From: Tejas Joshi <tejasjoshi9673@gmail.com>
To: gcc@gcc.gnu.org
Cc: Martin Jambor <mjambor@suse.cz>,
hubicka@ucw.cz, segher@kernel.crashing.org,
joseph@codesourcery.com
Subject: Re: Expansion of narrowing math built-ins into power instructions
Date: Sun, 25 Aug 2019 13:55:00 -0000 [thread overview]
Message-ID: <CACMrGjCeaPFVHh-chy+aFBHxYJOO0Q_fhkAZ52yUPFL4zLaSBQ@mail.gmail.com> (raw)
In-Reply-To: <mptimqmvqit.fsf@arm.com>
Hello.
>
> Similarly addtfsf3 that multiplies TFmode and produces an SFmode result, and so on.
I want to extend this patch for FADDL and DADDL. What operand
constraints should I use for TFmode alongside "f"?
> In cases where long double and double have the same mode,
>the daddl function should use the existing adddf3 pattern.
So, should I use adddf3 for DADDL directly? How would I map the
add<mode>3 optab with DADDL?
Thanks,
Tejas
On Sat, 24 Aug 2019 at 15:23, Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> Martin Jambor <mjambor@suse.cz> writes:
> > Hello,
> >
> > On Thu, Aug 22 2019, Segher Boessenkool wrote:
> >>> > Hi Tejas,
> >>> >
> >>> > [ Please do not top-post. ]
> >>
> >> On Thu, Aug 22, 2019 at 01:27:06PM +0530, Tejas Joshi wrote:
> >>> > What happens then? "It does not work" is very very vague. At least it
> >>> > seems the compiler does build now?
> >>>
> >>> Oh, compiler builds but instruction is still "bl fadd". It should be
> >>> "fadds" right?
> >>
> >> Yes, but that means the problem is earlier, before it hits RTL perhaps.
> >>
> >> Compile with -dap, look at the expand dump (the lowest numbered one, 234
> >> or so), and see what it looked like in the final Gimple, and then in the
> >> RTL generated from that. And then drill down.
> >>
> >
> > Tejas sent me his patch and I looked at why it did not work. I found
> > two reasons:
> >
> > 1. associated_internal_fn (in builtins.c) does not handle
> > DEF_INTERNAL_OPTAB_FN kind of internal functions, and Tejas
> > (sensibly, I'd say) used that macro to define the internal function.
> > But when I worked around that by manually adding a case for it in the
> > switch statement, I ran into an assert because...
> >
> > 2. direct_internal_fn_supported_p on which replacement_internal_fn
> > depends to expand built-ins as internal functions cannot handle
> > conversion optabs... and narrowing is a kind of conversion and the
> > optab is added as such with OPTAB_CD.
> >
> > Actually, the second statement is not entirely true because somehow it
> > can handle optab while_ult which is a conversion optab but a) the way it
> > is handled, if I can understand it at all, seems to be a big hack and
> > would be even worse if we decided to copy that for all narrowing math
> > functions
>
> Think "big hack" is a bit unfair. The way that the internal function
> maps argument types to the optab modes, and the way it expands calls
> into rtl, depends on the "optab type" argument (the final argument to
> DEF_INTERNAL_OPTAB_FN). This is relatively flexible in that it can use
> a single-mode "direct" optab or a dual-mode "conversion" optab, with the
> modes coming from whichever arguments are appropriate. New optab types
> can be added as needed.
>
> FWIW, several other DEF_INTERNAL_OPTAB_FNs are conversion optabs too
> (e.g. IFN_LOAD_LANES, IFN_STORE_LANES, IFN_MASK_LOAD, etc.).
>
> But...
>
> > and b) it gets both modes from argument types whereas we need one from
> > the result type and so we would have to rewrite
> > replacement_internal_fn anyway.
>
> ...yeah, I agree this breaks the current model. The reason IFN_WHILE_ULT
> doesn't rely on the return type is that if you have:
>
> _2 = .WHILE_ULT (_0, _1) // returning a vector of 4 booleans
> _3 = .WHILE_ULT (_0, _1) // returning a vector of 8 booleans
>
> then the calls look equivalent. So instead we pass an extra argument
> indicating the required boolean vector "shape".
>
> The same "problem" could in principle apply to FADD if we ever needed
> to support double+double->_Float16 for example.
>
> > Therefore, at least for now (GSoC deadline is kind of looming), I
> > decided that the best way forward would be to not rely on internal
> > functions but plug into expand_builtin() and I wrote the following,
> > lightly tested patch - which of course misses testcases and stuff - but
> > I'd be curious about any feedback now anyway. When I proposed a very
> > similar approach for the roundeven x86_64 expansion, Uros actually then
> > opted for a solution based on internal functions, so I am curious
> > whether there are simple alternatives I do not see.
> >
> > Tejas, of course cases for other fadd variants should at least be added
> > to expand_builtin.
> >
> > Thanks,
> >
> > Martin
> >
> >
> > 2019-08-23 Tejas Joshi <tejasjoshi9673@gmail.com>
> > Martin Jambor <mjambor@suse.cz>
> >
> > * builtins.c (expand_builtin_binary_conversion): New function.
> > (expand_builtin): Call it.
> > * config/rs6000/rs6000.md (unspec): Add UNSPEC_ADD_NARROWING.
> > (add_truncdfsf3): New define_insn.
> > * optabs.def (fadd_optab): New.
> >
> > [...]
> > diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
> > index 9461693bcd1..3f56880c23f 100644
> > --- a/gcc/internal-fn.def
> > +++ b/gcc/internal-fn.def
> > @@ -140,6 +140,8 @@ DEF_INTERNAL_OPTAB_FN (WHILE_ULT, ECF_CONST | ECF_NOTHROW, while_ult, while)
> > DEF_INTERNAL_OPTAB_FN (VEC_SHL_INSERT, ECF_CONST | ECF_NOTHROW,
> > vec_shl_insert, binary)
> >
> > +DEF_INTERNAL_OPTAB_FN (FADD, ECF_CONST, fadd, binary)
> > +
> > DEF_INTERNAL_OPTAB_FN (FMS, ECF_CONST, fms, ternary)
> > DEF_INTERNAL_OPTAB_FN (FNMA, ECF_CONST, fnma, ternary)
> > DEF_INTERNAL_OPTAB_FN (FNMS, ECF_CONST, fnms, ternary)
>
> Should be dropped now.
>
> OK with that change and the ones Segher asked for.
>
> Thanks,
> Richard
next prev parent reply other threads:[~2019-08-25 13:55 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 17:37 Martin Jambor
2019-07-29 18:40 ` Segher Boessenkool
2019-07-30 19:47 ` Joseph Myers
2019-07-30 9:20 ` Florian Weimer
2019-07-30 19:49 ` Joseph Myers
2019-07-31 6:47 ` Tejas Joshi
2019-07-31 14:47 ` Segher Boessenkool
2019-08-08 18:39 ` Tejas Joshi
2019-08-08 20:05 ` Segher Boessenkool
2019-08-08 23:09 ` Joseph Myers
2019-08-10 10:24 ` Tejas Joshi
2019-08-10 16:46 ` Segher Boessenkool
2019-08-11 4:58 ` Tejas Joshi
2019-08-11 7:20 ` Segher Boessenkool
2019-08-11 12:46 ` Tejas Joshi
2019-08-11 16:59 ` Segher Boessenkool
2019-08-12 17:25 ` Tejas Joshi
2019-08-12 17:55 ` Segher Boessenkool
2019-08-12 21:20 ` Joseph Myers
2019-08-12 21:52 ` Segher Boessenkool
2019-08-14 6:15 ` Tejas Joshi
2019-08-14 7:21 ` Segher Boessenkool
2019-08-14 16:11 ` Joseph Myers
2019-08-14 20:21 ` Segher Boessenkool
2019-08-14 20:23 ` Joseph Myers
2019-08-14 21:00 ` Segher Boessenkool
2019-08-15 9:52 ` Tejas Joshi
2019-08-15 12:47 ` Richard Sandiford
2019-08-15 13:55 ` Tejas Joshi
2019-08-15 18:45 ` Segher Boessenkool
2019-08-16 10:23 ` Richard Sandiford
2019-08-17 5:40 ` Tejas Joshi
2019-08-17 8:21 ` Richard Sandiford
2019-08-19 10:46 ` Tejas Joshi
2019-08-19 13:07 ` Segher Boessenkool
2019-08-20 7:41 ` Richard Sandiford
2019-08-20 12:11 ` Segher Boessenkool
2019-08-20 12:59 ` Richard Sandiford
2019-08-20 13:46 ` Segher Boessenkool
2019-08-20 14:43 ` Richard Sandiford
2019-08-20 15:12 ` Richard Sandiford
2019-08-20 19:42 ` Segher Boessenkool
2019-08-21 17:20 ` Tejas Joshi
2019-08-21 18:28 ` Segher Boessenkool
2019-08-21 19:17 ` Segher Boessenkool
2019-08-22 3:33 ` Tejas Joshi
2019-08-22 6:25 ` Segher Boessenkool
2019-08-22 7:57 ` Tejas Joshi
2019-08-22 9:56 ` Segher Boessenkool
2019-08-23 17:17 ` Martin Jambor
2019-08-23 19:13 ` Segher Boessenkool
2019-08-24 9:53 ` Richard Sandiford
2019-08-25 13:55 ` Tejas Joshi [this message]
2019-08-25 16:47 ` Segher Boessenkool
2019-08-26 7:07 ` Tejas Joshi
2019-08-26 7:42 ` Segher Boessenkool
2019-08-30 19:12 ` Tejas Joshi
2019-08-30 20:35 ` Segher Boessenkool
2019-09-02 3:19 ` Tejas Joshi
2019-09-02 11:30 ` Segher Boessenkool
2019-08-26 13:23 ` Martin Jambor
2019-08-20 16:04 ` Joseph Myers
2019-08-15 18:54 ` Segher Boessenkool
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