[Bug tree-optimization/56309] -O3 optimizer generates conditional moves instead of compare and branch resulting in almost 2x slower code

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56309



--- Comment #15 from Uros Bizjak <ubizjak at gmail dot com> 2013-02-14 17:34:15 
UTC ---

(In reply to comment #13)

> $ g++ --version

> g++ (GCC) 4.7.2 ...

> $ g++ -O3 -std=c++11 by-val-O3.ii ; ./a.out

> Took 14.31 seconds total.

> $ g++ -O3 -std=c++11 by-val-O3.ii -fvect-cost-model ; ./a.out

> Took 14.31 seconds total.

> $ g++ -O3 -std=c++11 by-val-O3.ii -fno-tree-vectorize ; ./a.out

> Took 10.25 seconds total.



This is red herring, see PR53346c11:



--q--

You are right. -ftree-vectorize implies -ftree-loop-if-convert and this option

makes all the difference!

--/q--



Please try wiht -ftree-vectorize -fno-tree-loop-if-convert.