| Issue |
77036
|
| Summary |
[x86_64][clang] Empty structure argument are ignored in function variable arguments.
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
CoTinker
|
demo
```
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
extern void *memset (void *__s, int __c, size_t __n);
struct S14 {
union{}a;
};
struct S14 s14;
void check14va (int z, ...) {
struct S14 arg, *p;
va_list ap;
__builtin_va_start(ap, z);
arg = __builtin_va_arg(ap, struct S14);
double va = __builtin_va_arg(ap, long double);
printf("%f\n", va);
if (va != 2.0L)
printf("Fail\n");
__builtin_va_end(ap);
}
int main() {
memset (&s14, '\0', sizeof(s14));
check14va(2, s14, 2.0L);
return 0;
}
```
clang output:
```
0.000000
Fail
```
gcc output:
```
2.000000
```
https://godbolt.org/z/6ErKWPq15
llvm IR
```
define dso_local noundef i32 @main() {
entry:
%retval = alloca i32, align 4
%agg.tmp = alloca %struct.S14, align 1
store i32 0, ptr %retval, align 4
call void @llvm.memset.p0.i64(ptr align 1 @s14, i8 0, i64 1, i1 false)
call void @llvm.memcpy.p0.p0.i64(ptr align 1 %agg.tmp, ptr align 1 @s14, i64 1, i1 false)
call void (i32, ...) @check14va(int, ...)(i32 noundef 2, x86_fp80 noundef 0xK40008000000000000000)
ret i32 0
}
```
I find that clang ignore the empty structure argument `s14`. As a result, the subsequent running result does not meet the expectation.
https://github.com/llvm/llvm-project/blob/597086c60959dd5b3c032552e8b42dd1d053f233/clang/lib/CodeGen/Targets/X86.cpp#L2698-L2701
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