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

[Paul Iannetta <piannetta@kalrayinc.com>]

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.

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__.

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

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.  */