate(bool IsSimple,
   // When doing tail-duplication during layout, the block ordering is in flux,
   // so canFallThrough returns a result based on incorrect information and
   // should just be ignored.
-  if (!LayoutMode && TailBB.canFallThrough())
-    return false;
 
   // Don't try to tail-duplicate single-block loops.
   if (TailBB.isSuccessor(&TailBB))