https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125969
Bug ID: 125969
Summary: Explicit instantiations for std::string are disabled
by -D_GLIBCXX_ASSERTIONS
Product: gcc
Version: 16.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
The libstdc++ c++config.h does this:
// Disable std::string explicit instantiation declarations in order to assert.
#ifdef _GLIBCXX_ASSERTIONS
# undef _GLIBCXX_EXTERN_TEMPLATE
# define _GLIBCXX_EXTERN_TEMPLATE -1
#endif
This ensures that hardened preconditions are checked, because otherwise we use
the explicit instantiations of std::string, which are typically compiled
without assertions.
But since r15-4208-g361d230fd7800a we define _GLIBCXX_ASSERTIONS by default at
-O0, which means that we disable the explicit instantiations by default. This
makes compilation slower.
It's unfortunate that you have to choose between two good things: safer code
due to precondition checks, and faster compilations due to explicit
instantiations.
We should at least document this interaction.
