[-Wunreachable-code] don't warn about dead 'return <string literal>' dominated by a 'noreturn' call, where literal becomes an std::string.

I have mixed feelings about this one.  It's used all over the codebase,
and is analogous to the current heuristic for ordinary C string literals.

This requires some ad hoc pattern matching of the AST.  While the
test case mirrors what we see std::string in libc++, it's not really
testing the libc++ headers.

llvm-svn: 203091

1 files changed, 21 insertions, 0 deletions

diff --git a/clang/test/SemaCXX/warn-unreachable.cpp b/clang/test/SemaCXX/warn-unreachable.cpp
index dbbcc8c50e0..1fbe15c0f02 100644
--- a/clang/test/SemaCXX/warn-unreachable.cpp
+++ b/clang/test/SemaCXX/warn-unreachable.cpp
@@ -129,4 +129,25 @@ PR19040_test_return_t PR19040_fn1 ()
     return PR19040_TEST_FAILURE; // expected-warning {{will never be executed}}
 }
 
+__attribute__((noreturn))
+void raze();
+
+namespace std {
+template<typename T> struct basic_string {
+  basic_string(const T* x) {}
+  ~basic_string() {};
+};
+typedef basic_string<char> string;
+}
+
+std::string testStr() {
+  raze();
+  return ""; // no-warning
+}
+
+std::string testStrWarn(const char *s) {
+  raze();
+  return s; // expected-warning {{will never be executed}}
+}
+