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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Fri, 10 Jul 2020 00:49:30 +0100
Message-ID: <CAH6eHdQkuZ39UOU3EjEfiym1E84BCsxmnu5sfuhn5riWDTZ5hA@mail.gmail.com>
Subject: Re: stdc++ issue: extremely long compile time with large number of
 string literals
To: Mandeep Sandhu <mandeepsandhu.chd@gmail.com>
Cc: gcc-help <gcc-help@gcc.gnu.org>
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On Thu, 9 Jul 2020 at 21:34, Mandeep Sandhu via Gcc-help
<gcc-help@gcc.gnu.org> wrote:
>
> Hi All,
>
> I have an strange (to me) issue, where trying to compile a header
> which has a single "std::unordered_set<std::string>" initialized with
> around 50K short strings is taking forever.
>
> The set is declared as:
> const std::unordered_set<std::string> my_set ({"item1", "item2", ....});

This constructs an enormous array of std::string. If construction of
any element of the array throws, then all previous elements need to be
destroyed.

There are known performance problems with the way G++ handles cases
like this, because the exception handling creates a huge amount of
overhead. You can find several bugs in bugzilla related to the
construction of large arrays of non-trivial types.