Merge commit '2e9f36d6d443' from apple/main into swift/next

Author: git apple-llvm automerger

compiler-rt/lib/asan/asan_thread.cpp

@@ -366,7 +366,9 @@ uptr AsanThread::GetStackVariableShadowStart(uptr addr) {
     bottom = stack_bottom();
   } else if (has_fake_stack()) {
     bottom = fake_stack()->AddrIsInFakeStack(addr);
-    CHECK(bottom);
+    if (bottom == 0) {
+      return 0;
+    }
   } else {
     return 0;
   }

compiler-rt/test/asan/TestCases/invalid-pointer-pairs-subtract-success.cpp

@@ -1,6 +1,7 @@
 // RUN: %clangxx_asan -O0 %s -o %t -mllvm -asan-detect-invalid-pointer-pair
 
 // RUN: %env_asan_opts=detect_invalid_pointer_pairs=2 %run %t
+// RUN: %env_asan_opts=detect_invalid_pointer_pairs=2,detect_stack_use_after_return=1 %run %t
 
 #include <assert.h>
 #include <stdlib.h>