gcc/c/c-convert.cc

   1 /* Language-level data type conversion for GNU C.
   2    Copyright (C) 1987-2023 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along 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 \f
  55 /* Subroutines of `convert'.  */
  56
  57
  58 \f
  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
  68 static tree
  69 c_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 (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 (TREE_CODE (TREE_TYPE (expr)) == VOID_TYPE)
 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       if (sanitize_flags_p (SANITIZE_FLOAT_CAST)
 121           && current_function_decl != NULL_TREE
 122           && TREE_CODE (TREE_TYPE (expr)) == REAL_TYPE
 123           && COMPLETE_TYPE_P (type))
 124         {
 125           expr = save_expr (expr);
 126           expr = c_fully_fold (expr, init_const, NULL);
 127           tree check = ubsan_instrument_float_cast (loc, type, expr);
 128           expr = fold_build1 (FIX_TRUNC_EXPR, type, expr);
 129           if (check == NULL_TREE)
 130             return expr;
 131           return fold_build2 (COMPOUND_EXPR, TREE_TYPE (expr), check, expr);
 132         }
 133       ret = convert_to_integer (type, e);
 134       goto maybe_fold;
 135
 136     case BOOLEAN_TYPE:
 137     convert_to_boolean:
 138       return fold_convert_loc
 139         (loc, type, c_objc_common_truthvalue_conversion (input_location, expr));
 140
 141     case POINTER_TYPE:
 142       /* The type nullptr_t may be converted to a pointer type.  The result is
 143          a null pointer value.  */
 144       if (NULLPTR_TYPE_P (TREE_TYPE (e)))
 145         {
 146           /* To make sure that (void *)nullptr is not a null pointer constant,
 147              build_c_cast will create an additional NOP_EXPR around the result
 148              of this conversion.  */
 149           if (TREE_SIDE_EFFECTS (e))
 150             ret = build2 (COMPOUND_EXPR, type, e, build_int_cst (type, 0));
 151           else
 152             ret = build_int_cst (type, 0);
 153           goto maybe_fold;
 154         }
 155       gcc_fallthrough ();
 156     case REFERENCE_TYPE:
 157       ret = convert_to_pointer (type, e);
 158       goto maybe_fold;
 159
 160     case NULLPTR_TYPE:
 161       /* A null pointer constant or value of type nullptr_t may be
 162          converted to nullptr_t.  The latter case has already been
 163          handled.  build_c_cast will create an additional NOP_EXPR to
 164          ensure the result of the conversion is not itself a null
 165          pointer constant.  */
 166       if (null_pointer_constant_p (expr))
 167         {
 168           ret = build_int_cst (type, 0);
 169           goto maybe_fold;
 170         }
 171       break;
 172
 173     case REAL_TYPE:
 174       ret = convert_to_real (type, e);
 175       goto maybe_fold;
 176
 177     case FIXED_POINT_TYPE:
 178       ret = convert_to_fixed (type, e);
 179       goto maybe_fold;
 180
 181     case COMPLEX_TYPE:
 182       ret = convert_to_complex (type, e);
 183       goto maybe_fold;
 184
 185     case VECTOR_TYPE:
 186       if (gnu_vector_type_p (type)
 187           || gnu_vector_type_p (TREE_TYPE (e))
 188           /* Allow conversions between compatible non-GNU vector types
 189              when -flax-vector-conversions is passed.  The whole purpose
 190              of the option is to bend the normal type rules and accept
 191              nonconforming code.  */
 192           || (flag_lax_vector_conversions
 193               && VECTOR_TYPE_P (TREE_TYPE (e))
 194               && vector_types_convertible_p (type, TREE_TYPE (e), false)))
 195         {
 196           ret = convert_to_vector (type, e);
 197           goto maybe_fold;
 198         }
 199       break;
 200
 201     case RECORD_TYPE:
 202     case UNION_TYPE:
 203       if (lang_hooks.types_compatible_p (type, TREE_TYPE (expr)))
 204         return e;
 205       break;
 206
 207     default:
 208       break;
 209
 210     maybe_fold:
 211       if (TREE_CODE (ret) != C_MAYBE_CONST_EXPR)
 212         ret = init_const ? fold_init (ret) : fold (ret);
 213       return ret;
 214     }
 215
 216   /* If we are converting to nullptr_t, don't say "non-scalar type" because
 217      the nullptr_t type is a scalar type.  Only nullptr_t or a null pointer
 218      constant shall be converted to nullptr_t.  */
 219   if (code == NULLPTR_TYPE)
 220     {
 221       error ("conversion from %qT to %qT", TREE_TYPE (e), type);
 222       inform (input_location,
 223               "only %qT or a null pointer constant can be converted to %qT",
 224               type, type);
 225     }
 226   else
 227     error ("conversion to non-scalar type requested");
 228   return error_mark_node;
 229 }
 230
 231 /* Create an expression whose value is that of EXPR, converted to type TYPE.
 232    The TREE_TYPE of the value is always TYPE.  This function implements all
 233    reasonable conversions; callers should filter out those that are not
 234    permitted by the language being compiled.  */
 235
 236 tree
 237 convert (tree type, tree expr)
 238 {
 239   return c_convert (type, expr, false);
 240 }
 241
 242 /* Create an expression whose value is that of EXPR, converted to type TYPE, in
 243    a static initializer.  The TREE_TYPE of the value is always TYPE.  This
 244    function implements all reasonable conversions; callers should filter out
 245    those that are not permitted by the language being compiled.  */
 246
 247 tree
 248 convert_init (tree type, tree expr)
 249 {
 250   return c_convert (type, expr, true);
 251 }