[LLVMdev] Vectors in structures

[Bob Wilson]

On Sep 21, 2010, at 5:40 PM, Alasdair Grant wrote:

>> They are defined as structures. The table in A.2 defines the exact
>> structure names. There is a requirement to mangle them as those
>> structures in A.2.1.
> 
> The mangling requirement doesn't require you to meet it in any
> particular way as long as you end up with the right strings.
> I.e. the mangling requirement places no requirements at all on
> the implementation, outside of mangled names.
> 
> The controversial statement is where A.2 requires the user types to
> map on to the __simd64 structures.  But that still isn't an argument
> for wrapping.  This sentence might be significant:
> 
> "The structures have 64-bit alignment and map directly onto the
> containerized vector fundamental data types."
> 
> So the structures map _directly_ on to the vector types - not on to
> wrappers around the vector types.

But regardless they are still structures, right?  What does it mean for them to map onto other types?  Is the parser supposed to treat them as if they _were_ those other types?  If so, I think you need to define a type system for those fundamental vector types.  I had read those statements to say something about the data types used in the generated code.

> 
>> The fields of the structure may be different in
>> this implementation, but the net effect here is that llvm-gcc and
>> clang avoid having to magically recognize NEON types and substitute
>> the proper mangling for them the way GCC does.
> 
> But mangling routines are self-contained and have to deal with this
> sort of target issue anyway, e.g. gcc for ARM deals with 16-bit
> floats as well as NEON types.  Saving 20 or so lines in a mangling
> routine makes no sense as an argument for a particular implementation
> strategy for arm_neon.h and a front end, let alone for inflating
> bitcode files with lots of wrapping around vector operations.

Agreed.  The mangling is a side issue.

> 
> Al
> 
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