Add a simulate_record_decl lang hook

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.

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.

1 files changed, 19 insertions, 0 deletions

diff --git a/gcc/langhooks.c b/gcc/langhooks.c
index 48c7237..49613b4 100644
--- a/gcc/langhooks.c
+++ b/gcc/langhooks.c
@@ -516,6 +516,25 @@ 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);
+  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.  */