https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117550
Bug ID: 117550
Summary: constexpr inlining and size optimizations
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: alexey.lapshin at espressif dot com
Target Milestone: ---
When building applications for embedded systems with size optimizations (-Os)
it appeared binary size boost when changed `-std=c++17` to `-std=c++2b`.
Investigation shows that functions that use string methods from libstdc++ grew
significantly because most of them have "constexpr" specifier that inlines
methods implicitly. GCC is smart enough not to inline the method if two or more
"constexpr" calls appear in the same translation unit. Otherwise, if only one
call in the translation unit appears the function will be inlined. This could
increase binary size significantly, depending on the project's structure. And
it is unexpected behavior when "-Os" is applied.
I did not find a solution how to suppress only "constexpr" functions inlining
without affecting functions that are explicitly marked to be inlined. Could you
please give me advice on how to achieve this?
For now, I have a temporary solution to overcome this "-std=gnu++2b -Os
-D_GLIBCXX20_CONSTEXPR=__attribute__((noinline)) -D__cpp_lib_constexpr_string=
-D__cpp_lib_string_resize_and_overwrite="
