-mgeneral-regs-only changes preprocessor macros

Jonathan Wakely jwakely.gcc@gmail.com
Thu Jun 27 08:26:00 GMT 2019


On Tue, 25 Jun 2019, 18:59 Xi Ruoyao wrote:
>
> On 2019-06-25 15:36 +0200, J.W. Jagersma wrote:
> > Say I have a header which defines a type conditionally based on the
> > __SSE__ macro:
> >
> > #ifdef __SSE__
> >      struct X { ... };
> > #else
> >      struct X { ... };
> > #endif
> >
> > This header is included in multiple compilation units, some of which are
> > compiled with -mgeneral-regs-only. I don't want any fpu/simd code there.
> > Now this flag also undefines __SSE__, which I suppose makes sense, but
> > it breaks the ABI between translation units.
> > Is there some way to avoid generating fpu code without affecting
> > preprocessor macros?
>
> How about just "pretend" to have __SSE__?
>
> cat > test.c << EOF
> #ifndef __SSE__
> #error
> #endif
> int main(){}
> EOF
>
> gcc test.c -mgeneral-regs-only -D__SSE__



Or use a different check to decide which definition of the struct to use.

If you want the first version even when __SSE__ is not defined, then
don't make it depend on __SSE__.



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