[SimplifyCFG] Don't kill empty cleanuppads with multiple uses

A basic block could contain:
  %cp = cleanuppad []
  cleanupret from %cp unwind to caller

This basic block is empty and is thus a candidate for removal.  However,
there can be other uses of %cp outside of this basic block.  This is
only possible in unreachable blocks.

Make our transform more correct by checking that the pad has a single
user before removing the BB.

This fixes PR28005.

llvm-svn: 271816

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 25baf1bf640..ec2c1af97ea 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3424,6 +3424,11 @@ static bool removeEmptyCleanup(CleanupReturnInst *RI) {
     // This isn't an empty cleanup.
     return false;
 
+  // We cannot kill the pad if it has multiple uses.  This typically arises
+  // from unreachable basic blocks.
+  if (!CPInst->hasOneUse())
+    return false;
+
   // Check that there are no other instructions except for benign intrinsics.
   BasicBlock::iterator I = CPInst->getIterator(), E = RI->getIterator();
   while (++I != E) {