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Re: [C++ Patch/RFC] PR 53025


On 10/02/2014 05:22 AM, Jason Merrill wrote:
On 10/01/2014 12:31 PM, Paolo Carlini wrote:
in this issue Daniel argued that the value of a noexcept expression
should not depend on constructor elision.

I'm open to that, but I don't think it's at all clear in the standard.
Ok. Personally, I find the analysis in the audit trail rather convincing. In practice, clang++ definitely agrees, likewise SolarisStudio. Current EDG seems inconsistent, the templated and non-templated cases are handled differently.

Then, in the audit trail Marc
tentatively suggested something like the parser.c hunk below, which just
disables our -felide-constructors optimization when parsing the noexcept
expression. Over the last couple of days, I had a look, noticed that in
any case we still have to handle templates, thus the pt.c hunk, and also
that maybe we can avoid completely disabling -felide-constructors in
noexcept expressions when we know for sure that the constructor at issue
doen't throw: for that in call.s I'm further abusing the
flag_elide_constructors global, in terms of using a special value of 2
when flag_elide_constructor is found == 1 when handling the expression.
The below passes testing, anyway.

Why do we want to avoid completely disabling -felide-constructors, since it's an unevaluated context anyway?
If you're going to mess with this flag you need to save/restore it in push/pop_to_top_level as well.
I see. But then if we have to do take care of that I find much more clean to just add a global?!? In any case, if I understand correctly the logic at the end of push_to_top_level, it would be tricky to reset the flag to a sensible value (by default would be 1, but the user may have passed -fno-elide-constructors on the command line).

The below passes testing.



Attachment: patch_53025_2
Description: Text document

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