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/* 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 (integer_type_node)

              || (outprec == TYPE_PRECISION (integer_type_node)

                  && !TYPE_UNSIGNED (type)))

            fn = mathfn_built_in (s_intype, BUILT_IN_ICEIL);

          else if (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 (integer_type_node)

              || (outprec == TYPE_PRECISION (integer_type_node)

                  && !TYPE_UNSIGNED (type)))

            fn = mathfn_built_in (s_intype, BUILT_IN_IFLOOR);

          else if (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):

          /* Only convert in ISO C99 mode.  */

          if (!TARGET_C99_FUNCTIONS)

            break;

          if (outprec < TYPE_PRECISION (integer_type_node)

              || (outprec == TYPE_PRECISION (integer_type_node)

                  && !TYPE_UNSIGNED (type)))

            fn = mathfn_built_in (s_intype, BUILT_IN_IROUND);

          else if (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):

          /* Only convert in ISO C99 mode.  */

          if (!TARGET_C99_FUNCTIONS)

            break;

          if (outprec < TYPE_PRECISION (integer_type_node)

              || (outprec == TYPE_PRECISION (integer_type_node)

                  && !TYPE_UNSIGNED (type)))

            fn = mathfn_built_in (s_intype, BUILT_IN_IRINT);

          else if (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_PRECISION (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_PRECISION (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;