Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 11 May 2020 17:09:20 -0700 | Subject | Re: [PATCH v2] Kconfig: default to CC_OPTIMIZE_FOR_PERFORMANCE_O3 for gcc >= 10 |
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On Mon, May 11, 2020 at 5:04 PM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > Not inlining as aggressively is not necessarily a bad thing. It can > be, of course. But I've actually also done gcc bugreports about gcc > inlining too much, and generating _worse_ code as a result (ie > inlinging things that were behind an "if (unlikely())" test, and > causing the likely path to grow a stack fram and stack spills as a > result).
In case people care, the bugzilla case I mentioned is this one:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49194
with example code on why it's actively wrong to inline.
Obviously, in the kernel, we can fix the obvious cases with "noinline" and "always_inline", but those take care of the outliers. Having a compiler that does reasonably well by default is a good thing, and that very much includes *not* inlining mindlessly.
Linus
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