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Date: Tue, 13 Jan 2015 18:25:00 -0000
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Richard Biener <richard.guenther@gmail.com>
Cc: Jeff Law <law@redhat.com>, Mike Stump <mikestump@comcast.net>,        GCC Patches <gcc-patches@gcc.gnu.org>,        Richard Sandiford <rdsandiford@googlemail.com>,        Eric Botcazou <ebotcazou@adacore.com>
Subject: Re: shift/extract SHIFT_COUNT_TRUNCATED combine bug
Message-ID: <20150113173834.GA6963@gate.crashing.org>
References: <8F47DDC3-F9FE-4E94-90F7-3A16A3FD47CE@comcast.net> <54B446B2.6080909@redhat.com> <CAFiYyc2t83m8mccgSdfa0k6wDXub-9uTwehXJxCmq9WzcNPVwg@mail.gmail.com>
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On Tue, Jan 13, 2015 at 10:51:27AM +0100, Richard Biener wrote:
> IMHO SHIFT_COUNT_TRUNCATED should be removed and instead
> backends should provide shift patterns with a (and:QI ...) for the
> shift amount which simply will omit that operation if suitable.

Note that that catches less though, e.g. in

int f(int x, int n) { return x << ((2*n) & 31); }

without SHIFT_COUNT_TRUNCATED it will try to match an AND with 30,
not with 31.


Segher