On Thu, Jul 9, 2026 at 9:41 AM H.J. Lu <[email protected]> wrote:
>
> In 64-bit mode, preserve_none attribute uses a different calling
> convention. Ignore MS ABI with preserve_none attribute to always
> use the preserve_none calling convention with preserve_none
> attribute.
>
> gcc/
>
>
> It has 8 registers. Tests show that
> x86_64_preserve_none_int_parameter_registers
> is used for functions with __attribute__ ((preserve_none, ms_abi)).
I mean for sse registers, init_cumulative_args sets the integer count
via the new predicate but leaves the SSE count keyed on the raw ABI
(i386.cc:1940):
927 /* Set up the number of registers to use for passing arguments. */
928 cum->nregs = ix86_regparm;
929 if (TARGET_64BIT)
930 {
931 cum->nregs = (x86_64_cumulative_ms_abi_p (cum)
932 ? X86_64_MS_REGPARM_MAX
933 : X86_64_REGPARM_MAX);
934 }
935 if (TARGET_SSE)
936 {
937 cum->sse_nregs = SSE_REGPARM_MAX;
938 if (TARGET_64BIT)
939 {
940 cum->sse_nregs = (cum->call_abi == SYSV_ABI
941 ? X86_64_SSE_REGPARM_MAX
942 : X86_64_MS_SSE_REGPARM_MAX);
943 }
944 }
if -mabi=ms is in the command line, with plain preserve_none in the
attribute, only 4 sse registers is used for parameter passing
But with __attribute__ ((preserve_none, ms_abi)), 8 sse registers are
used for parameter passing.
.i.e
void bar(double,double,double,double,double,double)
__attribute__((preserve_none));
void
entry (long a1, long a2, long a3, long a4, long a5, long a6)
{
bar (a1, a2, a3, a4, a5, a6);
}
--
BR,
Hongtao
