| Summary: | Class with deleted copy and move constructors uses wrong argument passing ABI | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Jonathan Wakely <redi> |
| Component: | c++ | Assignee: | Jason Merrill <jason> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | jason, richard-gccbugzilla, webrown.cpp |
| Priority: | P3 | Keywords: | ABI, wrong-code |
| Version: | 6.3.1 | ||
| Target Milestone: | 8.0 | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2017-04-04 00:00:00 | |
| Attachments: | fix | ||
Hmm, I don't see anything in the ABI about deleted constructors, and a deleted function isn't non-trivial (nor trivial). That said, I agree that it makes sense for a class with only deleted copy/move ctors to be passed by invisible reference in the case of copy-list-initialization. This example came from a Clang discussion, and they might also be changing how they handle this. We might want to bring it up on the cxxabi list if there's any doubt what the right behaviour is. CCing Richard, as I discussed it with him last week. Created attachment 41138 [details]
fix
Here's a fix. I'm nervous about applying it at this point in GCC 7, though.
Author: jason Date: Mon May 8 19:08:07 2017 New Revision: 247757 URL: https://gcc.gnu.org/viewcvs?rev=247757&root=gcc&view=rev Log: PR c++/80178 - parameter passing for uncopyable classes * tree.c (type_has_nontrivial_copy_init): True for classes with only deleted copy/move ctors. (remember_deleted_copy, maybe_warn_parm_abi): New. * decl.c (require_complete_types_for_parms, check_function_type): Call maybe_warn_parm_abi. * call.c (convert_for_arg_passing, build_cxx_call): Likewise. Added: trunk/gcc/testsuite/g++.dg/abi/invisiref1.C trunk/gcc/testsuite/g++.dg/abi/invisiref1a.C Modified: trunk/gcc/common.opt trunk/gcc/cp/ChangeLog trunk/gcc/cp/call.c trunk/gcc/cp/cp-tree.h trunk/gcc/cp/decl.c trunk/gcc/cp/tree.c Fixed for gcc 8. |
We pass this in a register, but I think the ABI says it should be an invisible reference, because both the copy ctor and move ctor are deleted. struct A { A(); A &operator=(A &&o); void *p; }; void foo(A); void bar() { foo({}); } In this example they're implicitly defined as deleted because of the user-provided move assignment operator, but the result is the same whether implicitly or explicitly deleted. EDG passes this by invisible reference. Clang passes by value, but that's acknowledged to be a bug.