From: Jeff Law <jeffreyalaw@gmail.com>
To: Jakub Jelinek <jakub@redhat.com>, Richard Biener <rguenther@suse.de>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] tree-ssa-math-opts: popcount (X) == 1 to (X ^ (X - 1)) > (X - 1) optimization [PR90693]
Date: Sat, 18 Nov 2023 20:59:36 -0700 [thread overview]
Message-ID: <1bc550fa-0883-4ea5-b4c7-a224a6c8aac1@gmail.com> (raw)
In-Reply-To: <ZVdyIFfKpN9rkOWh@tucnak>
On 11/17/23 07:01, Jakub Jelinek wrote:
> Hi!
>
> Per the earlier discussions on this PR, the following patch folds
> popcount (x) == 1 (and != 1) into (x ^ (x - 1)) > x - 1 (or <=)
> if the corresponding popcount optab isn't implemented (I think any
> double-word popcount or call will be necessarily slower than the
> above cheap 3 op check and even for -Os larger or same size).
>
> I've noticed e.g. C++ aligned new starts with std::has_single_bit
> which does popcount (x) == 1.
>
> As a follow-up, I'm considering changing in this routine the popcount
> call to IFN_POPCOUNT with 2 arguments and during expansion test costs.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2023-11-17 Jakub Jelinek <jakub@redhat.com>
>
> PR tree-optimization/90693
> * tree-ssa-math-opts.cc (match_single_bit_test): New function.
> (math_opts_dom_walker::after_dom_children): Call it for EQ_EXPR
> and NE_EXPR assignments and GIMPLE_CONDs.
>
> * gcc.target/i386/pr90693.c: New test.
OK.
Jeff
next prev parent reply other threads:[~2023-11-19 3:59 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-17 14:01 Jakub Jelinek
2023-11-18 10:27 ` [PATCH] tree-ssa-math-opts: popcount (X) == 1 to (X ^ (X - 1)) > (X - 1) optimization for direct optab [PR90693] Jakub Jelinek
2023-11-19 4:03 ` Jeff Law
2023-11-20 8:01 ` Richard Biener
2023-11-20 9:05 ` Jakub Jelinek
2023-11-19 3:59 ` Jeff Law [this message]
2023-11-20 7:54 ` [PATCH] tree-ssa-math-opts: popcount (X) == 1 to (X ^ (X - 1)) > (X - 1) optimization [PR90693] Richard Biener
2023-11-20 8:37 ` Jakub Jelinek
2023-11-20 8:39 ` Richard Biener
2023-11-20 8:41 ` Jakub Jelinek
2023-11-20 13:03 ` Jeff Law
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