Hi, Uros,
> On Oct 21, 2020, at 9:45 AM, Qing Zhao via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>>>
>>
>> Something like this:
>>
>> --cut here--
>> long double
>> __attribute__ ((noinline))
>> test (long double a, long double b)
>> {
>> long double r = a + b;
>>
>> asm volatile ("fldz; \
>> fldz; \
>> fldz; \
>> fldz; \
>> fldz; \
>> fldz; \
>> fldz; \
>> fstp %%st(0); \
>> fstp %%st(0); \
>> fstp %%st(0); \
>> fstp %%st(0); \
>> fstp %%st(0); \
>> fstp %%st(0); \
>> fstp %%st(0)" : : "X"(r));
>> return r;
>> }
>>
>> int
>> main ()
>> {
>> long double a = 1.1, b = 1.2;
>>
>> long double c = test (a, b);
>>
>> printf ("%Lf\n", c);
>>
>> return 0;
>> }
>> --cut here—
>
>
> Okay, so,
>
> 1. First compute how many st registers need to be zeroed, num_of_zeroed_st
> 2. Then issue (8 - num_of_zeroed_st) fldz to push 0 to the stack to clear all
> the dead stack slots;
> 3. Then issue (8 - num_of_zeroed_st) fstp %st(0) to pop the stack and empty
> the stack.
>
How to generate such asm volatile insn at i386 backend? Is there any code in
i386 backend I can refer for this ?
thanks.
Qing
