Hi, Here is the last patch of the fmin/fmax change, which adds the optabs to the arm backend.
Tested: arm-none-eabi: no regressions Good to go? David Sherwood. ChangeLog: 2015-12-08 David Sherwood <david.sherw...@arm.com> gcc/ * config/arm/iterators.md: New iterators. * config/arm/unspecs.md: New unspecs. * config/arm/neon.md: New pattern. * config/arm/vfp.md: Likewise. gcc/testsuite * gcc.target/arm/fmaxmin.c: New test. > -----Original Message----- > From: Richard Biener [mailto:richard.guent...@gmail.com] > Sent: 25 November 2015 12:39 > To: David Sherwood > Cc: GCC Patches; Richard Sandiford > Subject: Re: [PING][Patch] Add support for IEEE-conformant versions of scalar > fmin* and fmax* > > On Mon, Nov 23, 2015 at 10:21 AM, David Sherwood <david.sherw...@arm.com> > wrote: > > Hi, > > > > This is part 1 of a reworked version of a patch I originally submitted in > > August, rebased after Richard Sandiford's recent work on the internal > > functions. This first patch adds the internal function definitions and > > optabs > > that provide support for IEEE fmax()/fmin() functions. > > > > Later patches will add the appropriate aarch64/aarch32 vector instructions. > > Ok. > > Thanks, > Richard. > > > Tested: > > > > x86_64-linux: no regressions > > aarch64-none-elf: no regressions > > arm-none-eabi: no regressions > > > > Regards, > > David Sherwood. > > > > ChangeLog: > > > > 2015-11-19 David Sherwood <david.sherw...@arm.com> > > > > gcc/ > > * optabs.def: Add new optabs fmax_optab/fmin_optab. > > * internal-fn.def: Add new fmax/fmin internal functions. > > * config/aarch64/aarch64.md: New pattern. > > * config/aarch64/aarch64-simd.md: Likewise. > > * config/aarch64/iterators.md: New unspecs, iterators. > > * config/arm/iterators.md: New iterators. > > * config/arm/unspecs.md: New unspecs. > > * config/arm/neon.md: New pattern. > > * config/arm/vfp.md: Likewise. > > * doc/md.texi: Add fmin and fmax patterns. > > gcc/testsuite > > * gcc.target/aarch64/fmaxmin.c: New test. > > * gcc.target/arm/fmaxmin.c: New test. > > > > > >> -----Original Message----- > >> From: Richard Biener [mailto:richard.guent...@gmail.com] > >> Sent: 19 August 2015 13:35 > >> To: Richard Biener; David Sherwood; GCC Patches; Richard Sandiford > >> Subject: Re: [PING][Patch] Add support for IEEE-conformant versions of > >> scalar fmin* and fmax* > >> > >> On Wed, Aug 19, 2015 at 2:11 PM, Richard Sandiford > >> <richard.sandif...@arm.com> wrote: > >> > Richard Biener <richard.guent...@gmail.com> writes: > >> >> On Wed, Aug 19, 2015 at 11:54 AM, Richard Sandiford > >> >> <richard.sandif...@arm.com> wrote: > >> >>> Richard Biener <richard.guent...@gmail.com> writes: > >> >>>> On Tue, Aug 18, 2015 at 4:15 PM, Richard Sandiford > >> >>>> <richard.sandif...@arm.com> wrote: > >> >>>>> Richard Biener <richard.guent...@gmail.com> writes: > >> >>>>>> On Tue, Aug 18, 2015 at 1:07 PM, David Sherwood > >> >>>>>> <david.sherw...@arm.com> wrote: > >> >>>>>>>> On Mon, Aug 17, 2015 at 11:29 AM, David Sherwood > >> >>>>>>>> <david.sherw...@arm.com> wrote: > >> >>>>>>>> > Hi Richard, > >> >>>>>>>> > > >> >>>>>>>> > Thanks for the reply. I'd chosen to add new expressions as this > >> >>>>>>>> > seemed more > >> >>>>>>>> > consistent with the existing MAX_EXPR and MIN_EXPR tree codes. > >> >>>>>>>> > In > >> >>>>>>>> > addition it > >> >>>>>>>> > would seem to provide more opportunities for optimisation than a > >> >>>>>>>> > target-specific > >> >>>>>>>> > builtin implementation would. I accept that optimisation > >> >>>>>>>> > opportunities will > >> >>>>>>>> > be more limited for strict math compilation, but that it was > >> >>>>>>>> > still > >> >>>>>>>> > worth having > >> >>>>>>>> > them. Also, if we did map it to builtins then the scalar > >> >>>>>>>> > version would go > >> >>>>>>>> > through the optabs and the vector version would go through the > >> >>>>>>>> > target's builtin > >> >>>>>>>> > expansion, which doesn't seem very consistent. > >> >>>>>>>> > >> >>>>>>>> On another note ISTR you can't associate STRICT_MIN/MAX_EXPR and > >> >>>>>>>> thus > >> >>>>>>>> you can't vectorize anyway? (strict IEEE behavior is about NaNs, > >> >>>>>>>> correct?) > >> >>>>>>> I thought for this particular case associativity wasn't an issue? > >> >>>>>>> We're not doing any > >> >>>>>>> reductions here, just simply performing max/min operations on each > >> >>>>>>> pair of elements > >> >>>>>>> in the vectors. I thought for IEEE-compliant behaviour we just > >> >>>>>>> need to > >> >>>>>>> ensure that for > >> >>>>>>> each pair of elements if one element is a NaN we return the other > >> >>>>>>> one. > >> >>>>>> > >> >>>>>> Hmm, true. Ok, my comment still stands - I don't see that using a > >> >>>>>> tree code is the best thing to do here. You can add fmin/max optabs > >> >>>>>> and special expansion of BUILT_IN_FMIN/MAX and you can use a target > >> >>>>>> builtin for the vectorized variant. > >> >>>>>> > >> >>>>>> The reason I am pushing against a new tree code is that we'd have an > >> >>>>>> awful lot of similar codes when pushing other flag related IL > >> >>>>>> specialities to actual IL constructs. And we still need to find a > >> >>>>>> consistent way to do that. > >> >>>>> > >> >>>>> In this case though the new code is really the "native" min/max > >> >>>>> operation > >> >>>>> for fp, rather than some weird flag-dependent behaviour. Maybe it's > >> >>>>> a bit unfortunate that the non-strict min/max fp operation got mapped > >> >>>>> to the generic MIN_EXPR and MAX_EXPR when the non-strict version is > >> >>>>> really > >> >>>>> the flag-related modification. The STRICT_* prefix is forced by > >> >>>>> that and > >> >>>>> might make it seem like more of a special case than it really is. > >> >>>> > >> >>>> In some sense. But the "strict" version already has a builtin (just > >> >>>> no > >> >>>> special expander in builtins.c). We usually don't add 1:1 tree codes > >> >>>> for existing builtins (why have builtins at all then?). > >> >>> > >> >>> We still need the builtin to match the C function (and to allow direct > >> >>> calls to __builtin_fmin, etc., which are occasionally useful). > >> >>> > >> >>>>> If you're still not convinced, how about an internal function instead > >> >>>>> of a built-in function, so that we can continue to use optabs for all > >> >>>>> cases? I'd really like to avoid forcing such a generic concept down > >> >>>>> to > >> >>>>> target-specific builtins with target-specific expansion code, > >> >>>>> especially > >> >>>>> when the same concept is exposed by target-independent code for > >> >>>>> scalars. > >> >>>> > >> >>>> The target builtin is for the vectorized variant - not all targets > >> >>>> might have > >> >>>> that and we'd need to query the target about this. So using a IFN > >> >>>> would > >> >>>> mean adding a target hook for that query. > >> >>> > >> >>> No, the idea is that if we have a tree code or an internal function, > >> >>> the > >> >>> decision about whether we have target support is based on a query of > >> >>> the > >> >>> optabs (just like it is for scalar, and for other vectorisable tree > >> >>> codes). > >> >>> No new hooks are needed. > >> >>> > >> >>> The patch checked for target support that way. > >> >> > >> >> Fair enough. Still this means we should have tree codes for all > >> >> builtins > >> >> that eventually are vectorized? So why don't we have SIN_EXPR, > >> >> POW_EXPR (ok, I did argue and have patches for that in the past), > >> >> RINT_EXPR, SQRT_EXPR, etc? > >> > > >> > Yeah, it doesn't sound so bad to me :-) The choice of what's a function > >> > in C and what's inherent is pretty arbitrary. E.g. % on doubles could > >> > have implemented fmod() or remainder(). Casts from double to int could > >> > have used the current rounding mode, but instead they truncate and > >> > conversions using the rounding mode need to go through something like > >> > (l)lrint(). Like you say, pow() could have been an operator (and is in > >> > many languages), but instead it's a function. > >> > > >> >> This patch starts to go down that route which is why I ask for the > >> >> whole picture to be considered and hinted at the alternative > >> >> implementation > >> >> which follows existing practice. Add a expander in builtins.c, add an > >> >> optab, > >> >> and eventual support to vectorized_function. > >> >> > >> >> See for example ix86_builtin_vectorized_function which handles > >> >> sqrt, floor, ceil, etc. and even FMA (we only fold FMA to FMA_EXPR > >> >> if the target supports it for the scalar mode, so not sure if there is > >> >> any x86 ISA where it has vectorized FMA but not scalar FMA). > >> > > >> > Yeah. TBH I'm really against doing that unless (a) there's good reason > >> > to believe that the concept really is specific to one target and > >> > wouldn't be implemented on others or (b) there really is a function > >> > rather than an instruction underneath (usually the case for sin, etc.). > >> > But (b) could also be handled by the optab support library mechanism. > >> > > >> > Reasons against using target-specific builtins for operations that > >> > have direct support in the ISA: > >> > > >> > 1. Like you say, in practice vector ops only tend to be supported if the > >> > associated scalar op is also supported. Sticking to this approach > >> > means that vector ops follow a different path from scalar ops whereas > >> > (for example) division follows the same path for both. It just seems > >> > confusing to have some floating-point optabs that support both scalar > >> > and vector operands and others that only support scalar operands. > >> > > >> > 2. Once converted to a target-specific function, the target-independent > >> > code has no idea what the function does or how expensive it is. > >> > We might start out with just one hook to convert a scalar operation > >> > to a target-dependent built-in function, but I bet over time we'll > >> > grow other hooks to query properties about the function, such as > >> > costs. > >> > > >> > 3. builtin_vectorized_function returns a decl rather than a call. > >> > If the target's vector API doesn't already have a built-in for the > >> > operation we need, with the exact types and arguments that we expect, > >> > the target needs to define one, presumably marked so that it isn't > >> > callable by input code. > >> > > >> > E.g. on targets where FP conversion instructions allow an explicit > >> > rounding mode to be specified as an operand, it's reasonable for a > >> > target's vector API to expose that operand as a constant argument to > >> > the API function. There'd then be one API function for all vector- > >> > float-to-vector-float integer rounding operations, rather than one > >> > for vector rint(), one for vector ceil(), etc. (I'm thinking of > >> > System z instructions here, although I don't know offhand what the > >> > vector API is there.) IMO it doesn't make sense to force the target > >> > to define "fake" built-in functions for all those possibilities > >> > purely for the sake of the target hook. It's a lot of extra code, > >> > and it's extra code that would be duplicated on any target that needs > >> > to do this. > >> > > >> > IMO optabs are the best way for the target to tell the target-independent > >> > code what it can do. If it supports sqrt on df it defines sqrtdf and > >> > if it supports vector sqrt on v2df it defines sqrtv2df. These patterns > >> > will often be a single define_expand or define_insn template -- the > >> > vectorness often comes "for free" in terms of writing the pattern. > >> > > >> >>>> > TBH though I'm not sure why an internal_fn value (or a > >> >>>> > target-specific > >> >>>> > builtin enum value) is worse than a tree-code value, unless the > >> >>>> > limit > >> >>>> > of the tree_code bitfield is in sight (maybe it is). > >> >>>> > >> >>>> I think tree_code is 64bits now. > >> >>> > >> >>> Even better :-) > >> >> > >> >> Yes. > >> >> > >> >> I'm not against adding a corresponding tree code for all math builtin > >> >> functions, > >> >> we just have to decide whether this is the way to go (and of course > >> >> support > >> >> expanding those back to libcalls to libc/m rather than libgcc). There > >> >> are > >> >> also constraints on what kind of STRICT_FMIN_EXPR the compiler may > >> >> generate as the target may not be able to expand the long double variant > >> >> directly but needs a libcall but libm might not be linked or may not > >> >> have support > >> >> for it. That would be a new thing compared to libgcc providing a > >> >> fallback > >> >> for all other tree codes. > >> > > >> > True, but that doesn't seem too bad. The constraints would be the same > >> > if we're operating on built-in functions rather than codes. I suppose > >> > built-in functions make this more explicit, but at the end of the day > >> > it's a costing decision. We should no more be converting a cheap > >> > operation into an expensive libgcc function than converting a cheap > >> > operation into an expensive libm function, even if the libgcc conversion > >> > links. > >> > > >> > There's certainly precedent for introducing calls to things that libgcc > >> > doesn't define. E.g. we already introduce calls to memcpy in things > >> > like loop distribution, even though we don't provide a fallback memcpy > >> > in libgcc. > >> > >> As an additional point for many math functions we have to support errno > >> which means, like, BUILT_IN_SQRT can be rewritten to SQRT_EXPR > >> only if -fno-math-errno is in effect. But then code has to handle > >> both variants for things like constant folding and expression combining. > >> That's very unfortunate and something we want to avoid (one reason > >> the POW_EXPR thing didn't fly when I tried). STRICT_FMIN/MAX_EXPR > >> is an example where this doesn't apply, of course (but I detest the name, > >> just use FMIN/FMAX_EXPR?). Still you'd need to handle both, > >> FMIN_EXPR and BUILT_IN_FMIN, in code doing analysis/transform. > >> > >> Richard. > >> > >> > >> > Thanks, > >> > Richard > >> > > >
fmaxmin3.patch
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