Re: [PATCH v2] c++: parser - Support for target address spaces in C++

[Jason Merrill <jason@redhat.com>]

On 10/11/22 18:03, Paul Iannetta wrote:
> Thank you very much for the comments.
> 
> On Mon, Oct 10, 2022 at 03:20:13PM -0400, Jason Merrill wrote:
>> On 10/9/22 12:12, Paul Iannetta wrote:
>>> That's a nice feature! LLVM is using AS<number> to mangle the
>>> address-name qualified types but that would have required an update of
>>> libiberty's demangler in the binutils as well.
>>
>> And they haven't proposed this mangling to
>>
>>    https://github.com/itanium-cxx-abi/cxx-abi/
>>
>> yet, either.
> 
> When looking at clang/lib/AST/{Microsoft,Itamium}Mangle.cpp, the
> comments may suggest that they wanted to implement them as extended
> qualifiers prefixed by an `U' but that's not what they ended up doing.
> 
>> You certainly want some template tests, say
>>
>> template <class T>
>> int f (T *p) { return *p; }
>> __seg_fs int *a;
>> int main() { f(a); }
>> // test for mangling of f<__seg_fs int>
>>
>> -----
>>
>> template <class T>
>> int f (T __seg_gs *p) { return *p; }
>> __seg_fs int *a;
>> int main() { f(a); } // error, conflicting address spaces
> 
> Indeed, I was getting the first one right by a stroke of luck but not
> the second.  I've consequently adapted the part which checks and
> computes the unification of cv-qualifiers in the presence of address
> spaces.  The idea being that a type parameter T can match any address
> spaces but an address-space qualified parameter can't accept more
> general address spaces than itself.
> 
>>> +/* Return true if between two named address spaces, whether there is a superset
>>> +   named address space that encompasses both address spaces.  If there is a
>>> +   superset, return which address space is the superset.  */
>>> +
>>> +bool
>>> +addr_space_superset (addr_space_t as1, addr_space_t as2,
>>> +		     addr_space_t * common)
>>> +{
>>> +  if (as1 == as2)
>>> +    {
>>> +      *common = as1;
>>> +      return true;
>>> +    }
>>> +  else if (targetm.addr_space.subset_p (as1, as2))
>>> +    {
>>> +      *common = as2;
>>> +      return true;
>>> +    }
>>> +  else if (targetm.addr_space.subset_p (as2, as1))
>>> +    {
>>> +      *common = as1;
>>> +      return true;
>>> +    }
>>> +  else
>>> +    return false;
>>
>> So it's not possible for the two spaces to both be subsets of a third?
>>
> 
> According to the [N1275, page 38]:
> Address spaces may overlap in a nested fashion. For any two address
> spaces, either the address spaces must be disjoint, they must be
> equivalent, or one must be a subset of the other. [...] There is no
> requirement that named address spaces (intrinsic or otherwise) be
> subsets of the generic address space.
> [N1275]: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1275.pdf
> 
> Hence, two disjoint address spaces can't be subsets of a third, per
> the draft.
> 
>>
>> New non-bit-fields should be added before the bit-fields.
>>
> 
> Done.
> 
>>> diff --git a/gcc/cp/mangle.cc b/gcc/cp/mangle.cc
>>> index eb53e0ebeb4..06625ad9a4b 100644
>>> --- a/gcc/cp/mangle.cc
>>> +++ b/gcc/cp/mangle.cc
>>> @@ -2509,6 +2509,15 @@ write_CV_qualifiers_for_type (const tree type)
>>>         array.  */
>>>      cp_cv_quals quals = TYPE_QUALS (type);
>>> +  if (DECODE_QUAL_ADDR_SPACE (quals))
>>> +    {
>>> +      addr_space_t as = DECODE_QUAL_ADDR_SPACE (quals);
>>
>> This can be
>>
>> if (addr_space_t as = DECODE_QUAL_ADDR_SPACE (quals))
>>
>> so you don't need to repeat it.
> 
> I thought this was c++17 only, but in fact c++17 only broadened the
> idiom.  Nice! (It would be even nicer to have this feature in C as
> well)
>>> diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
>>> index 763df6f479b..110ceafc98b 100644
>>> --- a/gcc/cp/parser.cc
>>> +++ b/gcc/cp/parser.cc
>>> [...]
>>> @@ -23812,6 +23830,13 @@ cp_parser_cv_qualifier_seq_opt (cp_parser* parser)
>>>    	  break;
>>>    	}
>>> +      if (RID_FIRST_ADDR_SPACE <= token->keyword &&
>>> +	  token->keyword <= RID_LAST_ADDR_SPACE)
>>> +	{
>>> +	  cv_qualifier =
>>> +	    ENCODE_QUAL_ADDR_SPACE (token->keyword - RID_FIRST_ADDR_SPACE);
>>> +	}
>>
>> We usually omit braces around a single statement.
>>
> Done.
> 
> # ------------------------ >8 ------------------------
> Add support for custom address spaces in C++
> 
> gcc/
>          * tree.h (ENCODE_QUAL_ADDR_SPACE): Missing parentheses.
> 
> gcc/c/
>          * c-decl.cc: Remove c_register_addr_space.
> 
> gcc/c-family/
>          * c-common.cc (c_register_addr_space): Imported from c-decl.cc
>          (addr_space_superset): Imported from gcc/c/c-typecheck.cc
>          * c-common.h: Remove the FIXME.
>          (addr_space_superset): New declaration.
> 
> gcc/cp/
>          * cp-tree.h (enum cp_decl_spec): Add addr_space support.
>          (struct cp_decl_specifier_seq): Likewise.
>          * decl.cc (get_type_quals): Likewise.
>          (check_tag_decl): Likewise.
>          * parser.cc (cp_parser_type_specifier): Likewise.
>          (cp_parser_cv_qualifier_seq_opt): Likewise.
>          (cp_parser_postfix_expression): Likewise.
>          (cp_parser_type_specifier): Likewise.
>          (set_and_check_decl_spec_loc): Likewise.
>          * typeck.cc (composite_pointer_type): Likewise
>          (comp_ptr_ttypes_real): Likewise.
>          * pt.cc (check_cv_quals_for_unify): Likewise.
>          (unify): Likewise.
>          * tree.cc: Remove c_register_addr_space stub.
>          * mangle.cc (write_CV_qualifiers_for_type): Mangle address spaces
>            using the extended qualifier notation.
> 
> gcc/doc
>          * extend.texi (Named Address Spaces): add a mention about C++
>            support.
> 
> gcc/testsuite/
>          * g++.dg/abi/mangle-addr-space1.C: New test.
>          * g++.dg/abi/mangle-addr-space2.C: New test.
>          * g++.dg/parse/addr-space.C: New test.
>          * g++.dg/parse/addr-space1.C: New test.
>          * g++.dg/parse/addr-space2.C: New test.
>          * g++.dg/parse/template/spec-addr-space.C: New test.
> 
> # ------------------------ >8 ------------------------
> diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
> index bb0544eeaea..ff1146ecc25 100644
> --- a/gcc/c-family/c-common.cc
> +++ b/gcc/c-family/c-common.cc
> @@ -615,6 +615,33 @@ c_addr_space_name (addr_space_t as)
>     return IDENTIFIER_POINTER (ridpointers [rid]);
>   }
>   
> +/* Return true if between two named address spaces, whether there is a superset
> +   named address space that encompasses both address spaces.  If there is a
> +   superset, return which address space is the superset.  */
> +
> +bool
> +addr_space_superset (addr_space_t as1, addr_space_t as2,
> +		     addr_space_t * common)
> +{
> +  if (as1 == as2)
> +    {
> +      *common = as1;
> +      return true;
> +    }
> +  else if (targetm.addr_space.subset_p (as1, as2))
> +    {
> +      *common = as2;
> +      return true;
> +    }
> +  else if (targetm.addr_space.subset_p (as2, as1))
> +    {
> +      *common = as1;
> +      return true;
> +    }
> +  else
> +    return false;
> +}
> +
>   /* Push current bindings for the function name VAR_DECLS.  */
>   
>   void
> @@ -2809,6 +2836,25 @@ c_build_bitfield_integer_type (unsigned HOST_WIDE_INT width, int unsignedp)
>     return build_nonstandard_integer_type (width, unsignedp);
>   }
>   
> +/* Register reserved keyword WORD as qualifier for address space AS.  */
> +
> +void
> +c_register_addr_space (const char *word, addr_space_t as)
> +{
> +  int rid = RID_FIRST_ADDR_SPACE + as;
> +  tree id;
> +
> +  /* Address space qualifiers are only supported
> +     in C with GNU extensions enabled.  */
> +  if (c_dialect_objc () || flag_no_asm)
> +    return;
> +
> +  id = get_identifier (word);
> +  C_SET_RID_CODE (id, rid);
> +  TREE_LANG_FLAG_0 (id) = 1;
> +  ridpointers[rid] = id;
> +}
> +
>   /* The C version of the register_builtin_type langhook.  */
>   
>   void
> diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
> index 52a85bfb783..d36f9e4975b 100644
> --- a/gcc/c-family/c-common.h
> +++ b/gcc/c-family/c-common.h
> @@ -829,12 +829,11 @@ extern const struct attribute_spec c_common_format_attribute_table[];
>   
>   extern tree (*make_fname_decl) (location_t, tree, int);
>   
> -/* In c-decl.cc and cp/tree.cc.  FIXME.  */
> -extern void c_register_addr_space (const char *str, addr_space_t as);
> -
>   /* In c-common.cc.  */
>   extern bool in_late_binary_op;
>   extern const char *c_addr_space_name (addr_space_t as);
> +extern const char *c_addr_space_name (addr_space_t as);
> +extern bool addr_space_superset (addr_space_t, addr_space_t, addr_space_t *);
>   extern tree identifier_global_value (tree);
>   extern tree identifier_global_tag (tree);
>   extern bool names_builtin_p (const char *);
> @@ -952,6 +951,7 @@ extern void c_common_finish (void);
>   extern void c_common_parse_file (void);
>   extern FILE *get_dump_info (int, dump_flags_t *);
>   extern alias_set_type c_common_get_alias_set (tree);
> +extern void c_register_addr_space (const char *, addr_space_t);
>   extern void c_register_builtin_type (tree, const char*);
>   extern bool c_promoting_integer_type_p (const_tree);
>   extern bool self_promoting_args_p (const_tree);
> diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
> index c701f07befe..e1bb4f1cf37 100644
> --- a/gcc/c/c-decl.cc
> +++ b/gcc/c/c-decl.cc
> @@ -12337,25 +12337,6 @@ c_parse_final_cleanups (void)
>     ext_block = NULL;
>   }
>   
> -/* Register reserved keyword WORD as qualifier for address space AS.  */
> -
> -void
> -c_register_addr_space (const char *word, addr_space_t as)
> -{
> -  int rid = RID_FIRST_ADDR_SPACE + as;
> -  tree id;
> -
> -  /* Address space qualifiers are only supported
> -     in C with GNU extensions enabled.  */
> -  if (c_dialect_objc () || flag_no_asm)
> -    return;
> -
> -  id = get_identifier (word);
> -  C_SET_RID_CODE (id, rid);
> -  C_IS_RESERVED_WORD (id) = 1;
> -  ridpointers [rid] = id;
> -}
> -
>   /* Return identifier to look up for omp declare reduction.  */
>   
>   tree
> diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
> index b271af9bedb..c4b01368534 100644
> --- a/gcc/c/c-typeck.cc
> +++ b/gcc/c/c-typeck.cc
> @@ -296,32 +296,6 @@ c_type_promotes_to (tree type)
>     return type;
>   }
>   
> -/* Return true if between two named address spaces, whether there is a superset
> -   named address space that encompasses both address spaces.  If there is a
> -   superset, return which address space is the superset.  */
> -
> -static bool
> -addr_space_superset (addr_space_t as1, addr_space_t as2, addr_space_t *common)
> -{
> -  if (as1 == as2)
> -    {
> -      *common = as1;
> -      return true;
> -    }
> -  else if (targetm.addr_space.subset_p (as1, as2))
> -    {
> -      *common = as2;
> -      return true;
> -    }
> -  else if (targetm.addr_space.subset_p (as2, as1))
> -    {
> -      *common = as1;
> -      return true;
> -    }
> -  else
> -    return false;
> -}
> -
>   /* Return a variant of TYPE which has all the type qualifiers of LIKE
>      as well as those of TYPE.  */
>   
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index 72f4398a8f9..82a6d72f5df 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -6206,6 +6206,7 @@ enum cp_decl_spec {
>     ds_const,
>     ds_volatile,
>     ds_restrict,
> +  ds_addr_space,
>     ds_inline,
>     ds_virtual,
>     ds_explicit,
> @@ -6252,6 +6253,8 @@ struct cp_decl_specifier_seq {
>     cp_storage_class storage_class;
>     /* For the __intN declspec, this stores the index into the int_n_* arrays.  */
>     int int_n_idx;
> +  /* The address space that the declaration belongs to.  */
> +  addr_space_t address_space;
>     /* True iff TYPE_SPEC defines a class or enum.  */
>     BOOL_BITFIELD type_definition_p : 1;
>     /* True iff multiple types were (erroneously) specified for this
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index 9f78c500a15..16cc1917085 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -5280,6 +5280,8 @@ get_type_quals (const cp_decl_specifier_seq *declspecs)
>       type_quals |= TYPE_QUAL_VOLATILE;
>     if (decl_spec_seq_has_spec_p (declspecs, ds_restrict))
>       type_quals |= TYPE_QUAL_RESTRICT;
> +  if (decl_spec_seq_has_spec_p (declspecs, ds_addr_space))
> +    type_quals |= ENCODE_QUAL_ADDR_SPACE (declspecs->address_space);
>   
>     return type_quals;
>   }
> @@ -5402,6 +5404,10 @@ check_tag_decl (cp_decl_specifier_seq *declspecs,
>   	error_at (declspecs->locations[ds_restrict],
>   		  "%<__restrict%> can only be specified for objects and "
>   		  "functions");
> +      else if (decl_spec_seq_has_spec_p (declspecs, ds_addr_space))
> +	error_at (declspecs->locations[ds_addr_space],
> +		  "address space can only be specified for objects and "
> +		  "functions");
>         else if (decl_spec_seq_has_spec_p (declspecs, ds_thread))
>   	error_at (declspecs->locations[ds_thread],
>   		  "%<__thread%> can only be specified for objects "
> diff --git a/gcc/cp/mangle.cc b/gcc/cp/mangle.cc
> index eb53e0ebeb4..8ea6b7c903e 100644
> --- a/gcc/cp/mangle.cc
> +++ b/gcc/cp/mangle.cc
> @@ -2509,6 +2509,14 @@ write_CV_qualifiers_for_type (const tree type)
>        array.  */
>     cp_cv_quals quals = TYPE_QUALS (type);
>   
> +  if (addr_space_t as DECODE_QUAL_ADDR_SPACE (quals))

Let's still include the =, rather than rely on the parens from the macro.

> +    {
> +      const char *as_name = c_addr_space_name (as);
> +      write_char ('U');
> +      write_unsigned_number (strlen (as_name));
> +      write_string (as_name);
> +      ++num_qualifiers;
> +    }
>     if (quals & TYPE_QUAL_RESTRICT)
>       {
>         write_char ('r');
> diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> index 763df6f479b..f0169d83ab0 100644
> --- a/gcc/cp/parser.cc
> +++ b/gcc/cp/parser.cc
> @@ -7640,6 +7640,14 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p,
>   		    postfix_expression = error_mark_node;
>   		    break;
>   		  }
> +		if (type != error_mark_node
> +		    && !ADDR_SPACE_GENERIC_P (TYPE_ADDR_SPACE (type))
> +		    && current_function_decl)
> +		  {
> +		    error
> +		      ("compound literal qualified by address-space qualifier");
> +		    type = error_mark_node;
> +		  }

It surprises that this is the only place we complain about an object 
with an address-space qualifier.  Shouldn't we also complain about e.g. 
automatic variables/parameters or non-static data members with 
address-space qualified type?

>   		/* Form the representation of the compound-literal.  */
>   		postfix_expression
>   		  = finish_compound_literal (type, initializer,
> @@ -19408,6 +19416,15 @@ cp_parser_type_specifier (cp_parser* parser,
>         break;
>       }
>   
> +
> +  if (RID_FIRST_ADDR_SPACE <= keyword && keyword <= RID_LAST_ADDR_SPACE)
> +    {
> +      ds = ds_addr_space;
> +      if (is_cv_qualifier)
> +	*is_cv_qualifier = true;
> +    }
> +
> +
>     /* Handle simple keywords.  */
>     if (ds != ds_last)
>       {
> @@ -23776,6 +23793,7 @@ cp_parser_ptr_operator (cp_parser* parser,
>      GNU Extension:
>   
>      cv-qualifier:
> +     address-space-qualifier
>        __restrict__
>   
>      Returns a bitmask representing the cv-qualifiers.  */
> @@ -23812,6 +23830,11 @@ cp_parser_cv_qualifier_seq_opt (cp_parser* parser)
>   	  break;
>   	}
>   
> +      if (RID_FIRST_ADDR_SPACE <= token->keyword &&
> +	  token->keyword <= RID_LAST_ADDR_SPACE)
> +	cv_qualifier =
> +	  ENCODE_QUAL_ADDR_SPACE (token->keyword - RID_FIRST_ADDR_SPACE);
> +
>         if (!cv_qualifier)
>   	break;
>   
> @@ -32705,6 +32728,8 @@ set_and_check_decl_spec_loc (cp_decl_specifier_seq *decl_specs,
>         decl_specs->locations[ds] = location;
>         if (ds == ds_thread)
>   	decl_specs->gnu_thread_keyword_p = token_is__thread (token);
> +      else if (ds == ds_addr_space)
> +	decl_specs->address_space = token->keyword - RID_FIRST_ADDR_SPACE;
>       }
>     else
>       {
> @@ -32737,6 +32762,25 @@ set_and_check_decl_spec_loc (cp_decl_specifier_seq *decl_specs,
>   	      error_at (&richloc, "duplicate %qD", token->u.value);
>   	    }
>   	}
> +      else if (ds == ds_addr_space)
> +	{
> +	  addr_space_t as1 = decl_specs->address_space;
> +	  addr_space_t as2 = token->keyword - RID_FIRST_ADDR_SPACE;
> +
> +	  gcc_rich_location richloc (location);
> +	  richloc.add_fixit_remove ();
> +	  if (!ADDR_SPACE_GENERIC_P (as1) && !ADDR_SPACE_GENERIC_P (as2)
> +	      && as1 != as2)
> +	    error_at (&richloc,
> +		      "conflicting named address spaces (%s vs %s)",
> +		      c_addr_space_name (as1), c_addr_space_name (as2));
> +	  if (as1 == as2 && !ADDR_SPACE_GENERIC_P (as1))
> +	    error_at (&richloc,
> +		      "duplicate named address space %s",
> +		      c_addr_space_name (as1));
> +
> +	  decl_specs->address_space = as2;
> +	}
>         else
>   	{
>   	  static const char *const decl_spec_names[] = {
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index bef31416fb7..5bb5d657155 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -23655,8 +23655,19 @@ template_decl_level (tree decl)
>   static int
>   check_cv_quals_for_unify (int strict, tree arg, tree parm)
>   {
> -  int arg_quals = cp_type_quals (arg);
> -  int parm_quals = cp_type_quals (parm);
> +  int arg_quals = CLEAR_QUAL_ADDR_SPACE (cp_type_quals (arg));
> +  int parm_quals = CLEAR_QUAL_ADDR_SPACE (cp_type_quals (parm));
> +
> +  /*  Try to unify ARG's address space into PARM's address space.
> +      If PARM does not have any address space qualifiers (ie., as_parm is 0),
> +      there are no constraints on address spaces for this type.  */
> +  addr_space_t as_arg = DECODE_QUAL_ADDR_SPACE (cp_type_quals (arg));
> +  addr_space_t as_parm = DECODE_QUAL_ADDR_SPACE (cp_type_quals (parm));
> +  addr_space_t as_common;
> +  addr_space_superset (as_arg, as_parm, &as_common);
> +
> +  if (!(as_parm == as_common || as_parm == 0))
> +    return 0;
>   
>     if (TREE_CODE (parm) == TEMPLATE_TYPE_PARM
>         && !(strict & UNIFY_ALLOW_OUTER_MORE_CV_QUAL))
> @@ -24292,10 +24303,26 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
>   					 arg, parm))
>   	    return unify_cv_qual_mismatch (explain_p, parm, arg);
>   
> +	  int arg_cv_quals = cp_type_quals (arg);
> +	  int parm_cv_quals = cp_type_quals (parm);
> +
> +	  /* If PARM does not contain any address spaces constraints it can
> +	     fully match the address space of ARG.  However, if PARM contains an
> +	     address space constraints, it becomes the upper bound.  That is,
> +	     AS_ARG may be promoted to AS_PARM but not the converse.  If we
> +	     ended up here, it means that `check_cv_quals_for_unify' succeeded
> +	     and that either AS_PARM is 0 (ie., no constraints) or AS_COMMON ==
> +	     AS_PARM.  */
> +	  addr_space_t as_arg = DECODE_QUAL_ADDR_SPACE (arg_cv_quals);
> +	  addr_space_t as_parm = DECODE_QUAL_ADDR_SPACE (parm_cv_quals);
> +	  addr_space_t as_common = !as_parm ? as_arg : as_parm;
> +
>   	  /* Consider the case where ARG is `const volatile int' and
>   	     PARM is `const T'.  Then, T should be `volatile int'.  */
> -	  arg = cp_build_qualified_type_real
> -	    (arg, cp_type_quals (arg) & ~cp_type_quals (parm), tf_none);
> +	  int unified_cv =
> +	    CLEAR_QUAL_ADDR_SPACE (arg_cv_quals & ~parm_cv_quals)
> +	    | ENCODE_QUAL_ADDR_SPACE (as_common);
> +	  arg = cp_build_qualified_type_real (arg, unified_cv, tf_none);
>   	  if (arg == error_mark_node)
>   	    return unify_invalid (explain_p);
>   
> diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
> index 3b37567cbd7..5e14ac837fc 100644
> --- a/gcc/cp/tree.cc
> +++ b/gcc/cp/tree.cc
> @@ -6048,15 +6048,6 @@ cp_free_lang_data (tree t)
>       DECL_CHAIN (t) = NULL_TREE;
>   }
>   
> -/* Stub for c-common.  Please keep in sync with c-decl.cc.
> -   FIXME: If address space support is target specific, then this
> -   should be a C target hook.  But currently this is not possible,
> -   because this function is called via REGISTER_TARGET_PRAGMAS.  */
> -void
> -c_register_addr_space (const char * /*word*/, addr_space_t /*as*/)
> -{
> -}
> -
>   /* Return the number of operands in T that we care about for things like
>      mangling.  */
>   
> diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
> index ceb80d9744f..5d48920e687 100644
> --- a/gcc/cp/typeck.cc
> +++ b/gcc/cp/typeck.cc
> @@ -656,10 +656,26 @@ composite_pointer_type (const op_location_t &location,
>   	  else
>   	    return error_mark_node;
>           }
> +      /* If possible merge the address space into the superset of the address
> +	  spaces of t1 and t2, or raise an error. */
> +      addr_space_t as_t1 = TYPE_ADDR_SPACE (t1);
> +      addr_space_t as_t2 = TYPE_ADDR_SPACE (t2);
> +      addr_space_t as_common;
> +
> +      /* If the two named address spaces are different, determine the common
> +	 superset address space.  If there isn't one, raise an error.  */
> +      if (!addr_space_superset (as_t1, as_t2, &as_common))
> +	{
> +	  as_common = as_t1;
> +	  error_at (location,
> +		    "%qT and %qT are in disjoint named address spaces",
> +		    t1, t2);
> +	}
>         result_type
>   	= cp_build_qualified_type (void_type_node,
> -				   (cp_type_quals (TREE_TYPE (t1))
> -				    | cp_type_quals (TREE_TYPE (t2))));
> +				   (CLEAR_QUAL_ADDR_SPACE (cp_type_quals (TREE_TYPE (t1)))
> +				    | CLEAR_QUAL_ADDR_SPACE (cp_type_quals (TREE_TYPE (t2)))
> +				    | ENCODE_QUAL_ADDR_SPACE (as_common)));
>         result_type = build_pointer_type (result_type);
>         /* Merge the attributes.  */
>         attributes = (*targetm.merge_type_attributes) (t1, t2);
> @@ -10805,6 +10821,19 @@ comp_ptr_ttypes_real (tree to, tree from, int constp)
>   	      to_more_cv_qualified = true;
>   	    }
>   
> +      /* Warn about conversions between pointers to disjoint
> +	 address spaces.  */
> +      if (TREE_CODE (from) == POINTER_TYPE
> +	  && TREE_CODE (to) == POINTER_TYPE)
> +	{
> +	  addr_space_t as_from = TYPE_ADDR_SPACE (TREE_TYPE (from));
> +	  addr_space_t as_to = TYPE_ADDR_SPACE (TREE_TYPE (to));
> +	  addr_space_t as_common;
> +
> +	  if (!addr_space_superset (as_to, as_from, &as_common))
> +	    return false;
> +	}
> +
>   	  if (constp > 0)
>   	    constp &= TYPE_READONLY (to);
>   	}
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index ac3db88566d..1e0d436c02c 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -1448,7 +1448,7 @@ Fixed-point types are supported by the DWARF debug information format.
>   @section Named Address Spaces
>   @cindex Named Address Spaces
>   
> -As an extension, GNU C supports named address spaces as
> +As an extension, GNU C and GNU C++ support named address spaces as
>   defined in the N1275 draft of ISO/IEC DTR 18037.  Support for named
>   address spaces in GCC will evolve as the draft technical report
>   changes.  Calling conventions for any target might also change.  At
> diff --git a/gcc/testsuite/g++.dg/abi/mangle-addr-space1.C b/gcc/testsuite/g++.dg/abi/mangle-addr-space1.C
> new file mode 100644
> index 00000000000..c01f8d6054a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/abi/mangle-addr-space1.C
> @@ -0,0 +1,10 @@
> +// { dg-do run { target { i?86-*-* x86_64-*-* } } }
> +// { dg-options "-fabi-version=8 -Wabi -save-temps" }
> +// { dg-final { scan-assembler "_Z1fPU8__seg_fsVi" } }
> +
> +int f (int volatile __seg_fs *a)
> +{
> +  return *a;
> +}
> +
> +int main () {}
> diff --git a/gcc/testsuite/g++.dg/abi/mangle-addr-space2.C b/gcc/testsuite/g++.dg/abi/mangle-addr-space2.C
> new file mode 100644
> index 00000000000..862bbbdcdf2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/abi/mangle-addr-space2.C
> @@ -0,0 +1,9 @@
> +// { dg-do run { target { i?86-*-* x86_64-*-* } } }
> +// { dg-options "-fabi-version=8 -Wabi -save-temps" }
> +// { dg-final { scan-assembler "_Z1fIU8__seg_fsiEiPT_" } }
> +
> +template <class T>
> +int f (T *p) { return *p; }
> +int g (__seg_fs int *p) { return *p; }
> +__seg_fs int *a;
> +int main() { f(a); }
> diff --git a/gcc/testsuite/g++.dg/parse/addr-space.C b/gcc/testsuite/g++.dg/parse/addr-space.C
> new file mode 100644
> index 00000000000..ebb6316054a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/parse/addr-space.C
> @@ -0,0 +1,9 @@
> +// { dg-do compile { target { i?86-*-* x86_64-*-* } } }
> +
> +__seg_fs struct foo; // { dg-error "address space can only be specified for objects and functions" }
> +
> +int
> +main ()
> +{
> +	return 0;
> +}
> diff --git a/gcc/testsuite/g++.dg/parse/addr-space1.C b/gcc/testsuite/g++.dg/parse/addr-space1.C
> new file mode 100644
> index 00000000000..2e8ee32a885
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/parse/addr-space1.C
> @@ -0,0 +1,10 @@
> +// { dg-do compile { target { i?86-*-* x86_64-*-* } } }
> +// { dg-options "-std=gnu++98" }
> +
> +int
> +main ()
> +{
> +	struct foo {int a; char b[2];} structure;
> +	structure = ((__seg_fs struct foo) {1 + 2, 'a', 0}); // { dg-error "compound literal qualified by address-space qualifier" }
> +	return 0;
> +}
> diff --git a/gcc/testsuite/g++.dg/parse/addr-space2.C b/gcc/testsuite/g++.dg/parse/addr-space2.C
> new file mode 100644
> index 00000000000..5b2c0f28078
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/parse/addr-space2.C
> @@ -0,0 +1,9 @@
> +// { dg-do compile { target { i?86-*-* x86_64-*-* } } }
> +
> +__seg_fs __seg_gs int *a; // { dg-error "conflicting named address spaces .__seg_fs vs __seg_gs." }
> +
> +int
> +main ()
> +{
> +	return 0;
> +}
> diff --git a/gcc/testsuite/g++.dg/template/spec-addr-space.C b/gcc/testsuite/g++.dg/template/spec-addr-space.C
> new file mode 100644
> index 00000000000..ae9f4de0e1f
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/spec-addr-space.C
> @@ -0,0 +1,8 @@
> +// { dg-do compile { target { i?86-*-* x86_64-*-* } } }
> +
> +template <class T>
> +int f (T __seg_gs *p) { return *p; } // { dg-note "candidate: 'template<class T> int f.__seg_gs T\*." }
> +				     // { dg-note "template argument deduction/substitution failed:" "" { target *-*-* } .-1 }
> +__seg_fs int *a;
> +int main() { f(a); } // { dg-error "no matching" }
> +// { dg-note "types .__seg_gs T. and .__seg_fs int. have incompatible cv-qualifiers" "" { target *-*-* } .-1 }
> diff --git a/gcc/tree.h b/gcc/tree.h
> index 8844471e9a5..b7da4c5141a 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -2229,7 +2229,7 @@ extern tree vector_element_bits_tree (const_tree);
>   
>   /* Encode/decode the named memory support as part of the qualifier.  If more
>      than 8 qualifiers are added, these macros need to be adjusted.  */
> -#define ENCODE_QUAL_ADDR_SPACE(NUM) ((NUM & 0xFF) << 8)
> +#define ENCODE_QUAL_ADDR_SPACE(NUM) (((NUM) & 0xFF) << 8)
>   #define DECODE_QUAL_ADDR_SPACE(X) (((X) >> 8) & 0xFF)
>   
>   /* Return all qualifiers except for the address space qualifiers.  */
> 
> 
> 
>