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match.pd: Add std::pow folding optimizations.

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This patch adds the following two simplifications in match.pd for
POW_ALL 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, and !HONOR_INFINITIES.
The POW_ALL patterns are also gated under !flag_errno_math.
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 <jschmitz@nvidia.com>

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.
This commit is contained in:
Jennifer Schmitz 2024-10-17 08:40:34 -07:00
parent df4af89bc3
commit 07a8538d90
2 changed files with 70 additions and 0 deletions
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28
gcc/match.pd
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@ -8285,6 +8285,21 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(rdiv @0 (exps:s @1))
(mult @0 (exps (negate @1)))))
(for pow (POW_ALL)
(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
@ -8643,6 +8658,19 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(mult (POW:s @0 @1) (POW:s @2 @1))
(POW (mult @0 @2) @1))
(if (! HONOR_INFINITIES (type) && ! flag_trapping_math)
/* Simplify powi(1.0/x, y) into powi(x, -y). */
(simplify
(POWI (rdiv@3 real_onep@0 @1) @2)
(if (single_use (@3))
(POWI @1 (negate @2))))
/* Simplify powi(0.0, x) into 0.0. */
(if (! HONOR_NANS (type) && ! HONOR_SIGNED_ZEROS (type))
(simplify
(POWI real_zerop@0 @1)
@0)))
/* Simplify powi(x,y) * powi(z,y) -> powi(x*z,y). */
(simplify
(mult (POWI:s @0 @1) (POWI:s @2 @1))

42
gcc/testsuite/gcc.dg/tree-ssa/pow_fold_1.c Normal file
View file

@ -0,0 +1,42 @@
/* { dg-do compile } */
/* { dg-options "-Ofast -fdump-tree-optimized -fexcess-precision=16" } */
/* { 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" } } */