https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116756
--- Comment #2 from GCC 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:303cc73182db5ed367b184df813cd50864c55f83 commit r15-7118-g303cc73182db5ed367b184df813cd50864c55f83 Author: Patrick Palka <ppa...@redhat.com> Date: Tue Jan 21 21:57:02 2025 -0500 c++: 'this' capture clobbered during recursive inst [PR116756] Here during instantiation of generic lambda's op() [with I = 0] we substitute into the call self(self, cst<1>{}) which requires recursive instantiation of the same op() [with I = 1] (which isn't deferred due to lambda's deduced return type. During this recursive instantiation, the DECL_EXPR case of tsubst_stmt clobbers LAMBDA_EXPR_THIS_CAPTURE to point to the child op()'s specialized capture proxy instead of the parent's, and the original value is never restored. So later when substituting into the openSeries call in the parent op() maybe_resolve_dummy uses the 'this' proxy belonging to the child op(), which leads to a context mismatch ICE during gimplification of the proxy. An earlier version of this patch fixed this by making instantiate_body save/restore LAMBDA_EXPR_THIS_CAPTURE during a lambda op() instantiation. But it seems cleaner to avoid overwriting LAMBDA_EXPR_THIS_CAPTURE in the first place by making it point to the non-specialized capture proxy, and instead call retrieve_local_specialization as needed, which is what this patch implements. It's natural then to not clear LAMBDA_EXPR_THIS_CAPTURE after parsing/regenerating a lambda. PR c++/116756 gcc/cp/ChangeLog: * lambda.cc (lambda_expr_this_capture): Call retrieve_local_specialization on the result of LAMBDA_EXPR_THIS_CAPTURE for a generic lambda. * parser.cc (cp_parser_lambda_expression): Don't clear LAMBDA_EXPR_THIS_CAPTURE. * pt.cc (tsubst_stmt) <case DECL_EXPR>: Don't overwrite LAMBDA_EXPR_THIS_CAPTURE with the specialized capture. (tsubst_lambda_expr): Don't clear LAMBDA_EXPR_THIS_CAPTURE afterward. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/constexpr-if-lambda7.C: New test. Reviewed-by: Jason Merrill <ja...@redhat.com>
