[Bug preprocessor/64698] New: preprocessor ignores #pragma GCC diagnostic when using -save-temps

["markus at oberhumer dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64698

            Bug ID: 64698
           Summary: preprocessor ignores #pragma GCC diagnostic when using
                    -save-temps
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: markus at oberhumer dot com

This could be related to bug 53431, though this report is about C and not C++.

Actually I had thought that "-save-temps" just dumps the internal state, but
that does not seem to be true.

The following code:

#pragma GCC diagnostic ignored "-Wundef"
#if FOO
#endif
int main (void) { return 42; }

compiled with 

gcc-4.9 -Wundef -Werror -save-temps -c bug_wundef.c

gives:

bug_wundef.c:2:5: error: "FOO" is not defined [-Werror=undef]
 #if FOO
     ^
cc1: all warnings being treated as errors

On the contrary

gcc-4.9 -Wundef -Werror -c bug_wundef.c

does not give any error.