1/* Language-level data type conversion for GNU C.
2 Copyright (C) 1987-2023 Free Software Foundation, Inc.
3
4This file is part of GCC.
5
6GCC is free software; you can redistribute it and/or modify it under
7the terms of the GNU General Public License as published by the Free
8Software Foundation; either version 3, or (at your option) any later
9version.
10
11GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12WARRANTY; without even the implied warranty of MERCHANTABILITY or
13FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14for more details.
15
16You should have received a copy of the GNU General Public License
17along with GCC; see the file COPYING3. If not see
18<http://www.gnu.org/licenses/>. */
19
20
21/* This file contains the functions for converting C expressions
22 to different data types. The only entry point is `convert'.
23 Every language front end must have a `convert' function
24 but what kind of conversions it does will depend on the language. */
25
26#include "config.h"
27#include "system.h"
28#include "coretypes.h"
29#include "target.h"
30#include "c-tree.h"
31#include "convert.h"
32#include "langhooks.h"
33#include "ubsan.h"
34#include "stringpool.h"
35#include "attribs.h"
36#include "asan.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.cc, convert_to_integer.
49 In c-typeck.cc, build_binary_op (boolean ops), and
50 c_common_truthvalue_conversion.
51 In expr.cc: expand_expr, for operands of a MULT_EXPR.
52 In fold-const.cc: fold.
53 In tree.cc: 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 INIT_CONST is true if the conversion is for arithmetic types for a static
65 initializer and folding must apply accordingly (discarding floating-point
66 exceptions and assuming the default rounding mode is in effect). */
67
68static tree
69c_convert (tree type, tree expr, bool init_const)
70{
71 tree e = expr;
72 enum tree_code code = TREE_CODE (type);
73 const char *invalid_conv_diag;
74 tree ret;
75 location_t loc = EXPR_LOCATION (expr);
76
77 if (type == error_mark_node
78 || error_operand_p (t: expr))
79 return error_mark_node;
80
81 if ((invalid_conv_diag
82 = targetm.invalid_conversion (TREE_TYPE (expr), type)))
83 {
84 error (invalid_conv_diag);
85 return error_mark_node;
86 }
87
88 if (type == TREE_TYPE (expr))
89 return expr;
90 ret = targetm.convert_to_type (type, expr);
91 if (ret)
92 return ret;
93
94 STRIP_TYPE_NOPS (e);
95
96 if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE (expr))
97 && (TREE_CODE (TREE_TYPE (expr)) != COMPLEX_TYPE
98 || TREE_CODE (e) == COMPLEX_EXPR))
99 return fold_convert_loc (loc, type, expr);
100 if (TREE_CODE (TREE_TYPE (expr)) == ERROR_MARK)
101 return error_mark_node;
102 if (VOID_TYPE_P (TREE_TYPE (expr)))
103 {
104 error ("void value not ignored as it ought to be");
105 return error_mark_node;
106 }
107
108 switch (code)
109 {
110 case VOID_TYPE:
111 return fold_convert_loc (loc, type, e);
112
113 case ENUMERAL_TYPE:
114 if (ENUM_UNDERLYING_TYPE (type) != NULL_TREE
115 && TREE_CODE (ENUM_UNDERLYING_TYPE (type)) == BOOLEAN_TYPE)
116 goto convert_to_boolean;
117 gcc_fallthrough ();
118
119 case INTEGER_TYPE:
120 case BITINT_TYPE:
121 if (sanitize_flags_p (flag: SANITIZE_FLOAT_CAST)
122 && current_function_decl != NULL_TREE
123 && SCALAR_FLOAT_TYPE_P (TREE_TYPE (expr))
124 && COMPLETE_TYPE_P (type))
125 {
126 expr = save_expr (expr);
127 expr = c_fully_fold (expr, init_const, NULL);
128 tree check = ubsan_instrument_float_cast (loc, type, expr);
129 expr = fold_build1 (FIX_TRUNC_EXPR, type, expr);
130 if (check == NULL_TREE)
131 return expr;
132 return fold_build2 (COMPOUND_EXPR, TREE_TYPE (expr), check, expr);
133 }
134 ret = convert_to_integer (type, e);
135 goto maybe_fold;
136
137 case BOOLEAN_TYPE:
138 convert_to_boolean:
139 return fold_convert_loc
140 (loc, type, c_objc_common_truthvalue_conversion (input_location, expr));
141
142 case POINTER_TYPE:
143 /* The type nullptr_t may be converted to a pointer type. The result is
144 a null pointer value. */
145 if (NULLPTR_TYPE_P (TREE_TYPE (e)))
146 {
147 /* To make sure that (void *)nullptr is not a null pointer constant,
148 build_c_cast will create an additional NOP_EXPR around the result
149 of this conversion. */
150 if (TREE_SIDE_EFFECTS (e))
151 ret = build2 (COMPOUND_EXPR, type, e, build_int_cst (type, 0));
152 else
153 ret = build_int_cst (type, 0);
154 goto maybe_fold;
155 }
156 gcc_fallthrough ();
157 case REFERENCE_TYPE:
158 ret = convert_to_pointer (type, e);
159 goto maybe_fold;
160
161 case NULLPTR_TYPE:
162 /* A null pointer constant or value of type nullptr_t may be
163 converted to nullptr_t. The latter case has already been
164 handled. build_c_cast will create an additional NOP_EXPR to
165 ensure the result of the conversion is not itself a null
166 pointer constant. */
167 if (null_pointer_constant_p (expr))
168 {
169 ret = build_int_cst (type, 0);
170 goto maybe_fold;
171 }
172 break;
173
174 case REAL_TYPE:
175 ret = convert_to_real (type, e);
176 goto maybe_fold;
177
178 case FIXED_POINT_TYPE:
179 ret = convert_to_fixed (type, e);
180 goto maybe_fold;
181
182 case COMPLEX_TYPE:
183 ret = convert_to_complex (type, e);
184 goto maybe_fold;
185
186 case VECTOR_TYPE:
187 if (gnu_vector_type_p (type)
188 || gnu_vector_type_p (TREE_TYPE (e))
189 /* Allow conversions between compatible non-GNU vector types
190 when -flax-vector-conversions is passed. The whole purpose
191 of the option is to bend the normal type rules and accept
192 nonconforming code. */
193 || (flag_lax_vector_conversions
194 && VECTOR_TYPE_P (TREE_TYPE (e))
195 && vector_types_convertible_p (t1: type, TREE_TYPE (e), emit_lax_note: false)))
196 {
197 ret = convert_to_vector (type, e);
198 goto maybe_fold;
199 }
200 break;
201
202 case RECORD_TYPE:
203 case UNION_TYPE:
204 if (lang_hooks.types_compatible_p (type, TREE_TYPE (expr)))
205 return e;
206 break;
207
208 default:
209 break;
210
211 maybe_fold:
212 if (TREE_CODE (ret) != C_MAYBE_CONST_EXPR)
213 ret = init_const ? fold_init (ret) : fold (ret);
214 return ret;
215 }
216
217 /* If we are converting to nullptr_t, don't say "non-scalar type" because
218 the nullptr_t type is a scalar type. Only nullptr_t or a null pointer
219 constant shall be converted to nullptr_t. */
220 if (code == NULLPTR_TYPE)
221 {
222 error ("conversion from %qT to %qT", TREE_TYPE (e), type);
223 inform (input_location,
224 "only %qT or a null pointer constant can be converted to %qT",
225 type, type);
226 }
227 else
228 error ("conversion to non-scalar type requested");
229 return error_mark_node;
230}
231
232/* Create an expression whose value is that of EXPR, converted to type TYPE.
233 The TREE_TYPE of the value is always TYPE. This function implements all
234 reasonable conversions; callers should filter out those that are not
235 permitted by the language being compiled. */
236
237tree
238convert (tree type, tree expr)
239{
240 return c_convert (type, expr, init_const: false);
241}
242
243/* Create an expression whose value is that of EXPR, converted to type TYPE, in
244 a static initializer. The TREE_TYPE of the value is always TYPE. This
245 function implements all reasonable conversions; callers should filter out
246 those that are not permitted by the language being compiled. */
247
248tree
249convert_init (tree type, tree expr)
250{
251 return c_convert (type, expr, init_const: true);
252}
253

source code of gcc/c/c-convert.cc