From 072d3115c0e297d91c133c4214b357b0a50557b9 Mon Sep 17 00:00:00 2001 From: Jason Merrill Date: Wed, 24 Aug 2022 16:28:32 -0400 Subject: [PATCH] c++: block copy elision in delegating ctor CWG2403 deals with the issue that copy elision is not possible when the initialized object is a potentially-overlapping subobject and the initializer is a function that returns by value. Jonathan pointed out that this also affects delegating constructors, which might be used to construct a base subobject. gcc/cp/ChangeLog: * call.cc (unsafe_return_slot_p): Return 2 for *this in a constructor. gcc/testsuite/ChangeLog: * g++.dg/init/elide8.C: New test. --- gcc/cp/call.cc | 7 +++++++ gcc/testsuite/g++.dg/init/elide8.C | 11 +++++++++++ 2 files changed, 18 insertions(+) create mode 100644 gcc/testsuite/g++.dg/init/elide8.C diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index 370137e..d107a28 100644 --- a/gcc/cp/call.cc +++ b/gcc/cp/call.cc @@ -9022,6 +9022,13 @@ unsafe_return_slot_p (tree t) if (is_empty_base_ref (t)) return 2; + /* A delegating constructor might be used to initialize a base. */ + if (current_function_decl + && DECL_CONSTRUCTOR_P (current_function_decl) + && (t == current_class_ref + || tree_strip_nop_conversions (t) == current_class_ptr)) + return 2; + STRIP_NOPS (t); if (TREE_CODE (t) == ADDR_EXPR) t = TREE_OPERAND (t, 0); diff --git a/gcc/testsuite/g++.dg/init/elide8.C b/gcc/testsuite/g++.dg/init/elide8.C new file mode 100644 index 0000000..31f899b --- /dev/null +++ b/gcc/testsuite/g++.dg/init/elide8.C @@ -0,0 +1,11 @@ +// CWG 2403 case 3: we can't elide this copy because the delegating constructor +// might be used to initialize a base. +// { dg-do compile { target c++11 } } + +struct Noncopyable { + Noncopyable() = default; + Noncopyable(const Noncopyable &) = delete; + Noncopyable(int) : Noncopyable(make()) {} // { dg-error "deleted" } + + static Noncopyable make(); +}; -- 2.7.4