[x265] Compile error, high bit-depth and GCC 4.9.2

[Steve Borho]

On 01/16, Sami Inkinen wrote:
> Hi,
> 
> I got a compile error with GCC 4.9.2 when compiling a high bit-depth
> executable.
> 
> x265 version 1.4+382-f9a54da18713
> 
> [ 69%] Building CXX object encoder/CMakeFiles/encoder.dir/slicetype.cpp.obj
> c:/x265/x265/source/encoder/slicetype.cpp: In member function 'void
> x265::EstimateRow::estimateCUCost(x265::Lowres**, x265::ReferencePlanes*,
> int, int, int, int, int, bool*)':
> c:/x265/x265/source/encoder/slicetype.cpp:1702:121: warning: iteration 17u
> invokes undefined behavior [-Waggressive-loop-optimizations]
> neighbours[1][i]           = (neighbours[0][i - 1]      + (neighbours[0][i]
> << 1)      + neighbours[0][i + 1]      + 2) >> 2;

For the record, this is a compiler warning and if you don't enable the
WARNINGS_AS_ERRORS flag in cmake this will build and run just fine.

That said, the warning needs to be investigated

> cc1plus.exe: note: containing loop
> 
> The encoder doesn't seem to use weightp:
> 
> x265 [info]: Weighted P-Frames: Y:0.0% UV:0.0%
> 
> I also tested a different build and weighted P-frames are not used there
> either.

Weightp use is highly clip dependendent. You need sequences with
lighting changes.

-- 
Steve Borho