[Bug libstdc++/78717] no definition of string::find when lowered to gimple
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78717 --- Comment #4 from Jonathan Wakely --- This is because the std::basic_string::find function isn't marked 'inline' and there is an explicit instantiation declaration for std::string. GCC simply won't inline a non-inline function if there's an explicit instantiation of it. With GCC 12 and -std=c++20 all members of std::basic_string are 'constexpr' and so implicitly 'inline', and it gets inlined.
[Bug libstdc++/78717] no definition of string::find when lowered to gimple
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78717 --- Comment #3 from AK --- Even with a high inline limit, string::find didn't inline. g++-11.0.2 -O3 -finline-limit=10 -S -o a.s s.cpp cat a.s ``` _Z3fooRKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEES6_i: .LFB1240: .cfi_startproc endbr64 pushq %rbx .cfi_def_cfa_offset 16 .cfi_offset 3, -16 movq8(%rsi), %rcx movslq %edx, %rbx xorl%edx, %edx movq(%rsi), %rsi call _ZNKSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE4findEPKcmm@PLT cmpq%rax, %rbx popq%rbx .cfi_def_cfa_offset 8 sete%al movzbl %al, %eax ret ```
[Bug libstdc++/78717] no definition of string::find when lowered to gimple
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78717 --- Comment #2 from AK --- With -O3 I see only the following definition of find which calls the real find function I was expecting to be visible in the gimple. D.12805 = _ZNKSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE4findERKS4_mD.11635 (s1D.12794, s2D.12795, 0); std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::find(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) const But after I #defined _GLIBCXX_DEBUG in test.cpp (before including string), I can see the find function.
[Bug libstdc++/78717] no definition of string::find when lowered to gimple
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78717 --- Comment #1 from Marc Glisse --- Did you forget to enable optimizations? At -O0, there is no point keeping those extern templates around, so gcc saves time by dropping them. At -O1 and above, I do see some extra functions in the gimple dump. I don't see as many as if I change _GLIBCXX_EXTERN_TEMPLATE to 0 in bits/c++config.h, some heuristic likely decided to keep only the functions small enough that they are good candidates for inlining (I didn't try to tweak the inlining parameters to see if I could get it to keep all relevant functions). I agree that this is not nice, there are several PRs in bugzilla caused by those extern templates not being inlined aggressively enough. My hope is that LTO will make enough progress that we can have libstdc++ compiled with it and inline functions from the library.
