[PATCH v2] Try and get overlapping cases fixed.

[Cyril Brulebois]

Hi,

Cyril Brulebois <kibi at debian.org> (16/05/2011):
> From: Adam Jackson <ajax at redhat.com>
> 
> The memcpy fast path implicitly assumes that the copy walks
> left-to-right.  That's not something memcpy guarantees, and newer glibc
> on some processors will indeed break that assumption.  Since we walk a
> line at a time, check the source and destination against the width of
> the blit to determine whether we can be sloppy enough to allow memcpy.
> (Having done this, we can remove the check for !reverse as well.)
> 
> On an Intel Core i7-2630QM with an NVIDIA GeForce GTX 460M running in
> NoAccel, the broken code and various fixes for -copywinwin{10,100,500}
> gives (edited to fit in 80 columns):
> 
> 1: Disable the fastpath entirely
> 2: Replace memcpy with memmove
> 3: This fix
> 4: The code before this fix
> 
>   1            2                 3                 4           Operation
> ------   ---------------   ---------------   ---------------   ------------
> 258000   269000 (  1.04)   544000 (  2.11)   552000 (  2.14)   Copy 10x10
>  21300    23000 (  1.08)    43700 (  2.05)    47100 (  2.21)   Copy 100x100
>    960      962 (  1.00)     1990 (  2.09)     1990 (  2.07)   Copy 500x500
> 
> So it's a modest performance hit, but correctness demands it, and it's
> probably worth keeping the 2x speedup from having the fast path in the
> first place.
> 
> Signed-off-by: Adam Jackson <ajax at redhat.com>
> 
> v2: Fix limit cases thanks to Soeren Sandmann, and apply a tiny
>     optimization by Walter Harms.
> 
> Signed-off-by: Cyril Brulebois <kibi at debian.org>
> ---
>  fb/fbblt.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> 
> Tested on amd64 on top of xorg-server's server-1.10-branch.

except for the micro-opt suggested by Jeremy, no ACK/NACK for that
version?

Mraw,
KiBi.
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