[X86_64] va_arg with SSE type get error

[CoTinker]

demo.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

struct S271 { union{}a; double b;} ;
struct S271 s271;
void check271va (int z, ...) {
    struct S271 arg;
    va_list ap;
    __builtin_va_start(ap, z);
    arg = __builtin_va_arg(ap, struct S271);
    long double a = __builtin_va_arg(ap, long double);
    printf("%Lf\n", a);
    if (a != 2.0L)
       printf("Fail\n");
    __builtin_va_end(ap);
}
int main (void) {
    printf("%lu\n", sizeof(s271));
    check271va (2, s271, 2.0L);
}

clang

16
0.000000
Fail

gcc

16
2.000000

https://godbolt.org/z/o6v318vWM

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Longsheng Mou (CoTinker)

demo.c ```c #include <stdlib.h> #include <stdio.h> #include <string.h>

struct S271 { union{}a; double b;} ;
struct S271 s271;
void check271va (int z, ...) {
struct S271 arg;
va_list ap;
__builtin_va_start(ap, z);
arg = __builtin_va_arg(ap, struct S271);
long double a = __builtin_va_arg(ap, long double);
printf("%Lf\n", a);
if (a != 2.0L)
printf("Fail\n");
__builtin_va_end(ap);
}
int main (void) {
printf("%lu\n", sizeof(s271));
check271va (2, s271, 2.0L);
}

clang

16
0.000000
Fail

gcc

16
2.000000

https://godbolt.org/z/o6v318vWM
</details>

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Longsheng Mou (CoTinker)

demo.c ```c #include <stdlib.h> #include <stdio.h> #include <string.h>

struct S271 { union{}a; double b;} ;
struct S271 s271;
void check271va (int z, ...) {
struct S271 arg;
va_list ap;
__builtin_va_start(ap, z);
arg = __builtin_va_arg(ap, struct S271);
long double a = __builtin_va_arg(ap, long double);
printf("%Lf\n", a);
if (a != 2.0L)
printf("Fail\n");
__builtin_va_end(ap);
}
int main (void) {
printf("%lu\n", sizeof(s271));
check271va (2, s271, 2.0L);
}

clang

16
0.000000
Fail

gcc

16
2.000000

https://godbolt.org/z/o6v318vWM
</details>

[phoebewang]

I don't think #86377 fixed all the problem, see https://godbolt.org/z/9W8vjKrzn

[CoTinker]

Maybe it's a duplicate of #79790