https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100252
--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:1b661f3f5e712c951e774b3b91fffe4dac734cc7 commit r13-765-g1b661f3f5e712c951e774b3b91fffe4dac734cc7 Author: Marek Polacek <pola...@redhat.com> Date: Tue Apr 26 15:52:00 2022 -0400 c++: ICE with temporary of class type in DMI [PR100252] Consider struct A { int x; int y = x; }; struct B { int x = 0; int y = A{x}.y; // #1 }; where for #1 we end up with {.x=(&<PLACEHOLDER_EXPR struct B>)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x} that is, two PLACEHOLDER_EXPRs for different types on the same level in a {}. This crashes because our CONSTRUCTOR_PLACEHOLDER_BOUNDARY mechanism to avoid replacing unrelated PLACEHOLDER_EXPRs cannot deal with it. Here's why we wound up with those PLACEHOLDER_EXPRs: When we're performing cp_parser_late_parsing_nsdmi for "int y = A{x}.y;" we use finish_compound_literal on type=A, compound_literal={((struct B *) this)->x}. When digesting this initializer, we call get_nsdmi which creates a PLACEHOLDER_EXPR for A -- we don't have any object to refer to yet. After digesting, we have {.x=((struct B *) this)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x} and since we've created a PLACEHOLDER_EXPR inside it, we marked the whole ctor CONSTRUCTOR_PLACEHOLDER_BOUNDARY. f_c_l creates a TARGET_EXPR and returns TARGET_EXPR <D.2384, {.x=((struct B *) this)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}> Then we get to B b = {}; and call store_init_value, which digests the {}, which produces {.x=NON_LVALUE_EXPR <0>, .y=(TARGET_EXPR <D.2395, {.x=(&<PLACEHOLDER_EXPR struct B>)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}>).y} lookup_placeholder in constexpr won't find an object to replace the PLACEHOLDER_EXPR for B, because ctx->object will be D.2395 of type A, and we cannot search outward from D.2395 to find 'b'. The call to replace_placeholders in store_init_value will not do anything: we've marked the inner { } CONSTRUCTOR_PLACEHOLDER_BOUNDARY, and it's only a sub-expression, so replace_placeholders does nothing, so the <P_E struct B> stays even though now is the perfect time to replace it because we have an object for it: 'b'. Later, in cp_gimplify_init_expr the *expr_p is D.2395 = {.x=(&<PLACEHOLDER_EXPR struct B>)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x} where D.2395 is of type A, but we crash because we hit <P_E struct B>, which has a different type. My idea was to replace <P_E struct A> with D.2384 after creating the TARGET_EXPR because that means we have an object we can refer to. Then clear CONSTRUCTOR_PLACEHOLDER_BOUNDARY because we no longer have a PLACEHOLDER_EXPR in the {}. Then store_init_value will be able to replace <P_E struct B> with 'b', and we should be good to go. We must be careful not to break guaranteed copy elision, so this replacement happens in digest_nsdmi_init where we can see the whole initializer, and avoid replacing any placeholders in TARGET_EXPRs used in the context of initialization/copy elision. This is achieved via the new function called potential_prvalue_result_of. While fixing this problem, I found PR105550, thus the FIXMEs in the tests. PR c++/100252 gcc/cp/ChangeLog: * typeck2.cc (potential_prvalue_result_of): New. (replace_placeholders_for_class_temp_r): New. (digest_nsdmi_init): Call it. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/nsdmi-aggr14.C: New test. * g++.dg/cpp1y/nsdmi-aggr15.C: New test. * g++.dg/cpp1y/nsdmi-aggr16.C: New test. * g++.dg/cpp1y/nsdmi-aggr17.C: New test. * g++.dg/cpp1y/nsdmi-aggr18.C: New test. * g++.dg/cpp1y/nsdmi-aggr19.C: New test.
