+
+/* An array of functions used for self-referential size computation. */
+static GTY(()) VEC (tree, gc) *size_functions;
+
+/* Similar to copy_tree_r but do not copy component references involving
+ PLACEHOLDER_EXPRs. These nodes are spotted in find_placeholder_in_expr
+ and substituted in substitute_in_expr. */
+
+static tree
+copy_self_referential_tree_r (tree *tp, int *walk_subtrees, void *data)
+{
+ enum tree_code code = TREE_CODE (*tp);
+
+ /* Stop at types, decls, constants like copy_tree_r. */
+ if (TREE_CODE_CLASS (code) == tcc_type
+ || TREE_CODE_CLASS (code) == tcc_declaration
+ || TREE_CODE_CLASS (code) == tcc_constant)
+ {
+ *walk_subtrees = 0;
+ return NULL_TREE;
+ }
+
+ /* This is the pattern built in ada/make_aligning_type. */
+ else if (code == ADDR_EXPR
+ && TREE_CODE (TREE_OPERAND (*tp, 0)) == PLACEHOLDER_EXPR)
+ {
+ *walk_subtrees = 0;
+ return NULL_TREE;
+ }
+
+ /* Default case: the component reference. */
+ else if (code == COMPONENT_REF)
+ {
+ tree inner;
+ for (inner = TREE_OPERAND (*tp, 0);
+ REFERENCE_CLASS_P (inner);
+ inner = TREE_OPERAND (inner, 0))
+ ;
+
+ if (TREE_CODE (inner) == PLACEHOLDER_EXPR)
+ {
+ *walk_subtrees = 0;
+ return NULL_TREE;
+ }
+ }
+
+ /* We're not supposed to have them in self-referential size trees
+ because we wouldn't properly control when they are evaluated.
+ However, not creating superfluous SAVE_EXPRs requires accurate
+ tracking of readonly-ness all the way down to here, which we
+ cannot always guarantee in practice. So punt in this case. */
+ else if (code == SAVE_EXPR)
+ return error_mark_node;
+
+ return copy_tree_r (tp, walk_subtrees, data);
+}
+
+/* Given a SIZE expression that is self-referential, return an equivalent
+ expression to serve as the actual size expression for a type. */
+
+static tree
+self_referential_size (tree size)
+{
+ static unsigned HOST_WIDE_INT fnno = 0;
+ VEC (tree, heap) *self_refs = NULL;
+ tree param_type_list = NULL, param_decl_list = NULL, arg_list = NULL;
+ tree t, ref, return_type, fntype, fnname, fndecl;
+ unsigned int i;
+ char buf[128];
+
+ /* Do not factor out simple operations. */
+ t = skip_simple_arithmetic (size);
+ if (TREE_CODE (t) == CALL_EXPR)
+ return size;
+
+ /* Collect the list of self-references in the expression. */
+ find_placeholder_in_expr (size, &self_refs);
+ gcc_assert (VEC_length (tree, self_refs) > 0);
+
+ /* Obtain a private copy of the expression. */
+ t = size;
+ if (walk_tree (&t, copy_self_referential_tree_r, NULL, NULL) != NULL_TREE)
+ return size;
+ size = t;
+
+ /* Build the parameter and argument lists in parallel; also
+ substitute the former for the latter in the expression. */
+ for (i = 0; VEC_iterate (tree, self_refs, i, ref); i++)
+ {
+ tree subst, param_name, param_type, param_decl;
+
+ if (DECL_P (ref))
+ {
+ /* We shouldn't have true variables here. */
+ gcc_assert (TREE_READONLY (ref));
+ subst = ref;
+ }
+ /* This is the pattern built in ada/make_aligning_type. */
+ else if (TREE_CODE (ref) == ADDR_EXPR)
+ subst = ref;
+ /* Default case: the component reference. */
+ else
+ subst = TREE_OPERAND (ref, 1);
+
+ sprintf (buf, "p%d", i);
+ param_name = get_identifier (buf);
+ param_type = TREE_TYPE (ref);
+ param_decl
+ = build_decl (input_location, PARM_DECL, param_name, param_type);
+ if (targetm.calls.promote_prototypes (NULL_TREE)
+ && INTEGRAL_TYPE_P (param_type)
+ && TYPE_PRECISION (param_type) < TYPE_PRECISION (integer_type_node))
+ DECL_ARG_TYPE (param_decl) = integer_type_node;
+ else
+ DECL_ARG_TYPE (param_decl) = param_type;
+ DECL_ARTIFICIAL (param_decl) = 1;
+ TREE_READONLY (param_decl) = 1;
+
+ size = substitute_in_expr (size, subst, param_decl);
+
+ param_type_list = tree_cons (NULL_TREE, param_type, param_type_list);
+ param_decl_list = chainon (param_decl, param_decl_list);
+ arg_list = tree_cons (NULL_TREE, ref, arg_list);
+ }
+
+ VEC_free (tree, heap, self_refs);
+
+ /* Append 'void' to indicate that the number of parameters is fixed. */
+ param_type_list = tree_cons (NULL_TREE, void_type_node, param_type_list);
+
+ /* The 3 lists have been created in reverse order. */
+ param_type_list = nreverse (param_type_list);
+ param_decl_list = nreverse (param_decl_list);
+ arg_list = nreverse (arg_list);
+
+ /* Build the function type. */
+ return_type = TREE_TYPE (size);
+ fntype = build_function_type (return_type, param_type_list);
+
+ /* Build the function declaration. */
+ sprintf (buf, "SZ"HOST_WIDE_INT_PRINT_UNSIGNED, fnno++);
+ fnname = get_file_function_name (buf);
+ fndecl = build_decl (input_location, FUNCTION_DECL, fnname, fntype);
+ for (t = param_decl_list; t; t = TREE_CHAIN (t))
+ DECL_CONTEXT (t) = fndecl;
+ DECL_ARGUMENTS (fndecl) = param_decl_list;
+ DECL_RESULT (fndecl)
+ = build_decl (input_location, RESULT_DECL, 0, return_type);
+ DECL_CONTEXT (DECL_RESULT (fndecl)) = fndecl;
+
+ /* The function has been created by the compiler and we don't
+ want to emit debug info for it. */
+ DECL_ARTIFICIAL (fndecl) = 1;
+ DECL_IGNORED_P (fndecl) = 1;
+
+ /* It is supposed to be "const" and never throw. */
+ TREE_READONLY (fndecl) = 1;
+ TREE_NOTHROW (fndecl) = 1;
+
+ /* We want it to be inlined when this is deemed profitable, as
+ well as discarded if every call has been integrated. */
+ DECL_DECLARED_INLINE_P (fndecl) = 1;
+
+ /* It is made up of a unique return statement. */
+ DECL_INITIAL (fndecl) = make_node (BLOCK);
+ BLOCK_SUPERCONTEXT (DECL_INITIAL (fndecl)) = fndecl;
+ t = build2 (MODIFY_EXPR, return_type, DECL_RESULT (fndecl), size);
+ DECL_SAVED_TREE (fndecl) = build1 (RETURN_EXPR, void_type_node, t);
+ TREE_STATIC (fndecl) = 1;
+
+ /* Put it onto the list of size functions. */
+ VEC_safe_push (tree, gc, size_functions, fndecl);
+
+ /* Replace the original expression with a call to the size function. */
+ return build_function_call_expr (input_location, fndecl, arg_list);
+}
+
+/* Take, queue and compile all the size functions. It is essential that
+ the size functions be gimplified at the very end of the compilation
+ in order to guarantee transparent handling of self-referential sizes.
+ Otherwise the GENERIC inliner would not be able to inline them back
+ at each of their call sites, thus creating artificial non-constant
+ size expressions which would trigger nasty problems later on. */
+
+void
+finalize_size_functions (void)
+{
+ unsigned int i;
+ tree fndecl;
+
+ for (i = 0; VEC_iterate(tree, size_functions, i, fndecl); i++)
+ {
+ dump_function (TDI_original, fndecl);
+ gimplify_function_tree (fndecl);
+ dump_function (TDI_generic, fndecl);
+ cgraph_finalize_function (fndecl, false);
+ }
+
+ VEC_free (tree, gc, size_functions);
+}
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