view gcc/convert.c @ 14:f6334be47118

update gcc from gcc-4.6-20100522 to gcc-4.6-20110318
author nobuyasu <dimolto@cr.ie.u-ryukyu.ac.jp>
date Tue, 22 Mar 2011 17:18:12 +0900
parents b7f97abdc517
children 04ced10e8804
line wrap: on
line source

/* Utility routines for data type conversion for GCC.
   Copyright (C) 1987, 1988, 1991, 1992, 1993, 1994, 1995, 1997, 1998,
   2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
   Free Software Foundation, Inc.

This file is part of GCC.

GCC 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 3, or (at your option) any later
version.

GCC 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 GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */


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

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "flags.h"
#include "convert.h"
#include "diagnostic-core.h"
#include "langhooks.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 (tree type, tree expr)
{
  location_t loc = EXPR_LOCATION (expr);
  if (TREE_TYPE (expr) == type)
    return expr;

  /* Propagate overflow to the NULL pointer.  */
  if (integer_zerop (expr))
    return force_fit_type_double (type, double_int_zero, 0,
				  TREE_OVERFLOW (expr));

  switch (TREE_CODE (TREE_TYPE (expr)))
    {
    case POINTER_TYPE:
    case REFERENCE_TYPE:
      {
        /* If the pointers point to different address spaces, conversion needs
	   to be done via a ADDR_SPACE_CONVERT_EXPR instead of a NOP_EXPR.  */
	addr_space_t to_as = TYPE_ADDR_SPACE (TREE_TYPE (type));
	addr_space_t from_as = TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (expr)));

	if (to_as == from_as)
	  return fold_build1_loc (loc, NOP_EXPR, type, expr);
	else
	  return fold_build1_loc (loc, ADDR_SPACE_CONVERT_EXPR, type, expr);
      }

    case INTEGER_TYPE:
    case ENUMERAL_TYPE:
    case BOOLEAN_TYPE:
      {
	/* If the input precision differs from the target pointer type
	   precision, first convert the input expression to an integer type of
	   the target precision.  Some targets, e.g. VMS, need several pointer
	   sizes to coexist so the latter isn't necessarily POINTER_SIZE.  */
	unsigned int pprec = TYPE_PRECISION (type);
	unsigned int eprec = TYPE_PRECISION (TREE_TYPE (expr));

 	if (eprec != pprec)
	  expr = fold_build1_loc (loc, NOP_EXPR,
			      lang_hooks.types.type_for_size (pprec, 0),
			      expr);
      }

      return fold_build1_loc (loc, CONVERT_EXPR, type, expr);

    default:
      error ("cannot convert to a pointer type");
      return convert_to_pointer (type, integer_zero_node);
    }
}

/* Avoid any floating point extensions from EXP.  */
tree
strip_float_extensions (tree exp)
{
  tree sub, expt, subt;

  /*  For floating point constant look up the narrowest type that can hold
      it properly and handle it like (type)(narrowest_type)constant.
      This way we can optimize for instance a=a*2.0 where "a" is float
      but 2.0 is double constant.  */
  if (TREE_CODE (exp) == REAL_CST && !DECIMAL_FLOAT_TYPE_P (TREE_TYPE (exp)))
    {
      REAL_VALUE_TYPE orig;
      tree type = NULL;

      orig = TREE_REAL_CST (exp);
      if (TYPE_PRECISION (TREE_TYPE (exp)) > TYPE_PRECISION (float_type_node)
	  && exact_real_truncate (TYPE_MODE (float_type_node), &orig))
	type = float_type_node;
      else if (TYPE_PRECISION (TREE_TYPE (exp))
	       > TYPE_PRECISION (double_type_node)
	       && exact_real_truncate (TYPE_MODE (double_type_node), &orig))
	type = double_type_node;
      if (type)
	return build_real (type, real_value_truncate (TYPE_MODE (type), orig));
    }

  if (!CONVERT_EXPR_P (exp))
    return exp;

  sub = TREE_OPERAND (exp, 0);
  subt = TREE_TYPE (sub);
  expt = TREE_TYPE (exp);

  if (!FLOAT_TYPE_P (subt))
    return exp;

  if (DECIMAL_FLOAT_TYPE_P (expt) != DECIMAL_FLOAT_TYPE_P (subt))
    return exp;

  if (TYPE_PRECISION (subt) > TYPE_PRECISION (expt))
    return exp;

  return strip_float_extensions (sub);
}


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

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

tree
convert_to_real (tree type, tree expr)
{
  enum built_in_function fcode = builtin_mathfn_code (expr);
  tree itype = TREE_TYPE (expr);

  /* Disable until we figure out how to decide whether the functions are
     present in runtime.  */
  /* Convert (float)sqrt((double)x) where x is float into sqrtf(x) */
  if (optimize
      && (TYPE_MODE (type) == TYPE_MODE (double_type_node)
          || TYPE_MODE (type) == TYPE_MODE (float_type_node)))
    {
      switch (fcode)
        {
#define CASE_MATHFN(FN) case BUILT_IN_##FN: case BUILT_IN_##FN##L:
	  CASE_MATHFN (COSH)
	  CASE_MATHFN (EXP)
	  CASE_MATHFN (EXP10)
	  CASE_MATHFN (EXP2)
 	  CASE_MATHFN (EXPM1)
	  CASE_MATHFN (GAMMA)
	  CASE_MATHFN (J0)
	  CASE_MATHFN (J1)
	  CASE_MATHFN (LGAMMA)
	  CASE_MATHFN (POW10)
	  CASE_MATHFN (SINH)
	  CASE_MATHFN (TGAMMA)
	  CASE_MATHFN (Y0)
	  CASE_MATHFN (Y1)
	    /* The above functions may set errno differently with float
	       input or output so this transformation is not safe with
	       -fmath-errno.  */
	    if (flag_errno_math)
	      break;
	  CASE_MATHFN (ACOS)
	  CASE_MATHFN (ACOSH)
	  CASE_MATHFN (ASIN)
 	  CASE_MATHFN (ASINH)
 	  CASE_MATHFN (ATAN)
	  CASE_MATHFN (ATANH)
 	  CASE_MATHFN (CBRT)
 	  CASE_MATHFN (COS)
 	  CASE_MATHFN (ERF)
 	  CASE_MATHFN (ERFC)
 	  CASE_MATHFN (FABS)
	  CASE_MATHFN (LOG)
	  CASE_MATHFN (LOG10)
	  CASE_MATHFN (LOG2)
 	  CASE_MATHFN (LOG1P)
 	  CASE_MATHFN (LOGB)
 	  CASE_MATHFN (SIN)
	  CASE_MATHFN (SQRT)
 	  CASE_MATHFN (TAN)
 	  CASE_MATHFN (TANH)
#undef CASE_MATHFN
	    {
	      tree arg0 = strip_float_extensions (CALL_EXPR_ARG (expr, 0));
	      tree newtype = type;

	      /* We have (outertype)sqrt((innertype)x).  Choose the wider mode from
		 the both as the safe type for operation.  */
	      if (TYPE_PRECISION (TREE_TYPE (arg0)) > TYPE_PRECISION (type))
		newtype = TREE_TYPE (arg0);

	      /* Be careful about integer to fp conversions.
		 These may overflow still.  */
	      if (FLOAT_TYPE_P (TREE_TYPE (arg0))
		  && TYPE_PRECISION (newtype) < TYPE_PRECISION (itype)
		  && (TYPE_MODE (newtype) == TYPE_MODE (double_type_node)
		      || TYPE_MODE (newtype) == TYPE_MODE (float_type_node)))
	        {
		  tree fn = mathfn_built_in (newtype, fcode);

		  if (fn)
		  {
		    tree arg = fold (convert_to_real (newtype, arg0));
		    expr = build_call_expr (fn, 1, arg);
		    if (newtype == type)
		      return expr;
		  }
		}
	    }
	default:
	  break;
	}
    }
  if (optimize
      && (((fcode == BUILT_IN_FLOORL
	   || fcode == BUILT_IN_CEILL
	   || fcode == BUILT_IN_ROUNDL
	   || fcode == BUILT_IN_RINTL
	   || fcode == BUILT_IN_TRUNCL
	   || fcode == BUILT_IN_NEARBYINTL)
	  && (TYPE_MODE (type) == TYPE_MODE (double_type_node)
	      || TYPE_MODE (type) == TYPE_MODE (float_type_node)))
	  || ((fcode == BUILT_IN_FLOOR
	       || fcode == BUILT_IN_CEIL
	       || fcode == BUILT_IN_ROUND
	       || fcode == BUILT_IN_RINT
	       || fcode == BUILT_IN_TRUNC
	       || fcode == BUILT_IN_NEARBYINT)
	      && (TYPE_MODE (type) == TYPE_MODE (float_type_node)))))
    {
      tree fn = mathfn_built_in (type, fcode);

      if (fn)
	{
	  tree arg = strip_float_extensions (CALL_EXPR_ARG (expr, 0));

	  /* Make sure (type)arg0 is an extension, otherwise we could end up
	     changing (float)floor(double d) into floorf((float)d), which is
	     incorrect because (float)d uses round-to-nearest and can round
	     up to the next integer.  */
	  if (TYPE_PRECISION (type) >= TYPE_PRECISION (TREE_TYPE (arg)))
	    return build_call_expr (fn, 1, fold (convert_to_real (type, arg)));
	}
    }

  /* Propagate the cast into the operation.  */
  if (itype != type && FLOAT_TYPE_P (type))
    switch (TREE_CODE (expr))
      {
	/* Convert (float)-x into -(float)x.  This is safe for
	   round-to-nearest rounding mode.  */
	case ABS_EXPR:
	case NEGATE_EXPR:
	  if (!flag_rounding_math
	      && TYPE_PRECISION (type) < TYPE_PRECISION (TREE_TYPE (expr)))
	    return build1 (TREE_CODE (expr), type,
			   fold (convert_to_real (type,
						  TREE_OPERAND (expr, 0))));
	  break;
	/* Convert (outertype)((innertype0)a+(innertype1)b)
	   into ((newtype)a+(newtype)b) where newtype
	   is the widest mode from all of these.  */
	case PLUS_EXPR:
	case MINUS_EXPR:
	case MULT_EXPR:
	case RDIV_EXPR:
	   {
	     tree arg0 = strip_float_extensions (TREE_OPERAND (expr, 0));
	     tree arg1 = strip_float_extensions (TREE_OPERAND (expr, 1));

	     if (FLOAT_TYPE_P (TREE_TYPE (arg0))
		 && FLOAT_TYPE_P (TREE_TYPE (arg1))
		 && DECIMAL_FLOAT_TYPE_P (itype) == DECIMAL_FLOAT_TYPE_P (type))
	       {
		  tree newtype = type;

		  if (TYPE_MODE (TREE_TYPE (arg0)) == SDmode
		      || TYPE_MODE (TREE_TYPE (arg1)) == SDmode
		      || TYPE_MODE (type) == SDmode)
		    newtype = dfloat32_type_node;
		  if (TYPE_MODE (TREE_TYPE (arg0)) == DDmode
		      || TYPE_MODE (TREE_TYPE (arg1)) == DDmode
		      || TYPE_MODE (type) == DDmode)
		    newtype = dfloat64_type_node;
		  if (TYPE_MODE (TREE_TYPE (arg0)) == TDmode
		      || TYPE_MODE (TREE_TYPE (arg1)) == TDmode
		      || TYPE_MODE (type) == TDmode)
                    newtype = dfloat128_type_node;
		  if (newtype == dfloat32_type_node
		      || newtype == dfloat64_type_node
		      || newtype == dfloat128_type_node)
		    {
		      expr = build2 (TREE_CODE (expr), newtype,
				     fold (convert_to_real (newtype, arg0)),
				     fold (convert_to_real (newtype, arg1)));
		      if (newtype == type)
			return expr;
		      break;
		    }

		  if (TYPE_PRECISION (TREE_TYPE (arg0)) > TYPE_PRECISION (newtype))
		    newtype = TREE_TYPE (arg0);
		  if (TYPE_PRECISION (TREE_TYPE (arg1)) > TYPE_PRECISION (newtype))
		    newtype = TREE_TYPE (arg1);
		  /* Sometimes this transformation is safe (cannot
		     change results through affecting double rounding
		     cases) and sometimes it is not.  If NEWTYPE is
		     wider than TYPE, e.g. (float)((long double)double
		     + (long double)double) converted to
		     (float)(double + double), the transformation is
		     unsafe regardless of the details of the types
		     involved; double rounding can arise if the result
		     of NEWTYPE arithmetic is a NEWTYPE value half way
		     between two representable TYPE values but the
		     exact value is sufficiently different (in the
		     right direction) for this difference to be
		     visible in ITYPE arithmetic.  If NEWTYPE is the
		     same as TYPE, however, the transformation may be
		     safe depending on the types involved: it is safe
		     if the ITYPE has strictly more than twice as many
		     mantissa bits as TYPE, can represent infinities
		     and NaNs if the TYPE can, and has sufficient
		     exponent range for the product or ratio of two
		     values representable in the TYPE to be within the
		     range of normal values of ITYPE.  */
		  if (TYPE_PRECISION (newtype) < TYPE_PRECISION (itype)
		      && (flag_unsafe_math_optimizations
			  || (TYPE_PRECISION (newtype) == TYPE_PRECISION (type)
			      && real_can_shorten_arithmetic (TYPE_MODE (itype),
							      TYPE_MODE (type))
			      && !excess_precision_type (newtype))))
		    {
		      expr = build2 (TREE_CODE (expr), newtype,
				     fold (convert_to_real (newtype, arg0)),
				     fold (convert_to_real (newtype, arg1)));
		      if (newtype == type)
			return expr;
		    }
	       }
	   }
	  break;
	default:
	  break;
      }

  switch (TREE_CODE (TREE_TYPE (expr)))
    {
    case REAL_TYPE:
      /* Ignore the conversion if we don't need to store intermediate
	 results and neither type is a decimal float.  */
      return build1 ((flag_float_store
		     || DECIMAL_FLOAT_TYPE_P (type)
		     || DECIMAL_FLOAT_TYPE_P (itype))
		     ? CONVERT_EXPR : NOP_EXPR, type, expr);

    case INTEGER_TYPE:
    case ENUMERAL_TYPE:
    case BOOLEAN_TYPE:
      return build1 (FLOAT_EXPR, type, expr);

    case FIXED_POINT_TYPE:
      return build1 (FIXED_CONVERT_EXPR, type, expr);

    case COMPLEX_TYPE:
      return convert (type,
		      fold_build1 (REALPART_EXPR,
				   TREE_TYPE (TREE_TYPE (expr)), expr));

    case POINTER_TYPE:
    case REFERENCE_TYPE:
      error ("pointer value used where a floating point value was expected");
      return convert_to_real (type, integer_zero_node);

    default:
      error ("aggregate value used where a float was expected");
      return convert_to_real (type, integer_zero_node);
    }
}

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

   EXPR must be pointer, integer, discrete (enum, char, or bool), float,
   fixed-point or vector; 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 (tree type, tree expr)
{
  enum tree_code ex_form = TREE_CODE (expr);
  tree intype = TREE_TYPE (expr);
  unsigned int inprec = TYPE_PRECISION (intype);
  unsigned int outprec = TYPE_PRECISION (type);

  /* An INTEGER_TYPE cannot be incomplete, but an ENUMERAL_TYPE can
     be.  Consider `enum E = { a, b = (enum E) 3 };'.  */
  if (!COMPLETE_TYPE_P (type))
    {
      error ("conversion to incomplete type");
      return error_mark_node;
    }

  /* Convert e.g. (long)round(d) -> lround(d).  */
  /* If we're converting to char, we may encounter differing behavior
     between converting from double->char vs double->long->char.
     We're in "undefined" territory but we prefer to be conservative,
     so only proceed in "unsafe" math mode.  */
  if (optimize
      && (flag_unsafe_math_optimizations
	  || (long_integer_type_node
	      && outprec >= TYPE_PRECISION (long_integer_type_node))))
    {
      tree s_expr = strip_float_extensions (expr);
      tree s_intype = TREE_TYPE (s_expr);
      const enum built_in_function fcode = builtin_mathfn_code (s_expr);
      tree fn = 0;

      switch (fcode)
        {
	CASE_FLT_FN (BUILT_IN_CEIL):
	  /* Only convert in ISO C99 mode.  */
	  if (!TARGET_C99_FUNCTIONS)
	    break;
	  if (outprec < TYPE_PRECISION (long_integer_type_node)
	      || (outprec == TYPE_PRECISION (long_integer_type_node)
		  && !TYPE_UNSIGNED (type)))
	    fn = mathfn_built_in (s_intype, BUILT_IN_LCEIL);
	  else if (outprec == TYPE_PRECISION (long_long_integer_type_node)
		   && !TYPE_UNSIGNED (type))
	    fn = mathfn_built_in (s_intype, BUILT_IN_LLCEIL);
	  break;

	CASE_FLT_FN (BUILT_IN_FLOOR):
	  /* Only convert in ISO C99 mode.  */
	  if (!TARGET_C99_FUNCTIONS)
	    break;
	  if (outprec < TYPE_PRECISION (long_integer_type_node)
	      || (outprec == TYPE_PRECISION (long_integer_type_node)
		  && !TYPE_UNSIGNED (type)))
	    fn = mathfn_built_in (s_intype, BUILT_IN_LFLOOR);
	  else if (outprec == TYPE_PRECISION (long_long_integer_type_node)
		   && !TYPE_UNSIGNED (type))
	    fn = mathfn_built_in (s_intype, BUILT_IN_LLFLOOR);
	  break;

	CASE_FLT_FN (BUILT_IN_ROUND):
	  if (outprec < TYPE_PRECISION (long_integer_type_node)
	      || (outprec == TYPE_PRECISION (long_integer_type_node)
		  && !TYPE_UNSIGNED (type)))
	    fn = mathfn_built_in (s_intype, BUILT_IN_LROUND);
	  else if (outprec == TYPE_PRECISION (long_long_integer_type_node)
		   && !TYPE_UNSIGNED (type))
	    fn = mathfn_built_in (s_intype, BUILT_IN_LLROUND);
	  break;

	CASE_FLT_FN (BUILT_IN_NEARBYINT):
	  /* Only convert nearbyint* if we can ignore math exceptions.  */
	  if (flag_trapping_math)
	    break;
	  /* ... Fall through ...  */
	CASE_FLT_FN (BUILT_IN_RINT):
	  if (outprec < TYPE_PRECISION (long_integer_type_node)
	      || (outprec == TYPE_PRECISION (long_integer_type_node)
		  && !TYPE_UNSIGNED (type)))
	    fn = mathfn_built_in (s_intype, BUILT_IN_LRINT);
	  else if (outprec == TYPE_PRECISION (long_long_integer_type_node)
		   && !TYPE_UNSIGNED (type))
	    fn = mathfn_built_in (s_intype, BUILT_IN_LLRINT);
	  break;

	CASE_FLT_FN (BUILT_IN_TRUNC):
	  return convert_to_integer (type, CALL_EXPR_ARG (s_expr, 0));

	default:
	  break;
	}

      if (fn)
        {
	  tree newexpr = build_call_expr (fn, 1, CALL_EXPR_ARG (s_expr, 0));
	  return convert_to_integer (type, newexpr);
	}
    }

  /* Convert (int)logb(d) -> ilogb(d).  */
  if (optimize
      && flag_unsafe_math_optimizations
      && !flag_trapping_math && !flag_errno_math && flag_finite_math_only
      && integer_type_node
      && (outprec > TYPE_PRECISION (integer_type_node)
	  || (outprec == TYPE_PRECISION (integer_type_node)
	      && !TYPE_UNSIGNED (type))))
    {
      tree s_expr = strip_float_extensions (expr);
      tree s_intype = TREE_TYPE (s_expr);
      const enum built_in_function fcode = builtin_mathfn_code (s_expr);
      tree fn = 0;

      switch (fcode)
	{
	CASE_FLT_FN (BUILT_IN_LOGB):
	  fn = mathfn_built_in (s_intype, BUILT_IN_ILOGB);
	  break;

	default:
	  break;
	}

      if (fn)
        {
	  tree newexpr = build_call_expr (fn, 1, CALL_EXPR_ARG (s_expr, 0));
	  return convert_to_integer (type, newexpr);
	}
    }

  switch (TREE_CODE (intype))
    {
    case POINTER_TYPE:
    case REFERENCE_TYPE:
      if (integer_zerop (expr))
	return build_int_cst (type, 0);

      /* Convert to an unsigned integer of the correct width first, and from
	 there widen/truncate to the required type.  Some targets support the
	 coexistence of multiple valid pointer sizes, so fetch the one we need
	 from the type.  */
      expr = fold_build1 (CONVERT_EXPR,
			  lang_hooks.types.type_for_size
			    (TYPE_PRECISION (intype), 0),
			  expr);
      return fold_convert (type, expr);

    case INTEGER_TYPE:
    case ENUMERAL_TYPE:
    case BOOLEAN_TYPE:
    case OFFSET_TYPE:
      /* If this is a logical operation, which just returns 0 or 1, we can
	 change the type of the expression.  */

      if (TREE_CODE_CLASS (ex_form) == tcc_comparison)
	{
	  expr = copy_node (expr);
	  TREE_TYPE (expr) = type;
	  return expr;
	}

      /* If we are widening the type, put in an explicit conversion.
	 Similarly if we are not changing the width.  After this, we know
	 we are truncating EXPR.  */

      else if (outprec >= inprec)
	{
	  enum tree_code code;
	  tree tem;

	  /* If the precision of the EXPR's type is K bits and the
	     destination mode has more bits, and the sign is changing,
	     it is not safe to use a NOP_EXPR.  For example, suppose
	     that EXPR's type is a 3-bit unsigned integer type, the
	     TYPE is a 3-bit signed integer type, and the machine mode
	     for the types is 8-bit QImode.  In that case, the
	     conversion necessitates an explicit sign-extension.  In
	     the signed-to-unsigned case the high-order bits have to
	     be cleared.  */
	  if (TYPE_UNSIGNED (type) != TYPE_UNSIGNED (TREE_TYPE (expr))
	      && (TYPE_PRECISION (TREE_TYPE (expr))
		  != GET_MODE_BITSIZE (TYPE_MODE (TREE_TYPE (expr)))))
	    code = CONVERT_EXPR;
	  else
	    code = NOP_EXPR;

	  tem = fold_unary (code, type, expr);
	  if (tem)
	    return tem;

	  tem = build1 (code, type, expr);
	  TREE_NO_WARNING (tem) = 1;
	  return tem;
	}

      /* 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 (lang_hooks.types.type_for_mode
				(TYPE_MODE (type), TYPE_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_sgn (TREE_OPERAND (expr, 1)) <= 0)
	    goto trunc1;
	  break;

	case LSHIFT_EXPR:
	  /* We can pass truncation down through left shifting
	     when the shift count is a nonnegative constant and
	     the target type is unsigned.  */
	  if (TREE_CODE (TREE_OPERAND (expr, 1)) == INTEGER_CST
	      && tree_int_cst_sgn (TREE_OPERAND (expr, 1)) >= 0
	      && TYPE_UNSIGNED (type)
	      && 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 = build_int_cst (type, 0);

		  /* If the original expression had side-effects, we must
		     preserve it.  */
		  if (TREE_SIDE_EFFECTS (expr))
		    return build2 (COMPOUND_EXPR, type, expr, t);
		  else
		    return t;
		}
	    }
	  break;

	case TRUNC_DIV_EXPR:
	  {
	    tree arg0 = get_unwidened (TREE_OPERAND (expr, 0), type);
	    tree arg1 = get_unwidened (TREE_OPERAND (expr, 1), type);

	    /* Don't distribute unless the output precision is at least as big
	       as the actual inputs and it has the same signedness.  */
	    if (outprec >= TYPE_PRECISION (TREE_TYPE (arg0))
		&& outprec >= TYPE_PRECISION (TREE_TYPE (arg1))
		/* If signedness of arg0 and arg1 don't match,
		   we can't necessarily find a type to compare them in.  */
		&& (TYPE_UNSIGNED (TREE_TYPE (arg0))
		    == TYPE_UNSIGNED (TREE_TYPE (arg1)))
		/* Do not change the sign of the division.  */
		&& (TYPE_UNSIGNED (TREE_TYPE (expr))
		    == TYPE_UNSIGNED (TREE_TYPE (arg0)))
		/* Either require unsigned division or a division by
		   a constant that is not -1.  */
		&& (TYPE_UNSIGNED (TREE_TYPE (arg0))
		    || (TREE_CODE (arg1) == INTEGER_CST
			&& !integer_all_onesp (arg1))))
	      goto trunc1;
	    break;
	  }

	case MAX_EXPR:
	case MIN_EXPR:
	case MULT_EXPR:
	  {
	    tree arg0 = get_unwidened (TREE_OPERAND (expr, 0), type);
	    tree arg1 = get_unwidened (TREE_OPERAND (expr, 1), type);

	    /* Don't distribute unless the output precision is at least as big
	       as the actual inputs.  Otherwise, the comparison of the
	       truncated values will be wrong.  */
	    if (outprec >= TYPE_PRECISION (TREE_TYPE (arg0))
		&& outprec >= TYPE_PRECISION (TREE_TYPE (arg1))
		/* If signedness of arg0 and arg1 don't match,
		   we can't necessarily find a type to compare them in.  */
		&& (TYPE_UNSIGNED (TREE_TYPE (arg0))
		    == TYPE_UNSIGNED (TREE_TYPE (arg1))))
	      goto trunc1;
	    break;
	  }

	case PLUS_EXPR:
	case MINUS_EXPR:
	case BIT_AND_EXPR:
	case BIT_IOR_EXPR:
	case BIT_XOR_EXPR:
	trunc1:
	  {
	    tree arg0 = get_unwidened (TREE_OPERAND (expr, 0), type);
	    tree arg1 = get_unwidened (TREE_OPERAND (expr, 1), type);

	    if (outprec >= BITS_PER_WORD
		|| TRULY_NOOP_TRUNCATION (outprec, inprec)
		|| inprec > TYPE_PRECISION (TREE_TYPE (arg0))
		|| inprec > TYPE_PRECISION (TREE_TYPE (arg1)))
	      {
		/* Do the arithmetic in type TYPEX,
		   then convert result to TYPE.  */
		tree typex = type;

		/* Can't do arithmetic in enumeral types
		   so use an integer type that will hold the values.  */
		if (TREE_CODE (typex) == ENUMERAL_TYPE)
		  typex = lang_hooks.types.type_for_size
		    (TYPE_PRECISION (typex), TYPE_UNSIGNED (typex));

		/* But now perhaps TYPEX is as wide as INPREC.
		   In that case, do nothing special here.
		   (Otherwise would recurse infinitely in convert.  */
		if (TYPE_PRECISION (typex) != inprec)
		  {
		    /* Don't do unsigned arithmetic where signed was wanted,
		       or vice versa.
		       Exception: if both of the original operands were
		       unsigned then we can safely do the work as unsigned.
		       Exception: shift operations take their type solely
		       from the first argument.
		       Exception: the LSHIFT_EXPR case above requires that
		       we perform this operation unsigned lest we produce
		       signed-overflow undefinedness.
		       And we may need to do it as unsigned
		       if we truncate to the original size.  */
		    if (TYPE_UNSIGNED (TREE_TYPE (expr))
			|| (TYPE_UNSIGNED (TREE_TYPE (arg0))
			    && (TYPE_UNSIGNED (TREE_TYPE (arg1))
				|| ex_form == LSHIFT_EXPR
				|| ex_form == RSHIFT_EXPR
				|| ex_form == LROTATE_EXPR
				|| ex_form == RROTATE_EXPR))
			|| ex_form == LSHIFT_EXPR
			/* If we have !flag_wrapv, and either ARG0 or
			   ARG1 is of a signed type, we have to do
			   PLUS_EXPR, MINUS_EXPR or MULT_EXPR in an unsigned
			   type in case the operation in outprec precision
			   could overflow.  Otherwise, we would introduce
			   signed-overflow undefinedness.  */
			|| ((!TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg0))
			     || !TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg1)))
			    && ((TYPE_PRECISION (TREE_TYPE (arg0)) * 2u
				 > outprec)
				|| (TYPE_PRECISION (TREE_TYPE (arg1)) * 2u
				    > outprec))
			    && (ex_form == PLUS_EXPR
				|| ex_form == MINUS_EXPR
				|| ex_form == MULT_EXPR)))
		      typex = unsigned_type_for (typex);
		    else
		      typex = signed_type_for (typex);
		    return convert (type,
				    fold_build2 (ex_form, typex,
						 convert (typex, arg0),
						 convert (typex, arg1)));
		  }
	      }
	  }
	  break;

	case NEGATE_EXPR:
	case BIT_NOT_EXPR:
	  /* This is not correct for ABS_EXPR,
	     since we must test the sign before truncation.  */
	  {
	    tree typex = unsigned_type_for (type);
	    return convert (type,
			    fold_build1 (ex_form, typex,
					 convert (typex,
						  TREE_OPERAND (expr, 0))));
	  }

	case NOP_EXPR:
	  /* Don't introduce a
	     "can't convert between vector values of different size" error.  */
	  if (TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0))) == VECTOR_TYPE
	      && (GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (TREE_OPERAND (expr, 0))))
		  != GET_MODE_SIZE (TYPE_MODE (type))))
	    break;
	  /* If truncating after truncating, might as well do all at once.
	     If truncating after extending, we may get rid of wasted work.  */
	  return convert (type, get_unwidened (TREE_OPERAND (expr, 0), type));

	case COND_EXPR:
	  /* It is sometimes worthwhile to push the narrowing down through
	     the conditional and never loses.  A COND_EXPR may have a throw
	     as one operand, which then has void type.  Just leave void
	     operands as they are.  */
	  return fold_build3 (COND_EXPR, type, TREE_OPERAND (expr, 0),
			      VOID_TYPE_P (TREE_TYPE (TREE_OPERAND (expr, 1)))
			      ? TREE_OPERAND (expr, 1)
			      : convert (type, TREE_OPERAND (expr, 1)),
			      VOID_TYPE_P (TREE_TYPE (TREE_OPERAND (expr, 2)))
			      ? TREE_OPERAND (expr, 2)
			      : convert (type, TREE_OPERAND (expr, 2)));

	default:
	  break;
	}

      return build1 (CONVERT_EXPR, type, expr);

    case REAL_TYPE:
      return build1 (FIX_TRUNC_EXPR, type, expr);

    case FIXED_POINT_TYPE:
      return build1 (FIXED_CONVERT_EXPR, type, expr);

    case COMPLEX_TYPE:
      return convert (type,
		      fold_build1 (REALPART_EXPR,
				   TREE_TYPE (TREE_TYPE (expr)), expr));

    case VECTOR_TYPE:
      if (!tree_int_cst_equal (TYPE_SIZE (type), TYPE_SIZE (TREE_TYPE (expr))))
	{
	  error ("can%'t convert between vector values of different size");
	  return error_mark_node;
	}
      return build1 (VIEW_CONVERT_EXPR, type, expr);

    default:
      error ("aggregate value used where an integer was expected");
      return convert (type, integer_zero_node);
    }
}

/* Convert EXPR to the complex type TYPE in the usual ways.  */

tree
convert_to_complex (tree type, tree expr)
{
  tree subtype = TREE_TYPE (type);

  switch (TREE_CODE (TREE_TYPE (expr)))
    {
    case REAL_TYPE:
    case FIXED_POINT_TYPE:
    case INTEGER_TYPE:
    case ENUMERAL_TYPE:
    case BOOLEAN_TYPE:
      return build2 (COMPLEX_EXPR, type, convert (subtype, expr),
		     convert (subtype, integer_zero_node));

    case COMPLEX_TYPE:
      {
	tree elt_type = TREE_TYPE (TREE_TYPE (expr));

	if (TYPE_MAIN_VARIANT (elt_type) == TYPE_MAIN_VARIANT (subtype))
	  return expr;
	else if (TREE_CODE (expr) == COMPLEX_EXPR)
	  return fold_build2 (COMPLEX_EXPR, type,
			      convert (subtype, TREE_OPERAND (expr, 0)),
			      convert (subtype, TREE_OPERAND (expr, 1)));
	else
	  {
	    expr = save_expr (expr);
	    return
	      fold_build2 (COMPLEX_EXPR, type,
			   convert (subtype,
				    fold_build1 (REALPART_EXPR,
						 TREE_TYPE (TREE_TYPE (expr)),
						 expr)),
			   convert (subtype,
				    fold_build1 (IMAGPART_EXPR,
						 TREE_TYPE (TREE_TYPE (expr)),
						 expr)));
	  }
      }

    case POINTER_TYPE:
    case REFERENCE_TYPE:
      error ("pointer value used where a complex was expected");
      return convert_to_complex (type, integer_zero_node);

    default:
      error ("aggregate value used where a complex was expected");
      return convert_to_complex (type, integer_zero_node);
    }
}

/* Convert EXPR to the vector type TYPE in the usual ways.  */

tree
convert_to_vector (tree type, tree expr)
{
  switch (TREE_CODE (TREE_TYPE (expr)))
    {
    case INTEGER_TYPE:
    case VECTOR_TYPE:
      if (!tree_int_cst_equal (TYPE_SIZE (type), TYPE_SIZE (TREE_TYPE (expr))))
	{
	  error ("can%'t convert between vector values of different size");
	  return error_mark_node;
	}
      return build1 (VIEW_CONVERT_EXPR, type, expr);

    default:
      error ("can%'t convert value to a vector");
      return error_mark_node;
    }
}

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

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

tree
convert_to_fixed (tree type, tree expr)
{
  if (integer_zerop (expr))
    {
      tree fixed_zero_node = build_fixed (type, FCONST0 (TYPE_MODE (type)));
      return fixed_zero_node;
    }
  else if (integer_onep (expr) && ALL_SCALAR_ACCUM_MODE_P (TYPE_MODE (type)))
    {
      tree fixed_one_node = build_fixed (type, FCONST1 (TYPE_MODE (type)));
      return fixed_one_node;
    }

  switch (TREE_CODE (TREE_TYPE (expr)))
    {
    case FIXED_POINT_TYPE:
    case INTEGER_TYPE:
    case ENUMERAL_TYPE:
    case BOOLEAN_TYPE:
    case REAL_TYPE:
      return build1 (FIXED_CONVERT_EXPR, type, expr);

    case COMPLEX_TYPE:
      return convert (type,
		      fold_build1 (REALPART_EXPR,
				   TREE_TYPE (TREE_TYPE (expr)), expr));

    default:
      error ("aggregate value used where a fixed-point was expected");
      return error_mark_node;
    }
}