On Tue, 22 Oct 2024, Jennifer Schmitz wrote:
>
>
> > On 21 Oct 2024, at 10:51, Richard Biener <[email protected]> wrote:
> >
> > External email: Use caution opening links or attachments
> >
> >
> > On Fri, 18 Oct 2024, Jennifer Schmitz wrote:
> >
> >> This patch adds the following two simplifications in match.pd:
> >> - pow (1.0/x, y) to pow (x, -y), avoiding the division
> >> - pow (0.0, x) to 0.0, avoiding the call to pow.
> >> The patterns are guarded by flag_unsafe_math_optimizations,
> >> !flag_trapping_math, !flag_errno_math, !HONOR_SIGNED_ZEROS,
> >> and !HONOR_INFINITIES.
> >>
> >> Tests were added to confirm the application of the transform for float,
> >> double, and long double.
> >>
> >> The patch was bootstrapped and regtested on aarch64-linux-gnu and
> >> x86_64-linux-gnu, no regression.
> >> OK for mainline?
> >>
> >> Signed-off-by: Jennifer Schmitz <[email protected]>
> >>
> >> gcc/
> >> * match.pd: Fold pow (1.0/x, y) -> pow (x, -y) and
> >> pow (0.0, x) -> 0.0.
> >>
> >> gcc/testsuite/
> >> * gcc.dg/tree-ssa/pow_fold_1.c: New test.
> >> ---
> >> gcc/match.pd | 14 +++++++++
> >> gcc/testsuite/gcc.dg/tree-ssa/pow_fold_1.c | 34 ++++++++++++++++++++++
> >> 2 files changed, 48 insertions(+)
> >> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pow_fold_1.c
> >>
> >> diff --git a/gcc/match.pd b/gcc/match.pd
> >> index 12d81fcac0d..ba100b117e7 100644
> >> --- a/gcc/match.pd
> >> +++ b/gcc/match.pd
> >> @@ -8203,6 +8203,20 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> >> (rdiv @0 (exps:s @1))
> >> (mult @0 (exps (negate @1)))))
> >>
> >> + /* Simplify pow(1.0/x, y) into pow(x, -y). */
> >> + (if (! HONOR_INFINITIES (type)
> >> + && ! HONOR_SIGNED_ZEROS (type)
> >> + && ! flag_trapping_math
> >> + && ! flag_errno_math)
> >> + (simplify
> >> + (POW (rdiv:s real_onep@0 @1) @2)
> >> + (POW @1 (negate @2)))
> >
> > This one shouldn't need HONOR_SIGNED_ZEROS?
> >
> >> +
> >> + /* Simplify pow(0.0, x) into 0.0. */
> >> + (simplify
> >> + (POW real_zerop@0 @1)
> >
> > I think this needs !HONOR_NANS (type)?
> >
> > Otherwise OK.
> Thanks for the feedback, Richard and Andrew. I made the following changes to
> the patch (current version of the patch below):
> - also applied the pattern to POWI and added tests for pow, powif, powil
> - not gate first pattern under !HONOR_SIGNED_ZEROS, but second one
> additionally under !HONOR_NANS (type)
> - added tests for powf16
Note powi is GCC internal, it doesn't set errno and it should be subject
to different rules - I'd rather have patterns working on powi separate.
> Now, I am encountering two problems:
>
> First, the transform is not applied for float16 (even if
> -fexcess-precision=16). Do you know what the problem could be?
I think you want to use POW_ALL instead of POW. The generated
cfn-operators.pd shows
(define_operator_list POW
BUILT_IN_POWF
BUILT_IN_POW
BUILT_IN_POWL
IFN_POW)
(define_operator_list POW_FN
BUILT_IN_POWF16
BUILT_IN_POWF32
BUILT_IN_POWF64
BUILT_IN_POWF128
BUILT_IN_POWF32X
BUILT_IN_POWF64X
BUILT_IN_POWF128X
null)
(define_operator_list POW_ALL
BUILT_IN_POWF
BUILT_IN_POW
BUILT_IN_POWL
BUILT_IN_POWF16
...
note this comes at expense of more generated code (in
gimple/generic-match.pd).
> Second, validation on aarch64 shows a regression in tests
> - gcc.dg/recip_sqrt_mult_1.c and
> - gcc.dg/recip_sqrt_mult_5.c,
> because the pattern (POWI(1/x, y) -> POWI(x, -y)) is applied before the recip
> pass and prevents application of the recip-patterns. The reason for this
> might be that the single-use restriction only work if the integer argument is
> non-constant, but in the failing test cases, the integer argument is 2 and
> the pattern is applied despite the :s flag.
> For example, my pattern is **not** applied (single-use restriction works) for:
> double res, res2;
> void foo (double a, int b)
> {
> double f (double);
> double t1 = 1.0 / a;
> res = __builtin_powi (t1, b);
> res2 = f (t1);
> }
>
> But the pattern **is** applied and single-use restriction does **not** work
> for:
> double res, res2;
> void foo (double a)
> {
> double f (double);
> double t1 = 1.0 / a;
> res = __builtin_powi (t1, 2);
> res2 = f (t1);
> }
This must be because the result is a single operation. :s only applies
when the result has sub-expresions. This is to make CSE work.
The "fix" is to add explicit && single_use (@n) to override that
behavior. Note that I think the transform is good even when the
division is used because the result reduces the dependence chain length.
It's only when @2 is non-constant that we're introducing another
stmt for the negation that re-introduces this latency (even if in
practice it would be smaller).
> Possible options to resolve this are:
> - gate pattern to run after recip pass
> - do not apply pattern for POWI
- adjust the testcase (is the final outcome still good?)
> What are your thoughts on this?
> Thanks,
> Jennifer
>
> This patch adds the following two simplifications in match.pd for POW
> and POWI:
> - pow (1.0/x, y) to pow (x, -y), avoiding the division
> - pow (0.0, x) to 0.0, avoiding the call to pow.
> The patterns are guarded by flag_unsafe_math_optimizations,
> !flag_trapping_math, !flag_errno_math, and !HONOR_INFINITIES.
> The second pattern is also guarded by !HONOR_NANS and
> !HONOR_SIGNED_ZEROS.
>
> Tests were added to confirm the application of the transform for
> builtins pow, powf, powl, powi, powif, powil, and powf16.
>
> The patch was bootstrapped and regtested on aarch64-linux-gnu and
> x86_64-linux-gnu, no regression.
> OK for mainline?
>
> Signed-off-by: Jennifer Schmitz <[email protected]>
>
> gcc/
> * match.pd: Fold pow (1.0/x, y) -> pow (x, -y) and
> pow (0.0, x) -> 0.0.
>
> gcc/testsuite/
> * gcc.dg/tree-ssa/pow_fold_1.c: New test.
> ---
> gcc/match.pd | 15 ++++++++
> gcc/testsuite/gcc.dg/tree-ssa/pow_fold_1.c | 42 ++++++++++++++++++++++
> 2 files changed, 57 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pow_fold_1.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 12d81fcac0d..b061ef9dc91 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -8203,6 +8203,21 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> (rdiv @0 (exps:s @1))
> (mult @0 (exps (negate @1)))))
>
> + (for pow (POW POWI)
> + (if (! HONOR_INFINITIES (type)
> + && ! flag_trapping_math
> + && ! flag_errno_math)
> + /* Simplify pow(1.0/x, y) into pow(x, -y). */
> + (simplify
> + (pow (rdiv:s real_onep@0 @1) @2)
> + (pow @1 (negate @2)))
> +
> + /* Simplify pow(0.0, x) into 0.0. */
> + (if (! HONOR_NANS (type) && ! HONOR_SIGNED_ZEROS (type))
> + (simplify
> + (pow real_zerop@0 @1)
> + @0))))
> +
> (if (! HONOR_SIGN_DEPENDENT_ROUNDING (type)
> && ! HONOR_NANS (type) && ! HONOR_INFINITIES (type)
> && ! flag_trapping_math
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pow_fold_1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pow_fold_1.c
> new file mode 100644
> index 00000000000..c38b7390478
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pow_fold_1.c
> @@ -0,0 +1,42 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -ffast-math -fdump-tree-optimized" } */
> +/* { dg-add-options float16 } */
> +/* { dg-require-effective-target float16_runtime } */
> +/* { dg-require-effective-target c99_runtime } */
> +
> +extern void link_error (void);
> +
> +#define POW1OVER(TYPE1, TYPE2, CTY, TY) \
> + void \
> + pow1over_##TY (TYPE1 x, TYPE2 y) \
> + { \
> + TYPE1 t1 = 1.0##CTY / x; \
> + TYPE1 t2 = __builtin_pow##TY (t1, y); \
> + TYPE2 t3 = -y; \
> + TYPE1 t4 = __builtin_pow##TY (x, t3); \
> + if (t2 != t4) \
> + link_error (); \
> + } \
> +
> +#define POW0(TYPE1, TYPE2, CTY, TY) \
> + void \
> + pow0_##TY (TYPE2 x) \
> + { \
> + TYPE1 t1 = __builtin_pow##TY (0.0##CTY, x); \
> + if (t1 != 0.0##CTY) \
> + link_error (); \
> + } \
> +
> +#define TEST_ALL(TYPE1, TYPE2, CTY, TY) \
> + POW1OVER (TYPE1, TYPE2, CTY, TY) \
> + POW0 (TYPE1, TYPE2, CTY, TY)
> +
> +TEST_ALL (double, double, , )
> +TEST_ALL (float, float, f, f)
> +TEST_ALL (_Float16, _Float16, f16, f16)
> +TEST_ALL (long double, long double, L, l)
> +TEST_ALL (double, int, , i)
> +TEST_ALL (float, int, f, if)
> +TEST_ALL (long double, int, L, il)
> +
> +/* { dg-final { scan-tree-dump-not "link_error" "optimized" } } */
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
