> On 29 Oct 2024, at 6:59 PM, Richard Biener <rguent...@suse.de> wrote:
>
> External email: Use caution opening links or attachments
>
>
> On Mon, 28 Oct 2024, Soumya AR wrote:
>
>> This patch implements transformations for the following optimizations.
>>
>> logN(x) CMP CST -> x CMP expN(CST)
>> expN(x) CMP CST -> x CMP logN(CST)
>>
>> For example:
>>
>> int
>> foo (float x)
>> {
>> return __builtin_logf (x) < 0.0f;
>> }
>>
>> can just be:
>>
>> int
>> foo (float x)
>> {
>> return x < 1.0f;
>> }
>>
>> The patch was bootstrapped and regtested on aarch64-linux-gnu, no regression.
>> OK for mainline?
>
> + (for cmp (lt le gt ge eq ne)
> + (for logs (LOG LOG2 LOG10)
> + exps (EXP EXP2 EXP10)
> + /* Simplify logN (x) CMP CST into x CMP expN (CST) */
> + (simplify
> + (cmp:c (logs:s @0) @1)
> + (cmp @0 (exps @1)))
> +
> + /* Simplify expN (x) CMP CST into x CMP logN (CST) */
> + (simplify
> + (cmp:c (exps:s @0) @1)
> + (cmp @0 (logs @1))))))
>
> this doesn't restrict @1 to be constant. You should use
>
> (cmp:c (exps:s @0) REAL_CST@1)Fixed. > I think this transform is also very susceptible to rounding > issues - esp. using it for eq and ne looks very dangerous > to me. Unless you check a roundtrip through exp/log gets > you back exactly the original constant. > > I think the compare kinds "most safe" would be le and ge. This makes sense, I’ve updated the patch to only optimize for le and ge. Thanks, Soumya > You can look at fold-const-call.cc:do_mpfr_arg1, mpfr gets > you the information on whether the result is exact for example. > > Richard. > > >> Signed-off-by: Soumya AR <soum...@nvidia.com> >> >> gcc/ChangeLog: >> >> * match.pd: Fold logN(x) CMP CST -> x CMP expN(CST) >> and expN(x) CMP CST -> x CMP logN(CST) >> >> gcc/testsuite/ChangeLog: >> >> * gcc.dg/tree-ssa/log_exp.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)
v2-0001-Match-Optimize-log-x-CMP-CST-and-exp-x-CMP-CST.patch
Description: v2-0001-Match-Optimize-log-x-CMP-CST-and-exp-x-CMP-CST.patch
