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

Abhiroop Sarkar asiamgenius at gmail.com
Fri Jul 13 15:32:03 UTC 2018


The formatting of the function[1] got spoilt in the last mail. It is
modified from:

globalRegType _ (XmmReg  _) = cmmVec 4 (cmmBits W32)


to


globalRegType _      (XmmReg _ m ty)   = let (l,w) = fromMaybe (2, W64) m
                                          in  case fromMaybe Float ty of
                                                Integer -> cmmVec l
(cmmBits w)
                                                Float   -> cmmVec l
(cmmFloat w)

Thank,
Abhiroop

[1]
https://github.com/Abhiroop/ghc-1/blob/wip/simd-ncg-support/compiler/cmm/CmmExpr.hs#L596

On Fri, Jul 13, 2018 at 4:26 PM Abhiroop Sarkar <asiamgenius at gmail.com>
wrote:

> Sorry I mistyped and forgot to include the register number in the mail but
> it is present in the patch. So it is:
>
> data GlobalReg = ...
>                           |  XmmReg  !Int
>                               (Maybe (Length, Width))
>                               (Maybe GlobalVecRegTy)
>
> The purpose of the GlobalVecRegTy field is to rewrite this function
> definition :
> https://github.com/ghc/ghc/blob/master/compiler/cmm/CmmExpr.hs#L585-L587
>
> globalRegType _ (XmmReg _) = cmmVec 4 (cmmBits W32)
>
> and rewrite it to :
>
> globalRegType _ (XmmReg _ m ty) = let (l,w) = fromMaybe (2, W64) m -- a
> random default value of 2 and W64 chosen in case fromMaybe Float ty of
> Integer -> cmmVec l (cmmBits w) Float -> cmmVec l (cmmFloat w) Thanks,
> Abhiroop
>
>
> On Fri, Jul 13, 2018 at 4:12 PM Simon Peyton Jones <simonpj at microsoft.com>
> wrote:
>
>> What is the GlobalVecRegTy field doing?
>>
>> Don’t you need an Int for the register number, like all the rest?
>>
>>
>>
>> Generally, sounds good though
>>
>>
>>
>> S
>>
>>
>>
>> *From:* Abhiroop Sarkar <asiamgenius at gmail.com>
>> *Sent:* 13 July 2018 14:07
>> *To:* Simon Peyton Jones <simonpj at microsoft.com>
>> *Cc:* ghc-devs at haskell.org
>> *Subject:* Re: Is it possible to enhance the vector STG registers(Xmm,
>> Ymm, Zmm) with more information?
>>
>>
>>
>> Hello Simon,
>>
>>
>>
>> Thanks for your response. I had written a patch[1] for this and the
>> approach I took was quite similar to what you pointed out.
>>
>>
>>
>> data GlobalReg = ...
>>                           |  XmmReg
>>
>>                               (Maybe (Length, Width))
>>
>>                               (Maybe GlobalVecRegTy)
>>
>>
>>
>> data GlobalVecRegTy = Integer | Float
>>
>>
>>
>> -- Width and Length are already defined
>>
>> data Width = W8 | W16 | W32 .....
>>
>> type Length = Int
>>
>>
>>
>>
>>
>> I wrapped the types inside a `Maybe` because when initializing a
>> GlobalReg (in the `activeStgRegs`[2] function), I was not sure what value
>> to initialize the register with, so I used a `Nothing` when initializing.
>>
>>
>>
>> I see now in the case of `VanillaReg` it is initialized with the `VGcPtr`
>> constructor: VanillaReg 1 VGcPtr etc
>>
>>
>>
>> I think I should modify my patch as well to remove the Maybe and
>> initialize with some default Length, Width and GlobalRegTy.  Thanks for the
>> help.
>>
>>
>>
>> Abhiroop
>>
>>
>>
>>
>>
>> [1] https://phabricator.haskell.org/D4922
>>
>> [2]
>> https://github.com/ghc/ghc/blob/master/includes/CodeGen.Platform.hs#L450-L623
>> <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc%2Fghc%2Fblob%2Fmaster%2Fincludes%2FCodeGen.Platform.hs%23L450&data=02%7C01%7Csimonpj%40microsoft.com%7Ccb18f3003224456cfd5b08d5e8c19b21%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636670840587296823&sdata=quBJxkG7r6a7ylFqrh4VMgP8y0P1i1Xc79Xj10kV9ts%3D&reserved=0>
>>
>>
>>
>> On Fri, Jul 13, 2018 at 10:58 AM Simon Peyton Jones <
>> simonpj at microsoft.com> wrote:
>>
>> Abhiroop
>>
>>
>>
>> Did anyone reply?
>>
>>
>>
>> My instinct is this. You want to use the same register (say Xmm reg 3) in
>> different ways.  We already have this for ‘VanillaReg’:
>>
>> data GlobalReg
>>
>>   = VanillaReg      -- pointers, unboxed ints and chars
>>
>>         Int         -- its number
>>
>>         VGcPtr
>>
>>    | …
>>
>>
>>
>> data VGcPtr = VGcPtr | VNonGcPtr
>>
>>
>>
>> We use VanillaReg for both pointers and non-pointers, so (VanillaReg 3
>> VGcPtr) is register 3 used as a pointer, and (VanillaReg 3 VNonGcPtr) is
>> register 3 used as a non-pointer.  And notice that globalRegType looks at
>> this field to decide what type to return.
>>
>>
>>
>> I think you can do exactly the same: add a field to Xmm that explains how
>> you are gong to divide it up.  Would that work?
>>
>>
>>
>> Simon
>>
>>
>>
>> *From:* ghc-devs <ghc-devs-bounces at haskell.org> *On Behalf Of *Abhiroop
>> Sarkar
>> *Sent:* 27 June 2018 22:32
>> *To:* ghc-devs at haskell.org
>> *Subject:* Is it possible to enhance the vector STG registers(Xmm, Ymm,
>> Zmm) with more information?
>>
>>
>>
>> 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
>> <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc%2Fghc%2Fblob%2Fmaster%2Fcompiler%2Fcmm%2FCmmExpr.hs%23L585-L587&data=02%7C01%7Csimonpj%40microsoft.com%7Ccb18f3003224456cfd5b08d5e8c19b21%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636670840587296823&sdata=Ct2zsaFgEsRTclglezuPAg05zlSWwuyU45KZrrzcZCc%3D&reserved=0>
>>
>>
>>
>> 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
>> <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc%2Fghc%2Fblob%2F838b69032566ce6ab3918d70e8d5e098d0bcee02%2Fcompiler%2Fcmm%2FCmmExpr.hs%23L275&data=02%7C01%7Csimonpj%40microsoft.com%7Ccb18f3003224456cfd5b08d5e8c19b21%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636670840587296823&sdata=yi3CN5tdL%2FEteEwBRH6Pt%2B3QB7Ji0sGWnnlE02eyMqk%3D&reserved=0>)
>> 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
>>
>>
>>
>>
>> --
>>
>> Kloona - Coming Soon!
>>
>
>
> --
> Kloona - Coming Soon!
>


-- 
Kloona - Coming Soon!
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