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

[Jason Merrill <jason@redhat.com>]

On 10/6/22 10:34, Paul Iannetta wrote:
> Hi,
> 
> Presently, GCC supports target address spaces as a GNU extension (cf.
> `info -n "(gcc)Named Address Spaces"`).  This is however supported
> only by the C frontend, which is a bit sad, since all the GIMPLE
> machinery is readily available and, moreover, LLVM supports this GNU
> extension both for C and C++.
> 
> Here is a first attempt at a patch to enable the support for target
> address spaces in C++.  The basic idea is only to make the parser
> recognize address spaces, and lower them into GIMPLE, in the same
> fashion as the C parser.  This also makes it possible to merge the
> function `c_register_addr_space` in one place which is better than
> before.

Great.

> The patch still has some drawbacks compared to its C counterpart.
> Namely, much like the `__restrict__` keyword, it is always enabled and
> -std=c++11 won't disable it (whereas -std=c11) would reject address
> spaces.  Not also that the mangler ignores address spaces, much like
> it ignores __restrict__.

Hmm?  We mangle __restrict:

void f(int *__restrict *p) { } // _Z1fPrPi

but cv-qualifiers (including restrict) are dropped on the top-level type 
of a parameter.

If address spaces should be mangled, it probably makes sense to use the 
same <extended-qualifier> mangling that we already use for attributes in 
write_CV_qualifiers_for_type.

> Depending on the reception, I'll add further testcases and will update
> the relevant part of the documentation.

Please.

> Cheers,
> Paul
> 
> Author: Paul Iannetta <piannetta@kalray.eu>
> Date:   Wed Oct 5 16:44:36 2022 +0200
> 
>      Add support for custom address spaces in C++
> 
> gcc/
> 	* tree.h (ENCODE_QUAL_ADDR_SPACE): Missing parentheses.
> 
> gcc/c/
> 	* c-decl.c: Remove c_register_addr_space.
> 
> gcc/c-family/
> 	* c-common.c (c_register_addr_space): Imported from c-decl.c
> 	* c-common.h: Remove the FIXME.
> 
> gcc/cp/
> 	* cp-tree.h (enum cp_decl_spec): Add addr_space support.
>              (struct cp_decl_specifier_seq): Likewise.
> 	* decl.c (get_type_quals): Likewise.
> 	* parser.c (cp_parser_type_specifier): Likewise.
>              (cp_parser_cv_qualifier_seq_opt): Likewise
> 	* tree.c: Remove c_register_addr_space stub.
> 
> Signed-off-by: Paul Iannetta <piannetta@kalray.eu>
> 
> diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
> index 064c2f263f0..282ba54ab70 100644
> --- a/gcc/c-family/c-common.c
> +++ b/gcc/c-family/c-common.c
> @@ -2615,6 +2615,25 @@ 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 ed39b7764bf..f2c1df0c8de 100644
> --- a/gcc/c-family/c-common.h
> +++ b/gcc/c-family/c-common.h
> @@ -808,9 +808,6 @@ extern const struct attribute_spec c_common_format_attribute_table[];
>   
>   extern tree (*make_fname_decl) (location_t, tree, int);
>   
> -/* In c-decl.c and cp/tree.c.  FIXME.  */
> -extern void c_register_addr_space (const char *str, addr_space_t as);
> -
>   /* In c-common.c.  */
>   extern bool in_late_binary_op;
>   extern const char *c_addr_space_name (addr_space_t as);
> @@ -926,6 +923,7 @@ 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.c b/gcc/c/c-decl.c
> index 8e24b522ee4..278d1248d1c 100644
> --- a/gcc/c/c-decl.c
> +++ b/gcc/c/c-decl.c
> @@ -11927,25 +11927,6 @@ 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/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index 15ec4cd199f..4ae971ccb90 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -5974,6 +5974,7 @@ enum cp_decl_spec {
>     ds_const,
>     ds_volatile,
>     ds_restrict,
> +  ds_addr_space,
>     ds_inline,
>     ds_virtual,
>     ds_explicit,
> @@ -6046,6 +6047,8 @@ struct cp_decl_specifier_seq {
>     /* True iff the alternate "__intN__" form of the __intN type has been
>        used.  */
>     BOOL_BITFIELD int_n_alt: 1;
> +  /* The address space that the declaration belongs to.  */
> +  addr_space_t address_space;
>   };
>   
>   /* The various kinds of declarators.  */
> diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
> index 03cd0a3a238..b8fc8b58ac7 100644
> --- a/gcc/cp/decl.c
> +++ b/gcc/cp/decl.c
> @@ -4954,6 +4954,8 @@ 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;
>   }
> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
> index f48c856fa94..8d6b2a44086 100644
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -17796,6 +17796,16 @@ 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;
> +      decl_specs->address_space = keyword - RID_FIRST_ADDR_SPACE;
> +    }
> +
> +
>     /* Handle simple keywords.  */
>     if (ds != ds_last)
>       {
> @@ -21853,6 +21863,7 @@ cp_parser_ptr_operator (cp_parser* parser,
>      GNU Extension:
>   
>      cv-qualifier:
> +     address-space-qualifier
>        __restrict__
>   
>      Returns a bitmask representing the cv-qualifiers.  */
> @@ -21889,6 +21900,13 @@ 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);
> +	}
> +
>         if (!cv_qualifier)
>   	break;
>   
> diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
> index 10b818d1370..55b57085618 100644
> --- a/gcc/cp/tree.c
> +++ b/gcc/cp/tree.c
> @@ -5749,15 +5749,6 @@ cp_free_lang_data (tree t)
>       DECL_CHAIN (t) = NULL_TREE;
>   }
>   
> -/* Stub for c-common.  Please keep in sync with c-decl.c.
> -   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/tree.h b/gcc/tree.h
> index bb80e81d389..210ef7b85d7 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -2108,7 +2108,7 @@ extern machine_mode vector_type_mode (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.  */
> 
> 
> 
>