From 8c4b6172035bb0b4424fe92654336b5aa3b89f4a Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Sat, 4 Jun 2016 23:50:03 +0000
Subject: [PATCH] [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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@271816 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyCFG.cpp            |  5 +++++
 test/Transforms/SimplifyCFG/empty-cleanuppad.ll | 24 ++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 25baf1bf640..ec2c1af97ea 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/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) {
diff --git a/test/Transforms/SimplifyCFG/empty-cleanuppad.ll b/test/Transforms/SimplifyCFG/empty-cleanuppad.ll
index e83cbb50e58..9f657a81a05 100644
--- a/test/Transforms/SimplifyCFG/empty-cleanuppad.ll
+++ b/test/Transforms/SimplifyCFG/empty-cleanuppad.ll
@@ -434,6 +434,30 @@ try.cont:
   ret i32 0
 }
 
+; CHECK-LABEL: define void @f10(
+define void @f10(i32 %V) personality i32 (...)* @__CxxFrameHandler3 {
+entry:
+  invoke void @g()
+          to label %unreachable unwind label %cleanup
+; CHECK:       call void @g()
+; CHECK-NEXT:  unreachable
+
+unreachable:
+  unreachable
+
+cleanup:
+  %cp = cleanuppad within none []
+  switch i32 %V, label %cleanupret1 [
+    i32 0, label %cleanupret2
+  ]
+
+cleanupret1:
+  cleanupret from %cp unwind to caller
+
+cleanupret2:
+  cleanupret from %cp unwind to caller
+}
+
 %struct.S = type { i8 }
 %struct.S2 = type { i8 }
 declare void @"\01??1S2@@QEAA@XZ"(%struct.S2*)
-- 
2.11.0