Re: Optimize glyph row clearing and copying routines

[Dmitry Antipov <dmantipov@yandex.ru>]

On 09/24/2013 10:35 AM, Eli Zaretskii wrote:

> Does this change really speed up the code?

YMMV, as usual with benchmarks. Time is in CPU cycles, smaller is better:

It was:

                          gcc 4.8.1  gcc 4.8.1           Intel C 13.1.3   clang 3.3
                          -O2 -g3    -O3 -march=native   -O3 -xHOST       -O3 -march=native
------------------------------------------------------------------------------------------
clear_glyph_row          100        140                 90               40
copy_row_except_pointers 90         160                 80               100


Now it is:

                          gcc 4.8.1  gcc 4.8.1           Intel C 13.1.3   clang 3.3
                          -O2 -g3    -O3 -march=native   -O3 -xHOST       -O3 -march=native
------------------------------------------------------------------------------------------
clear_glyph_row          75         60                  35               35
copy_row_except_pointers 95         150                 50               70

(Intel C and clang makes heavy use of SSE, but gcc isn't).

It would be interesting to add MSVC to this table :-).

In short, I believe that a good compiler should get more optimization opportunities from
new code rather than from old. For this particular case, Intel C is "definitely good",
and gcc, hm...looks controversial at least.

Dmitry