path: root/gcc/rust/backend/rust-tree.cc

// Copyright (C) 2020-2023 Free Software Foundation, Inc.

// This file is part of GCC.

// GCC is free software; you can redistribute it and/or modify it under
// the terms of the GNU General Public License as published by the Free
// Software Foundation; either version 3, or (at your option) any later
// version.

// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
// for more details.

// You should have received a copy of the GNU General Public License
// along with GCC; see the file COPYING3.  If not see
// <http://www.gnu.org/licenses/>.

#include "rust-tree.h"
#include "fold-const.h"
#include "stringpool.h"
#include "attribs.h"
#include "escaped_string.h"

namespace Rust {

void
mark_exp_read (tree exp)
{
  if (exp == NULL)
    return;

  switch (TREE_CODE (exp))
    {
    case VAR_DECL:
      gcc_fallthrough ();
    case PARM_DECL:
      DECL_READ_P (exp) = 1;
      break;
    case ARRAY_REF:
    case COMPONENT_REF:
    case MODIFY_EXPR:
    case REALPART_EXPR:
    case IMAGPART_EXPR:
    CASE_CONVERT:
    case ADDR_EXPR:
    case INDIRECT_REF:
    case FLOAT_EXPR:
    case NON_DEPENDENT_EXPR:
    case VIEW_CONVERT_EXPR:
      mark_exp_read (TREE_OPERAND (exp, 0));
      break;
    case COMPOUND_EXPR:
      mark_exp_read (TREE_OPERAND (exp, 1));
      break;
    case COND_EXPR:
      if (TREE_OPERAND (exp, 1))
	mark_exp_read (TREE_OPERAND (exp, 1));
      if (TREE_OPERAND (exp, 2))
	mark_exp_read (TREE_OPERAND (exp, 2));
      break;
    default:
      break;
    }
}

tree
convert_from_reference (tree val)
{
  if (TREE_TYPE (val) && TYPE_REF_P (TREE_TYPE (val)))
    {
      tree t = TREE_TYPE (TREE_TYPE (val));
      tree ref = build1 (INDIRECT_REF, t, val);

      mark_exp_read (val);

      TREE_SIDE_EFFECTS (ref)
	= (TREE_THIS_VOLATILE (ref) || TREE_SIDE_EFFECTS (val));
      val = ref;
    }

  return val;
}

tree
mark_use (tree expr, bool rvalue_p, bool read_p,
	  location_t loc /* = UNKNOWN_LOCATION */,
	  bool reject_builtin /* = true */)
{
#define RECUR(t) mark_use ((t), rvalue_p, read_p, loc, reject_builtin)

  if (expr == NULL_TREE || error_operand_p (expr))
    return expr;

  if (reject_builtin)
    return error_mark_node;

  if (read_p)
    mark_exp_read (expr);

  bool recurse_op[3] = {false, false, false};
  switch (TREE_CODE (expr))
    {
    case COMPONENT_REF:
    case NON_DEPENDENT_EXPR:
      recurse_op[0] = true;
      break;
    case COMPOUND_EXPR:
      recurse_op[1] = true;
      break;
    case COND_EXPR:
      recurse_op[2] = true;
      if (TREE_OPERAND (expr, 1))
	recurse_op[1] = true;
      break;
    case INDIRECT_REF:
      if (REFERENCE_REF_P (expr))
	{
	  /* Try to look through the reference.  */
	  tree ref = TREE_OPERAND (expr, 0);
	  tree r = mark_rvalue_use (ref, loc, reject_builtin);
	  if (r != ref)
	    expr = convert_from_reference (r);
	}
      break;

    case VIEW_CONVERT_EXPR:
      if (location_wrapper_p (expr))
	{
	  loc = EXPR_LOCATION (expr);
	  tree op = TREE_OPERAND (expr, 0);
	  tree nop = RECUR (op);
	  if (nop == error_mark_node)
	    return error_mark_node;
	  else if (op == nop)
	    /* No change.  */;
	  else if (DECL_P (nop) || CONSTANT_CLASS_P (nop))
	    {
	      /* Reuse the location wrapper.  */
	      TREE_OPERAND (expr, 0) = nop;
	      /* If we're replacing a DECL with a constant, we also need to
		 change the TREE_CODE of the location wrapper.  */
	      if (rvalue_p)
		TREE_SET_CODE (expr, NON_LVALUE_EXPR);
	    }
	  else
	    {
	      /* Drop the location wrapper.  */
	      expr = nop;
	      protected_set_expr_location (expr, loc);
	    }
	  return expr;
	}
      gcc_fallthrough ();
    CASE_CONVERT:
      recurse_op[0] = true;
      break;

    default:
      break;
    }

  for (int i = 0; i < 3; ++i)
    if (recurse_op[i])
      {
	tree op = TREE_OPERAND (expr, i);
	op = RECUR (op);
	if (op == error_mark_node)
	  return error_mark_node;
	TREE_OPERAND (expr, i) = op;
      }

  return expr;
#undef RECUR
}

tree
mark_rvalue_use (tree e, location_t loc /* = UNKNOWN_LOCATION */,
		 bool reject_builtin /* = true */)
{
  return mark_use (e, true, true, loc, reject_builtin);
}

tree
mark_lvalue_use (tree expr)
{
  return mark_use (expr, false, true, input_location, false);
}

tree
mark_lvalue_use_nonread (tree expr)
{
  return mark_use (expr, false, false, input_location, false);
}

tree
mark_discarded_use (tree expr)
{
  if (expr == NULL_TREE)
    return expr;

  STRIP_ANY_LOCATION_WRAPPER (expr);

  switch (TREE_CODE (expr))
    {
    case COND_EXPR:
      TREE_OPERAND (expr, 2) = mark_discarded_use (TREE_OPERAND (expr, 2));
      gcc_fallthrough ();
    case COMPOUND_EXPR:
      TREE_OPERAND (expr, 1) = mark_discarded_use (TREE_OPERAND (expr, 1));
      return expr;

    case COMPONENT_REF:
    case ARRAY_REF:
    case INDIRECT_REF:
    case MEMBER_REF:
      break;
    default:
      if (DECL_P (expr))
	break;
      else
	return expr;
    }

  return mark_use (expr, true, true, input_location, false);
}

tree
convert_to_void (tree expr, impl_conv_void implicit)
{
  location_t loc = expr_loc_or_input_loc (expr);
  if (expr == error_mark_node || TREE_TYPE (expr) == error_mark_node)
    return error_mark_node;

  expr = mark_discarded_use (expr);
  if (implicit == ICV_CAST)
    /* An explicit cast to void avoids all -Wunused-but-set* warnings.  */
    mark_exp_read (expr);

  if (!TREE_TYPE (expr))
    return expr;

  if (VOID_TYPE_P (TREE_TYPE (expr)))
    return expr;
  switch (TREE_CODE (expr))
    {
      case COND_EXPR: {
	/* The two parts of a cond expr might be separate lvalues.  */
	tree op1 = TREE_OPERAND (expr, 1);
	tree op2 = TREE_OPERAND (expr, 2);
	bool side_effects
	  = ((op1 && TREE_SIDE_EFFECTS (op1)) || TREE_SIDE_EFFECTS (op2));
	tree new_op1, new_op2;
	new_op1 = NULL_TREE;
	if (implicit != ICV_CAST && !side_effects)
	  {
	    if (op1)
	      new_op1 = convert_to_void (op1, ICV_SECOND_OF_COND);
	    new_op2 = convert_to_void (op2, ICV_THIRD_OF_COND);
	  }
	else
	  {
	    if (op1)
	      new_op1 = convert_to_void (op1, ICV_CAST);
	    new_op2 = convert_to_void (op2, ICV_CAST);
	  }

	expr = build3_loc (loc, COND_EXPR, TREE_TYPE (new_op2),
			   TREE_OPERAND (expr, 0), new_op1, new_op2);
	break;
      }

      case COMPOUND_EXPR: {
	/* The second part of a compound expr contains the value.  */
	tree op1 = TREE_OPERAND (expr, 1);
	tree new_op1;
	if (implicit != ICV_CAST
	    && !warning_suppressed_p (expr /* What warning? */))
	  new_op1 = convert_to_void (op1, ICV_RIGHT_OF_COMMA);
	else
	  new_op1 = convert_to_void (op1, ICV_CAST);

	if (new_op1 != op1)
	  {
	    tree t = build2_loc (loc, COMPOUND_EXPR, TREE_TYPE (new_op1),
				 TREE_OPERAND (expr, 0), new_op1);
	    expr = t;
	  }

	break;
      }

    case NON_LVALUE_EXPR:
    case NOP_EXPR:
      /* These have already decayed to rvalue.  */
      break;

    case CALL_EXPR:
      maybe_warn_nodiscard (expr, implicit);
      break;

      case INDIRECT_REF: {
	tree type = TREE_TYPE (expr);
	int is_reference = TYPE_REF_P (TREE_TYPE (TREE_OPERAND (expr, 0)));
	int is_volatile = TYPE_VOLATILE (type);
	int is_complete = COMPLETE_TYPE_P (type);

	/* Can't load the value if we don't know the type.  */
	if (is_volatile && !is_complete)
	  {
	    switch (implicit)
	      {
	      case ICV_CAST:
		warning_at (loc, 0,
			    "conversion to void will not access "
			    "object of incomplete type %qT",
			    type);
		break;
	      case ICV_SECOND_OF_COND:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "incomplete type %qT in second operand "
			    "of conditional expression",
			    type);
		break;
	      case ICV_THIRD_OF_COND:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "incomplete type %qT in third operand "
			    "of conditional expression",
			    type);
		break;
	      case ICV_RIGHT_OF_COMMA:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "incomplete type %qT in right operand of "
			    "comma operator",
			    type);
		break;
	      case ICV_LEFT_OF_COMMA:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "incomplete type %qT in left operand of "
			    "comma operator",
			    type);
		break;
	      case ICV_STATEMENT:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "incomplete type %qT in statement",
			    type);
		break;
	      case ICV_THIRD_IN_FOR:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "incomplete type %qT in for increment "
			    "expression",
			    type);
		break;
	      default:
		gcc_unreachable ();
	      }
	  }
	/* Don't load the value if this is an implicit dereference, or if
	   the type needs to be handled by ctors/dtors.  */
	else if (is_volatile && is_reference)
	  {
	    switch (implicit)
	      {
	      case ICV_CAST:
		warning_at (loc, 0,
			    "conversion to void will not access "
			    "object of type %qT",
			    type);
		break;
	      case ICV_SECOND_OF_COND:
		warning_at (loc, 0,
			    "implicit dereference will not access "
			    "object of type %qT in second operand of "
			    "conditional expression",
			    type);
		break;
	      case ICV_THIRD_OF_COND:
		warning_at (loc, 0,
			    "implicit dereference will not access "
			    "object of type %qT in third operand of "
			    "conditional expression",
			    type);
		break;
	      case ICV_RIGHT_OF_COMMA:
		warning_at (loc, 0,
			    "implicit dereference will not access "
			    "object of type %qT in right operand of "
			    "comma operator",
			    type);
		break;
	      case ICV_LEFT_OF_COMMA:
		warning_at (loc, 0,
			    "implicit dereference will not access "
			    "object of type %qT in left operand of comma "
			    "operator",
			    type);
		break;
	      case ICV_STATEMENT:
		warning_at (loc, 0,
			    "implicit dereference will not access "
			    "object of type %qT in statement",
			    type);
		break;
	      case ICV_THIRD_IN_FOR:
		warning_at (loc, 0,
			    "implicit dereference will not access "
			    "object of type %qT in for increment expression",
			    type);
		break;
	      default:
		gcc_unreachable ();
	      }
	  }
	else if (is_volatile && TREE_ADDRESSABLE (type))
	  {
	    switch (implicit)
	      {
	      case ICV_CAST:
		warning_at (loc, 0,
			    "conversion to void will not access "
			    "object of non-trivially-copyable type %qT",
			    type);
		break;
	      case ICV_SECOND_OF_COND:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "non-trivially-copyable type %qT in second "
			    "operand of conditional expression",
			    type);
		break;
	      case ICV_THIRD_OF_COND:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "non-trivially-copyable type %qT in third "
			    "operand of conditional expression",
			    type);
		break;
	      case ICV_RIGHT_OF_COMMA:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "non-trivially-copyable type %qT in right "
			    "operand of comma operator",
			    type);
		break;
	      case ICV_LEFT_OF_COMMA:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "non-trivially-copyable type %qT in left "
			    "operand of comma operator",
			    type);
		break;
	      case ICV_STATEMENT:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "non-trivially-copyable type %qT in statement",
			    type);
		break;
	      case ICV_THIRD_IN_FOR:
		warning_at (loc, 0,
			    "indirection will not access object of "
			    "non-trivially-copyable type %qT in for "
			    "increment expression",
			    type);
		break;
	      default:
		gcc_unreachable ();
	      }
	  }
	if (is_reference || !is_volatile || !is_complete
	    || TREE_ADDRESSABLE (type))
	  {
	    /* Emit a warning (if enabled) when the "effect-less" INDIRECT_REF
	       operation is stripped off. Note that we don't warn about
	       - an expression with TREE_NO_WARNING set. (For an example of
		 such expressions, see build_over_call in call.cc.)
	       - automatic dereferencing of references, since the user cannot
		 control it. (See also warn_if_unused_value() in c-common.cc.)
	     */
	    if (warn_unused_value && implicit != ICV_CAST
		&& !warning_suppressed_p (expr, OPT_Wunused_value)
		&& !is_reference)
	      warning_at (loc, OPT_Wunused_value, "value computed is not used");
	    expr = TREE_OPERAND (expr, 0);
	    if (TREE_CODE (expr) == CALL_EXPR)
	      maybe_warn_nodiscard (expr, implicit);
	  }

	break;
      }

      case VAR_DECL: {
	/* External variables might be incomplete.  */
	tree type = TREE_TYPE (expr);
	int is_complete = COMPLETE_TYPE_P (type);

	if (TYPE_VOLATILE (type) && !is_complete)
	  switch (implicit)
	    {
	    case ICV_CAST:
	      warning_at (loc, 0,
			  "conversion to void will not access "
			  "object %qE of incomplete type %qT",
			  expr, type);
	      break;
	    case ICV_SECOND_OF_COND:
	      warning_at (loc, 0,
			  "variable %qE of incomplete type %qT will "
			  "not be accessed in second operand of "
			  "conditional expression",
			  expr, type);
	      break;
	    case ICV_THIRD_OF_COND:
	      warning_at (loc, 0,
			  "variable %qE of incomplete type %qT will "
			  "not be accessed in third operand of "
			  "conditional expression",
			  expr, type);
	      break;
	    case ICV_RIGHT_OF_COMMA:
	      warning_at (loc, 0,
			  "variable %qE of incomplete type %qT will "
			  "not be accessed in right operand of comma operator",
			  expr, type);
	      break;
	    case ICV_LEFT_OF_COMMA:
	      warning_at (loc, 0,
			  "variable %qE of incomplete type %qT will "
			  "not be accessed in left operand of comma operator",
			  expr, type);
	      break;
	    case ICV_STATEMENT:
	      warning_at (loc, 0,
			  "variable %qE of incomplete type %qT will "
			  "not be accessed in statement",
			  expr, type);
	      break;
	    case ICV_THIRD_IN_FOR:
	      warning_at (loc, 0,
			  "variable %qE of incomplete type %qT will "
			  "not be accessed in for increment expression",
			  expr, type);
	      break;
	    default:
	      gcc_unreachable ();
	    }

	break;
      }

    default:;
    }

  if (!TREE_SIDE_EFFECTS (expr))
    expr = void_node;

  return expr;
}

void
maybe_warn_nodiscard (tree expr, impl_conv_void implicit)
{
  tree call = expr;
  if (TREE_CODE (expr) == TARGET_EXPR)
    call = TARGET_EXPR_INITIAL (expr);

  location_t loc = expr_loc_or_input_loc (call);
  tree callee = CALL_EXPR_FN (call);
  if (!callee)
    return;

  tree type = TREE_TYPE (callee);
  if (INDIRECT_TYPE_P (type))
    type = TREE_TYPE (type);

  tree rettype = TREE_TYPE (type);
  tree fn = get_fndecl_from_callee (callee);
  tree attr;
  if (implicit != ICV_CAST && fn
      && (attr = lookup_attribute ("nodiscard", DECL_ATTRIBUTES (fn))))
    {
      escaped_string msg;
      tree args = TREE_VALUE (attr);
      if (args)
	msg.escape (TREE_STRING_POINTER (TREE_VALUE (args)));
      const char *format
	= (msg ? G_ ("ignoring return value of %qD, that must be used: %<%s%>")
	       : G_ ("ignoring return value of %qD, that must be used"));
      const char *raw_msg = msg ? (const char *) msg : "";
      auto_diagnostic_group d;
      if (warning_at (loc, OPT_Wunused_result, format, fn, raw_msg))
	inform (DECL_SOURCE_LOCATION (fn), "declared here");
    }
  else if (implicit != ICV_CAST
	   && (attr
	       = lookup_attribute ("nodiscard", TYPE_ATTRIBUTES (rettype))))
    {
      escaped_string msg;
      tree args = TREE_VALUE (attr);
      if (args)
	msg.escape (TREE_STRING_POINTER (TREE_VALUE (args)));
      const char *format
	= (msg ? G_ (
	     "ignoring returned value of type %qT, that must be used: %<%s%>")
	       : G_ ("ignoring returned value of type %qT, that must be used"));
      const char *raw_msg = msg ? (const char *) msg : "";
      auto_diagnostic_group d;
      if (warning_at (loc, OPT_Wunused_result, format, rettype, raw_msg))
	{
	  if (fn)
	    inform (DECL_SOURCE_LOCATION (fn), "in call to %qD, declared here",
		    fn);
	  inform (DECL_SOURCE_LOCATION (TYPE_NAME (rettype)),
		  "%qT declared here", rettype);
	}
    }
}

location_t
expr_loc_or_loc (const_tree t, location_t or_loc)
{
  location_t loc = EXPR_LOCATION (t);
  if (loc == UNKNOWN_LOCATION)
    loc = or_loc;
  return loc;
}

location_t
expr_loc_or_input_loc (const_tree t)
{
  return expr_loc_or_loc (t, input_location);
}

// FN is the callee of a CALL_EXPR or AGGR_INIT_EXPR; return the FUNCTION_DECL
// if we can.
tree
get_fndecl_from_callee (tree fn)
{
  if (fn == NULL_TREE)
    return fn;
  if (TREE_CODE (fn) == FUNCTION_DECL)
    return fn;
  tree type = TREE_TYPE (fn);
  if (type == NULL_TREE || !INDIRECT_TYPE_P (type))
    return NULL_TREE;

  STRIP_NOPS (fn);
  if (TREE_CODE (fn) == ADDR_EXPR || TREE_CODE (fn) == FDESC_EXPR)
    fn = TREE_OPERAND (fn, 0);
  if (TREE_CODE (fn) == FUNCTION_DECL)
    return fn;
  return NULL_TREE;
}

tree
pointer_offset_expression (tree base_tree, tree index_tree, location_t location)
{
  tree element_type_tree = TREE_TYPE (TREE_TYPE (base_tree));
  if (base_tree == error_mark_node || TREE_TYPE (base_tree) == error_mark_node
      || index_tree == error_mark_node || element_type_tree == error_mark_node)
    return error_mark_node;

  tree element_size = TYPE_SIZE_UNIT (element_type_tree);
  index_tree = fold_convert_loc (location, sizetype, index_tree);
  tree offset
    = fold_build2_loc (location, MULT_EXPR, sizetype, index_tree, element_size);

  return fold_build2_loc (location, POINTER_PLUS_EXPR, TREE_TYPE (base_tree),
			  base_tree, offset);
}

// forked from gcc/cp/tree.cc cp_walk_subtrees
/* Apply FUNC to all language-specific sub-trees of TP in a pre-order
   traversal.  Called from walk_tree.  */

tree
rs_walk_subtrees (tree *tp, int *walk_subtrees_p, walk_tree_fn func, void *data,
		  hash_set<tree> *pset)
{
  enum tree_code code = TREE_CODE (*tp);
  tree result;

#define WALK_SUBTREE(NODE)                                                     \
  do                                                                           \
    {                                                                          \
      result = rs_walk_tree (&(NODE), func, data, pset);                       \
      if (result)                                                              \
	goto out;                                                              \
    }                                                                          \
  while (0)

  if (TYPE_P (*tp))
    {
      /* If *WALK_SUBTREES_P is 1, we're interested in the syntactic form of
	 the argument, so don't look through typedefs, but do walk into
	 template arguments for alias templates (and non-typedefed classes).

	 If *WALK_SUBTREES_P > 1, we're interested in type identity or
	 equivalence, so look through typedefs, ignoring template arguments for
	 alias templates, and walk into template args of classes.

	 See find_abi_tags_r for an example of setting *WALK_SUBTREES_P to 2
	 when that's the behavior the walk_tree_fn wants.  */
      if (*walk_subtrees_p == 1 && typedef_variant_p (*tp))
	{
	  *walk_subtrees_p = 0;
	  return NULL_TREE;
	}
    }

  /* Not one of the easy cases.  We must explicitly go through the
     children.  */
  result = NULL_TREE;
  switch (code)
    {
    case TREE_LIST:
      WALK_SUBTREE (TREE_PURPOSE (*tp));
      break;

    case RECORD_TYPE:
      if (TYPE_PTRMEMFUNC_P (*tp))
	WALK_SUBTREE (TYPE_PTRMEMFUNC_FN_TYPE_RAW (*tp));
      break;

    case CONSTRUCTOR:
      if (COMPOUND_LITERAL_P (*tp))
	WALK_SUBTREE (TREE_TYPE (*tp));
      break;

    case DECL_EXPR:
      /* User variables should be mentioned in BIND_EXPR_VARS
	 and their initializers and sizes walked when walking
	 the containing BIND_EXPR.  Compiler temporaries are
	 handled here.  And also normal variables in templates,
	 since do_poplevel doesn't build a BIND_EXPR then.  */
      if (VAR_P (TREE_OPERAND (*tp, 0))
	  && (DECL_ARTIFICIAL (TREE_OPERAND (*tp, 0))
	      && !TREE_STATIC (TREE_OPERAND (*tp, 0))))
	{
	  tree decl = TREE_OPERAND (*tp, 0);
	  WALK_SUBTREE (DECL_INITIAL (decl));
	  WALK_SUBTREE (DECL_SIZE (decl));
	  WALK_SUBTREE (DECL_SIZE_UNIT (decl));
	}
      break;

    default:
      return NULL_TREE;
    }

  /* We didn't find what we were looking for.  */
out:
  return result;

#undef WALK_SUBTREE
}

// forked from gcc/cp/tree.cc cp_expr_location

/* Like EXPR_LOCATION, but also handle some tcc_exceptional that have
   locations.  */

location_t
rs_expr_location (const_tree t_)
{
  tree t = CONST_CAST_TREE (t_);
  if (t == NULL_TREE)
    return UNKNOWN_LOCATION;

  return EXPR_LOCATION (t);
}

// forked from gcc/cp/class.cc is_really_empty_class

/* Returns true if TYPE contains no actual data, just various
   possible combinations of empty classes.  If IGNORE_VPTR is true,
   a vptr doesn't prevent the class from being considered empty.  Typically
   we want to ignore the vptr on assignment, and not on initialization.  */

bool
is_really_empty_class (tree type, bool ignore_vptr)
{
  if (CLASS_TYPE_P (type))
    {
      tree field;
      tree binfo;
      tree base_binfo;
      int i;

      /* CLASSTYPE_EMPTY_P isn't set properly until the class is actually laid
	 out, but we'd like to be able to check this before then.  */
      if (COMPLETE_TYPE_P (type) && is_empty_class (type))
	return true;

      if (!ignore_vptr && TYPE_CONTAINS_VPTR_P (type))
	return false;

      for (binfo = TYPE_BINFO (type), i = 0;
	   BINFO_BASE_ITERATE (binfo, i, base_binfo); ++i)
	if (!is_really_empty_class (BINFO_TYPE (base_binfo), ignore_vptr))
	  return false;
      for (field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
	if (TREE_CODE (field) == FIELD_DECL
	    && !DECL_ARTIFICIAL (field)
	    /* An unnamed bit-field is not a data member.  */
	    && !DECL_UNNAMED_BIT_FIELD (field)
	    && !is_really_empty_class (TREE_TYPE (field), ignore_vptr))
	  return false;
      return true;
    }
  else if (TREE_CODE (type) == ARRAY_TYPE)
    return (integer_zerop (array_type_nelts_top (type))
	    || is_really_empty_class (TREE_TYPE (type), ignore_vptr));
  return false;
}

// forked from gcc/cp/class.cc is_empty_class

/* Returns 1 if TYPE contains only padding bytes.  */

int
is_empty_class (tree type)
{
  if (type == error_mark_node)
    return 0;

  if (!CLASS_TYPE_P (type))
    return 0;

  return CLASSTYPE_EMPTY_P (type);
}

// forked from gcc/cp/tree.cc array_type_nelts_top

/* Return, as an INTEGER_CST node, the number of elements for TYPE
   (which is an ARRAY_TYPE).  This counts only elements of the top
   array.  */

tree
array_type_nelts_top (tree type)
{
  return fold_build2_loc (input_location, PLUS_EXPR, sizetype,
			  array_type_nelts (type), size_one_node);
}

// forked from gcc/cp/tree.cc builtin_valid_in_constant_expr_p

/* Test whether DECL is a builtin that may appear in a
   constant-expression. */

bool
builtin_valid_in_constant_expr_p (const_tree decl)
{
  STRIP_ANY_LOCATION_WRAPPER (decl);
  if (TREE_CODE (decl) != FUNCTION_DECL)
    /* Not a function.  */
    return false;
  if (DECL_BUILT_IN_CLASS (decl) != BUILT_IN_NORMAL)
    {
      if (fndecl_built_in_p (decl, BUILT_IN_FRONTEND))
	switch (DECL_FE_FUNCTION_CODE (decl))
	  {
	  case RS_BUILT_IN_IS_CONSTANT_EVALUATED:
	  case RS_BUILT_IN_SOURCE_LOCATION:
	  case RS_BUILT_IN_IS_CORRESPONDING_MEMBER:
	  case RS_BUILT_IN_IS_POINTER_INTERCONVERTIBLE_WITH_CLASS:
	    return true;
	  default:
	    break;
	  }
      /* Not a built-in.  */
      return false;
    }
  switch (DECL_FUNCTION_CODE (decl))
    {
      /* These always have constant results like the corresponding
	 macros/symbol.  */
    case BUILT_IN_FILE:
    case BUILT_IN_FUNCTION:
    case BUILT_IN_LINE:

      /* The following built-ins are valid in constant expressions
	 when their arguments are.  */
    case BUILT_IN_ADD_OVERFLOW_P:
    case BUILT_IN_SUB_OVERFLOW_P:
    case BUILT_IN_MUL_OVERFLOW_P:

      /* These have constant results even if their operands are
	 non-constant.  */
    case BUILT_IN_CONSTANT_P:
    case BUILT_IN_ATOMIC_ALWAYS_LOCK_FREE:
      return true;
    default:
      return false;
    }
}

// forked from gcc/cp/decl2.cc decl_maybe_constant_var_p

/* Returns true if DECL could be a symbolic constant variable, depending on
   its initializer.  */

bool
decl_maybe_constant_var_p (tree decl)
{
  tree type = TREE_TYPE (decl);
  if (!VAR_P (decl))
    return false;
  if (DECL_DECLARED_CONSTEXPR_P (decl))
    return true;
  if (DECL_HAS_VALUE_EXPR_P (decl))
    /* A proxy isn't constant.  */
    return false;
  if (TYPE_REF_P (type))
    /* References can be constant.  */;
  else if (RS_TYPE_CONST_NON_VOLATILE_P (type)
	   && INTEGRAL_OR_ENUMERATION_TYPE_P (type))
    /* And const integers.  */;
  else
    return false;

  if (DECL_INITIAL (decl) && !DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl))
    /* We know the initializer, and it isn't constant.  */
    return false;
  else
    return true;
}

// forked from gcc/cp/typeck.cc cp_type_quals

/* Returns the type qualifiers for this type, including the qualifiers on the
   elements for an array type.  */

int
rs_type_quals (const_tree type)
{
  int quals;
  /* This CONST_CAST is okay because strip_array_types returns its
     argument unmodified and we assign it to a const_tree.  */
  type = strip_array_types (CONST_CAST_TREE (type));
  if (type == error_mark_node
      /* Quals on a FUNCTION_TYPE are memfn quals.  */
      || TREE_CODE (type) == FUNCTION_TYPE)
    return TYPE_UNQUALIFIED;
  quals = TYPE_QUALS (type);
  /* METHOD and REFERENCE_TYPEs should never have quals.  */
  gcc_assert (
    (TREE_CODE (type) != METHOD_TYPE && !TYPE_REF_P (type))
    || ((quals & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE)) == TYPE_UNQUALIFIED));
  return quals;
}

} // namespace Rust