convert.c

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/* Utility routines for data type conversion for GNU C.
   Copyright (C) 1987, 88, 91, 92, 94, 95, 1997 Free Software Foundation, Inc.

This file is part of GNU C.

GNU CC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU CC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */


/* These routines are somewhat language-independent utility function
   intended to be called by the language-specific convert () functions.  */

#include "config.h"
#include "tree.h"
#include "flags.h"
#include "convert.h"

/* Convert EXPR to some pointer or reference type TYPE.

   EXPR must be pointer, reference, integer, enumeral, or literal zero;
   in other cases error is called.  */

tree
convert_to_pointer (type, expr)
     tree type, expr;
{
  register tree intype = TREE_TYPE (expr);
  register enum tree_code form = TREE_CODE (intype);
  
  if (integer_zerop (expr))
    {
      expr = build_int_2 (0, 0);
      TREE_TYPE (expr) = type;
      return expr;
    }

  if (form == POINTER_TYPE || form == REFERENCE_TYPE)
    return build1 (NOP_EXPR, type, expr);


  if (form == INTEGER_TYPE || form == ENUMERAL_TYPE)
    {
      if (type_precision (intype) == POINTER_SIZE)
	return build1 (CONVERT_EXPR, type, expr);
      expr = convert (type_for_size (POINTER_SIZE, 0), expr);
      /* Modes may be different but sizes should be the same.  */
      if (GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (expr)))
	  != GET_MODE_SIZE (TYPE_MODE (type)))
	/* There is supposed to be some integral type
	   that is the same width as a pointer.  */
	abort ();
      return convert_to_pointer (type, expr);
    }

  error ("cannot convert to a pointer type");

  expr = build_int_2 (0, 0);
  TREE_TYPE (expr) = type;
  return expr;
}

/* Convert EXPR to some floating-point type TYPE.

   EXPR must be float, integer, or enumeral;
   in other cases error is called.  */

tree
convert_to_real (type, expr)
     tree type, expr;
{
  register enum tree_code form = TREE_CODE (TREE_TYPE (expr));

  if (form == REAL_TYPE)
    return build1 (flag_float_store ? CONVERT_EXPR : NOP_EXPR,
		   type, expr);

  if (INTEGRAL_TYPE_P (TREE_TYPE (expr)))
    return build1 (FLOAT_EXPR, type, expr);

  if (form == COMPLEX_TYPE)
    return convert (type, fold (build1 (REALPART_EXPR,
					TREE_TYPE (TREE_TYPE (expr)), expr)));

  if (form == POINTER_TYPE || form == REFERENCE_TYPE)
    error ("pointer value used where a floating point value was expected");
  else
    error ("aggregate value used where a float was expected");

  {
    register tree tem = make_node (REAL_CST);
    TREE_TYPE (tem) = type;
    TREE_REAL_CST (tem) = REAL_VALUE_ATOF ("0.0", TYPE_MODE (type));
    return tem;
  }
}

/* Convert EXPR to some integer (or enum) type TYPE.

   EXPR must be pointer, integer, discrete (enum, char, or bool), or float;
   in other cases error is called.

   The result of this is always supposed to be a newly created tree node
   not in use in any existing structure.  */

tree
convert_to_integer (type, expr)
     tree type, expr;
{
  register tree intype = TREE_TYPE (expr);
  register enum tree_code form = TREE_CODE (intype);

  if (form == POINTER_TYPE || form == REFERENCE_TYPE)
    {
      if (integer_zerop (expr))
	expr = integer_zero_node;
      else
	expr = fold (build1 (CONVERT_EXPR,
			     type_for_size (POINTER_SIZE, 0), expr));
      intype = TREE_TYPE (expr);
      form = TREE_CODE (intype);
      if (intype == type)
	return expr;
    }

  if (form == INTEGER_TYPE || form == ENUMERAL_TYPE
      || form == BOOLEAN_TYPE || form == CHAR_TYPE)
    {
      register unsigned outprec = TYPE_PRECISION (type);
      register unsigned inprec = TYPE_PRECISION (intype);
      register enum tree_code ex_form = TREE_CODE (expr);

      /* If we are widening the type, put in an explicit conversion.
	 Similarly if we are not changing the width.  However, if this is
	 a logical operation that just returns 0 or 1, we can change the
	 type of the expression.  For logical operations, we must
	 also change the types of the operands to maintain type
	 correctness.  */

      if (TREE_CODE_CLASS (ex_form) == '<')
	{
	  TREE_TYPE (expr) = type;
	  return expr;
	}
      else if (ex_form == TRUTH_AND_EXPR || ex_form == TRUTH_ANDIF_EXPR
	       || ex_form == TRUTH_OR_EXPR || ex_form == TRUTH_ORIF_EXPR
	       || ex_form == TRUTH_XOR_EXPR)
	{
	  TREE_OPERAND (expr, 0) = convert (type, TREE_OPERAND (expr, 0));
	  TREE_OPERAND (expr, 1) = convert (type, TREE_OPERAND (expr, 1));
	  TREE_TYPE (expr) = type;
	  return expr;
	}
      else if (ex_form == TRUTH_NOT_EXPR)
	{
	  TREE_OPERAND (expr, 0) = convert (type, TREE_OPERAND (expr, 0));
	  TREE_TYPE (expr) = type;
	  return expr;
	}
      else if (outprec >= inprec)
	return build1 (NOP_EXPR, type, expr);

      /* If TYPE is an enumeral type or a type with a precision less
	 than the number of bits in its mode, do the conversion to the
	 type corresponding to its mode, then do a nop conversion
	 to TYPE.  */
      else if (TREE_CODE (type) == ENUMERAL_TYPE
	       || outprec != GET_MODE_BITSIZE (TYPE_MODE (type)))
	return build1 (NOP_EXPR, type,
		       convert (type_for_mode (TYPE_MODE (type),
					       TREE_UNSIGNED (type)),
				expr));

      /* Here detect when we can distribute the truncation down past some
	 arithmetic.  For example, if adding two longs and converting to an
	 int, we can equally well convert both to ints and then add.
	 For the operations handled here, such truncation distribution
	 is always safe.
	 It is desirable in these cases:
	 1) when truncating down to full-word from a larger size
	 2) when truncating takes no work.
	 3) when at least one operand of the arithmetic has been extended
	 (as by C's default conversions).  In this case we need two conversions
	 if we do the arithmetic as already requested, so we might as well
	 truncate both and then combine.  Perhaps that way we need only one.

	 Note that in general we cannot do the arithmetic in a type
	 shorter than the desired result of conversion, even if the operands
	 are both extended from a shorter type, because they might overflow
	 if combined in that type.  The exceptions to this--the times when
	 two narrow values can be combined in their narrow type even to
	 make a wider result--are handled by "shorten" in build_binary_op.  */

      switch (ex_form)
	{
	case RSHIFT_EXPR:
	  /* We can pass truncation down through right shifting
	     when the shift count is a nonpositive constant.  */
	  if (TREE_CODE (TREE_OPERAND (expr, 1)) == INTEGER_CST
	      && tree_int_cst_lt (TREE_OPERAND (expr, 1),
				  convert (TREE_TYPE (TREE_OPERAND (expr, 1)),
					   integer_one_node)))
	    goto trunc1;
	  break;

	case LSHIFT_EXPR:
	  /* We can pass truncation down through left shifting
	     when the shift count is a nonnegative constant.  */
	  if (TREE_CODE (TREE_OPERAND (expr, 1)) == INTEGER_CST
	      && tree_int_cst_sgn (TREE_OPERAND (expr, 1)) >= 0
	      && TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST)
	    {
	      /* If shift count is less than the width of the truncated type,
		 really shift.  */
	      if (tree_int_cst_lt (TREE_OPERAND (expr, 1), TYPE_SIZE (type)))
		/* In this case, shifting is like multiplication.  */
		goto trunc1;
	      else
		{
		  /* If it is >= that width, result is zero.
		     Handling this with trunc1 would give the wrong result:
		     (int) ((long long) a << 32) is well defined (as 0)
		     but (int) a << 32 is undefined and would get a
		     warning.  */

		  tree t = convert_to_integer (type, integer_zero_node);