[LLVMdev] PTX builtin functions.
Villmow, Micah
Micah.Villmow at amd.com
Tue Nov 22 09:01:18 PST 2011
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
> -----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
> >
>
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