------- Comment #4 from vda dot linux at googlemail dot com 2007-07-22 00:02
-------
With t.c being a timing program from comment #3 and serpent.c from attachment,
I build testing program for 3.4.3, 3.4.6 and 4.2.1, -Os and -O3, like this:
ver=NNN
gcc -Os -o serpent-${ver}-Os serpent.c t.c
gcc -Os -o serpent-${ver}-Os.o -c serpent.c
gcc -O3 -o serpent-${ver}-O3 serpent.c t.c
gcc -O3 -o serpent-${ver}-O3.o -c serpent.c
Performance regression on -O3 (runs at 2/3 speed of 3.4.x). Did four runs of
each:
343-O3
ops/second=712888
ops/second=722059
ops/second=718909
ops/second=713506
346-O3
ops/second=643833
ops/second=712619
ops/second=721724
ops/second=719445
421-O3
ops/second=495349
ops/second=496887
ops/second=490650
ops/second=494522
Size: improved relative to 3.4.x:
# size *-Os.o
text data bss dec hex filename
4302 0 0 4302 10ce serpent-343-Os.o
4335 0 0 4335 10ef serpent-346-Os.o
3877 0 0 3877 f25 serpent-421-Os.o
...but 3.4.x was even smaller at -O3 than 4.2.1 at -Os:
# size *-O3.o
text data bss dec hex filename
3292 0 0 3292 cdc serpent-343-O3.o
3292 0 0 3292 cdc serpent-346-O3.o
3877 0 0 3877 f25 serpent-421-O3.o
Actually, 4.2.1 seems to generate same code for -Os/-O2/-O3:
# size *421*.o
text data bss dec hex filename
3877 0 0 3877 f25 serpent-421-O2.o
3877 0 0 3877 f25 serpent-421-O3.o
3877 0 0 3877 f25 serpent-421-Os.o
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28481
