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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109942] Function template declared extern is implicitly
 instantiated on -O optimization level when return type is auto
Date: Tue, 23 May 2023 13:30:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109942

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think it's debatable whether GCC's behaviour is incorrect. The definition=
 of
the function template can be seen, and no explicit specialization has been
declared for foo<int>, so the compiler is allowed to inline the definition.

It *has* to instantiate it the definition, to determine the return type. Si=
nce
it has to instantiate it anyway, it might as well inline it as well.

So even if this failed to link, you wouldn't get faster compile times becau=
se
the definition must be instantiated anyway.=