[PATCH] Add a simulate_record_decl lang hook

[Jason Merrill]

On 9/24/21 13:53, Richard Sandiford wrote:
> This patch adds a lang hook for defining a struct/RECORD_TYPE
> “as if” it had appeared directly in the source code.  It follows
> the similar existing hook for enums.
> 
> It's the caller's responsibility to create the fields
> (as FIELD_DECLs) but the hook's responsibility to create
> and declare the associated RECORD_TYPE.
> 
> For now the hook is hard-coded to do the equivalent of:
> 
>    typedef struct NAME { FIELDS } NAME;
> 
> but this could be controlled by an extra parameter if some callers
> want a different behaviour in future.
> 
> The motivating use case is to allow the long list of struct
> definitions in arm_neon.h to be provided by the compiler,
> which in turn unblocks various arm_neon.h optimisations.
> 
> Tested on aarch64-linux-gnu, individually and with a follow-on
> patch from Jonathan that makes use of the hook.  OK to install?
> 
> Richard
> 
> 
> gcc/
> 	* langhooks.h (lang_hooks_for_types::simulate_record_decl): New hook.
> 	* langhooks-def.h (lhd_simulate_record_decl): Declare.
> 	(LANG_HOOKS_SIMULATE_RECORD_DECL): Define.
> 	(LANG_HOOKS_FOR_TYPES_INITIALIZER): Include it.
> 	* langhooks.c (lhd_simulate_record_decl): New function.
> 
> gcc/c/
> 	* c-tree.h (c_simulate_record_decl): Declare.
> 	* c-objc-common.h (LANG_HOOKS_SIMULATE_RECORD_DECL): Override.
> 	* c-decl.c (c_simulate_record_decl): New function.
> 
> gcc/cp/
> 	* decl.c: Include langhooks-def.h.
> 	(cxx_simulate_record_decl): New function.
> 	* cp-objcp-common.h (cxx_simulate_record_decl): Declare.
> 	(LANG_HOOKS_SIMULATE_RECORD_DECL): Override.
> ---
>   gcc/c/c-decl.c           | 31 +++++++++++++++++++++++++++++++
>   gcc/c/c-objc-common.h    |  2 ++
>   gcc/c/c-tree.h           |  2 ++
>   gcc/cp/cp-objcp-common.h |  4 ++++
>   gcc/cp/decl.c            | 38 ++++++++++++++++++++++++++++++++++++++
>   gcc/langhooks-def.h      |  4 ++++
>   gcc/langhooks.c          | 21 +++++++++++++++++++++
>   gcc/langhooks.h          | 10 ++++++++++
>   8 files changed, 112 insertions(+)
> 
> diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
> index 771efa3eadf..8d1324b118c 100644
> --- a/gcc/c/c-decl.c
> +++ b/gcc/c/c-decl.c
> @@ -9436,6 +9436,37 @@ c_simulate_enum_decl (location_t loc, const char *name,
>     input_location = saved_loc;
>     return enumtype;
>   }
> +
> +/* Implement LANG_HOOKS_SIMULATE_RECORD_DECL.  */
> +
> +tree
> +c_simulate_record_decl (location_t loc, const char *name,
> +			array_slice<const tree> fields)
> +{
> +  location_t saved_loc = input_location;
> +  input_location = loc;
> +
> +  class c_struct_parse_info *struct_info;
> +  tree ident = get_identifier (name);
> +  tree type = start_struct (loc, RECORD_TYPE, ident, &struct_info);
> +
> +  for (unsigned int i = 0; i < fields.size (); ++i)
> +    {
> +      DECL_FIELD_CONTEXT (fields[i]) = type;
> +      if (i > 0)
> +	DECL_CHAIN (fields[i - 1]) = fields[i];
> +    }
> +
> +  finish_struct (loc, type, fields[0], NULL_TREE, struct_info);
> +
> +  tree decl = build_decl (loc, TYPE_DECL, ident, type);
> +  TYPE_NAME (type) = decl;
> +  TYPE_STUB_DECL (type) = decl;
> +  lang_hooks.decls.pushdecl (decl);
> +
> +  input_location = saved_loc;
> +  return type;
> +}
>   

>   /* Create the FUNCTION_DECL for a function definition.
>      DECLSPECS, DECLARATOR and ATTRIBUTES are the parts of
> diff --git a/gcc/c/c-objc-common.h b/gcc/c/c-objc-common.h
> index 7d35a0621e4..f4e8271f06c 100644
> --- a/gcc/c/c-objc-common.h
> +++ b/gcc/c/c-objc-common.h
> @@ -81,6 +81,8 @@ along with GCC; see the file COPYING3.  If not see
>   
>   #undef LANG_HOOKS_SIMULATE_ENUM_DECL
>   #define LANG_HOOKS_SIMULATE_ENUM_DECL c_simulate_enum_decl
> +#undef LANG_HOOKS_SIMULATE_RECORD_DECL
> +#define LANG_HOOKS_SIMULATE_RECORD_DECL c_simulate_record_decl
>   #undef LANG_HOOKS_TYPE_FOR_MODE
>   #define LANG_HOOKS_TYPE_FOR_MODE c_common_type_for_mode
>   #undef LANG_HOOKS_TYPE_FOR_SIZE
> diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
> index d50d0cb7f2d..8578d2d1e77 100644
> --- a/gcc/c/c-tree.h
> +++ b/gcc/c/c-tree.h
> @@ -598,6 +598,8 @@ extern tree finish_struct (location_t, tree, tree, tree,
>   			   class c_struct_parse_info *);
>   extern tree c_simulate_enum_decl (location_t, const char *,
>   				  vec<string_int_pair> *);
> +extern tree c_simulate_record_decl (location_t, const char *,
> +				    array_slice<const tree>);
>   extern struct c_arg_info *build_arg_info (void);
>   extern struct c_arg_info *get_parm_info (bool, tree);
>   extern tree grokfield (location_t, struct c_declarator *,
> diff --git a/gcc/cp/cp-objcp-common.h b/gcc/cp/cp-objcp-common.h
> index f1704aad557..d5859406e8f 100644
> --- a/gcc/cp/cp-objcp-common.h
> +++ b/gcc/cp/cp-objcp-common.h
> @@ -39,6 +39,8 @@ extern bool cp_handle_option (size_t, const char *, HOST_WIDE_INT, int,
>   extern tree cxx_make_type_hook			(tree_code);
>   extern tree cxx_simulate_enum_decl (location_t, const char *,
>   				    vec<string_int_pair> *);
> +extern tree cxx_simulate_record_decl (location_t, const char *,
> +				      array_slice<const tree>);
>   
>   /* Lang hooks that are shared between C++ and ObjC++ are defined here.  Hooks
>      specific to C++ or ObjC++ go in cp/cp-lang.c and objcp/objcp-lang.c,
> @@ -139,6 +141,8 @@ extern tree cxx_simulate_enum_decl (location_t, const char *,
>   #define LANG_HOOKS_MAKE_TYPE cxx_make_type_hook
>   #undef LANG_HOOKS_SIMULATE_ENUM_DECL
>   #define LANG_HOOKS_SIMULATE_ENUM_DECL cxx_simulate_enum_decl
> +#undef LANG_HOOKS_SIMULATE_RECORD_DECL
> +#define LANG_HOOKS_SIMULATE_RECORD_DECL cxx_simulate_record_decl
>   #undef LANG_HOOKS_TYPE_FOR_MODE
>   #define LANG_HOOKS_TYPE_FOR_MODE c_common_type_for_mode
>   #undef LANG_HOOKS_TYPE_FOR_SIZE
> diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
> index 58ddc6a537e..38f065c1c36 100644
> --- a/gcc/cp/decl.c
> +++ b/gcc/cp/decl.c
> @@ -56,6 +56,7 @@ along with GCC; see the file COPYING3.  If not see
>   #include "context.h"  /* For 'g'.  */
>   #include "omp-general.h"
>   #include "omp-offload.h"  /* For offload_vars.  */
> +#include "langhooks-def.h"  /* For lhd_simulate_record_decl  */
>   
>   /* Possible cases of bad specifiers type used by bad_specifiers. */
>   enum bad_spec_place {
> @@ -16597,6 +16598,43 @@ cxx_simulate_enum_decl (location_t loc, const char *name,
>     input_location = saved_loc;
>     return enumtype;
>   }
> +
> +/* Implement LANG_HOOKS_SIMULATE_RECORD_DECL.  */
> +
> +tree
> +cxx_simulate_record_decl (location_t loc, const char *name,
> +			  array_slice<const tree> fields)
> +{
> +  iloc_sentinel ils (loc);
> +
> +  tree ident = get_identifier (name);
> +  tree type = xref_tag (/*tag_code=*/record_type, ident);
> +  if (type != error_mark_node
> +      && (TREE_CODE (type) != RECORD_TYPE || COMPLETE_TYPE_P (type)))
> +    {
> +      error ("redefinition of %q#T", type);
> +      type = error_mark_node;
> +    }
> +  if (type == error_mark_node)
> +    return lhd_simulate_record_decl (loc, name, fields);

Why fall back to the language-independent function on error?  Is there a 
case where that gives better error recovery than just returning 
error_mark_node?

> +  xref_basetypes (type, NULL_TREE);
> +  type = begin_class_definition (type);
> +  if (type == error_mark_node)
> +    return lhd_simulate_record_decl (loc, name, fields);
> +
> +  for (tree field : fields)
> +    finish_member_declaration (field);
> +
> +  type = finish_struct (type, NULL_TREE);
> +
> +  tree decl = build_decl (loc, TYPE_DECL, ident, type);
> +  TYPE_NAME (type) = decl;
> +  TYPE_STUB_DECL (type) = decl;

Setting TYPE_NAME and TYPE_STUB_DECL to the typedef is wrong; it should 
work to just remove these two lines.  I expect they're also wrong for C.

For C++ only, I wonder if you need this typedef at all.

If you do want it, you need to use set_underlying_type to create a real 
typedef.  I expect that's also true for C.

> +  lang_hooks.decls.pushdecl (decl);
> +
> +  return type;
> +}
>   

>   /* We're defining DECL.  Make sure that its type is OK.  */
>   
> diff --git a/gcc/langhooks-def.h b/gcc/langhooks-def.h
> index 02b4681dd96..5f17620aaeb 100644
> --- a/gcc/langhooks-def.h
> +++ b/gcc/langhooks-def.h
> @@ -56,6 +56,8 @@ extern void lhd_overwrite_decl_assembler_name (tree decl, tree name);
>   extern bool lhd_warn_unused_global_decl (const_tree);
>   extern tree lhd_simulate_enum_decl (location_t, const char *,
>   				    vec<string_int_pair> *);
> +extern tree lhd_simulate_record_decl (location_t, const char *,
> +				      array_slice<const tree>);
>   extern tree lhd_type_for_size (unsigned precision, int unsignedp);
>   extern void lhd_incomplete_type_error (location_t, const_tree, const_tree);
>   extern tree lhd_type_promotes_to (tree);
> @@ -183,6 +185,7 @@ extern tree lhd_unit_size_without_reusable_padding (tree);
>   
>   #define LANG_HOOKS_MAKE_TYPE lhd_make_node
>   #define LANG_HOOKS_SIMULATE_ENUM_DECL	lhd_simulate_enum_decl
> +#define LANG_HOOKS_SIMULATE_RECORD_DECL	lhd_simulate_record_decl
>   #define LANG_HOOKS_CLASSIFY_RECORD	NULL
>   #define LANG_HOOKS_TYPE_FOR_SIZE	lhd_type_for_size
>   #define LANG_HOOKS_INCOMPLETE_TYPE_ERROR lhd_incomplete_type_error
> @@ -217,6 +220,7 @@ extern tree lhd_unit_size_without_reusable_padding (tree);
>   #define LANG_HOOKS_FOR_TYPES_INITIALIZER { \
>     LANG_HOOKS_MAKE_TYPE, \
>     LANG_HOOKS_SIMULATE_ENUM_DECL, \
> +  LANG_HOOKS_SIMULATE_RECORD_DECL, \
>     LANG_HOOKS_CLASSIFY_RECORD, \
>     LANG_HOOKS_TYPE_FOR_MODE, \
>     LANG_HOOKS_TYPE_FOR_SIZE, \
> diff --git a/gcc/langhooks.c b/gcc/langhooks.c
> index 48c72377778..b54da177137 100644
> --- a/gcc/langhooks.c
> +++ b/gcc/langhooks.c
> @@ -516,6 +516,27 @@ lhd_simulate_enum_decl (location_t loc, const char *name,
>     return enumtype;
>   }
>   
> +/* Default implementation of LANG_HOOKS_SIMULATE_RECORD_DECL.
> +   Just create a normal RECORD_TYPE and a TYPE_DECL for it.  */
> +tree
> +lhd_simulate_record_decl (location_t loc, const char *name,
> +			  array_slice<const tree> fields)
> +{
> +  for (unsigned int i = 1; i < fields.size (); ++i)
> +    /* Reversed by finish_builtin_struct.  */
> +    DECL_CHAIN (fields[i]) = fields[i - 1];
> +
> +  tree type = lang_hooks.types.make_type (RECORD_TYPE);
> +  finish_builtin_struct (type, name, fields.back (), NULL_TREE);
> +
> +  tree decl = build_decl (loc, TYPE_DECL, get_identifier (name), type);
> +  TYPE_NAME (type) = decl;
> +  TYPE_STUB_DECL (type) = decl;
> +  lang_hooks.decls.pushdecl (decl);
> +
> +  return type;
> +}
> +
>   /* Default implementation of LANG_HOOKS_TYPE_FOR_SIZE.
>      Return an integer type with PRECISION bits of precision,
>      that is unsigned if UNSIGNEDP is nonzero, otherwise signed.  */
> diff --git a/gcc/langhooks.h b/gcc/langhooks.h
> index ffd3e0bf2db..3e89134e8b4 100644
> --- a/gcc/langhooks.h
> +++ b/gcc/langhooks.h
> @@ -68,6 +68,16 @@ struct lang_hooks_for_types
>        them all with the given source location.  */
>     tree (*simulate_enum_decl) (location_t, const char *, vec<string_int_pair> *);
>   
> +  /* Do the equivalent of:
> +
> +       typedef struct NAME { FIELDS; } NAME;
> +
> +     associating it with location LOC.  Return the associated RECORD_TYPE.
> +
> +     FIELDS is a list of FIELD_DECLs, in layout order.  */
> +  tree (*simulate_record_decl) (location_t loc, const char *name,
> +				array_slice<const tree> fields);
> +
>     /* Return what kind of RECORD_TYPE this is, mainly for purposes of
>        debug information.  If not defined, record types are assumed to
>        be structures.  */
>