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Re: [Xen-devel] [PATCH] xen/typesafe: Force helpers to be always_inline
- To: George Dunlap <george.dunlap@xxxxxxxxxx>
- From: Jan Beulich <JBeulich@xxxxxxxx>
- Date: Wed, 23 Oct 2019 10:43:50 +0000
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- Cc: Juergen Gross <JGross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, WeiLiu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 23 Oct 2019 10:53:59 +0000
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- Thread-topic: [PATCH] xen/typesafe: Force helpers to be always_inline
On 23.10.2019 11:37, George Dunlap wrote:
> On 10/23/19 8:27 AM, Jan Beulich wrote:
>> On 21.10.2019 13:10, George Dunlap wrote:
>>> Let's do a cost-benefits analysis of always_inline vs clang_inline.
>>>
>>> For each future gcc version, either it will choose to inline this
>>> function with the `inline` key word or not.
>>>
>>> 1. Use always_inline
>>> 1a. gcc would have done inline anyway. No cost.
>>> 1b. gcc would not have inlined it. always_inline takes effect and
>>> there's no cost.
>>> 2. Use clang_inline
>>> 2a. gcc would have done inline anyway. No cost.
>>> 2b. gcc doesn't inline it. We have random bugs, a discussion, then a
>>> patch to s/clang_inline/always_inline/g;.
>>>
>>> IOW, I only see a cost here to 2, and no benefit.
>>
>> The benefit of 2 would be the easier way of identifying what was
>> changed just for clang's sake, perhaps with the simple goal of
>> reverting the whole lot without having to fish out all the individual
>> commits that may accumulate over time.
>
> But they weren't done for clang's sake; they were done for symbol clash
> sake. If some future version of gcc happened to not inline these, then
> we'd get the same problem.
>
> So if you want to take this approach, I'd say make the names something
> like, `inline_symbol_clash`. That tells future people exactly what
> needs to be done to switch them back to "bare" inline; and if we never
> get around to fixing the symbol clash issue, then it will prevent gcc
> from "developing" this issue as well.
Oh, yes, good point.
Jan
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