Is it possible to enhance the vector STG registers(Xmm, Ymm, Zmm) with more information?

[Carter Schonwald]

hrmm, i think i can help with this tomorrow/ rest of the week, (esp since
i'm one of your mentors :) )

but if other folks have design ideas, more than happy to use as many ideas
as possible!

On Wed, Jun 27, 2018 at 5:32 PM Abhiroop Sarkar <asiamgenius at gmail.com>
wrote:

> Hello all,
>
> I am currently working on adding support for SIMD operations to the native
> code generator. One of the roadblocks I faced recently was the definition
> of the `globalRegType` function in "compiler/cmm/CmmExpr.hs". The
> `globalRegType` function maps the STG registers to the respective `CmmType`
> datatype.
>
> For Xmm, Ymm, Zmm registers the function defines globalRegType like this:
> https://github.com/ghc/ghc/blob/master/compiler/cmm/CmmExpr.hs#L585-L587
>
> Consider the case for an Xmm register, the above definition limits an Xmm
> register to hold only vectors of size 4. However we can store 2 64-bit
> Doubles or 16 Int8s or 8 Int16s and so on
>
> The function `globalRegType` is internally called by the function
> `cmmRegType` (
> https://github.com/ghc/ghc/blob/838b69032566ce6ab3918d70e8d5e098d0bcee02/compiler/cmm/CmmExpr.hs#L275)
> which is itself used in a number of places in the x86 code generator.
>
> In fact depending on the result of the `cmmRegType` function is another
> important function `cmmTypeFormat` defined in Format.hs whose result is
> used to print the actual assembly instruction.
>
> I have extended all the other Format types to include VectorFormats,
> however this definition of the `globalRegType` seems incorrect to me.
> Looking at the signature of the function itself:
>
> `globalRegType :: DynFlags -> GlobalReg -> CmmType`
>
> its actually difficult to predict the CmmType by just looking at the
> GlobalReg in case of Xmm, Ymm, Zmm. So thats why my original question how
> do I go about solving this. Should I modify the GlobalReg type to contain
> more information like Width and Length(for Xmm, Ymm, Zmm)  or do I somehow
> pass the length and width information to the globalRegType function?
>
> Thanks
> Abhiroop Sakar
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