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概要[]

  • gcc-4.1.0/gcc/c-convert.cにて定義
  • C 言語レベルの型変換.ちなみに c-convert.c には,この関数しかない.
  1 /* Language-level data type conversion for GNU C.
 41 /* Change of width--truncation and extension of integers or reals--
 42    is represented with NOP_EXPR.  Proper functioning of many things
 43    assumes that no other conversions can be NOP_EXPRs.
 44 
 45    Conversion between integer and pointer is represented with CONVERT_EXPR.
 46    Converting integer to real uses FLOAT_EXPR
 47    and real to integer uses FIX_TRUNC_EXPR.
 48 
 49    Here is a list of all the functions that assume that widening and
 50    narrowing is always done with a NOP_EXPR:
 51      In convert.c, convert_to_integer.
 52      In c-typeck.c, build_binary_op (boolean ops), and
 53         c_common_truthvalue_conversion.
 54      In expr.c: expand_expr, for operands of a MULT_EXPR.
 55      In fold-const.c: fold.
 56      In tree.c: get_narrower and get_unwidened.  */
 57
 58 /* Subroutines of `convert'.  */
 59 
 60 
 61
 62 /* Create an expression whose value is that of EXPR,
 63    converted to type TYPE.  The TREE_TYPE of the value
 64    is always TYPE.  This function implements all reasonable
 65    conversions; callers should filter out those that are
 66    not permitted by the language being compiled.  */

引数[]

  • tree type
    • 型を表すノード (式の型を,この型に変換する)
  • tree expr
    • 式を表す木構造

実装[]

68 tree
69 convert (tree type, tree expr)
70 {
71   tree e = expr;
72   enum tree_code code = TREE_CODE (type);
73   const char *invalid_conv_diag;
74 
75   if (type == error_mark_node
76       || expr == error_mark_node
77       || TREE_TYPE (expr) == error_mark_node)
78     return error_mark_node;
79 
80   if ((invalid_conv_diag
81        = targetm.invalid_conversion (TREE_TYPE (expr), type)))
82     {
83       error (invalid_conv_diag);
84       return error_mark_node;
85     }
86 
87   if (type == TREE_TYPE (expr))
88     return expr;
89 
90   if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE (expr)))
91     return fold_build1 (NOP_EXPR, type, expr);
92   if (TREE_CODE (TREE_TYPE (expr)) == ERROR_MARK)
93     return error_mark_node;
94   if (TREE_CODE (TREE_TYPE (expr)) == VOID_TYPE)
95     {
96       error ("void value not ignored as it ought to be");
97       return error_mark_node;
98     }
99   if (code == VOID_TYPE)
100     return build1 (CONVERT_EXPR, type, e);
101 #if 0
102   /* This is incorrect.  A truncation can't be stripped this way.
103      Extensions will be stripped by the use of get_unwidened.  */
104   if (TREE_CODE (expr) == NOP_EXPR)
105     return convert (type, TREE_OPERAND (expr, 0));
106 #endif
107   if (code == INTEGER_TYPE || code == ENUMERAL_TYPE)
108     return fold (convert_to_integer (type, e));
109   if (code == BOOLEAN_TYPE)
110     {
111       tree t = c_objc_common_truthvalue_conversion (expr);
112       if (TREE_CODE (t) == ERROR_MARK)
113         return t;
114 
 115       /* If it returns a NOP_EXPR, we must fold it here to avoid
 116          infinite recursion between fold () and convert ().  */
117       if (TREE_CODE (t) == NOP_EXPR)
118         return fold_build1 (NOP_EXPR, type, TREE_OPERAND (t, 0));
119       else
120         return fold_build1 (NOP_EXPR, type, t);
121     }
122   if (code == POINTER_TYPE || code == REFERENCE_TYPE)
123     return fold (convert_to_pointer (type, e));
124   if (code == REAL_TYPE)
125     return fold (convert_to_real (type, e));
126   if (code == COMPLEX_TYPE)
127     return fold (convert_to_complex (type, e));
128   if (code == VECTOR_TYPE)
129     return fold (convert_to_vector (type, e));
130   if ((code == RECORD_TYPE || code == UNION_TYPE)
131       && lang_hooks.types_compatible_p (type, TREE_TYPE (expr)))
132       return e;
133 
134   error ("conversion to non-scalar type requested");
135   return error_mark_node;
136 }



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