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SubjectRe: Suboptimal inline heuristics due to non-code sections
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Nadav Amit <namit@vmware.com> wrote:

> Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>> On Tue, May 1, 2018 at 6:40 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>>
>>> But if I remove the section completely by removing the
>>> pushsection/popsection, then copy_overflow() gets inlined.
>>
>>> So GCC's inlining decisions are somehow influenced by the existence of
>>> some random empty section. This definitely seems like a GCC bug to me.
>>
>> I think gcc uses the size of the string to approximate the size of an
>> inline asm.
>>
>> So I don't think it's the "empty section" that makes gcc do this, I think
>> it's literally "our inline asms _look_ big”.
>
> I didn’t think about that.
>
> Playing with the code a bit more, it seems that it is actually related to
> the number of “new-lines” in the inline assembly. Removing 4 new-lines from
> _BUG_FLAGS (those that can be removed without breaking assembly) eliminated
> most of the non-inlined versions of copy_overflow().
>
> Would it be reasonable to remove new-lines in such cases?

My bad. It’s not the new-line. Let me do some more digging.

Nadav

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