c-convert.c revision 132718 
1/* Language-level data type conversion for GNU C.
2   Copyright (C) 1987, 1988, 1991, 1998, 2002, 2003
3   Free Software Foundation, Inc.
4
5This file is part of GCC.
6
7GCC is free software; you can redistribute it and/or modify it under
8the terms of the GNU General Public License as published by the Free
9Software Foundation; either version 2, or (at your option) any later
10version.
11
12GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13WARRANTY; without even the implied warranty of MERCHANTABILITY or
14FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
15for more details.
16
17You should have received a copy of the GNU General Public License
18along with GCC; see the file COPYING.  If not, write to the Free
19Software Foundation, 59 Temple Place - Suite 330, Boston, MA
2002111-1307, USA.  */
21
22
23/* This file contains the functions for converting C expressions
24   to different data types.  The only entry point is `convert'.
25   Every language front end must have a `convert' function
26   but what kind of conversions it does will depend on the language.  */
27
28#include "config.h"
29#include "system.h"
30#include "coretypes.h"
31#include "tm.h"
32#include "tree.h"
33#include "flags.h"
34#include "convert.h"
35#include "c-common.h"
36#include "toplev.h"
37
38/* Change of width--truncation and extension of integers or reals--
39   is represented with NOP_EXPR.  Proper functioning of many things
40   assumes that no other conversions can be NOP_EXPRs.
41
42   Conversion between integer and pointer is represented with CONVERT_EXPR.
43   Converting integer to real uses FLOAT_EXPR
44   and real to integer uses FIX_TRUNC_EXPR.
45
46   Here is a list of all the functions that assume that widening and
47   narrowing is always done with a NOP_EXPR:
48     In convert.c, convert_to_integer.
49     In c-typeck.c, build_binary_op (boolean ops), and
50	c_common_truthvalue_conversion.
51     In expr.c: expand_expr, for operands of a MULT_EXPR.
52     In fold-const.c: fold.
53     In tree.c: get_narrower and get_unwidened.  */
54
55/* Subroutines of `convert'.  */
56
57
58
59/* Create an expression whose value is that of EXPR,
60   converted to type TYPE.  The TREE_TYPE of the value
61   is always TYPE.  This function implements all reasonable
62   conversions; callers should filter out those that are
63   not permitted by the language being compiled.  */
64
65tree
66convert (tree type, tree expr)
67{
68  tree e = expr;
69  enum tree_code code = TREE_CODE (type);
70
71  if (type == TREE_TYPE (expr)
72      || TREE_CODE (expr) == ERROR_MARK
73      || code == ERROR_MARK || TREE_CODE (TREE_TYPE (expr)) == ERROR_MARK)
74    return expr;
75
76  if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE (expr)))
77    return fold (build1 (NOP_EXPR, type, expr));
78  if (TREE_CODE (TREE_TYPE (expr)) == ERROR_MARK)
79    return error_mark_node;
80  if (TREE_CODE (TREE_TYPE (expr)) == VOID_TYPE)
81    {
82      error ("void value not ignored as it ought to be");
83      return error_mark_node;
84    }
85  if (code == VOID_TYPE)
86    return build1 (CONVERT_EXPR, type, e);
87#if 0
88  /* This is incorrect.  A truncation can't be stripped this way.
89     Extensions will be stripped by the use of get_unwidened.  */
90  if (TREE_CODE (expr) == NOP_EXPR)
91    return convert (type, TREE_OPERAND (expr, 0));
92#endif
93  if (code == INTEGER_TYPE || code == ENUMERAL_TYPE)
94    return fold (convert_to_integer (type, e));
95  if (code == BOOLEAN_TYPE)
96    {
97      tree t = c_common_truthvalue_conversion (expr);
98      /* If it returns a NOP_EXPR, we must fold it here to avoid
99	 infinite recursion between fold () and convert ().  */
100      if (TREE_CODE (t) == NOP_EXPR)
101	return fold (build1 (NOP_EXPR, type, TREE_OPERAND (t, 0)));
102      else
103	return fold (build1 (NOP_EXPR, type, t));
104    }
105  if (code == POINTER_TYPE || code == REFERENCE_TYPE)
106    return fold (convert_to_pointer (type, e));
107  if (code == REAL_TYPE)
108    return fold (convert_to_real (type, e));
109  if (code == COMPLEX_TYPE)
110    return fold (convert_to_complex (type, e));
111  if (code == VECTOR_TYPE)
112    return fold (convert_to_vector (type, e));
113
114  error ("conversion to non-scalar type requested");
115  return error_mark_node;
116}
117