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[209.6.216.142]) by smtp.gmail.com with ESMTPSA id v57sm14099453qtv.80.2018.12.05.08.16.25 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 05 Dec 2018 08:16:25 -0800 (PST) Subject: Re: [PATCH 2/9]: C++ P0482R5 char8_t: Core language support To: Tom Honermann , gcc-patches References: <3649a3a5-df5e-b198-dcd5-a17a29df1ef5@redhat.com> <6bc5ae56-be78-865f-481a-36d257fffcb7@redhat.com> <6fc1fe2e-2330-c57e-3722-081cf95ffd8f@honermann.net> From: Jason Merrill Message-ID: <015f32d4-8651-8f82-45a5-5d8a3f813894@redhat.com> Date: Wed, 05 Dec 2018 16:16:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <6fc1fe2e-2330-c57e-3722-081cf95ffd8f@honermann.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-IsSubscribed: yes X-SW-Source: 2018-12/txt/msg00292.txt.bz2 On 12/5/18 2:09 AM, Tom Honermann wrote: > On 12/3/18 5:01 PM, Jason Merrill wrote: >> On 12/3/18 4:51 PM, Jason Merrill wrote: >>> On 11/5/18 2:39 PM, Tom Honermann wrote: >>>> This patch adds support for the P0482R5 core language changes.  This >>>> includes: >>>> - The -fchar8_t and -fno_char8_t command line options. >>>> - char8_t as a keyword. >>>> - The char8_t builtin type as a non-aliasing unsigned integral >>>>    character type of size 1. >>>> - Use of char8_t as a simple type specifier. >>>> - u8 character literals with type char8_t. >>>> - u8 string literals with type array of const char8_t. >>>> - User defined literal operators that accept char8_1 and char8_t >>>> pointer >>>>    types. >>>> - New __cpp_char8_t predefined feature test macro. >>>> - New __CHAR8_TYPE__ and __GCC_ATOMIC_CHAR8_T_LOCK_FREE predefined >>>>    macros . >>>> - Name mangling and demangling for char8_t (using Du). >>>> >>>> gcc/ChangeLog: >>>> >>>> 2018-11-04  Tom Honermann  >>>> >>>>       * defaults.h: Define CHAR8_TYPE. >>>> >>>> gcc/c-family/ChangeLog: >>>> >>>> 2018-11-04  Tom Honermann  >>>>       * c-family/c-common.c (c_common_reswords): Add char8_t. >>>>       (fix_string_type): Use char8_t for the type of u8 string >>>> literals. >>>>       (c_common_get_alias_set): char8_t doesn't alias. >>>>       (c_common_nodes_and_builtins): Define char8_t as a builtin >>>> type in >>>>       C++. >>>>       (c_stddef_cpp_builtins): Add __CHAR8_TYPE__. >>>>       (keyword_begins_type_specifier): Add RID_CHAR8. >>>>       * gcc/c-family/c-common.h (rid): Add RID_CHAR8. >>>>       (c_tree_index): Add CTI_CHAR8_TYPE and CTI_CHAR8_ARRAY_TYPE. >>>>       Define D_CXX_CHAR8_T and D_CXX_CHAR8_T_FLAGS. >>>>       Define char8_type_node and char8_array_type_node. >>>>       * c-family/c-cppbuiltin.c (cpp_atomic_builtins): Predefine >>>>       __GCC_ATOMIC_CHAR8_T_LOCK_FREE. >>>>       (c_cpp_builtins): Predefine __cpp_char8_t. >>>>       * c-family/c-lex.c (lex_string): Use char8_array_type_node as the >>>>       type of CPP_UTF8STRING. >>>>       (lex_charconst): Use char8_type_node as the type of CPP_UTF8CHAR. >>>>       * c-family/c.opt: Add the -fchar8_t command line option. >>>> >>>> gcc/c/ChangeLog: >>>> >>>> 2018-11-04  Tom Honermann  >>>> >>>>       * c/c-typeck.c (char_type_p): Add char8_type_node. >>>>       (digest_init): Handle initialization by a u8 string literal of >>>>       char8_t type. >>>> >>>> gcc/cp/ChangeLog: >>>> >>>> 2018-11-04  Tom Honermann  >>>> >>>>       * cp/cvt.c (type_promotes_to): Handle char8_t promotion. >>>>       * cp/decl.c (grokdeclarator): Handle invalid type specifier >>>>       combinations involving char8_t. >>>>       * cp/lex.c (init_reswords): Add char8_t as a reserved word. >>>>       * cp/mangle.c (write_builtin_type): Add name mangling for char8_t >>>>       (Du). >>>>       * cp/parser.c (cp_keyword_starts_decl_specifier_p, >>>>       cp_parser_simple_type_specifier): Recognize char8_t as a simple >>>>       type specifier. >>>>       (cp_parser_string_literal): Use char8_array_type_node for the >>>> type >>>>       of CPP_UTF8STRING. >>>>       (cp_parser_set_decl_spec_type): Tolerate char8_t typedefs in >>>> system >>>>       headers. >>>>       * cp/rtti.c (emit_support_tinfos): type_info support for char8_t. >>>>       * cp/tree.c (char_type_p): Recognize char8_t as a character type. >>>>       * cp/typeck.c (string_conv_p): Handle conversions of u8 string >>>>       literals of char8_t type. >>>>       (check_literal_operator_args): Handle UDLs with u8 string >>>> literals >>>>       of char8_t type. >>>>       * cp/typeck2.c (digest_init_r): Disallow initializing a char >>>> array >>>>       with a u8 string literal. >>>> >>>> libiberty/ChangeLog: >>>> >>>> 2018-10-31  Tom Honermann  >>>>       * cp-demangle.c (cplus_demangle_builtin_types, >>>>       cplus_demangle_type): Add name demangling for char8_t (Du). >>>>       * cp-demangle.h: Increase D_BUILTIN_TYPE_COUNT to accommodate the >>>>       new char8_t type. >>> >>>> @@ -3543,6 +3556,10 @@ c_common_get_alias_set (tree t) >>>>    if (!TYPE_P (t)) >>>>      return -1; >>> >>>> +  /* Unlike char, char8_t doesn't alias. */ >>>> +  if (flag_char8_t && t == char8_type_node) >>>> +    return -1; >>> >>> This seems unnecessary; doesn't the existing code have the same >>> effect? I think we could do with just an adjustment to the existing >>> comment. > I'm not sure.  I had concerns about unintended matching due to char8_t > having an underlying type of unsigned char. That shouldn't be a problem: if char8_t is a distinct type, it won't match unsigned char, and if it's the same as unsigned char, flag_char8_t will be false. >>>> +  else if (flag_char8_t && TREE_TYPE (value) == char8_array_type_node) >>>> +      || (flag_char8_t && type == char8_type_node) >>>> +      bool char8_array = (flag_char8_t && !!comptypes (typ1, >>>> char8_type_node)); >>>> +       || (flag_char8_t && type == char8_type_node >>> In many places you check the flag and then for one of the char8 >>> types. Since the types won't be used without the flag, checking the >>> flag seems redundant? > > This was again protection against unintended matching of the underlying > unsigned char type, particularly when compiling as C. char8_type_node is > constructed (in c_common_nodes_and_builtins) following the pattern in > place for char16_t and char32_t with the following code: > > +  char8_type_node = get_identifier (CHAR8_TYPE); > +  char8_type_node = TREE_TYPE (identifier_global_value (char8_type_node)); > +  char8_type_size = TYPE_PRECISION (char8_type_node); > +  if (c_dialect_cxx ()) > +    { > +      char8_type_node = make_unsigned_type (char8_type_size); > + > +      if (flag_char8_t) > +        record_builtin_type (RID_CHAR8, "char8_t", char8_type_node); > +    } > > My knowledge of gcc internals is weak, but I understand this to be, > effectively, defining a type alias (of unsigned char) and then, if > compiling as C++, re-defining it as a strong unsigned type. > > I don't recall the details now, but at one point, I was missing a check > for flag_char8_t in some location and I encountered some test failures > as a result. Since char8_type_node is always a distinct type in C++, we shouldn't need these checks in the C++ front end. And since it's never a distinct type in C, the C front end (c/*) doesn't need to change at all. >>>> -      if (TYPE_PRECISION (typ1) == BITS_PER_UNIT) >>>> +      if (TYPE_PRECISION (typ1) == BITS_PER_UNIT >>>> +          && (typ1 == char_type_node || !flag_char8_t)) >>> >>> This looks wrong, or at least incomplete; we want to complain about >>> mismatched types here even with -fchar8-t.  Perhaps we should replace >>> all of this if/else with simply comparing typ1 and char_type, and >>> complaining if they're different.  Talking about wide and non-wide >>> isn't as useful as the actual types would be. >> >> Well, I suppose it isn't quite that simple, since we still need to >> treat the ordinary character types as interchangeable. > > We do need to complain about mismatched types and test > gcc/testsuite/g++.dg/ext/char8_t-init-2.C was added to ensure that happens. You don't seem to test initializing an array of signed/unsigned char, which I think will be broken by the change only considering char_type_node. I think we want to specifically allow conversion from array of one ordinary character type to another, and otherwise complain about the types being different with a message like "cannot initialize array of %qT from array of %qT" rather than mess with terms like int-array and (non-)wide string. Jason