[FFmpeg-devel] [PATCH 4/7] Use alias-safe types in AV_[RW] macros

Måns Rullgård mans
Fri Jan 29 04:43:08 CET 2010

Michael Niedermayer <michaelni at gmx.at> writes:

> On Fri, Jan 29, 2010 at 02:12:11AM +0000, Mans Rullgard wrote:
>> ---
>>  libavutil/intreadwrite.h |   14 +++++++-------
>>  1 files changed, 7 insertions(+), 7 deletions(-)
> id like to see some benchmark done with the latest gcc release
> and h264/h263/aac decoding as well as mpeg4 encoding on x86_64 (codecs
> randomly picked based more on what is used alot than what uses alot of funny
> accesses)
> if nothing gets slower then iam not against this otherwise i think
> more investigation is needed
> Also how does this stuff interact with restrict ?
> Which overrides the other? can we still use restrict to make sure the
> gcc is aware that aliasing does not happen?

This is the opposite of restrict.  Qualifying a pointer with restrict
informs the compiler that aliasing will *never* happen even with the
normal type rules would allow it.  This is to be used in cases where
we *intentionally* violate the basic aliasing rules.  This is causing
actual errors with some compilers on some targets.

M?ns Rullg?rd
mans at mansr.com

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