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Annotation of gcc/c-convert.c, revision 1.1.1.5

1.1       root        1: /* Language-level data type conversion for GNU C.
                      2:    Copyright (C) 1987, 1988, 1991 Free Software Foundation, Inc.
                      3: 
                      4: This file is part of GNU CC.
                      5: 
                      6: GNU CC is free software; you can redistribute it and/or modify
                      7: it under the terms of the GNU General Public License as published by
                      8: the Free Software Foundation; either version 2, or (at your option)
                      9: any later version.
                     10: 
                     11: GNU CC is distributed in the hope that it will be useful,
                     12: but WITHOUT ANY WARRANTY; without even the implied warranty of
                     13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
                     14: GNU General Public License for more details.
                     15: 
                     16: You should have received a copy of the GNU General Public License
                     17: along with GNU CC; see the file COPYING.  If not, write to
1.1.1.5 ! root       18: the Free Software Foundation, 59 Temple Place - Suite 330,
        !            19: Boston, MA 02111-1307, USA.  */
1.1       root       20: 
                     21: 
                     22: /* This file contains the functions for converting C expressions
                     23:    to different data types.  The only entry point is `convert'.
                     24:    Every language front end must have a `convert' function
                     25:    but what kind of conversions it does will depend on the language.  */
                     26: 
                     27: #include "config.h"
                     28: #include "tree.h"
                     29: #include "flags.h"
1.1.1.4   root       30: #include "convert.h"
1.1       root       31: 
                     32: /* Change of width--truncation and extension of integers or reals--
                     33:    is represented with NOP_EXPR.  Proper functioning of many things
                     34:    assumes that no other conversions can be NOP_EXPRs.
                     35: 
                     36:    Conversion between integer and pointer is represented with CONVERT_EXPR.
                     37:    Converting integer to real uses FLOAT_EXPR
                     38:    and real to integer uses FIX_TRUNC_EXPR.
                     39: 
                     40:    Here is a list of all the functions that assume that widening and
                     41:    narrowing is always done with a NOP_EXPR:
1.1.1.4   root       42:      In convert.c, convert_to_integer.
1.1       root       43:      In c-typeck.c, build_binary_op (boolean ops), and truthvalue_conversion.
                     44:      In expr.c: expand_expr, for operands of a MULT_EXPR.
                     45:      In fold-const.c: fold.
                     46:      In tree.c: get_narrower and get_unwidened.  */
                     47: 
                     48: /* Subroutines of `convert'.  */
                     49: 
                     50: 
                     51: 
                     52: /* Create an expression whose value is that of EXPR,
                     53:    converted to type TYPE.  The TREE_TYPE of the value
                     54:    is always TYPE.  This function implements all reasonable
                     55:    conversions; callers should filter out those that are
                     56:    not permitted by the language being compiled.  */
                     57: 
                     58: tree
                     59: convert (type, expr)
                     60:      tree type, expr;
                     61: {
                     62:   register tree e = expr;
                     63:   register enum tree_code code = TREE_CODE (type);
                     64: 
1.1.1.3   root       65:   if (type == TREE_TYPE (expr)
                     66:       || TREE_CODE (expr) == ERROR_MARK)
1.1       root       67:     return expr;
1.1.1.3   root       68:   if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE (expr)))
                     69:     return fold (build1 (NOP_EXPR, type, expr));
1.1       root       70:   if (TREE_CODE (TREE_TYPE (expr)) == ERROR_MARK)
                     71:     return error_mark_node;
                     72:   if (TREE_CODE (TREE_TYPE (expr)) == VOID_TYPE)
                     73:     {
                     74:       error ("void value not ignored as it ought to be");
                     75:       return error_mark_node;
                     76:     }
                     77:   if (code == VOID_TYPE)
                     78:     return build1 (CONVERT_EXPR, type, e);
                     79: #if 0
                     80:   /* This is incorrect.  A truncation can't be stripped this way.
                     81:      Extensions will be stripped by the use of get_unwidened.  */
                     82:   if (TREE_CODE (expr) == NOP_EXPR)
                     83:     return convert (type, TREE_OPERAND (expr, 0));
                     84: #endif
                     85:   if (code == INTEGER_TYPE || code == ENUMERAL_TYPE)
                     86:     return fold (convert_to_integer (type, e));
                     87:   if (code == POINTER_TYPE)
                     88:     return fold (convert_to_pointer (type, e));
                     89:   if (code == REAL_TYPE)
                     90:     return fold (convert_to_real (type, e));
1.1.1.4   root       91:   if (code == COMPLEX_TYPE)
                     92:     return fold (convert_to_complex (type, e));
1.1       root       93: 
                     94:   error ("conversion to non-scalar type requested");
                     95:   return error_mark_node;
                     96: }

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