Re: [PATCH RFC] c++: streamline process for adding new builtin trait

[Jason Merrill <jason@redhat.com>]

On 10/3/22 08:48, Patrick Palka wrote:
> On Fri, 30 Sep 2022, Jason Merrill wrote:
> 
>> On 9/30/22 11:14, Patrick Palka wrote:
>>> On Thu, 29 Sep 2022, Jason Merrill wrote:
>>>
>>>> On 9/29/22 11:05, Patrick Palka wrote:
>>>>> Adding a new builtin trait currently involves some boilerplate (as can
>>>>> be seen in r13-2956-g9ca147154074a0) of defining corresponding RID_ and
>>>>> CPTK_ enumerators and adding them to various switch statements across
>>>>> many files.  The exact switch statements we need to change is determined
>>>>> by whether the proposed trait yields a type or an expression.
>>>>>
>>>>> This RFC patch attempts to streamline this process via a centralized
>>>>> cp-trait.def file for declaring the important parts about a builtin
>>>>> trait
>>>>> (whether it yields a type or an expression, its code, its spelling and
>>>>> its arity) and using this file to automate away the switch statement
>>>>> addition boilerplate.  It also converts 9 traits to use this approach
>>>>> by way of example (we can convert all the traits once the design is
>>>>> settled).
>>>>>
>>>>> After this change, the process of adding a new builtin trait is just
>>>>> (modulo tests): declare it in cp-trait.def, define its behavior in
>>>>> finish_trait_type/expr, and handle it in diagnose_trait_expr if it's
>>>>> an expression-yielding trait (this last step is unfortunate but since
>>>>> the switch has no default case, we'll at least get a diagnostic if we
>>>>> forget to do it).
>>>>>
>>>>> Does this look like a good approach?
>>>>
>>>> OK.
>>>
>>> Thanks a lot, I committed the following (which migrates all the
>>> C++-specific traits to the new approach):
>>>
>>> -- >8 --
>>>
>>> Subject: [PATCH] c++: streamline built-in trait addition process
>>>
>>> Adding a new built-in trait currently involves manual boilerplate
>>> consisting of defining an rid enumerator for the identifier as well as a
>>> corresponding cp_trait_kind enumerator and handling them in various switch
>>> statements, the exact set of which depends on whether the proposed trait
>>> yields (and thus is recognized as) a type or an expression.
>>>
>>> To streamline the process, this patch adds a central cp-trait.def file
>>> that tabulates the essential details about each built-in trait (whether
>>> it yields a type or an expression, its code, its spelling and its arity)
>>> and uses this file to automate away the manual boilerplate.  It also
>>> migrates all the existing C++-specific built-in traits to use this
>>> approach.
>>>
>>> After this change, adding a new built-in trait just entails declaring
>>> it in cp-trait.def and defining its behavior in finish_trait_expr/type
>>> (and handling it in diagnose_trait_expr, if it's an expression-yielding
>>> trait).
>>>
>>> gcc/c-family/ChangeLog:
>>>
>>> 	* c-common.cc (c_common_reswords): Use cp/cp-trait.def to handle
>>> 	C++ traits.
>>> 	* c-common.h (enum rid): Likewise.
>>>
>>> gcc/cp/ChangeLog:
>>>
>>> 	* constraint.cc (diagnose_trait_expr): Likewise.
>>> 	* cp-objcp-common.cc (names_builtin_p): Likewise.
>>> 	* cp-tree.h (enum cp_trait_kind): Likewise.
>>> 	* cxx-pretty-print.cc (pp_cxx_trait): Likewise.
>>> 	* parser.cc (cp_keyword_starts_decl_specifier_p): Likewise.
>>> 	(cp_parser_primary_expression): Likewise.
>>> 	(cp_parser_trait): Likewise.
>>> 	(cp_parser_simple_type_specifier): Likewise.
>>> 	* cp-trait.def: New file.
>>> ---
>>>    gcc/c-family/c-common.cc   |  54 ++-------
>>>    gcc/c-family/c-common.h    |  33 ++----
>>>    gcc/cp/constraint.cc       |  12 +-
>>>    gcc/cp/cp-objcp-common.cc  |  44 +-------
>>>    gcc/cp/cp-trait.def        | 106 ++++++++++++++++++
>>>    gcc/cp/cp-tree.h           |  46 +-------
>>>    gcc/cp/cxx-pretty-print.cc | 126 +--------------------
>>>    gcc/cp/parser.cc           | 217 ++++---------------------------------
>>>    8 files changed, 161 insertions(+), 477 deletions(-)
>>>    create mode 100644 gcc/cp/cp-trait.def
>>>
>>> diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
>>> index 6e0af863a49..3c60a89bfe2 100644
>>> --- a/gcc/c-family/c-common.cc
>>> +++ b/gcc/c-family/c-common.cc
>>> @@ -378,7 +378,6 @@ const struct c_common_resword c_common_reswords[] =
>>>      { "__attribute",	RID_ATTRIBUTE,	0 },
>>>      { "__attribute__",	RID_ATTRIBUTE,	0 },
>>>      { "__auto_type",	RID_AUTO_TYPE,	D_CONLY },
>>> -  { "__bases",          RID_BASES, D_CXXONLY },
>>>      { "__builtin_addressof", RID_ADDRESSOF, D_CXXONLY },
>>>      { "__builtin_bit_cast", RID_BUILTIN_BIT_CAST, D_CXXONLY },
>>>      { "__builtin_call_with_static_chain",
>>> @@ -401,44 +400,12 @@ const struct c_common_resword c_common_reswords[] =
>>>      { "__const__",	RID_CONST,	0 },
>>>      { "__constinit",	RID_CONSTINIT,	D_CXXONLY },
>>>      { "__decltype",       RID_DECLTYPE,   D_CXXONLY },
>>> -  { "__direct_bases",   RID_DIRECT_BASES, D_CXXONLY },
>>>      { "__extension__",	RID_EXTENSION,	0 },
>>>      { "__func__",		RID_C99_FUNCTION_NAME, 0 },
>>> -  { "__has_nothrow_assign", RID_HAS_NOTHROW_ASSIGN, D_CXXONLY },
>>> -  { "__has_nothrow_constructor", RID_HAS_NOTHROW_CONSTRUCTOR, D_CXXONLY },
>>> -  { "__has_nothrow_copy", RID_HAS_NOTHROW_COPY, D_CXXONLY },
>>> -  { "__has_trivial_assign", RID_HAS_TRIVIAL_ASSIGN, D_CXXONLY },
>>> -  { "__has_trivial_constructor", RID_HAS_TRIVIAL_CONSTRUCTOR, D_CXXONLY },
>>> -  { "__has_trivial_copy", RID_HAS_TRIVIAL_COPY, D_CXXONLY },
>>> -  { "__has_trivial_destructor", RID_HAS_TRIVIAL_DESTRUCTOR, D_CXXONLY },
>>> -  { "__has_unique_object_representations",
>>> RID_HAS_UNIQUE_OBJ_REPRESENTATIONS,
>>> -					D_CXXONLY },
>>> -  { "__has_virtual_destructor", RID_HAS_VIRTUAL_DESTRUCTOR, D_CXXONLY },
>>>      { "__imag",		RID_IMAGPART,	0 },
>>>      { "__imag__",		RID_IMAGPART,	0 },
>>>      { "__inline",		RID_INLINE,	0 },
>>>      { "__inline__",	RID_INLINE,	0 },
>>> -  { "__is_abstract",	RID_IS_ABSTRACT, D_CXXONLY },
>>> -  { "__is_aggregate",	RID_IS_AGGREGATE, D_CXXONLY },
>>> -  { "__is_base_of",	RID_IS_BASE_OF, D_CXXONLY },
>>> -  { "__is_class",	RID_IS_CLASS,	D_CXXONLY },
>>> -  { "__is_empty",	RID_IS_EMPTY,	D_CXXONLY },
>>> -  { "__is_enum",	RID_IS_ENUM,	D_CXXONLY },
>>> -  { "__is_final",	RID_IS_FINAL,	D_CXXONLY },
>>> -  { "__is_layout_compatible", RID_IS_LAYOUT_COMPATIBLE, D_CXXONLY },
>>> -  { "__is_literal_type", RID_IS_LITERAL_TYPE, D_CXXONLY },
>>> -  { "__is_pointer_interconvertible_base_of",
>>> -			RID_IS_POINTER_INTERCONVERTIBLE_BASE_OF, D_CXXONLY },
>>> -  { "__is_pod",		RID_IS_POD,	D_CXXONLY },
>>> -  { "__is_polymorphic",	RID_IS_POLYMORPHIC, D_CXXONLY },
>>> -  { "__is_same",     RID_IS_SAME_AS, D_CXXONLY },
>>> -  { "__is_same_as",     RID_IS_SAME_AS, D_CXXONLY },
>>> -  { "__is_standard_layout", RID_IS_STD_LAYOUT, D_CXXONLY },
>>> -  { "__is_trivial",     RID_IS_TRIVIAL, D_CXXONLY },
>>> -  { "__is_trivially_assignable", RID_IS_TRIVIALLY_ASSIGNABLE, D_CXXONLY },
>>> -  { "__is_trivially_constructible", RID_IS_TRIVIALLY_CONSTRUCTIBLE,
>>> D_CXXONLY },
>>> -  { "__is_trivially_copyable", RID_IS_TRIVIALLY_COPYABLE, D_CXXONLY },
>>> -  { "__is_union",	RID_IS_UNION,	D_CXXONLY },
>>>      { "__label__",	RID_LABEL,	0 },
>>>      { "__null",		RID_NULL,	0 },
>>>      { "__real",		RID_REALPART,	0 },
>>> @@ -453,7 +420,6 @@ const struct c_common_resword c_common_reswords[] =
>>>      { "__transaction_cancel", RID_TRANSACTION_CANCEL, 0 },
>>>      { "__typeof",		RID_TYPEOF,	0 },
>>>      { "__typeof__",	RID_TYPEOF,	0 },
>>> -  { "__underlying_type", RID_UNDERLYING_TYPE, D_CXXONLY },
>>>      { "__volatile",	RID_VOLATILE,	0 },
>>>      { "__volatile__",	RID_VOLATILE,	0 },
>>>      { "__GIMPLE",		RID_GIMPLE,	D_CONLY },
>>> @@ -537,19 +503,13 @@ const struct c_common_resword c_common_reswords[] =
>>>      { "volatile",		RID_VOLATILE,	0 },
>>>      { "wchar_t",		RID_WCHAR,	D_CXXONLY },
>>>      { "while",		RID_WHILE,	0 },
>>> -  { "__is_assignable", RID_IS_ASSIGNABLE, D_CXXONLY },
>>> -  { "__is_constructible", RID_IS_CONSTRUCTIBLE, D_CXXONLY },
>>> -  { "__is_nothrow_assignable", RID_IS_NOTHROW_ASSIGNABLE, D_CXXONLY },
>>> -  { "__is_nothrow_constructible", RID_IS_NOTHROW_CONSTRUCTIBLE, D_CXXONLY
>>> },
>>> -  { "__is_convertible", RID_IS_CONVERTIBLE, D_CXXONLY },
>>> -  { "__is_nothrow_convertible", RID_IS_NOTHROW_CONVERTIBLE, D_CXXONLY },
>>> -  { "__reference_constructs_from_temporary",
>>> RID_REF_CONSTRUCTS_FROM_TEMPORARY,
>>> -					D_CXXONLY },
>>> -  { "__reference_converts_from_temporary", RID_REF_CONVERTS_FROM_TEMPORARY,
>>> -					D_CXXONLY },
>>> -  { "__remove_cv", RID_REMOVE_CV, D_CXXONLY },
>>> -  { "__remove_reference", RID_REMOVE_REFERENCE, D_CXXONLY },
>>> -  { "__remove_cvref", RID_REMOVE_CVREF, D_CXXONLY },
>>> +
>>> +#define DEFTRAIT(TCC, CODE, NAME, ARITY) \
>>> +  { NAME,		RID_##CODE,	D_CXXONLY },
>>> +#include "cp/cp-trait.def"
>>> +#undef DEFTRAIT
>>> +  /* An alias for __is_same.  */
>>> +  { "__is_same_as",	RID_IS_SAME_AS, D_CXXONLY },
>>>        /* C++ transactional memory.  */
>>>      { "synchronized",	RID_SYNCHRONIZED, D_CXX_OBJC | D_TRANSMEM },
>>> diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
>>> index d5c98d306ce..5f470d94f4a 100644
>>> --- a/gcc/c-family/c-common.h
>>> +++ b/gcc/c-family/c-common.h
>>> @@ -163,31 +163,14 @@ enum rid
>>>      RID_CONSTCAST, RID_DYNCAST, RID_REINTCAST, RID_STATCAST,
>>>        /* C++ extensions */
>>> -  RID_ADDRESSOF,               RID_BASES,
>>> -  RID_BUILTIN_LAUNDER,         RID_DIRECT_BASES,
>>> -  RID_HAS_NOTHROW_ASSIGN,      RID_HAS_NOTHROW_CONSTRUCTOR,
>>> -  RID_HAS_NOTHROW_COPY,        RID_HAS_TRIVIAL_ASSIGN,
>>> -  RID_HAS_TRIVIAL_CONSTRUCTOR, RID_HAS_TRIVIAL_COPY,
>>> -  RID_HAS_TRIVIAL_DESTRUCTOR,  RID_HAS_UNIQUE_OBJ_REPRESENTATIONS,
>>> -  RID_HAS_VIRTUAL_DESTRUCTOR,  RID_BUILTIN_BIT_CAST,
>>> -  RID_IS_ABSTRACT,             RID_IS_AGGREGATE,
>>> -  RID_IS_BASE_OF,              RID_IS_CLASS,
>>> -  RID_IS_EMPTY,                RID_IS_ENUM,
>>> -  RID_IS_FINAL,                RID_IS_LAYOUT_COMPATIBLE,
>>> -  RID_IS_LITERAL_TYPE,
>>> -  RID_IS_POINTER_INTERCONVERTIBLE_BASE_OF,
>>> -  RID_IS_POD,                  RID_IS_POLYMORPHIC,
>>> -  RID_IS_SAME_AS,
>>> -  RID_IS_STD_LAYOUT,           RID_IS_TRIVIAL,
>>> -  RID_IS_TRIVIALLY_ASSIGNABLE, RID_IS_TRIVIALLY_CONSTRUCTIBLE,
>>> -  RID_IS_TRIVIALLY_COPYABLE,
>>> -  RID_IS_UNION,                RID_UNDERLYING_TYPE,
>>> -  RID_IS_ASSIGNABLE,           RID_IS_CONSTRUCTIBLE,
>>> -  RID_IS_NOTHROW_ASSIGNABLE,   RID_IS_NOTHROW_CONSTRUCTIBLE,
>>> -  RID_IS_CONVERTIBLE,		RID_IS_NOTHROW_CONVERTIBLE,
>>> -  RID_REF_CONSTRUCTS_FROM_TEMPORARY,
>>> -  RID_REF_CONVERTS_FROM_TEMPORARY,
>>> -  RID_REMOVE_CV, RID_REMOVE_REFERENCE, RID_REMOVE_CVREF,
>>> +  RID_ADDRESSOF,
>>> +  RID_BUILTIN_LAUNDER,
>>> +  RID_BUILTIN_BIT_CAST,
>>> +
>>> +#define DEFTRAIT(TCC, CODE, NAME, ARITY) \
>>> +  RID_##CODE,
>>> +#include "cp/cp-trait.def"
>>> +#undef DEFTRAIT
>>>        /* C++11 */
>>>      RID_CONSTEXPR, RID_DECLTYPE, RID_NOEXCEPT, RID_NULLPTR,
>>> RID_STATIC_ASSERT,
>>> diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
>>> index ca73aff3f38..f4145571d92 100644
>>> --- a/gcc/cp/constraint.cc
>>> +++ b/gcc/cp/constraint.cc
>>> @@ -3711,13 +3711,11 @@ diagnose_trait_expr (tree expr, tree args)
>>>          inform (loc, "  %qT is not a reference that binds to a temporary "
>>>    	      "object of type %qT (copy-initialization)", t1, t2);
>>>          break;
>>> -    case CPTK_BASES:
>>> -    case CPTK_DIRECT_BASES:
>>> -    case CPTK_UNDERLYING_TYPE:
>>> -    case CPTK_REMOVE_CV:
>>> -    case CPTK_REMOVE_REFERENCE:
>>> -    case CPTK_REMOVE_CVREF:
>>> -      /* We shouldn't see these non-expression traits.  */
>>> +#define DEFTRAIT_TYPE(CODE, NAME, ARITY) \
>>> +    case CPTK_##CODE:
>>> +#include "cp-trait.def"
>>> +#undef DEFTRAIT_TYPE
>>> +      /* Type-yielding traits aren't expressions.  */
>>>          gcc_unreachable ();
>>>        /* We deliberately omit the default case so that when adding a new
>>>           trait we'll get reminded (by way of a warning) to handle it here.
>>> */
>>> diff --git a/gcc/cp/cp-objcp-common.cc b/gcc/cp/cp-objcp-common.cc
>>> index 2d3f206b530..e4df30d9720 100644
>>> --- a/gcc/cp/cp-objcp-common.cc
>>> +++ b/gcc/cp/cp-objcp-common.cc
>>> @@ -430,46 +430,10 @@ names_builtin_p (const char *name)
>>>        case RID_BUILTIN_ASSOC_BARRIER:
>>>        case RID_BUILTIN_BIT_CAST:
>>>        case RID_OFFSETOF:
>>> -    case RID_HAS_NOTHROW_ASSIGN:
>>> -    case RID_HAS_NOTHROW_CONSTRUCTOR:
>>> -    case RID_HAS_NOTHROW_COPY:
>>> -    case RID_HAS_TRIVIAL_ASSIGN:
>>> -    case RID_HAS_TRIVIAL_CONSTRUCTOR:
>>> -    case RID_HAS_TRIVIAL_COPY:
>>> -    case RID_HAS_TRIVIAL_DESTRUCTOR:
>>> -    case RID_HAS_UNIQUE_OBJ_REPRESENTATIONS:
>>> -    case RID_HAS_VIRTUAL_DESTRUCTOR:
>>> -    case RID_IS_ABSTRACT:
>>> -    case RID_IS_AGGREGATE:
>>> -    case RID_IS_BASE_OF:
>>> -    case RID_IS_CLASS:
>>> -    case RID_IS_EMPTY:
>>> -    case RID_IS_ENUM:
>>> -    case RID_IS_FINAL:
>>> -    case RID_IS_LAYOUT_COMPATIBLE:
>>> -    case RID_IS_LITERAL_TYPE:
>>> -    case RID_IS_POINTER_INTERCONVERTIBLE_BASE_OF:
>>> -    case RID_IS_POD:
>>> -    case RID_IS_POLYMORPHIC:
>>> -    case RID_IS_SAME_AS:
>>> -    case RID_IS_STD_LAYOUT:
>>> -    case RID_IS_TRIVIAL:
>>> -    case RID_IS_TRIVIALLY_ASSIGNABLE:
>>> -    case RID_IS_TRIVIALLY_CONSTRUCTIBLE:
>>> -    case RID_IS_TRIVIALLY_COPYABLE:
>>> -    case RID_IS_UNION:
>>> -    case RID_IS_ASSIGNABLE:
>>> -    case RID_IS_CONSTRUCTIBLE:
>>> -    case RID_IS_NOTHROW_ASSIGNABLE:
>>> -    case RID_IS_NOTHROW_CONSTRUCTIBLE:
>>> -    case RID_UNDERLYING_TYPE:
>>> -    case RID_IS_CONVERTIBLE:
>>> -    case RID_IS_NOTHROW_CONVERTIBLE:
>>> -    case RID_REF_CONSTRUCTS_FROM_TEMPORARY:
>>> -    case RID_REF_CONVERTS_FROM_TEMPORARY:
>>> -    case RID_REMOVE_CV:
>>> -    case RID_REMOVE_REFERENCE:
>>> -    case RID_REMOVE_CVREF:
>>> +#define DEFTRAIT(TCC, CODE, NAME, ARITY) \
>>> +    case RID_##CODE:
>>> +#include "cp-trait.def"
>>> +#undef DEFTRAIT
>>>          return true;
>>>        default:
>>>          break;
>>> diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
>>> new file mode 100644
>>> index 00000000000..922348a1659
>>> --- /dev/null
>>> +++ b/gcc/cp/cp-trait.def
>>> @@ -0,0 +1,106 @@
>>> +/* This file contains the definitions for C++-specific built-in traits.
>>> +
>>> +   Copyright The GNU Toolchain Authors.
>>> +
>>> +   This file is part of GCC.
>>> +
>>> +   GCC is free software; you can redistribute it and/or modify
>>> +   it under the terms of the GNU General Public License as published by
>>> +   the Free Software Foundation; either version 3, or (at your option)
>>> +   any later version.
>>> +
>>> +   GCC is distributed in the hope that it will be useful,
>>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> +   GNU General Public License for more details.
>>> +
>>> +   You should have received a copy of the GNU General Public License
>>> +   along with GCC; see the file COPYING3.  If not see
>>> +   <http://www.gnu.org/licenses/>.  */
>>> +
>>> +/* Add a DEFTRAIT_EXPR (CODE, NAME, N) line to this file to define an
>>> +   expression-yielding built-in trait that has internal code name CODE, is
>>> +   spelled as NAME and takes N type arguments (where N is either 1, 2, or
>>> +   the special value -1 which denotes that it takes at least one argument).
>>> +   Such traits are represented as TRAIT_EXPR tree whose TRAIT_EXPR_KIND is
>>> +   CPTK_CODE.  Define the behavior of the trait in finish_trait_expr.  */
>>> +
>>> +/* Add a DEFTRAIT_TYPE (CODE, NAME, N) line to this file to define a
>>> +   type-yielding built-in trait as described above.  Such traits are
>>> +   generally represented as a TRAIT_TYPE tree whose TRAIT_TYPE_KIND is
>>> +   CPTK_CODE (exceptions are BASES and DIRECT_BASES below).  Define the
>>> +   behavior of the trait in finish_trait_type.  */
>>> +
>>> +#ifdef DEFTRAIT
>>> +#define DEFTRAIT_EXPR(CODE, NAME, ARITY) DEFTRAIT(tcc_expression, CODE,
>>> NAME, ARITY)
>>> +#define DEFTRAIT_TYPE(CODE, NAME, ARITY) DEFTRAIT(tcc_type, CODE, NAME,
>>> ARITY)
>>> +#define DEFTRAIT_EXPR_DEFAULTED
>>> +#define DEFTRAIT_TYPE_DEFAULTED
>>> +#endif
>>> +
>>> +#ifndef DEFTRAIT_EXPR
>>> +#define DEFTRAIT_EXPR(CODE, NAME, ARITY)
>>> +#define DEFTRAIT_EXPR_DEFAULTED
>>> +#endif
>>> +
>>> +#ifndef DEFTRAIT_TYPE
>>> +#define DEFTRAIT_TYPE(CODE, NAME, ARITY)
>>> +#define DEFTRAIT_TYPE_DEFAULTED
>>> +#endif
>>> +
>>> +DEFTRAIT_EXPR (HAS_NOTHROW_ASSIGN, "__has_nothrow_assign", 1)
>>> +DEFTRAIT_EXPR (HAS_NOTHROW_CONSTRUCTOR, "__has_nothrow_constructor", 1)
>>> +DEFTRAIT_EXPR (HAS_NOTHROW_COPY, "__has_nothrow_copy", 1)
>>> +DEFTRAIT_EXPR (HAS_TRIVIAL_ASSIGN, "__has_trivial_assign", 1)
>>> +DEFTRAIT_EXPR (HAS_TRIVIAL_CONSTRUCTOR, "__has_trivial_constructor", 1)
>>> +DEFTRAIT_EXPR (HAS_TRIVIAL_COPY, "__has_trivial_copy", 1)
>>> +DEFTRAIT_EXPR (HAS_TRIVIAL_DESTRUCTOR, "__has_trivial_destructor", 1)
>>> +DEFTRAIT_EXPR (HAS_UNIQUE_OBJ_REPRESENTATIONS,
>>> "__has_unique_object_representations", 1)
>>> +DEFTRAIT_EXPR (HAS_VIRTUAL_DESTRUCTOR, "__has_virtual_destructor", 1)
>>> +DEFTRAIT_EXPR (IS_ABSTRACT, "__is_abstract", 1)
>>> +DEFTRAIT_EXPR (IS_AGGREGATE, "__is_aggregate", 1)
>>> +DEFTRAIT_EXPR (IS_ASSIGNABLE, "__is_assignable", 2)
>>> +DEFTRAIT_EXPR (IS_BASE_OF, "__is_base_of", 2)
>>> +DEFTRAIT_EXPR (IS_CLASS, "__is_class", 1)
>>> +DEFTRAIT_EXPR (IS_CONSTRUCTIBLE, "__is_constructible", -1)
>>> +DEFTRAIT_EXPR (IS_CONVERTIBLE, "__is_convertible", 2)
>>> +DEFTRAIT_EXPR (IS_EMPTY, "__is_empty", 1)
>>> +DEFTRAIT_EXPR (IS_ENUM, "__is_enum", 1)
>>> +DEFTRAIT_EXPR (IS_FINAL, "__is_final", 1)
>>> +DEFTRAIT_EXPR (IS_LAYOUT_COMPATIBLE, "__is_layout_compatible", 2)
>>> +DEFTRAIT_EXPR (IS_LITERAL_TYPE, "__is_literal_type", 1)
>>> +DEFTRAIT_EXPR (IS_NOTHROW_ASSIGNABLE, "__is_nothrow_assignable", 2)
>>> +DEFTRAIT_EXPR (IS_NOTHROW_CONSTRUCTIBLE, "__is_nothrow_constructible", -1)
>>> +DEFTRAIT_EXPR (IS_NOTHROW_CONVERTIBLE, "__is_nothrow_convertible", 2)
>>> +DEFTRAIT_EXPR (IS_POINTER_INTERCONVERTIBLE_BASE_OF,
>>> "__is_pointer_interconvertible_base_of", 2)
>>> +DEFTRAIT_EXPR (IS_POD, "__is_pod", 1)
>>> +DEFTRAIT_EXPR (IS_POLYMORPHIC, "__is_polymorphic", 1)
>>> +DEFTRAIT_EXPR (IS_SAME_AS, "__is_same", 2)
>>
>> Can we make the code and name agree?  I don't feel strongly about which way.
> 
> I suppose we should keep __is_same as the canonical spelling (as per
> PR92271), so changing the code name seems preferable.  Like so?

OK, thanks.

> -- >8 --
> 
> Subject: [PATCH] c++: rename IS_SAME_AS trait code to IS_SAME
> 
> ... to match the canonical spelling __is_same of the trait itself
> (also spelled as __is_same_as).
> 
> gcc/c-family/ChangeLog:
> 
> 	* c-common.cc (c_common_reswords): Use RID_IS_SAME instead of
> 	RID_IS_SAME_AS.
> 
> gcc/cp/ChangeLog:
> 
> 	* constraint.cc (diagnose_trait_expr): Use CPTK_IS_SAME instead
> 	of CPTK_IS_SAME_AS.
> 	* cp-trait.def (IS_SAME_AS): Rename to ...
> 	(IS_SAME): ... this.
> 	* pt.cc (alias_ctad_tweaks): Use CPTK_IS_SAME instead of
> 	CPTK_IS_SAME_AS.
> 	* semantics.cc (trait_expr_value): Likewise.
> 	(finish_trait_expr): Likewise.
> ---
>   gcc/c-family/c-common.cc | 2 +-
>   gcc/cp/constraint.cc     | 2 +-
>   gcc/cp/cp-trait.def      | 2 +-
>   gcc/cp/pt.cc             | 2 +-
>   gcc/cp/semantics.cc      | 4 ++--
>   5 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
> index 3c60a89bfe2..4f9878d2695 100644
> --- a/gcc/c-family/c-common.cc
> +++ b/gcc/c-family/c-common.cc
> @@ -509,7 +509,7 @@ const struct c_common_resword c_common_reswords[] =
>   #include "cp/cp-trait.def"
>   #undef DEFTRAIT
>     /* An alias for __is_same.  */
> -  { "__is_same_as",	RID_IS_SAME_AS, D_CXXONLY },
> +  { "__is_same_as",	RID_IS_SAME,	D_CXXONLY },
>   
>     /* C++ transactional memory.  */
>     { "synchronized",	RID_SYNCHRONIZED, D_CXX_OBJC | D_TRANSMEM },
> diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> index f4145571d92..74898ca1a23 100644
> --- a/gcc/cp/constraint.cc
> +++ b/gcc/cp/constraint.cc
> @@ -3649,7 +3649,7 @@ diagnose_trait_expr (tree expr, tree args)
>       case CPTK_IS_POLYMORPHIC:
>         inform (loc, "  %qT is not a polymorphic type", t1);
>         break;
> -    case CPTK_IS_SAME_AS:
> +    case CPTK_IS_SAME:
>         inform (loc, "  %qT is not the same as %qT", t1, t2);
>         break;
>       case CPTK_IS_STD_LAYOUT:
> diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
> index 922348a1659..823899a26c5 100644
> --- a/gcc/cp/cp-trait.def
> +++ b/gcc/cp/cp-trait.def
> @@ -75,7 +75,7 @@ DEFTRAIT_EXPR (IS_NOTHROW_CONVERTIBLE, "__is_nothrow_convertible", 2)
>   DEFTRAIT_EXPR (IS_POINTER_INTERCONVERTIBLE_BASE_OF, "__is_pointer_interconvertible_base_of", 2)
>   DEFTRAIT_EXPR (IS_POD, "__is_pod", 1)
>   DEFTRAIT_EXPR (IS_POLYMORPHIC, "__is_polymorphic", 1)
> -DEFTRAIT_EXPR (IS_SAME_AS, "__is_same", 2)
> +DEFTRAIT_EXPR (IS_SAME, "__is_same", 2)
>   DEFTRAIT_EXPR (IS_STD_LAYOUT, "__is_standard_layout", 1)
>   DEFTRAIT_EXPR (IS_TRIVIAL, "__is_trivial", 1)
>   DEFTRAIT_EXPR (IS_TRIVIALLY_ASSIGNABLE, "__is_trivially_assignable", 2)
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 258f76d6e47..bce2a777922 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -30029,7 +30029,7 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
>   	      /* FIXME this should mean they don't compare as equivalent.  */
>   	      || dependent_alias_template_spec_p (atype, nt_opaque))
>   	    {
> -	      tree same = finish_trait_expr (loc, CPTK_IS_SAME_AS, atype, ret);
> +	      tree same = finish_trait_expr (loc, CPTK_IS_SAME, atype, ret);
>   	      ci = append_constraint (ci, same);
>   	    }
>   
> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> index 4fb0675cca9..5cc5a001498 100644
> --- a/gcc/cp/semantics.cc
> +++ b/gcc/cp/semantics.cc
> @@ -12007,7 +12007,7 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
>       case CPTK_IS_POLYMORPHIC:
>         return CLASS_TYPE_P (type1) && TYPE_POLYMORPHIC_P (type1);
>   
> -    case CPTK_IS_SAME_AS:
> +    case CPTK_IS_SAME:
>         return same_type_p (type1, type2);
>   
>       case CPTK_IS_STD_LAYOUT:
> @@ -12193,7 +12193,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
>       case CPTK_IS_CLASS:
>       case CPTK_IS_ENUM:
>       case CPTK_IS_UNION:
> -    case CPTK_IS_SAME_AS:
> +    case CPTK_IS_SAME:
>         break;
>   
>       case CPTK_IS_LAYOUT_COMPATIBLE: