https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127193
Sam Gardner <samuelgardner101 at gmail dot com> changed:
What |Removed |Added
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CC| |samuelgardner101 at gmail dot
com
--- Comment #1 from Sam Gardner <samuelgardner101 at gmail dot com> ---
also seeing this on trunk (cloned master 03/09/2026). i think alignment
attribute applied through a typedef is not surviving BMI roundtrip.
```
attrs.h:
typedef long long vec_u __attribute__((__vector_size__(16), __may_alias__,
__aligned__(1)));
typedef long long vec_a __attribute__((__vector_size__(16)));
typedef int int_under __attribute__((__aligned__(1)));
typedef int int_over __attribute__((__aligned__(32)));
struct __attribute__((__aligned__(64))) AttrBig { char c; };
struct alignas(64) AlignasBig { char c; };
struct __attribute__((__packed__)) Packed { char c; int i; };
t.ixx:
module;
#include "attrs.h"
export module t;
export using ::vec_u;
export using ::vec_a;
export using ::int_under;
export using ::int_over;
export using ::AttrBig;
export using ::AlignasBig;
export using ::Packed;
t_use.cpp:
import t;
#define SHOW(T, want) static_assert(alignof(T) == want, "alignof(" #T ") !=
" #want);
SHOW(vec_u, 1)
SHOW(vec_a, 16)
SHOW(int_under, 1)
SHOW(int_over, 32)
SHOW(AttrBig, 64)
SHOW(AlignasBig, 64)
static_assert(sizeof(Packed) == 5, "sizeof(Packed) != 5");
int main() {}
$ g++ -std=c++20 -fmodules-ts -c t.ixx -o t.o
$ g++ -std=c++20 -fmodules-ts -fsyntax-only t_use.cpp
t_use.cpp:2:48: error: static assertion failed: alignof(vec_u) != 1
* the comparison reduces to '(16 == 1)'
t_use.cpp:2:48: error: static assertion failed: alignof(int_under) != 1
* the comparison reduces to '(4 == 1)'
t_use.cpp:2:48: error: static assertion failed: alignof(int_over) != 32
* the comparison reduces to '(4 == 32)'
```
but replacing `import t;` with `#include "attrs.h"` makes all seven pass
then the intrinsic stuff is downstream of it because theyre all defined with
alignments of 1 like
```
typedef long long __m128i_u __attribute__ ((__vector_size__ (16),
__may_alias__, __aligned__ (1)));
typedef double __m128d_u __attribute__ ((__vector_size__ (16), __may_alias__,
__aligned__ (1)));
typedef double __x86_double_u __attribute__ ((__may_alias__, __aligned__ (1)));
```
with results of
```
intrinsic direct via import
----------------- ------ ----------
_mm_loadu_si128 movdqu movdqu (survives)
_mm_storeu_si128 movups movaps
_mm_loadu_pd movupd movapd
_mm_storeu_pd movups movaps
_mm_loadu_ps movups movaps
_mm_storeu_ps movups movaps
```
because they cast like `return *(__m128d_u *)__P;` in their body or deference
that type when assigning into it etc.
