[cfe-dev] Additional instantiations of anonymous enum inside a template

[Richard Smith]

On Mon, Oct 13, 2014 at 12:48 PM, Richard Smith <richard at metafoo.co.uk>
wrote:

> On Mon, Oct 13, 2014 at 12:02 PM, András Kucsma <r0maikx02b at gmail.com>
> wrote:
>
>> Hi,
>>
>> I'm one of the developers of Metashell (
>> https://github.com/sabel83/metashell), more specifically the developer
>> of metadebugger, which was used to reproduce this issue.
>>
>> Metashell uses Templight (http://plc.inf.elte.hu/templight/) to gather
>> information about the template instantiations.
>>
>> I put together a small test which reproduces the issue without Metashell,
>> using only a clang patched with Templight:
>> https://gist.github.com/r0mai/4d90fdc8007af96c2dd1
>>
>
> I don't see any Clang bug here. Templight is not reporting template
> instantiations; you're misinterpreting its output. 129 of the 130 instances
> are of kind "Memoization", which is Templight's way of saying "Clang
> checked whether the type was complete". There are no additional
> instantiations here.
>

Sorry, I missed one; there are two TemplateInstantiations in that log, not
one. One for fib<2> and one for int_<1>.

You can find the trace that Templight produced in the gist as well.
>> Memoization events of ENUM appear 130 times while instantiating
>> int_<fib<2>::value>.
>>
>> I CC-ed in two guys (Zoltán Porkoláb and Zoltán Borók-Nagy). They will be
>> able to help with Templight related questions.
>>
>> Regards,
>> András
>>
>> On Mon, Oct 13, 2014 at 6:02 PM, Richard Smith <richard at metafoo.co.uk>
>> wrote:
>>
>>>
>>> On 13 Oct 2014 01:06, "Pavel Morozkin" <pavel.morozkin at gmail.com> wrote:
>>> >
>>> > On 13 October 2014 03:53, Richard Smith <richard at metafoo.co.uk> wrote:
>>> >>
>>> >> On Sun, Oct 12, 2014 at 3:29 AM, Pavel Morozkin <
>>> pavel.morozkin at gmail.com> wrote:
>>> >>>
>>> >>> Hello cfe-dev group,
>>> >>>
>>> >>> Consider this template metaprogram:
>>> >>> template <unsigned N> struct fib { enum { value = fib<N-1>::value +
>>> fib<N-2>::value}; };
>>> >>> template <> struct fib<1> { enum { value = 1 }; };
>>> >>> template <> struct fib<0> { enum { value = 0 }; };
>>> >>>
>>> >>> During compilation of 'fib<2>::value' (after finally getting
>>> memoized result of instantiation of struct fib<0>) Clang «instantiates the
>>> anonymous enum inside fib<0> and fib<1>» 129 times in sum.
>>> >>
>>> >>
>>> >> That sounds like a bug. How are you observing it?
>>> >
>>> >
>>> > I debugged the metaprogram with use of Metashell tool.
>>>
>>> Possibly this is a bug in metashell? How does it get this information?
>>>
>>> >>> In case, when we use 'constexpr static auto' instead of 'enum', no
>>> additional instantiations occurs. Why Clang performs additional
>>> instantiations in the first case?
>>> >>>
>>> >>> Thank you,
>>> >>> Pavel
>>> >>>
>>> >>> _______________________________________________
>>> >>> cfe-dev mailing list
>>> >>> cfe-dev at cs.uiuc.edu
>>> >>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>>> >>>
>>> >>
>>> >
>>>
>>
>>
>
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