https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103827
--- Comment #19 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jan Hubicka <hubi...@gcc.gnu.org>: https://gcc.gnu.org/g:9c5505a35d9d71705464f9254f55407192d31ec3 commit r15-9047-g9c5505a35d9d71705464f9254f55407192d31ec3 Author: Jan Hubicka <hubi...@ucw.cz> Date: Sun Mar 30 23:49:49 2025 +0200 Optimize string constructor this patch improves code generation on string constructors. We currently have _M_construct which takes as a parameter two iterators (begin/end pointers to other string) and produces new string. This patch adds special case of constructor where instead of begining/end pointers we readily know the string size and also special case when we know that source is 0 terminated. This happens commonly when producing stirng copies. Moreover currently ipa-prop is not able to propagate information that beg-end is known constant (copied string size) which makes it impossible for inliner to spot the common case where string size is known to be shorter than 15 bytes and fits in local buffer. Finally I made new constructor inline. Because it is explicitely instantiated without C++20 constexpr we do not produce implicit instantiation (as required by standard) which prevents inlining, ipa-modref and any other IPA analysis to happen. I think we need to make many of the other functions inline, since optimization accross string manipulation is quite important. There is PR94960 to track this issue. Bootstrapped/regtested x86_64-linux, OK? libstdc++-v3/ChangeLog: PR tree-optimization/103827 PR tree-optimization/80331 PR tree-optimization/87502 * config/abi/pre/gnu.ver: Add version for _M_construct<bool> * include/bits/basic_string.h: (basic_string::_M_construct<bool>): Declare. (basic_string constructors): Use it. * include/bits/basic_string.tcc: (basic_string::_M_construct<bool>): New template. * src/c++11/string-inst.cc: Instantated S::_M_construct<bool>. gcc/testsuite/ChangeLog: * g++.dg/tree-ssa/pr80331.C: New test. * g++.dg/tree-ssa/pr87502.C: New test.
