Add size_of intrinsic

This is another type of intrisic since the function contains no parameters
but the argument for the size_of is the generic parameter T. Which uses
TYPE_SIZE_UNIT to get the type size in bytes. GCC will optimize the
function call away when you turn optimizations on.

Addresses #658

Author: philberty

gcc/rust/backend/rust-compile-intrinsic.cc

@@ -172,10 +172,13 @@ class SimpleIntrinsics
 
 static tree
 offset_intrinsic_handler (Context *ctx, TyTy::BaseType *fntype);
+static tree
+sizeof_intrinsic_handler (Context *ctx, TyTy::BaseType *fntype);
 
 static const std::map<std::string,
 		      std::function<tree (Context *, TyTy::BaseType *)>>
-  generic_intrinsics = {{"offset", &offset_intrinsic_handler}};
+  generic_intrinsics = {{"offset", &offset_intrinsic_handler},
+			{"size_of", &sizeof_intrinsic_handler}};
 
 Intrinsics::Intrinsics (Context *ctx) : ctx (ctx) {}
 
@@ -308,5 +311,94 @@ offset_intrinsic_handler (Context *ctx, TyTy::BaseType *fntype_tyty)
   return fndecl;
 }
 
+static tree
+sizeof_intrinsic_handler (Context *ctx, TyTy::BaseType *fntype_tyty)
+{
+  rust_assert (fntype_tyty->get_kind () == TyTy::TypeKind::FNDEF);
+  TyTy::FnType *fntype = static_cast<TyTy::FnType *> (fntype_tyty);
+  const Resolver::CanonicalPath &canonical_path = fntype->get_ident ().path;
+
+  // items can be forward compiled which means we may not need to invoke this
+  // code. We might also have already compiled this generic function as well.
+  tree lookup = NULL_TREE;
+  if (ctx->lookup_function_decl (fntype->get_ty_ref (), &lookup,
+				 fntype->get_id (), fntype))
+    {
+      // has this been added to the list then it must be finished
+      if (ctx->function_completed (lookup))
+	{
+	  tree dummy = NULL_TREE;
+	  if (!ctx->lookup_function_decl (fntype->get_ty_ref (), &dummy))
+	    {
+	      ctx->insert_function_decl (fntype, lookup);
+	    }
+	  return lookup;
+	}
+    }
+
+  if (fntype->has_subsititions_defined ())
+    {
+      // override the Hir Lookups for the substituions in this context
+      fntype->override_context ();
+    }
+
+  // offset intrinsic has two params dst pointer and offset isize
+  if (fntype->get_params ().size () != 0)
+    {
+      rust_error_at (fntype->get_ident ().locus,
+		     "invalid number of parameters for size of intrinsic");
+      return error_mark_node;
+    }
+
+  // get the template parameter type tree fn size_of<T>();
+  rust_assert (fntype->get_num_substitutions () == 1);
+  auto &param_mapping = fntype->get_substs ().at (0);
+  const TyTy::ParamType *param_tyty = param_mapping.get_param_ty ();
+  TyTy::BaseType *resolved_tyty = param_tyty->resolve ();
+  tree template_parameter_type
+    = TyTyResolveCompile::compile (ctx, resolved_tyty);
+
+  // build the intrinsic function
+  tree compiled_fn_type = TyTyResolveCompile::compile (ctx, fntype);
+  std::string ir_symbol_name
+    = canonical_path.get () + fntype->subst_as_string ();
+  std::string asm_name = ctx->mangle_item (fntype, canonical_path);
+
+  unsigned int flags = 0;
+  tree fndecl
+    = ctx->get_backend ()->function (compiled_fn_type, ir_symbol_name, asm_name,
+				     flags, fntype->get_ident ().locus);
+  TREE_PUBLIC (fndecl) = 0;
+  TREE_READONLY (fndecl) = 1;
+  DECL_ARTIFICIAL (fndecl) = 1;
+  DECL_EXTERNAL (fndecl) = 0;
+  DECL_DECLARED_INLINE_P (fndecl) = 1;
+
+  tree enclosing_scope = NULL_TREE;
+  Location start_location = Location ();
+  Location end_location = Location ();
+
+  tree code_block = ctx->get_backend ()->block (fndecl, enclosing_scope, {},
+						start_location, end_location);
+  ctx->push_block (code_block);
+
+  // BUILTIN size_of FN BODY BEGIN
+  tree size_expr = TYPE_SIZE_UNIT (template_parameter_type);
+  auto return_statement
+    = ctx->get_backend ()->return_statement (fndecl, {size_expr}, Location ());
+  ctx->add_statement (return_statement);
+  // BUILTIN size_of FN BODY END
+
+  tree bind_tree = ctx->pop_block ();
+
+  gcc_assert (TREE_CODE (bind_tree) == BIND_EXPR);
+  DECL_SAVED_TREE (fndecl) = bind_tree;
+
+  ctx->pop_fn ();
+  ctx->push_function (fndecl);
+
+  return fndecl;
+}
+
 } // namespace Compile
 } // namespace Rust