559d2f1e0e
When cxx_bind_parameters_in_call is called e.g. on a method on an automatic variable, we evaluate the argument and because ADDR_EXPR of an automatic decl is not TREE_CONSTANT, we set *non_constant_args and don't cache it. But when it is called on an object located on the heap (allocated using C++20 constexpr new) where we represent it as TREE_STATIC artificial var, or when it is called on a static var that is currently being constructed, such ADDR_EXPRs are TREE_CONSTANT and we happily cache such calls, but they can in those cases have side-effects in the heap or static var objects and so caching them means such side-effects will happen only once and not as many times as that method or function is called. Furthermore, as Patrick mentioned in the PR, the argument doesn't need to be just ADDR_EXPR of the heap or static var or its components, but it could be a CONSTRUCTOR that has the ADDR_EXPR embedded anywhere. And the incorrectly cached function doesn't need to modify the pointed vars or their components, but some caller could be changing them in between the call that was cached and the call that used the cached result. The following patch fixes it by setting *non_constant_args also when the argument contains somewhere such an ADDR_EXPR, either of a heap artificial var or component thereof, or of a static var currently being constructed (where for that it uses the same check as cxx_eval_store_expression, ctx->global->values.get (...); addresses of other static variables would be rejected by cxx_eval_store_expression and therefore it is ok to cache such calls). 2021-04-08 Jakub Jelinek <jakub@redhat.com> PR c++/99859 * constexpr.c (addr_of_non_const_var): New function. (cxx_bind_parameters_in_call): Set *non_constant_args to true even if cp_walk_tree on arg with addr_of_non_const_var callback returns true. * g++.dg/cpp1y/constexpr-99859-1.C: New test. * g++.dg/cpp1y/constexpr-99859-2.C: New test. * g++.dg/cpp2a/constexpr-new18.C: New test. * g++.dg/cpp2a/constexpr-new19.C: New test. |
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