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Re: [PATCH] rvalue reference implementation for C++0x

On 5/30/07, Jason Merrill <> wrote:
> Also in this patch, I've also included my patch to re-enable the
> return value optimization for types with move constructors, which was
> (accidentally) disabled by code that move-constructs from an rvalue.
> See the following (short) thread for more information about this
> patch:

This looks OK, except that I wouldn't check for c++0x mode in
build_over_call.  If you can't have a move constructor except in c++0x
mode and you think shortcutting will speed up non-0x mode significantly,
put the test in the macro or in move_fn_p.

Please put back the explanation in convert_like_real of why we need the


Go ahead and check this all in with these changes if it passes testing.

Done, tested on powerpc-apple-darwin8.9.0. For reference, the committed patch and its ChangeLog follow.

- Doug

2007-05-30  Russell Yanofsky <>
           Douglas Gregor <>
           Pedro Lamarao <>
           Howard Hinnant <>

	PR c++/7412
	PR c++/29939
       * g++.dg/cpp0x/rv8p.C: New.
       * g++.dg/cpp0x/temp-constructor-bug.C: New.
       * g++.dg/cpp0x/cast-bug.C: New.
       * g++.dg/cpp0x/elision_weak.C: New.
       * g++.dg/cpp0x/collapse-bug.C: New.
       * g++.dg/cpp0x/rv3p.C: New.
       * g++.dg/cpp0x/rv7n.C: New.
       * g++.dg/cpp0x/overload-conv-1.C: New.
       * g++.dg/cpp0x/rv2n.C: New.
       * g++.dg/cpp0x/deduce.C: New.
       * g++.dg/cpp0x/temp-va-arg-bug.C: New.
       * g++.dg/cpp0x/rv6p.C: New.
       * g++.dg/cpp0x/template_deduction.C: New.
       * g++.dg/cpp0x/implicit-copy.C: New.
       * g++.dg/cpp0x/rv1p.C: New.
       * g++.dg/cpp0x/cast.C: New.
       * g++.dg/cpp0x/rv5n.C: New.
       * g++.dg/cpp0x/collapse.C: New.
       * g++.dg/cpp0x/overload-conv-2.C: New.
       * g++.dg/cpp0x/rv4p.C: New.
	* g++.dg/cpp0x/rvo.C: New.
       * g++.dg/cpp0x/iop.C: New.
       * g++.dg/cpp0x/rv3n.C: New.
       * g++.dg/cpp0x/rv7p.C: New.
       * g++.dg/cpp0x/reference_collapsing.C: New.
       * g++.dg/cpp0x/overload.C: New.
       * g++.dg/cpp0x/named.C: New.
       * g++.dg/cpp0x/rv2p.C: New.
       * g++.dg/cpp0x/rv6n.C: New.
       * g++.dg/cpp0x/not_special.C: New.
       * g++.dg/cpp0x/bind.C: New.
       * g++.dg/cpp0x/rv1n.C: New.
       * g++.dg/cpp0x/rv5p.C: New.
       * g++.dg/cpp0x/elision.C: New.
       * g++.dg/cpp0x/named_refs.C: New.
       * g++.dg/cpp0x/unnamed_refs.C: New.
       * g++.dg/cpp0x/rv4n.C: New.
       * g++.dg/cpp0x/elision_neg.C: New.
       * g++.dg/init/copy7.C: Run in C++98 mode.
       * g++.dg/overload/arg1.C: Ditto.
       * g++.dg/overload/arg4.C: Ditto.
2007-05-30  Russell Yanofsky <>
           Douglas Gregor <>
           Pedro Lamarao <>
           Howard Hinnant <>

	PR c++/7412
	PR c++/29939
	* typeck.c (comptypes): Don't consider rvalue and lvalue
	reference types to be equivalent.
	(check_return_expr): Move from certain lvalues when returning
	* decl.c (grokdeclarator): Implement reference collapsing.
	(copy_fn_p): Don't consider constructors taking rvalue references
	to be copy constructors.
	(move_fn_p): New.
       * call.c (conversion): New "rvaluedness_matches_p" member.
	(convert_class_to_reference): Require reference type as first
	parameter instead of base type.
	(reference_binding): Add logic to handle rvalue references.
	(implicit_conversion): Update inaccurate comment.
	(convert_like_real): Disable creation of temporaries that are
	impossible to initialize for types with move constructors.
	(build_over_call): Elide move constructors when possible.
	(maybe_handle_implicit_object): Set "rvaluedness_matches_p".
	(maybe_handle_ref_bind): Return conversion instead of type node.
	(compare_ics): Add logic to use "rvaluedness_matches_p" values to
	determine preferred conversion sequences.
	* cp-tree.h (TYPE_REF_IS_RVALUE): New.
	(struct cp_declarator): Add "reference" member for reference
	types, with new "rvalue_ref" flag.
	(cp_build_reference_type): Declare.
	(move_fn_p): Declare.
	* error.c (dump_type_prefix): Format rvalue reference types
	correctly in error messages.
	* except.c (build_throw): Move from certain lvalues when
	* mangle.c (write_type): Mangle rvalue references differently
	than regular references.
	* parser.c (make_reference_declarator): Add boolean parameter for
	rvalue references.
	(cp_parser_make_indirect_declarator): New.
	(cp_parser_new_declarator_opt): Call
	(cp_parser_conversion_declarator_opt): Ditto.
	(cp_parser_declarator): Ditto.
	(cp_parser_ptr_operator): Parse "&&" tokens into rvalue reference
	* pt.c (tsubst): Implement reference collapsing.
	(maybe_adjust_types_for_deduction): Implement special template
	parameter deduction rule for rvalue references.
	(type_unification_real): Update calls to
	(try_one_overload): Ditto.
	(unify_pack_expansion): Ditto.
	* tree.c (lvalue_p_1): Handle rvalue reference types.
	(cp_build_reference_type): New.

Attachment: rvalue-refs.patch.gz
Description: GNU Zip compressed data

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