From: Richard Biener <richard.guenther@gmail.com>
To: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cc: Jackson Woodruff <jackson.woodruff@foss.arm.com>,
"kyrylo.tkachov@foss.arm.com" <kyrylo.tkachov@foss.arm.com>,
"Joseph S. Myers" <joseph@codesourcery.com>,
GCC Patches <gcc-patches@gcc.gnu.org>, nd <nd@arm.com>
Subject: Re: [PATCH] Factor out division by squares and remove division around comparisons (1/2)
Date: Thu, 17 Aug 2017 10:20:00 -0000 [thread overview]
Message-ID: <CAFiYyc0wGaBuujfTUSVrsAOUoOkoO6SCYB9Mh+kPJ7DP68pSUA@mail.gmail.com> (raw)
In-Reply-To: <DB6PR0801MB205392EDB2B58B757167CC26838D0@DB6PR0801MB2053.eurprd08.prod.outlook.com>
On Tue, Aug 15, 2017 at 4:11 PM, Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
> Richard Biener wrote:
>> > We also change the association of
>> >
>> > x / (y * C) -> (x / C) / y
>> >
>> > If C is a constant.
>>
>> Why's that profitable?
>
> It enables (x * C1) / (y * C2) -> (x * C1/C2) / y for example.
> Also 1/y is now available to the reciprocal optimization, see
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71026 for details.
Sure, but on its own it's going to be slower. So this isn't the
correct way to enable those followup transforms.
>> > x / (- y) -> (-x) / y
>>
>> Why? (it's only one of the possible canonicalizations)
>
> Same here, y is now available for reciprocal optimization. The
> negate may now be optimized, for example (a * b) / -y -> (-a*b) / y
> will use a negated multiple on various targets.
Fair enough. Though if it were x / -(a*b) you'd regress that case.
Richard.
>
> Wilco
next prev parent reply other threads:[~2017-08-17 9:38 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-10 14:11 Jackson Woodruff
2017-08-10 15:26 ` Jackson Woodruff
2017-08-11 0:15 ` Joseph Myers
2017-08-15 14:22 ` Richard Biener
2017-08-15 14:43 ` Wilco Dijkstra
2017-08-17 10:20 ` Richard Biener [this message]
2017-08-17 10:29 ` Wilco Dijkstra
2017-08-17 10:39 ` Richard Biener
2017-08-17 12:46 ` Joseph Myers
2017-08-24 21:26 ` Jeff Law
2017-08-29 12:13 ` Jackson Woodruff
2017-08-29 13:31 ` Richard Biener
2017-08-30 10:45 ` Jackson Woodruff
2017-08-30 13:26 ` Richard Biener
2017-09-06 9:55 ` Jackson Woodruff
2017-09-13 18:37 ` Jeff Law
2017-09-13 21:20 ` Wilco Dijkstra
2017-09-15 12:07 ` Richard Biener
2017-09-15 16:50 ` Jeff Law
2017-09-16 21:39 ` Bernhard Reutner-Fischer
2017-10-13 18:18 ` Jeff Law
2017-10-13 18:53 ` Wilco Dijkstra
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