[Bug c++/106151] Inconsistent optimization when defaulting aggregate vs non-aggregate

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106151

--- Comment #3 from Andrew Pinski  ---
(In reply to Barry Revzin from comment #2)
> I guess that's like:
> 
> C++11/14: neither is an aggregate (base class).
> C++17: both are aggregates.
> C++20: Bar is an aggregate, but Foo is not (user-declared constructor).
> 
> But that really shouldn't affect the code-gen here? (right???)

It changes because if the constructor is used or it is zero-initialized . And
it just happens GCC is not able to optimize it back to what the
zero-initialized can be done.

[Bug c++/106151] Inconsistent optimization when defaulting aggregate vs non-aggregate

[barry.revzin at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106151

--- Comment #2 from Barry Revzin  ---
I guess that's like:

C++11/14: neither is an aggregate (base class).
C++17: both are aggregates.
C++20: Bar is an aggregate, but Foo is not (user-declared constructor).

But that really shouldn't affect the code-gen here? (right???)

[Bug c++/106151] Inconsistent optimization when defaulting aggregate vs non-aggregate

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106151

Andrew Pinski  changed:

   What|Removed |Added

  Component|middle-end  |c++

--- Comment #1 from Andrew Pinski  ---
This is really interesting.
-std=c++17 produces {} for both. -std=c++11/-std=c++14 produces the long code
for both while -std=c++20 produces the wrose code for Foo::clear.