On Mon, 28 Oct 2024, Soumya AR wrote:
> This patch transforms the following POW calls to equivalent LDEXP calls, as
> discussed in PR57492:
>
> powi (2.0, i) -> ldexp (1.0, i)
>
> a * powi (2.0, i) -> ldexp (a, i)
>
> 2.0 * powi (2.0, i) -> ldexp (1.0, i + 1)
>
> pow (powof2, i) -> ldexp (1.0, i * log2 (powof2))
>
> powof2 * pow (2, i) -> ldexp (1.0, i + log2 (powof2))
For the multiplication cases why not handle powof2 * ldexp (1., i)
to ldexp (1., i + log2 (powof2)) and a * ldexp (1., i) -> ldexp (a, i)
instead? exp2 * ldexp (1., i) is another candidate.
So please split out the multiplication parts.
+ /* Simplify pow (powof2, i) to ldexp (1, i * log2 (powof2)). */
the below pattern handles POWI, not POW.
+ (simplify
+ (POWI REAL_CST@0 @1)
+ (with { HOST_WIDE_INT tmp = 0;
+ tree integer_arg1 = NULL_TREE; }
+ (if (integer_valued_real_p (@0)
+ && real_isinteger (&TREE_REAL_CST (@0), &tmp)
+ && integer_pow2p (integer_arg1 = build_int_cst (integer_type_node,
tmp)))
&& tmp > 0
&& pow2p_hwi (tmp)
+ (LDEXP { build_one_cst (type); }
+ (mult @1 { build_int_cst (integer_type_node,
+ tree_log2 (integer_arg1)); })))))
build_int_cst (integer_type_node, exact_log2 (tmp))
+ /* Simplify powi (2.0, i) to ldexp (1, i). */
+ (simplify
+ (POWI REAL_CST@0 @1)
+ (if (real_equal (TREE_REAL_CST_PTR (@0), &dconst2))
+ (LDEXP { build_one_cst (type); } @1)))
+
You'll have a duplicate pattern here, instead merge them. 2.0
is power-of-two so I wonder why the pattern is needed.
Richard.
>
> This is especially helpful for SVE architectures as LDEXP calls can be
> implemented using the FSCALE instruction, as seen in the following patch:
> https://gcc.gnu.org/pipermail/gcc-patches/2024-September/664160.html
>
> SPEC2017 was run with this patch, while there are no noticeable improvements,
> there are no non-noise regressions either.
>
> The patch was bootstrapped and regtested on aarch64-linux-gnu, no regression.
> OK for mainline?
>
> Signed-off-by: Soumya AR <soum...@nvidia.com>
>
> gcc/ChangeLog:
> PR target/57492
> * match.pd: Added patterns to fold certain calls to pow to ldexp.
>
> gcc/testsuite/ChangeLog:
> PR target/57492
> * gcc.dg/tree-ssa/pow-to-ldexp.c: New test.
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
