On Mar 30, 2012, at 11:08 AM, Anton Korobeynikov <[email protected]>
wrote:
> Hi Bob
>
>> * Given that ABIArgInfo::Expand will only be used for unions that are
>> homogeneous, does it really make sense to put code in
>> CodeGenTypes::GetExpandedTypes and CodeGenFunction::ExpandTypeToArgs to
>> search through members of a union to find the largest field? For the
>> current usage, it should be sufficient to just grab the first one.
> No. Consider e.g.
>
> union {
> float bar[3];
> struct {
> float baz[4];
> };
> };
>
> Here we should select float[4] as proper h. aggregate.
You're right. I didn't think about that case.
>> * When I first implemented this, I intentionally limited it for C++ to
>> aggregate-like types. Can you give an example of a non-aggregate-like C++
>> type that you think should be passed as a homogeneous aggregate? Certainly
>> anything with a vtable pointer isn't going to work.
> Easily. Consider e.g.
>
> class Vector2 {
> float32x2_t vec;
> };
>
> Vector2 foo(const Vector2 &v) { return v; }
>
> Vector2 is not C++ aggregate, because it contains private fields.
> However, it's h. aggregate per ARM specs, because check for
> homogeneity should be performed w/o language-specific restrictions.
It seems that I misunderstood the meaning of the "isAggregate" method. I
didn't realize that having private fields would cause that to return false. As
long as you exclude classes with vtables, that should be fine.
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