https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113835
--- Comment #19 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:764f02327f7b2dc6ac5abaf89038e51cf0ee6d13 commit r15-9474-g764f02327f7b2dc6ac5abaf89038e51cf0ee6d13 Author: Jason Merrill <ja...@redhat.com> Date: Sat Apr 12 11:35:18 2025 -0400 c++: shortcut constexpr vector ctor [PR113835] Since std::vector became usable in constant evaluation in C++20, a vector variable with static storage duration might be manifestly constant-evaluated, so we properly try to constant-evaluate its initializer. But it can never succeed since the result will always refer to the result of operator new, so trying is a waste of time. Potentially a large waste of time for a large vector, as in the testcase in the PR. So, let's recognize this case and skip trying constant-evaluation. I do this only for the case of an integer argument, as that's the case that's easy to write but slow to (fail to) evaluate. In the test, I use dg-timeout-factor to lower the default timeout from 300 seconds to 15; on my laptop, compilation without the patch takes about 20 seconds versus about 2 with the patch. PR c++/113835 gcc/cp/ChangeLog: * constexpr.cc (cxx_eval_outermost_constant_expr): Bail out early for std::vector(N). gcc/testsuite/ChangeLog: * g++.dg/cpp2a/constexpr-vector1.C: New test.
