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[Bug libstdc++/86590] Codegen is poor when passing std::string by value with _GLIBCXX_EXTERN_TEMPLATE undefined
- From: "jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 16 Aug 2018 16:36:15 +0000
- Subject: [Bug libstdc++/86590] Codegen is poor when passing std::string by value with _GLIBCXX_EXTERN_TEMPLATE undefined
- Auto-submitted: auto-generated
- References: <bug-86590-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86590
--- Comment #30 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The thing is that even with the foo that doesn't contain all those
__builtin_constant_p 's after early inlining, we with -std=c++17 -O3 don't
inline for some reason _M_construct.constprop, while we do inline it with
-std=c++14.
With -std=c++14 -O3 we are considering inlining _M_construct.constprop 4 times,
into basic_string ctor twice and into foo twice, with -std=c++17 -O3 only 2
times, both into the ctor.
Richard or Honza, can you please find out why the inliner doesn't consider
inlining it into foo?