[LLVMdev] PTX builtin functions.
Justin Holewinski
justin.holewinski at gmail.com
Thu Dec 8 10:42:48 PST 2011
On Thu, Dec 8, 2011 at 11:36 AM, Villmow, Micah <Micah.Villmow at amd.com>wrote:
> It is my understanding that all you need to do is specify let isTarget =
> 1 in your .td file and it will generate target specific intrinsics. This
> should allow you to keep the IntrinsicsPTX.td file in the same location.
>
So we keep the intrinsics defined in include/llvm/IntrinsicsPTX.td? How do
we then get at the generated files in the PTXIntrinsicInfo class in the
back-end?
What exactly does isTarget do? It seems to remove a lot of the intrinsic
information in the Intrinsics.gen file, but I can't find any documentation
on it.
> ****
>
> ** **
>
> Micah****
>
> ** **
>
> *From:* Justin Holewinski [mailto:justin.holewinski at gmail.com]
> *Sent:* Monday, December 05, 2011 6:13 AM
> *To:* Alberto Magni
> *Cc:* Villmow, Micah; LLVM Developers Mailing List
>
> *Subject:* Re: [LLVMdev] PTX builtin functions.****
>
> ** **
>
> On Sun, Dec 4, 2011 at 1:10 PM, Alberto Magni <alberto.magni86 at gmail.com>
> wrote:****
>
> Hi Justin,
>
> sorry for the delay, I have been busy.
>
> Micah's proposal requires to move the definitions of the intrinsics
> from include/llvm/IntrinsicsPTX.td to lib/Target/PTX/PTXIntrinsics.td
> thus allowing the generation of the file PTXGenIntrinsics.inc which
> will be included by PTXIntrinsicInfo.cpp.
> This is a quite big modification, do you agree with this ?
> Or do you have a better solution.****
>
> ** **
>
> I'm opposed to this, mainly because we need the intrinsic definitions to
> be defined during LLVM IR optimization and not just at code-gen time. This
> is particularly important for pure intrinsics, like llvm.ptx.read.tid.x(),
> where the optimizers can fold multiple calls to these functions into a
> single call. Without the intrinsic definitions in
> include/llvm/IntrinsicsPTX.td, this optimization would be illegal.****
>
> ** **
>
> At the moment, I'm not seeing a clean solution to this. Overloading the
> intrinsics by writing custom code in PTXIntrinsicInfo.h/.cpp is only a
> partial solution, with the problems mentioned above. In my mind, the
> cleanest solution would be to just write out explicit intrinsics for each
> possible type. We can still use multiclasses to an extent:****
>
> ** **
>
> multiclass PTXBinaryIntrinsic<string prefix> {****
>
> def _u16 : Intrinsic<[llvm_i16_ty], [llvm_i16_ty, llvm_i16_ty],
> [InstrNoMem]>,****
>
> GCCBuiltin<!strconcat(prefix, "_u16")>;****
>
> // Repeat for s16, u32, s32, u64, s64, f32, f64****
>
> }****
>
> ** **
>
> defm int_ptx_mad<"__builtin_ptx_mad">;****
>
> ** **
>
> It's not the cleanest, but it gets the job done (unless I'm missing
> something).****
>
> ****
>
>
> Also I don't know yet how to make llvm recognize the intrinsics
> defined in lib/Target/PTX/PTXIntrinsics.td, the only other
> backend that does so is MBlaze.
>
> A tentative patch is attached.
>
> Bye,
> Alberto
>
> On Wed, Nov 23, 2011 at 2:36 PM, Justin Holewinski****
>
> <justin.holewinski at gmail.com> wrote:
> >
> > On Nov 23, 2011 8:33 AM, "Justin Holewinski" <
> justin.holewinski at gmail.com>
> > wrote:
> >>
> >>
> >> On Nov 23, 2011 6:57 AM, "Alberto Magni" <alberto.magni86 at gmail.com>
> >> wrote:
> >> >
> >> > On Tue, Nov 22, 2011 at 5:01 PM, Villmow, Micah <
> Micah.Villmow at amd.com>
> >> > wrote:
> >> > > Alberto,
> >> > > The AMDIL backend solves your problem with intrinsic overloading
> this
> >> > > way:
> >> > > def int_AMDIL_mad : GCCBuiltin<"__amdil_mad">, TernaryIntFloat;
> >> > >
> >> > > Where TernaryIntFloat is defined as:
> >> > > class TernaryIntFloat :
> >> > > Intrinsic<[llvm_anyfloat_ty], [LLVMMatchType<0>,
> >> > > LLVMMatchType<0>, LLVMMatchType<0>], []>;
> >> > >
> >> > > This allows us to write a multi-def for int_AMDIL_mad like so:
> >> > > defm MAD : TernaryIntrinsicFloat<IL_OP_MAD, int_AMDIL_mad>;
> >> > >
> >> > > Where TernaryIntrinsicFloat is defined as:
> >> > > multiclass TernaryIntrinsicFloat<ILOpCode opcode, Intrinsic intr>
> >> > > {
> >> > > def _f32 : ThreeInOneOut<opcode, (outs GPRF32:$dst),
> >> > > (ins GPRF32:$src, GPRF32:$src2, GPRF32:$src3),
> >> > > !strconcat(opcode.Text, " $dst, $src, $src2, $src3"),
> >> > > [(set GPRF32:$dst,
> >> > > (intr GPRF32:$src, GPRF32:$src2, GPRF32:$src3))]>;
> >> > > def _v2f32 : ThreeInOneOut<opcode, (outs GPRV2F32:$dst),
> >> > > (ins GPRV2F32:$src, GPRV2F32:$src2, GPRV2F32:$src3),
> >> > > !strconcat(opcode.Text, " $dst, $src, $src2, $src3"),
> >> > > [(set GPRV2F32:$dst,
> >> > > (intr GPRV2F32:$src, GPRV2F32:$src2, GPRV2F32:$src3))]>;
> >> > > ...
> >> > > }
> >> > >
> >> > > Now, this doesn't completely work, because LLVM does not allow
> >> > > overloading of intrinsics values, so there needs to be a little
> coding in
> >> > > *IntrinsicInfo class.
> >> > > AMD always encodes builtin names as __amdil_mad_f32,
> >> > > __amdil_mad_v2f32, __amdil_mad_v4f32, etc....
> >> > > So in the function "*IntrinsicInfo::lookup_name", when attempting to
> >> > > find out what intrinsic the function maps to, the AMDIL backend
> strips off
> >> > > the type, and then looks up for just '__amdil_mad'.
> >> > >
> >> > > This is how you can do intrinsic overloading in LLVM.
> >> > >
> >> > > Hope this helps,
> >> > > Micah
> >> >
> >> > Thank you Micah, it really does.
> >> >
> >> > At the moment the PTX backend does not have a PTXIntrinsicInfo class,
> >> > the only backend which does so is MBlaze.
> >> > If Justin agrees with the approach I will look on how to generate the
> >> > PTXGenIntrinsics.inc file (I am still learning TableGen)
> >> > required by PTXIntrinsicInfo and write the lookUp method.
> >>
> >> Looks good to me. For OpenCL support in clang, we definitely need the
> >> built-in function support. And the total number of intrinsics like this
> >> should be relatively minimal.
> >
> > One thing I forgot to mention: once these are implemented, it may be
> worth
> > implementing some instruction selection patterns to collapse icmp/fcmp
> and
> > select pairs into Max/min whenever it makes sense.
> >
> >>
> >> >
> >> > Cheers,
> >> >
> >> > Alberto
> >> >
> >> > >
> >> > >> -----Original Message-----
> >> > >> From: llvmdev-bounces at cs.uiuc.edu
> >> > >> [mailto:llvmdev-bounces at cs.uiuc.edu]
> >> > >> On Behalf Of Alberto Magni
> >> > >> Sent: Tuesday, November 22, 2011 8:41 AM
> >> > >> To: Justin Holewinski
> >> > >> Cc: LLVM Developers Mailing List
> >> > >> Subject: Re: [LLVMdev] PTX builtin functions.
> >> > >>
> >> > >> On Mon, Nov 21, 2011 at 5:31 PM, Justin Holewinski
> >> > >> <justin.holewinski at gmail.com> wrote:
> >> > >> > On Mon, Nov 21, 2011 at 11:45 AM, Alberto Magni
> >> > >> <alberto.magni86 at gmail.com>
> >> > >> > wrote:
> >> > >> >>
> >> > >> >> On Mon, Nov 21, 2011 at 3:36 PM, Justin Holewinski
> >> > >> >> <justin.holewinski at gmail.com> wrote:
> >> > >> >> > On Mon, Nov 21, 2011 at 7:01 AM, Alberto Magni
> >> > >> >> > <alberto.magni86 at gmail.com>
> >> > >> >> > wrote:
> >> > >> >> >>
> >> > >> >> >> Hi Justin,
> >> > >> >> >>
> >> > >> >> >> attached you find the patch for the integer max instruction.
> >> > >> >> >> The multiclass PTX_INTRINSIC_INT3 in file
> >> > >> PTXIntrinsicInstrInfo.td
> >> > >> >> >> is almost an exact copy of PTX_INT3 in PTXInstrInfo.td,
> maybe
> >> > >> >> >> a modification of this class can be defined in a separate
> file.
> >> > >> >> >
> >> > >> >> >
> >> > >> >> > I'm copying llvmdev. We should keep discussions like this on
> >> > >> >> > the
> >> > >> list
> >> > >> >> > for
> >> > >> >> > the benefit of others.
> >> > >> >>
> >> > >> >> I always forget "Reply to All".
> >> > >> >>
> >> > >> >> > We can probably factor out a generic description, or even just
> >> > >> >> > use
> >> > >> the
> >> > >> >> > PTX_INT3 multiclass directly. The PTXIntrinsicInstrInfo.td
> file
> >> > >> is
> >> > >> >> > included
> >> > >> >> > by PTXInstrInfo.td, so anything defined in PTXInstrInfo.td is
> >> > >> available
> >> > >> >> > in
> >> > >> >> > PTXIntrinsicInstrInfo.td.
> >> > >> >>
> >> > >> >> I agree with you but my class PTX_INTRINSIC_INT3 works with an
> >> > >> Intrinsic
> >> > >> >> and not with a SDNode, like PTX_INT3.
> >> > >> >> PTX_INTRINSIC_INT3 also requires the presence of the type of
> >> > >> >> the immediate in the pattern, e.g. (i32 imm:$b).
> >> > >> >
> >> > >> >
> >> > >> > Alright, I'm fine with that.
> >> > >> >
> >> > >> >>
> >> > >> >>
> >> > >> >> >>
> >> > >> >> >>
> >> > >> >> >> Do you agree with this approach ?
> >> > >> >> >> Also, do you think that a class like
> PTX_INTRINSIC_INT3_SIGNED
> >> > >> >> >> (a clone of PTX_INT3_SIGNED) is required ?
> >> > >> >> >
> >> > >> >> >
> >> > >> >> > Yes, I believe we should split these into signed and unsigned
> >> > >> variants.
> >> > >> >> > The
> >> > >> >> > results of max/min operations can definitely be different
> >> > >> depending on
> >> > >> >> > whether the operands are signed or unsigned. Since this
> >> > >> information is
> >> > >> >> > not
> >> > >> >> > encoded in LLVM types, we may want to create two versions for
> >> > >> >> > each
> >> > >> >> > integer
> >> > >> >> > type; something like:
> >> > >> >> >
> >> > >> >> > i32 @llvm.ptx.max.signed.i32(i32, i32)
> >> > >> >> > i32 @llvm.ptx.max.unsigned.i32(i32, i32)
> >> > >> >>
> >> > >> >> Yes, this the only way.
> >> > >> >
> >> > >> >
> >> > >> > A couple more comments:
> >> > >> >
> >> > >> > Please make sure to set TargetPrefix="ptx" for the intrinsics
> >> > >> (probably best
> >> > >> > in the multiclass, see PTXReadSpecialRegisterIntrinsic_r32)]
> >> > >>
> >> > >> Ok
> >> > >>
> >> > >> > I'm not sure how to define a GCCBuiltin for an intrinsic that can
> >> > >> take
> >> > >> > multiple types, but it's probably worth looking into so we can
> >> > >> > expose
> >> > >> this
> >> > >> > intrinsic to Clang.
> >> > >>
> >> > >> This could be an issue. I looked for something similar in other
> >> > >> backends
> >> > >> and I found no previous examples. It may be worth to ask on the ML
> >> > >> explicitly for this.
> >> > >> The only fallback that I see is to define explicitly every
> intrinsic
> >> > >> for every data type,
> >> > >> but this would prevent the usage of the multiclass for the
> definition
> >> > >> of the patterns.
> >> > >>
> >> > >>
> >> > >> Bye.
> >> > >>
> >> > >> >
> >> > >> >
> >> > >> >>
> >> > >> >>
> >> > >> >> >
> >> > >> >> > Otherwise, the patch looks good.
> >> > >> >> >
> >> > >> >> >>
> >> > >> >> >>
> >> > >> >> >> Thanks,
> >> > >> >> >>
> >> > >> >> >> Alberto
> >> > >> >> >>
> >> > >> >> >> On Wed, Nov 16, 2011 at 5:44 PM, Alberto Magni
> >> > >> >> >> <alberto.magni86 at gmail.com> wrote:
> >> > >> >> >> > On Wed, Nov 16, 2011 at 2:17 PM, Justin Holewinski
> >> > >> >> >> > <justin.holewinski at gmail.com> wrote:
> >> > >> >> >> >> On Wed, Nov 16, 2011 at 9:16 AM, Justin Holewinski
> >> > >> >> >> >> <justin.holewinski at gmail.com> wrote:
> >> > >> >> >> >>>
> >> > >> >> >> >>> On Wed, Nov 16, 2011 at 8:05 AM, Alberto Magni
> >> > >> >> >> >>> <alberto.magni86 at gmail.com>
> >> > >> >> >> >>> wrote:
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> Dear Justin,
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> I am trying to add the support for some OpenCL builtin
> >> > >> functions
> >> > >> >> >> >>>> to
> >> > >> >> >> >>>> the PTX backend.
> >> > >> >> >> >>>> The attached file represent the first stub of a patch
> for
> >> > >> the fmax
> >> > >> >> >> >>>> builtin function.
> >> > >> >> >> >>>
> >> > >> >> >> >>> First off, thanks for helping to improve the PTX
> back-end!
> >> > >> >> >> >>> There are really two main issues here. First, OpenCL
> >> > >> >> >> >>> built-
> >> > >> in
> >> > >> >> >> >>> functions
> >> > >> >> >> >>> do not belong in the PTX back-end. These will be
> >> > >> >> >> >>> implemented
> >> > >> in
> >> > >> >> >> >>> the
> >> > >> >> >> >>> libclc
> >> > >> >> >> >>> library (http://www.pcc.me.uk/~peter/libclc). The
> back-end
> >> > >> will
> >> > >> >> >> >>> only
> >> > >> >> >> >>> implement PTX intrinsics, which may be used by the OpenCL
> >> > >> built-in
> >> > >> >> >> >>> functions
> >> > >> >> >> >>> in libclc. However, this particular function (max)
> >> > >> corresponds to
> >> > >> >> >> >>> a
> >> > >> >> >> >>> PTX
> >> > >> >> >> >>> instruction, so it makes sense to implement it as an
> >> > >> intrinsic in
> >> > >> >> >> >>> the
> >> > >> >> >> >>> back-end.
> >> > >> >> >> >>> Second, intrinsic functions require a bit more work.
> >> > >> >> >> >>> You're
> >> > >> off to
> >> > >> >> >> >>> a
> >> > >> >> >> >>> great start, but intrinsics are implemented a bit
> >> > >> differently. It
> >> > >> >> >> >>> looks
> >> > >> >> >> >>> like LLVM does not have a max intrinsic, so we'll need to
> >> > >> create
> >> > >> >> >> >>> one.
> >> > >> >> >> >>> Have
> >> > >> >> >> >>> a look at include/llvm/IntrinsicsPTX.td. This file
> defines
> >> > >> the
> >> > >> >> >> >>> PTX-specific
> >> > >> >> >> >>> intrinsics. You can add an intrinsic for max here, and
> >> > >> >> >> >>> then
> >> > >> >> >> >>> implement
> >> > >> >> >> >>> a
> >> > >> >> >> >>> pattern-match in the PTXInstrInfo.td file. There is no
> >> > >> >> >> >>> need
> >> > >> to
> >> > >> >> >> >>> create
> >> > >> >> >> >>> a new
> >> > >> >> >> >>> SDNode type for intrinsics, unless they require some
> >> > >> >> >> >>> special
> >> > >> >> >> >>> handling
> >> > >> >> >> >>> in the
> >> > >> >> >> >>> C++ code, which I do not see being the case here.
> >> > >> >> >> >>
> >> > >> >> >> >> Sorry, there's a typo here. The intrinsic pattern
> matching
> >> > >> goes in
> >> > >> >> >> >> PTXInstrinsicInstrInfo.td.
> >> > >> >> >> >>
> >> > >> >> >> >
> >> > >> >> >> > Thank you for the pointers I will let you know when I have
> >> > >> >> >> > the
> >> > >> first
> >> > >> >> >> > patch.
> >> > >> >> >> >
> >> > >> >> >> >>>
> >> > >> >> >> >>> When you define a new intrinsic, use the following
> template
> >> > >> as a
> >> > >> >> >> >>> name:
> >> > >> >> >> >>> int_ptx_max. This will define the LLVM intrinsic as
> >> > >> >> >> >>> @llvm.ptx.max().
> >> > >> >> >> >>> Please follow the same convention when naming the
> >> > >> __builtin_*
> >> > >> >> >> >>> function.
> >> > >> >> >> >>>
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> The test case I am trying is the following:
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> define ptx_device float @f(float %x, float %y) {
> >> > >> >> >> >>>> entry:
> >> > >> >> >> >>>> %z = call float @fmax(float %x, float %y)
> >> > >> >> >> >>>> ret float %z
> >> > >> >> >> >>>> }
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> declare float @fmax(float, float)
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> But at the moment llc crashes saying that "calls are not
> >> > >> >> >> >>>> supported",
> >> > >> >> >> >>>> this does not
> >> > >> >> >> >>>> happens with llvm builtins like llvm.sqrt.f32
> >> > >> >> >> >>>
> >> > >> >> >> >>> Which version of LLVM are you using? Calls to PTX device
> >> > >> functions
> >> > >> >> >> >>> have
> >> > >> >> >> >>> been implemented for a little while now, so I'm surprised
> >> > >> >> >> >>> to
> >> > >> see
> >> > >> >> >> >>> that
> >> > >> >> >> >>> error.
> >> > >> >> >> >>> Perhaps it's because the fmax function is not defined as
> >> > >> >> >> >>> ptx_device.
> >> > >> >> >> >>>
> >> > >> >> >> >
> >> > >> >> >> > This is the testcase that I am using to verify I the max
> >> > >> builtin
> >> > >> >> >> > function I am impementing
> >> > >> >> >> > is actually recognised. I took inspiration from the llvm-
> >> > >> intrinsic.ll
> >> > >> >> >> > test case.
> >> > >> >> >> > The command I am using to compile is:
> >> > >> >> >> >
> >> > >> >> >> > llc -march=ptx32 -mattr=+ptx22 fmax.ll
> >> > >> >> >> >
> >> > >> >> >> > The option -mattr does not seem to have any effect.
> >> > >> >> >> > I tried also with the ptx_device qualifier with the same
> >> > >> outcome.
> >> > >> >> >> > I am using llvm from the svn repository.
> >> > >> >> >> >
> >> > >> >> >> > Bye,
> >> > >> >> >> >
> >> > >> >> >> > Alberto
> >> > >> >> >> >
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> Can you please give me a hint on what I am missing, or
> >> > >> >> >> >>>> some
> >> > >> >> >> >>>> general
> >> > >> >> >> >>>> advice on how
> >> > >> >> >> >>>> to add builtin functions.
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> Thank you in advance,
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> Alberto.
> >> > >> >> >> >>>>
> >> > >> >> >> >>>> _______________________________________________
> >> > >> >> >> >>>> LLVM Developers mailing list
> >> > >> >> >> >>>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> >> > >> >> >> >>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >> > >> >> >> >>>>
> >> > >> >> >> >>>
> >> > >> >> >> >>>
> >> > >> >> >> >>>
> >> > >> >> >> >>> --
> >> > >> >> >> >>>
> >> > >> >> >> >>> Thanks,
> >> > >> >> >> >>> Justin Holewinski
> >> > >> >> >> >>
> >> > >> >> >> >>
> >> > >> >> >> >>
> >> > >> >> >> >> --
> >> > >> >> >> >>
> >> > >> >> >> >> Thanks,
> >> > >> >> >> >> Justin Holewinski
> >> > >> >> >> >>
> >> > >> >> >
> >> > >> >> >
> >> > >> >> >
> >> > >> >> >
> >> > >> >> > --
> >> > >> >> >
> >> > >> >> > Thanks,
> >> > >> >> >
> >> > >> >> > Justin Holewinski
> >> > >> >> >
> >> > >> >
> >> > >> >
> >> > >> >
> >> > >> >
> >> > >> > --
> >> > >> >
> >> > >> > Thanks,
> >> > >> >
> >> > >> > Justin Holewinski
> >> > >> >
> >> > >>
> >> > >> _______________________________________________
> >> > >> LLVM Developers mailing list
> >> > >> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> >> > >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >> > >
> >> > >****
>
>
>
> ****
>
> ** **
>
> -- ****
>
> Thanks,****
>
> ** **
>
> Justin Holewinski****
>
> ** **
>
--
Thanks,
Justin Holewinski
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