[Bug target/41868] cell microcode instruction (addic.) is generated for a trivial loop with -O2 optimizations, hurting performance badly

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2009-11-02 17:05 -------
In fact changing the the addic. into addic/cmpwi does not improve the speed of
the code:


With the change:
[apinski@dhcp-10-98-10-216 local]$ time ./a.out
56.316u 0.084s 0:57.09 98.7%    0+0k 0+0io 0pf+0w

Without:
56.276u 0.088s 0:57.08 98.7%    0+0k 0+0io 0pf+0w


So the warning is only invalid.  

With -Os on the trunk:
24.144u 0.032s 0:24.45 98.8%    0+0k 0+0io 0pf+0w


I don't know why off hand -Os is faster than -O2.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41868