[Bug target/20020] x86_64 - 128 bit structs not targeted to TImode

[gary at intrepid dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20020

--- Comment #28 from Gary Funck <gary at intrepid dot com> 2012-08-12 22:43:16 UTC ---
(In reply to comment #27)
> Please try this patch:
> 
> diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
> index c4d85b7..6c4c2ce 100644
> --- a/gcc/config/i386/i386.h
> +++ b/gcc/config/i386/i386.h
> @@ -1853,6 +1853,10 @@ do {                            \
> 
>  /* #define SLOW_UNALIGNED_ACCESS(MODE, ALIGN) 0 */
> 
> +/* An integer expression for the size in bits of the largest integer machine
> +   mode that should actually be used.  We allow pairs of registers.  */
> +#define MAX_FIXED_MODE_SIZE GET_MODE_BITSIZE (TARGET_64BIT ? TImode : DImode)
> +
>  /* Define this macro if it is as good or better to call a constant
>     function address than to call an address kept in a register.

That's the patch that I have been using and testing against (ref: comment #9).

I suggested this:
#define MAX_FIXED_MODE_SIZE targetm.scalar_mode_supported_p (TImode) ? TImode :
DImode
because it might allow x86 targets with SSE to also target TIMode for 128 bit
struct's (on the assumption that TImode will be more efficient).