> Well, this could explain but unfortunatly I dont have this option set :
>
> # grep OPTIMIZE .config
> # CONFIG_CC_OPTIMIZE_FOR_SIZE is not set
>
> # gcc -v
> Using built-in specs.
> Target: x86_64-unknown-linux-gnu
> Configured with: ../gcc-4.1.1/configure --enable-languages=c,c++
Ah. Looking more closely the problem is different (sorry for the wrong
explanation earlier, it fit too well and it really happened elsewhere)
The code is
#define TG3_RX_RCB_RING_SIZE(tp) \
((tp->tg3_flags2 & TG3_FLG2_5705_PLUS) ? 512 : 1024)
...
sw_idx %= TG3_RX_RCB_RING_SIZE(tp);
The problem is that gcc doesn't rewrite the x % (cond ? const1 : const2)
expression
to the more optimizable cond ? (x % const1 : x % const2). For the first it sees
a full variable division, for which div* is the best code to generate.
Your patch is probably correct or alternatively rewrite the expression
to the optimizable form by hand.
Arguably gcc should do this by itself. Perhaps file a gcc bug about this
missing optimization.
-Andi
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