[llvm-dev] Static assert fails when compiler for i386

[kamlesh kumar via llvm-dev]

Thank you, Rui for clarification.

On Thu, Oct 17, 2019 at 10:25 AM Rui Ueyama <ruiu at google.com> wrote:

> max_align_t is a type whose alignment requirement is as large as any
> *scalar* type, but your int4 is not a scalar type but a union containing
> a vector _int4, so it looks like your assertion is simply incorrect.
>
> On Thu, Oct 17, 2019 at 12:58 PM kamlesh kumar via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi Devs,
>> Consider below testcase.
>> $cat test.cpp
>> #include <vector>
>> #include<type_traits>
>> typedef int _int4 __attribute__((vector_size(16)));
>> typedef union{
>> int data[4];
>> struct {int x, y, z, w;};
>> _int4 vec;
>> } int4;
>> typedef int4 int3;
>> int main()
>> {
>> static_assert(std::alignment_of<int4>::value <= alignof(max_align_t), "over
>> aligned!");
>> }
>>
>> $clang++ -m32
>> error: static_assert failed due to requirement
>> 'std::alignment_of<int4>::value <= alignof(max_align_t)' "over aligned
>> it goes smooth when compile for x86_64.
>> Following changes fixes this.
>>
>> diff --git a/clang/lib/Headers/__stddef_max_align_t.h
>> b/clang/lib/Headers/__stddef_max_align_t.h
>> index e3b439285d0..46f705a09c3 100644
>> --- a/clang/lib/Headers/__stddef_max_align_t.h
>> +++ b/clang/lib/Headers/__stddef_max_align_t.h
>> @@ -21,6 +21,10 @@ typedef struct {
>>        __attribute__((__aligned__(__alignof__(long long))));
>>    long double __clang_max_align_nonce2
>>        __attribute__((__aligned__(__alignof__(long double))));
>> +  #ifdef __i386__
>> +  typedef double xx __attribute__((vector_size(16)));
>> +  xx __clang_max_align_nonce3
>>  __attribute__((__aligned__(__alignof__(xx))));
>> +  #endif
>>  } max_align_t;
>>  #endif
>>
>> Like to know community thought on this?
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>>
>
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