[llvm-dev] Removing LLVM_ALWAYS_INLINE from ADT classes

[Mehdi AMINI via llvm-dev]

On Mon, Jan 7, 2019 at 1:46 PM Jonas Devlieghere <jonas at devlieghere.com>
wrote:

>
>
> On Mon, Jan 7, 2019 at 8:33 AM via llvm-dev <llvm-dev at lists.llvm.org>
> wrote:
>
>> IIRC the issues with defaulting to –DLLVM_OPTIMIZE_TABLEGEN=ON came up in
>> two places:
>>
>> First, if it's not a Debug build, this actually slows down the build. The
>> defaulting has to be for Debug config only.  This is arguably bad UI,
>> because it makes the default modal, but there's a clear benefit in build
>> time so I think we can live with that.
>>
>> Second, if it's a multi-config builder (e.g. MSBuild) then it gets a
>> little weird, I don't remember exactly how.
>>
>> --paulr
>>
>
> Out of curiosity, why does it slow down a non-debug build?
>

The way it is implemented is to create another build directory inside the
build directory (called "native" IIRC) and call cmake into it and build
llvm-tblgen there. However that means that a library like Support is built
here before being rebuilt in the main build directory.

-- 
Mehdi


>
>
>>
>>
>> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *Mehdi
>> AMINI via llvm-dev
>> *Sent:* Saturday, January 05, 2019 7:42 PM
>> *To:* Paweł Bylica; Chris Bieneman
>> *Cc:* LLVM Dev
>> *Subject:* Re: [llvm-dev] Removing LLVM_ALWAYS_INLINE from ADT classes
>>
>>
>>
>>
>>
>>
>>
>> On Fri, Jan 4, 2019 at 3:52 PM Paweł Bylica via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>> On Sat, Jan 5, 2019 at 12:38 AM Duncan P. N. Exon Smith via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>> This makes sense to me.
>>
>> One concern is that this in itself will slow down the build, since
>> tablegen will get even slower.  Ideally, there would be some (perhaps
>> default?) configuration where we build the tablegen binaries with
>> optimizations on and then use them in the build, as if we were
>> cross-compiling.
>>
>>
>>
>> Maybe something simple like -DLLVM_OPTIMIZE_TABLEGEN=ON (enabled by
>> default for Debug builds). You would need to set it to off only if you want
>> to debug tablegen.
>>
>>
>>
>> I proposed this a while back, but it think there were some problems with
>> it, I don't remember what exactly but maybe related to bootstrapping /
>> 2-stages builds?
>>
>>
>>
>> + Chris, maybe he remembers something?
>>
>>
>>
>> --
>>
>> Mehdi
>>
>>
>>
>>
>>
>>
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>>
>>
>>
>> > On Jan 4, 2019, at 15:14, Davide Italiano via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>> >
>> > Hi,
>> > I would like to propose, based on a previous discussion on llvm-dev,
>> > the following change.
>> > https://reviews.llvm.org/D56337
>> >
>> > The main motivation for annotating member functions of ADT clases with
>> > LLVM_ALWAYS_INLINE  was that of speeding up `check-llvm` at `-O0`.
>> > Turns out this significantly degrades the debuggability of fundamental
>> > classes in llvm itself, e.g. StringRef or SmallVector.
>> >
>> > After discussing we agreed that it's reasonable to drop
>> > LLVM_ALWYAS_INLINE from ADT classes  member functions and add a note
>> > in the developer's manual.
>> >
>> > If you have any feedbacks or concerns, please speak up.
>> > If nothing major arises, I'm going to commit this patch in a week (or
>> such).
>> >
>> > Thanks for your time,
>> >
>> > --
>> > Davide
>> >
>> > "There are no solved problems; there are only problems that are more
>> > or less solved" -- Henri Poincare
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
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