Re: [PATCH][c++] Do not warn about unused macros while processing #pragma GCC optimize

[Martin Sebor <msebor at gmail dot com>]

On 8/5/19 7:53 PM, Piotr H. Dabrowski wrote:
> Fixes c++/91318.
>
> libcpp/ChangeLog:
>
> 2019-08-06  Piotr Henryk Dabrowski  <phd@phd.re>
>
> 	PR c++/91318
> 	* include/cpplib.h: Added cpp_define_unused(), cpp_define_formatted_unused()
> 	* directives.c: Likewise.
>
> gcc/c-family/ChangeLog:
>
> 2019-08-06  Piotr Henryk Dabrowski  <phd@phd.re>
>
> 	PR c++/91318
> 	* c-cppbuiltin.c: c_cpp_builtins_optimize_pragma(): use cpp_define_unused()

This isn't my area so I can't comment on the correctness of
the changes but I would recommend to also add a regression
test case to the test suite along with the fix.

It might be interesting to check whether the macros are defined
the same way in C and in C++, and if they correspond to the effect
of the options set by the pragmas (i.e., "later in the source file"
as documented).

Martin

> diff --git a/gcc/c-family/c-cppbuiltin.c b/gcc/c-family/c-cppbuiltin.c
> index d389f8ca4a0..47d0cefb85a 100644
> --- a/gcc/c-family/c-cppbuiltin.c
> +++ b/gcc/c-family/c-cppbuiltin.c
> @@ -576,41 +576,41 @@ c_cpp_builtins_optimize_pragma (cpp_reader *pfile, tree prev_tree,
>     /* Other target-independent built-ins determined by command-line
>        options.  */
>     if (!prev->x_optimize_size && cur->x_optimize_size)
> -    cpp_define (pfile, "__OPTIMIZE_SIZE__");
> +    cpp_define_unused (pfile, "__OPTIMIZE_SIZE__");
>     else if (prev->x_optimize_size && !cur->x_optimize_size)
>       cpp_undef (pfile, "__OPTIMIZE_SIZE__");
>   
>     if (!prev->x_optimize && cur->x_optimize)
> -    cpp_define (pfile, "__OPTIMIZE__");
> +    cpp_define_unused (pfile, "__OPTIMIZE__");
>     else if (prev->x_optimize && !cur->x_optimize)
>       cpp_undef (pfile, "__OPTIMIZE__");
>   
>     prev_fast_math = fast_math_flags_struct_set_p (prev);
>     cur_fast_math  = fast_math_flags_struct_set_p (cur);
>     if (!prev_fast_math && cur_fast_math)
> -    cpp_define (pfile, "__FAST_MATH__");
> +    cpp_define_unused (pfile, "__FAST_MATH__");
>     else if (prev_fast_math && !cur_fast_math)
>       cpp_undef (pfile, "__FAST_MATH__");
>   
>     if (!prev->x_flag_signaling_nans && cur->x_flag_signaling_nans)
> -    cpp_define (pfile, "__SUPPORT_SNAN__");
> +    cpp_define_unused (pfile, "__SUPPORT_SNAN__");
>     else if (prev->x_flag_signaling_nans && !cur->x_flag_signaling_nans)
>       cpp_undef (pfile, "__SUPPORT_SNAN__");
>   
>     if (!prev->x_flag_errno_math && cur->x_flag_errno_math)
>       cpp_undef (pfile, "__NO_MATH_ERRNO__");
>     else if (prev->x_flag_errno_math && !cur->x_flag_errno_math)
> -    cpp_define (pfile, "__NO_MATH_ERRNO__");
> +    cpp_define_unused (pfile, "__NO_MATH_ERRNO__");
>   
>     if (!prev->x_flag_finite_math_only && cur->x_flag_finite_math_only)
>       {
>         cpp_undef (pfile, "__FINITE_MATH_ONLY__");
> -      cpp_define (pfile, "__FINITE_MATH_ONLY__=1");
> +      cpp_define_unused (pfile, "__FINITE_MATH_ONLY__=1");
>       }
>     else if (prev->x_flag_finite_math_only && !cur->x_flag_finite_math_only)
>       {
>         cpp_undef (pfile, "__FINITE_MATH_ONLY__");
> -      cpp_define (pfile, "__FINITE_MATH_ONLY__=0");
> +      cpp_define_unused (pfile, "__FINITE_MATH_ONLY__=0");
>       }
>   }
>   
> diff --git a/libcpp/directives.c b/libcpp/directives.c
> index ddf8979d513..9a774c9ed04 100644
> --- a/libcpp/directives.c
> +++ b/libcpp/directives.c
> @@ -2392,6 +2392,15 @@ cpp_define (cpp_reader *pfile, const char *str)
>     run_directive (pfile, T_DEFINE, buf, count);
>   }
>   
> +/* Like cpp_define, but does not warn about unused macro.  */
> +void
> +cpp_define_unused (cpp_reader *pfile, const char *str)
> +{
> +    unsigned char warn_unused_macros = CPP_OPTION (pfile, warn_unused_macros);
> +    CPP_OPTION (pfile, warn_unused_macros) = 0;
> +    cpp_define (pfile, str);
> +    CPP_OPTION (pfile, warn_unused_macros) = warn_unused_macros;
> +}
>   
>   /* Use to build macros to be run through cpp_define() as
>      described above.
> @@ -2411,6 +2420,20 @@ cpp_define_formatted (cpp_reader *pfile, const char *fmt, ...)
>     free (ptr);
>   }
>   
> +/* Like cpp_define_formatted, but does not warn about unused macro.  */
> +void
> +cpp_define_formatted_unused (cpp_reader *pfile, const char *fmt, ...)
> +{
> +  char *ptr;
> +
> +  va_list ap;
> +  va_start (ap, fmt);
> +  ptr = xvasprintf (fmt, ap);
> +  va_end (ap);
> +
> +  cpp_define_unused (pfile, ptr);
> +  free (ptr);
> +}
>   
>   /* Slight variant of the above for use by initialize_builtins.  */
>   void
> diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
> index a645f8136a6..8d3f9082601 100644
> --- a/libcpp/include/cpplib.h
> +++ b/libcpp/include/cpplib.h
> @@ -1052,8 +1052,12 @@ extern cppchar_t cpp_host_to_exec_charset (cpp_reader *, cppchar_t);
>   /* Used to register macros and assertions, perhaps from the command line.
>      The text is the same as the command line argument.  */
>   extern void cpp_define (cpp_reader *, const char *);
> +extern void cpp_define_unused (cpp_reader *, const char *);
>   extern void cpp_define_formatted (cpp_reader *pfile,
>   				  const char *fmt, ...) ATTRIBUTE_PRINTF_2;
> +extern void cpp_define_formatted_unused (cpp_reader *pfile,
> +					 const char *fmt,
> +					 ...) ATTRIBUTE_PRINTF_2;
>   extern void cpp_assert (cpp_reader *, const char *);
>   extern void cpp_undef (cpp_reader *, const char *);
>   extern void cpp_unassert (cpp_reader *, const char *);