[PATCH] D76612: [Matrix] Add draft specification for matrix support in Clang.

[Sjoerd Meijer via Phabricator via cfe-commits]

SjoerdMeijer added inline comments.


================
Comment at: clang/docs/MatrixTypes.rst:27
+internal layout, overall size and alignment are implementation-defined.
+A *matrix element type* must be a real type (as in C99 6.2.5p17) excluding
+enumeration types or an implementation-defined half-precision floating point
----------------
fhahn wrote:
> SjoerdMeijer wrote:
> > fhahn wrote:
> > > SjoerdMeijer wrote:
> > > > above you're using *element type* and here *matrix element type*. Since hopefully we're talking about the same things, "matrix *element type*" would be more consistent.
> > > > 
> > > > But this is just a nit, my main question is about the types:
> > > > why not e.g. define this to be the C11 types, that include _FloatN types, so that we can include N=16? Or is this intentionally omitted? I haven't even checked if this is supported in the architecture extension, but might make sense? And also, an element type cannot be an integer type? 
> > > > 
> > > >  
> > > > above you're using *element type* and here *matrix element type*. Since hopefully we're talking about the same things, "matrix *element type*" would be more consistent.
> > > 
> > > Yes it is referring to the same thing. I had a look at most uses, and in most cases `element type` is used to refer to the element type of a given matrix type. In that context it seems a bit verbose to use `matrix element type`, although I am more than happy to change that if it helps with clarifying things.
> > > 
> > > I intentionally used `matrix element type` in `Arithmetic Conversions`, because there it is standing on its own and refers exactly to the set of types defined as valid matrix element types here.
> > > 
> > > > why not e.g. define this to be the C11 types, that include _FloatN types, so that we can include N=16? Or is this intentionally omitted? I haven't even checked if this is supported in the architecture extension, but might make sense?
> > > 
> > > I couldn't find any reference to _FloatN types in the C11 draft version I checked. Do you by any chance have a reference to the _FloatN types?
> > > 
> > > > And also, an element type cannot be an integer type?
> > > 
> > > The current definition should include it (real types include integer and real floating point types according to  C99 6.2.5p17). I don't think there is any reason to exclude them I think.
> > >>    why not e.g. define this to be the C11 types, that include _FloatN types, so that we can include N=16? Or is this intentionally omitted? I haven't even checked if this is supported in the architecture extension, but might make sense?
> > >>
> > > I couldn't find any reference to _FloatN types in the C11 draft version I checked. Do you by any chance have a reference to the _FloatN types?
> > 
> > Sorry, I was a bit imprecise here, it's an extension of C11: ISO/IEC TS 18661-3:2015.
> > My thinking was it would be cool to support the "proper" half-precision type. I thought about this, because of "or an implementation-defined half-precision" mentioned just below here, of which probably __fp16 is an example.  If you refer to the C99 types, you probably don't even need to mention this (although it won't do any harm)?
> > 
> > >>  And also, an element type cannot be an integer type?
> > >
> > > The current definition should include it (real types include integer and real floating point types according to C99 6.2.5p17). I don't think there is any reason to exclude them I think.
> > 
> > Ok, cheers, wrote this from memory (forgot this), and didn't check the standard.
> > Sorry, I was a bit imprecise here, it's an extension of C11: ISO/IEC TS 18661-3:2015.
> > My thinking was it would be cool to support the "proper" half-precision type. I thought about this, because of "or an implementation-defined half-precision" mentioned just below here, of which probably __fp16 is an example. If you refer to the C99 types, you probably don't even need to mention this (although it won't do any harm)?
> 
> I am not sure what the exact wording should be, but the intention is to include both __fp16 and _Float16. I was hoping that would be covered as is, but I would be happy to clarify (unfortunately it is not entirely clear to me how to best word this)
Ah, okay, I got it. How about a simple enumeration, e.g.:  

  A *matrix element type* must be a C99 real type, excluding enumeration types, the C11 ISO/IEC TS 18661 _Float16 type, the ARM ACLE __fp16 type, or an implementation-defined half-precision floating point type, otherwise the program is ill-formed.


================
Comment at: clang/docs/MatrixTypes.rst:29
+A *matrix element type* must be a real type (as in C99 6.2.5p17) excluding
+enumeration types or an implementation-defined half-precision floating point
+type, otherwise the program is ill-formed.
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Now I am wondering if this requires some explanations on binary operations for these implemenation-defined types? For example, for `__fp16` and matrices with this `__fp16` element type, I assume arithmetic is performed in at least the (single) floating-point precision. So I guess in section "Arithmetic Conversions" a rule needs to be added that the conversion of these implementation defined types need to performed?



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