Messages in this thread | | | Date | Thu, 8 Jan 2009 19:46:30 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning |
| |
On Thu, 8 Jan 2009, H. Peter Anvin wrote: > > Right. gcc simply doesn't have any way to know how heavyweight an > asm() statement is
I don't think that's relevant.
First off, gcc _does_ have a perfectly fine notion of how heavy-weight an "asm" statement is: just count it as a single instruction (and count the argument setup cost that gcc _can_ estimate).
That would be perfectly fine. If people use inline asms, they tend to use it for a reason.
However, I doubt that it's the inline asm that was the biggest reason why gcc decided not to inline - it was probably the constant "switch()" statement. The inline function actually looks pretty large, if it wasn't for the fact that we have a constant argument, and that one makes the switch statement go away.
I suspect gcc has some pre-inlining heuristics that don't take constant folding and simplifiation into account - if you look at just the raw tree of the function without taking the optimization into account, it will look big.
Linus
| |