On Thu, 19 Aug 2021, Jirui Wu wrote:
> Hi all,
>
> This patch generates FRINTZ instruction to optimize type casts.
>
> The changes in this patch covers:
> * Generate FRINTZ for (double)(int) casts.
> * Add new test cases.
>
> The intermediate type is not checked according to the C99 spec.
> Overflow of the integral part when casting floats to integers causes
> undefined behavior.
> As a result, optimization to trunc() is not invalid.
> I've confirmed that Boolean type does not match the matching condition.
>
> Regtested on aarch64-none-linux-gnu and no issues.
>
> Ok for master? If OK can it be committed for me, I have no commit rights.
+/* Detected a fix_trunc cast inside a float type cast,
+ use IFN_TRUNC to optimize. */
+#if GIMPLE
+(simplify
+ (float (fix_trunc @0))
+ (if (direct_internal_fn_supported_p (IFN_TRUNC, type,
+ OPTIMIZE_FOR_BOTH)
+ && flag_unsafe_math_optimizations
+ && type == TREE_TYPE (@0))
types_match (type, TREE_TYPE (@0))
please. Please perform cheap tests first (the flag test).
+ (IFN_TRUNC @0)))
+#endif
why only for GIMPLE? I'm not sure flag_unsafe_math_optimizations
is a good test here. If you say we can use undefined behavior
of any overflow of the fix_trunc operation what do we guard here?
If it's Inf/NaN input then flag_finite_math_only would be more
appropriate, if it's behavior for -0. (I suppose trunc (-0.0) == -0.0
and thus "wrong") then a && !HONOR_SIGNED_ZEROS (type) is missing
instead. If it's setting of FENV state and possibly trapping on
overflow (but it's undefined?!) then flag_trapping_math covers
the latter but we don't have any flag for eliding FENV state affecting
transforms, so there the kitchen-sink flag_unsafe_math_optimizations
might apply.
So - which is it?
Note there's also the pattern
/* Handle cases of two conversions in a row. */
(for ocvt (convert float fix_trunc)
(for icvt (convert float)
(simplify
(ocvt (icvt@1 @0))
(with
{
...
which is related so please put the new pattern next to that (the
set of conversions handled there does not include (float (fix_trunc @0)))
Thanks,
Richard.
> Thanks,
> Jirui
>
> gcc/ChangeLog:
>
> * match.pd: Generate IFN_TRUNC.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/aarch64/merge_trunc1.c: New test.
>
> > -----Original Message-----
> > From: Richard Biener <richard.guent...@gmail.com>
> > Sent: Tuesday, August 17, 2021 9:13 AM
> > To: Andrew Pinski <pins...@gmail.com>
> > Cc: Jirui Wu <jirui...@arm.com>; Richard Sandiford
> > <richard.sandif...@arm.com>; i...@airs.com; gcc-patches@gcc.gnu.org;
> > rguent...@suse.de
> > Subject: Re: [Patch][GCC][middle-end] - Generate FRINTZ for (double)(int)
> > under -ffast-math on aarch64
> >
> > On Mon, Aug 16, 2021 at 8:48 PM Andrew Pinski via Gcc-patches <gcc-
> > patc...@gcc.gnu.org> wrote:
> > >
> > > On Mon, Aug 16, 2021 at 9:15 AM Jirui Wu via Gcc-patches
> > > <gcc-patches@gcc.gnu.org> wrote:
> > > >
> > > > Hi all,
> > > >
> > > > This patch generates FRINTZ instruction to optimize type casts.
> > > >
> > > > The changes in this patch covers:
> > > > * Opimization of a FIX_TRUNC_EXPR cast inside a FLOAT_EXPR using
> > IFN_TRUNC.
> > > > * Change of corresponding test cases.
> > > >
> > > > Regtested on aarch64-none-linux-gnu and no issues.
> > > >
> > > > Ok for master? If OK can it be committed for me, I have no commit
> > > > rights.
> > >
> > > Is there a reason why you are doing the transformation manually inside
> > > forwprop rather than handling it inside match.pd?
> > > Also can't this only be done for -ffast-math case?
> >
> > You definitely have to look at the intermediate type - that could be a
> > uint8_t
> > or even a boolean type. So unless the intermediate type can represent all
> > float values optimizing to trunc() is invalid. Also if you emit IFN_TRUNC
> > you
> > have to make sure there's target support - we don't emit calls to a library
> > trunc() from an internal function call (and we wouldn't want to optimize it
> > that way).
> >
> > Richard.
> >
> > >
> > > Thanks,
> > > Andrew Pinski
> > >
> > > >
> > > > Thanks,
> > > > Jirui
> > > >
> > > > gcc/ChangeLog:
> > > >
> > > > * tree-ssa-forwprop.c (pass_forwprop::execute): Optimize with
> > > > frintz.
> > > >
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * gcc.target/aarch64/fix_trunc1.c: Update to new expectation.
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
