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

Tue Jul 17 03:07:26 UTC 2018

Indeed xmm registers can hold richer structures than just scalar floats and
doubles.

They can do 4 32 bit floats or 32bit ints or words

or 2 64 bit doubles or 64bit ints or words.

Or scalar 32/64bit ints or words! (Distinct from the gpr registers!)

Xmm registers are the lower half of ymm/ lower quarter of zmm simd
registers (when they exist on newer x86-64 cpus )

Agreed, the maybes are definitely going to be removed before end of summer.
Though Andreas and I may try to go over things a tad closely in our code
reviews

On Fri, Jul 13, 2018 at 6:22 PM Simon Peyton Jones via ghc-devs <
ghc-devs at haskell.org> wrote:

> Typesetting is really strange here.  Hard to read.
>
>
>
> Yes, let’s get rid of those Maybes if poss.  What does Nothing  mean???
>
>
>
> Does this mean that Xmm regs really can contain multiple integers or
> multiple floats?  I did not know that.
>
>
>
> the general direction looks right.
>
>
>
> Thanks
>
>
>
> Simon
>
>
>
> *From:* Abhiroop Sarkar <asiamgenius at gmail.com>
> *Sent:* 13 July 2018 16:32
>
>
> *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?
>
>
>
> 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
> <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FAbhiroop%2Fghc-1%2Fblob%2Fwip%2Fsimd-ncg-support%2Fcompiler%2Fcmm%2FCmmExpr.hs%23L596&data=02%7C01%7Csimonpj%40microsoft.com%7Cee2fb4d91cfc45ae307808d5e8d5d097%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636670927384427518&sdata=XngOwITn9xqGS417NO16ftCgC8%2BGa1NidVraLD7KS1I%3D&reserved=0>
>
>
>
> 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
> <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%7Cee2fb4d91cfc45ae307808d5e8d5d097%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636670927384437535&sdata=50vVucmqx1KOIVJUMnqby1%2BxRkE2nv7CG5qbkDZ0g3c%3D&reserved=0>
>
> 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%7Cee2fb4d91cfc45ae307808d5e8d5d097%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636670927384447548&sdata=4zBPD6H62ynzybNQWXm3FkFuvZS3Jnvzi98sT69zvmY%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%7Cee2fb4d91cfc45ae307808d5e8d5d097%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636670927384457557&sdata=PRvCQNU2vMMBuI4RJHcXiuy2vHdf9oK5IyzLq%2BroAvA%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%7Cee2fb4d91cfc45ae307808d5e8d5d097%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636670927384457557&sdata=uPI1WMQzitwsatfNc5XvO7DpunpziVtE75R3maBVAz4%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!
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>
> --
>
> Kloona - Coming Soon!
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