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Re: [PATCH] Fix bswap regression: expand 8bit rotations of 16bit values into bswaphi patterns

From: Jeff Law <law at redhat dot com>
To: "Thomas Preud'homme" <thomas dot preudhomme at arm dot com>, "'Jakub Jelinek'" <jakub at redhat dot com>
Cc: gcc-patches at gcc dot gnu dot org, Richard Biener <richard dot guenther at gmail dot com>
Date: Fri, 07 Nov 2014 13:19:00 -0700
Subject: Re: [PATCH] Fix bswap regression: expand 8bit rotations of 16bit values into bswaphi patterns
Authentication-results: sourceware.org; auth=none
References: <000101cffaa3$9be23460$d3a69d20$ at arm dot com> <545D2384 dot 6050103 at redhat dot com> <20141107200123 dot GS5026 at tucnak dot redhat dot com> <000301cffac7$1a7588e0$4f609aa0$ at arm dot com>

On 11/07/14 13:11, Thomas Preud'homme wrote:

From: Jakub Jelinek [mailto:jakub@redhat.com]
Sent: Friday, November 07, 2014 8:01 PM

Why restrict this to 8 bit rotate of a 16 bit value?  Shouldn't it apply to
a 16 bit rotate of a 32 bit value, or 32 bit rotate of 64 bit value?


That isn't a byteswap, but halfword swap or wordswap.
32 bit byteswap reverses 0x01020304 byte ordering into 0x04030201,
while rotate
16 is 0x03040102.


If this patch gets approved as is I'll add a comment to explain this as this is
the third time someone ask me this.

Then I don't feel like such a bloody idiot after reading Jakub's reply :-)

Jeff

References:
- [PATCH] Fix bswap regression: expand 8bit rotations of 16bit values into bswaphi patterns
  - From: Thomas Preud'homme
- Re: [PATCH] Fix bswap regression: expand 8bit rotations of 16bit values into bswaphi patterns
  - From: Jeff Law
- Re: [PATCH] Fix bswap regression: expand 8bit rotations of 16bit values into bswaphi patterns
  - From: Jakub Jelinek
- RE: [PATCH] Fix bswap regression: expand 8bit rotations of 16bit values into bswaphi patterns
  - From: Thomas Preud'homme

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