[WinEH] Ignore lifetime.end PHI nodes in empty cleanuppads

This fixes a bug where a PHI node that is only referenced by a lifetime.end intrinsic in an otherwise empty cleanuppad can cause SimplyCFG to create an SSA violation while removing the empty cleanuppad. Theoretically the same problem can occur with debug intrinsics.

Differential Revision: https://reviews.llvm.org/D72540

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -4083,9 +4083,10 @@ static bool removeEmptyCleanup(CleanupReturnInst *RI) {
       // The iterator must be incremented here because the instructions are
       // being moved to another block.
       PHINode *PN = cast<PHINode>(I++);
-      if (PN->use_empty())
-        // If the PHI node has no uses, just leave it.  It will be erased
-        // when we erase BB below.
+      if (PN->use_empty() || !PN->isUsedOutsideOfBlock(BB))
+        // If the PHI node has no uses or all of its uses are in this basic
+        // block (meaning they are debug or lifetime intrinsics), just leave
+        // it.  It will be erased when we erase BB below.
         continue;
 
       // Otherwise, sink this PHI node into UnwindDest.

llvm/test/Transforms/SimplifyCFG/empty-cleanuppad.ll

@@ -458,6 +458,55 @@ cleanupret2:
   cleanupret from %cp unwind to caller
 }
 
+; CHECK-LABEL: define void @f11(
+;   This case tests the handling of an empty cleanup pad that
+;   contains a lifetime_end intrinsic and does not dominate its
+;   successor.
+; CHECK: entry:
+; CHECK:   invoke void @g()
+; CHECK: invoke.cont:
+; CHECK:   invoke void @g()
+; CHECK: invoke.cont2:
+; CHECK:   invoke void @g()
+; CHECK-NOT: ehcleanup:
+; CHECK-NOT:   phi
+; CHECK-NOT:   cleanuppad
+; CHECK-NOT:   lifetime.end
+; CHECK: catch.dispatch:
+; CHECK:   catchswitch
+; CHECK: catch:
+; CHECK:   catchret
+; CHECK: }
+define void @f11() personality i8* bitcast (i32 (...)* @__CxxFrameHandler3 to i8*) {
+entry:
+  invoke void @g()
+          to label %invoke.cont unwind label %ehcleanup
+
+invoke.cont:                                      ; preds = %entry
+  invoke void @g()
+          to label %invoke.cont2 unwind label %ehcleanup
+
+invoke.cont2:                                     ; preds = %invoke.cont
+  invoke void @g()
+          to label %return unwind label %catch.dispatch
+
+ehcleanup:                                        ; preds = %invoke.cont, %entry
+  %x = phi i8* [ undef, %invoke.cont ], [ undef, %entry ]
+  %0 = cleanuppad within none []
+  call void @llvm.lifetime.end.p0i8(i64 16, i8* nonnull %x)
+  cleanupret from %0 unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %ehcleanup, %invoke.cont
+  %cs1 = catchswitch within none [label %catch] unwind to caller
+
+catch:                                            ; preds = %catch.dispatch
+  %1 = catchpad within %cs1 [i8* null, i32 u0x40, i8* null]
+  catchret from %1 to label %return
+
+return:                                           ; preds = %invoke.cont, %catch.cont
+  ret void
+}
+
 %struct.S = type { i8 }
 %struct.S2 = type { i8 }
 declare void @"\01??1S2@@QEAA@XZ"(%struct.S2*)