https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94038
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:a700b4a9f18fd6213de51f4259ee9a8ce7eefdbb commit r11-56-ga700b4a9f18fd6213de51f4259ee9a8ce7eefdbb Author: Patrick Palka <ppa...@redhat.com> Date: Mon May 4 18:30:32 2020 -0400 c++: Avoid unnecessary copying in cp_fold [PR94038] When folding a CALL_EXPR, we can avoid copying it until folding changes one of its arguments. And when folding a TREE_VEC, we can avoid using an intermediate releasing_vec by copying the TREE_VEC as soon as folding changes one of its arguments, like we do in the CALL_EXPR case. Incidentally, the CALL_EXPR change also fixes the testcase in PR94038. The reason is that the call to maybe_constant_value from cp_fold on the call 'bar<int>()' now reuses the result of the earlier call to maybe_constant_value from fold_for_warn, via the cv_cache. This earlier call passes uid_sensitive=true, whereas the call from cp_fold passes uid_sensitive=false, and so by reusing the cached result of the earlier call we now avoid instantiating bar<int> at all. gcc/cp/ChangeLog: PR c++/94038 * cp-gimplify.c (cp_fold) <case CALL_EXPR>: Move some variable declarations closer to their uses. Copy the CALL_EXPR only when one of its arguments has changed. <case TREE_VEC>: Instead of first collecting the folded arguments into a releasing_vec, just make a copy of the TREE_VEC as soon as folding changes one of its arguments. gcc/testsuite/ChangeLog: PR c++/94038 * g++.dg/warn/pr94038.C: New test.
