llvm dev - Sep 2014 - [LLVMdev] Conditions that cause Clang refuse inlining a function

Hi Anton,
Thanks for the answer.

The link you provided doesn't answer the question. It lists the ways to
overcome the linking error if the inline was not successful.
The only condition that is found there to make the compiler not inline is
"when
compiling without optimization".

I asked the question in the forum because I think that this info is not
documented and most chances that the people that know the code inside-out
will know the answer.

Thanks,
David



On Thu, Sep 4, 2014 at 3:30 PM, Anton Korobeynikov <anton at
korobeynikov.info>
wrote:
> Hello
>
> First of all, such a question definitely belongs to cfe-dev, not llvmdev.
>
> Next, 'inline' is certainly a hint, and the full the answer is a
first
> entry here: http://clang.llvm.org/compatibility.html#inline
>
> On Thu, Sep 4, 2014 at 3:42 PM, David Sela <sela.david at gmail.com>
wrote:
> > Hi,
> >
> > I want to have some functions in my code inline so I use the inline
> keyword:
> >
> > inline void foo() {}
> >
> > On some functions the compiler inlines the function but it fails to do
> so on
> > other functions and thus I get a linkage error:
> >
> > error: undefined reference to 'foo'
> >
> > What are the conditions that make the compiler refuse inline?
> >
> > Thanks,
> > David
> >
> > p.s. I know that there are ways to pass compilation and let the
compiler
> > decide if to inline like using __attribute__((always_inline)) but I
must
> > have the function inline.
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
>
>
>
> --
> With best regards, Anton Korobeynikov
> Faculty of Mathematics and Mechanics, Saint Petersburg State University
>
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There are lots of reasons a compiler will choose not to inline a function
(inlining, while usually a win for performance is a time/space tradeoff, so
often a compiler will try not to make a function 'too large' by inlining
too many functions into it - it will simply so at some threshold)

In any case, if the correctness of your program depends on the function
being inlined, you can use the always_inline attribute.
On Sep 4, 2014 5:46 AM, "David Sela" <sela.david at gmail.com>
wrote:
> Hi Anton,
> Thanks for the answer.
>
> The link you provided doesn't answer the question. It lists the ways to
> overcome the linking error if the inline was not successful.
> The only condition that is found there to make the compiler not inline is
"when
> compiling without optimization".
>
> I asked the question in the forum because I think that this info is not
> documented and most chances that the people that know the code inside-out
> will know the answer.
>
> Thanks,
> David
>
>
>
> On Thu, Sep 4, 2014 at 3:30 PM, Anton Korobeynikov <
> anton at korobeynikov.info> wrote:
>
>> Hello
>>
>> First of all, such a question definitely belongs to cfe-dev, not
llvmdev.
>>
>> Next, 'inline' is certainly a hint, and the full the answer is
a first
>> entry here: http://clang.llvm.org/compatibility.html#inline
>>
>> On Thu, Sep 4, 2014 at 3:42 PM, David Sela <sela.david at
gmail.com> wrote:
>> > Hi,
>> >
>> > I want to have some functions in my code inline so I use the
inline
>> keyword:
>> >
>> > inline void foo() {}
>> >
>> > On some functions the compiler inlines the function but it fails
to do
>> so on
>> > other functions and thus I get a linkage error:
>> >
>> > error: undefined reference to 'foo'
>> >
>> > What are the conditions that make the compiler refuse inline?
>> >
>> > Thanks,
>> > David
>> >
>> > p.s. I know that there are ways to pass compilation and let the
compiler
>> > decide if to inline like using __attribute__((always_inline)) but
I must
>> > have the function inline.
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>> >
>>
>>
>>
>> --
>> With best regards, Anton Korobeynikov
>> Faculty of Mathematics and Mechanics, Saint Petersburg State University
>>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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Can these thresholds be customized with flags?
The always_inline attribute is only a hint and I can't know if the compiler
will actually do the inline or not.


On Thu, Sep 4, 2014 at 4:08 PM, David Blaikie <dblaikie at gmail.com>
wrote:
> There are lots of reasons a compiler will choose not to inline a function
> (inlining, while usually a win for performance is a time/space tradeoff, so
> often a compiler will try not to make a function 'too large' by
inlining
> too many functions into it - it will simply so at some threshold)
>
> In any case, if the correctness of your program depends on the function
> being inlined, you can use the always_inline attribute.
> On Sep 4, 2014 5:46 AM, "David Sela" <sela.david at
gmail.com> wrote:
>
>> Hi Anton,
>> Thanks for the answer.
>>
>> The link you provided doesn't answer the question. It lists the
ways to
>> overcome the linking error if the inline was not successful.
>> The only condition that is found there to make the compiler not inline
is
>> "when compiling without optimization".
>>
>> I asked the question in the forum because I think that this info is not
>> documented and most chances that the people that know the code
inside-out
>> will know the answer.
>>
>> Thanks,
>> David
>>
>>
>>
>> On Thu, Sep 4, 2014 at 3:30 PM, Anton Korobeynikov <
>> anton at korobeynikov.info> wrote:
>>
>>> Hello
>>>
>>> First of all, such a question definitely belongs to cfe-dev, not
llvmdev.
>>>
>>> Next, 'inline' is certainly a hint, and the full the answer
is a first
>>> entry here: http://clang.llvm.org/compatibility.html#inline
>>>
>>> On Thu, Sep 4, 2014 at 3:42 PM, David Sela <sela.david at
gmail.com> wrote:
>>> > Hi,
>>> >
>>> > I want to have some functions in my code inline so I use the
inline
>>> keyword:
>>> >
>>> > inline void foo() {}
>>> >
>>> > On some functions the compiler inlines the function but it
fails to do
>>> so on
>>> > other functions and thus I get a linkage error:
>>> >
>>> > error: undefined reference to 'foo'
>>> >
>>> > What are the conditions that make the compiler refuse inline?
>>> >
>>> > Thanks,
>>> > David
>>> >
>>> > p.s. I know that there are ways to pass compilation and let
the
>>> compiler
>>> > decide if to inline like using __attribute__((always_inline))
but I
>>> must
>>> > have the function inline.
>>> >
>>> > _______________________________________________
>>> > LLVM Developers mailing list
>>> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>> >
>>>
>>>
>>>
>>> --
>>> With best regards, Anton Korobeynikov
>>> Faculty of Mathematics and Mechanics, Saint Petersburg State
University
>>>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
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