https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101371
--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:da47a84e277c7fbeebbf9c1e7dc1e8ba3277fe53 commit r11-9710-gda47a84e277c7fbeebbf9c1e7dc1e8ba3277fe53 Author: Marek Polacek <pola...@redhat.com> Date: Tue Jul 13 17:16:54 2021 -0400 c++: constexpr array reference and value-initialization [PR101371] This PR gave me a hard time: I saw multiple issues starting with different revisions. But ultimately the root cause seems to be the following, and the attached patch fixes all issues I've found here. In cxx_eval_array_reference we create a new constexpr context for the CP_AGGREGATE_TYPE_P case, but we also have to create it for the non-aggregate case. In this test, we are evaluating ((B *)this)->a = rhs->a which means that we set ctx.object to ((B *)this)->a. Then we proceed to evaluate the initializer, rhs->a. For *rhs, we eval rhs, a PARM_DECL, for which we have (const B &) &c.arr[0] in the hash table. Then cxx_fold_indirect_ref gives us c.arr[0]. c is evaluated to {.arr={}} so c.arr is {}. Now we want c.arr[0], so we end up in cxx_eval_array_reference and since we're initializing from {}, we call build_value_init which gives us an AGGR_INIT_EXPR that calls 'constexpr B::B()'. Then we evaluate this AGGR_INIT_EXPR and since its first argument is dummy, we take ctx.object instead. But that is the wrong object, we're not initializing ((B *)this)->a here. And so we wound up with an initializer for A, and then crash in cxx_eval_component_reference: gcc_assert (DECL_CONTEXT (part) == TYPE_MAIN_VARIANT (TREE_TYPE (whole))); where DECL_CONTEXT (part) is B (as it should be) but the type of whole was A. So create a new object, if there already was one, and the element type is not a scalar. PR c++/101371 gcc/cp/ChangeLog: * constexpr.c (cxx_eval_array_reference): Create a new .object and .ctor for the non-aggregate non-scalar case too when value-initializing. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/constexpr-101371-2.C: New test. * g++.dg/cpp1y/constexpr-101371.C: New test. (cherry picked from commit a42f8120442cf3ba25d621bed857b5be19019d0c)
