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Re: pr43550 - remove unnecessary uxts in bswap

From: Jeff Law <law at redhat dot com>
To: Kugan <kugan dot vivekanandarajah at linaro dot org>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
Cc: Jakub Jelinek <jakub at redhat dot com>
Date: Thu, 11 Sep 2014 15:04:41 -0600
Subject: Re: pr43550 - remove unnecessary uxts in bswap
Authentication-results: sourceware.org; auth=none
References: <54093647 dot 3000200 at linaro dot org>

On 09/04/14 22:04, Kugan wrote:

Hi All,

For the bswap built-in, there are unnecessary uxts generated as reported
in pr43550. Can we rely on the argument being unsigned and set the
SUBREG promoted accordingly.

At least in ARM ABI, arguments are supposed to be properly zero/sign
extended.

Any thoughts?

Bootstrapped and regression tested on x86_64 and arm.

Thanks,
Kugan

gcc/testsuite
2014-09-05  Kugan Vivekanandarajah  <kuganv@linaro.org>

	PR target/43550
	* gcc.target/arm/pr43550.c: New test.

gcc/
2014-09-05  Kugan Vivekanandarajah  <kuganv@linaro.org>

	PR target/43550
	* builtins.c (expand_builtin_bswap): Generate promoted subreg.

I'm not 100% sure you can depend on arguments being extended. It'lloften be true, but I don't think it's something you can rely on.


Jeff

References:
- pr43550 - remove unnecessary uxts in bswap
  - From: Kugan

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