Ah, yes, I hadn't noticed that, the "volatile" is indeed why it ends up
with three "mov"s. But take the "volatile"s out of constant_test_bit(),
and DEBUG_ADD_PAGE still expands to three tests and three (four if 2.97)
jumps - which is what originally offended me.
But Mark (in test program in private mail) shows gcc combining bits
into one test and one jump, just as we'd hope (and I wrongly thought
forbidden). Perhaps the inline function nature of constant_test_bit()
(which Mark didn't use) gets in the way of combining those tests.
> You could try to remove the volatile from test_bit, and see if that fixes
> it - but then we'd have to find and add the proper "rmb()" calls to people
> who do the endless loop kind of thing like above.
That is not an inviting path to me, at least not any time soon!
I think this all argues for the little patch I suggested - just avoid
test_bit() here. But it was only intended as a quick little suggestion:
looks like our tastes differ, and you prefer taking the _tiny_ hit of
using the regular macros, to seeing "1<<PG_bitshift"s in DEBUG_ADD_PAGE.
Hugh
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