path: root/gdb/eval.c

/* Evaluate expressions for GDB.
   Copyright (C) 1986, 1987 Free Software Foundation, Inc.

GDB is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY.  No author or distributor accepts responsibility to anyone
for the consequences of using it or for whether it serves any
particular purpose or works at all, unless he says so in writing.
Refer to the GDB General Public License for full details.

Everyone is granted permission to copy, modify and redistribute GDB,
but only under the conditions described in the GDB General Public
License.  A copy of this license is supposed to have been given to you
along with GDB so you can know your rights and responsibilities.  It
should be in a file named COPYING.  Among other things, the copyright
notice and this notice must be preserved on all copies.

In other words, go ahead and share GDB, but don't try to stop
anyone else from sharing it farther.  Help stamp out software hoarding!
*/

#include "defs.h"
#include "param.h"
#include "symtab.h"
#include "value.h"
#include "expression.h"


/* Parse the string EXP as a C expression, evaluate it,
   and return the result as a number.  */

CORE_ADDR
parse_and_eval_address (exp)
     char *exp;
{
  struct expression *expr = parse_c_expression (exp);
  register CORE_ADDR addr;
  register struct cleanup *old_chain
    = make_cleanup (free_current_contents, &expr);

  addr = (CORE_ADDR) value_as_long (evaluate_expression (expr));
  do_cleanups (old_chain);
  return addr;
}

/* Like parse_and_eval_address but takes a pointer to a char * variable
   and advanced that variable across the characters parsed.  */

CORE_ADDR
parse_and_eval_address_1 (expptr)
     char **expptr;
{
  struct expression *expr = parse_c_1 (expptr, 0, 0);
  register CORE_ADDR addr;
  register struct cleanup *old_chain
    = make_cleanup (free_current_contents, &expr);

  addr = value_as_long (evaluate_expression (expr));
  do_cleanups (old_chain);
  return addr;
}

value
parse_and_eval (exp)
     char *exp;
{
  struct expression *expr = parse_c_expression (exp);
  register value val;
  register struct cleanup *old_chain
    = make_cleanup (free_current_contents, &expr);

  val = evaluate_expression (expr);
  do_cleanups (old_chain);
  return val;
}

/* Parse up to a comma (or to a closeparen)
   in the string EXPP as an expression, evaluate it, and return the value.
   EXPP is advanced to point to the comma.  */

value
parse_to_comma_and_eval (expp)
     char **expp;
{
  struct expression *expr = parse_c_1 (expp, 0, 1);
  register value val;
  register struct cleanup *old_chain
    = make_cleanup (free_current_contents, &expr);

  val = evaluate_expression (expr);
  do_cleanups (old_chain);
  return val;
}

/* Evaluate an expression in internal prefix form
   such as is constructed by expread.y.

   See expression.h for info on the format of an expression.  */

static value evaluate_subexp ();
static value evaluate_subexp_for_address ();
static value evaluate_subexp_for_sizeof ();
static value evaluate_subexp_with_coercion ();

/* Values of NOSIDE argument to eval_subexp.  */
enum noside
{ EVAL_NORMAL,
  EVAL_SKIP,			/* Only effect is to increment pos.  */
  EVAL_AVOID_SIDE_EFFECTS,	/* Don't modify any variables or
				   call any functions.  Correct type
				   is returned.  */
};

value
evaluate_expression (exp)
     struct expression *exp;
{
  int pc = 0;
  return evaluate_subexp (0, exp, &pc, EVAL_NORMAL);
}

/* Evaluate an expression, avoiding all memory references
   and getting a value whose type alone is correct.  */

value
evaluate_type (exp)
     struct expression *exp;
{
  int pc = 0;
  return evaluate_subexp (0, exp, &pc, EVAL_AVOID_SIDE_EFFECTS);
}

static value
evaluate_subexp (expect_type, exp, pos, noside)
     struct type *expect_type;
     register struct expression *exp;
     register int *pos;
     enum noside noside;
{
  enum exp_opcode op;
  int tem;
  register int pc, pc2, oldpos;
  register value arg1, arg2, arg3;
  int nargs;
  value *argvec;

  pc = (*pos)++;
  op = exp->elts[pc].opcode;

  switch (op)
    {
    case OP_SCOPE:
      tem = strlen (&exp->elts[pc + 2].string);
      (*pos) += 3 + (tem + sizeof (union exp_element)) / sizeof (union exp_element);
      return value_static_field (exp->elts[pc + 1].type,
				 &exp->elts[pc + 2].string, -1);

    case OP_LONG:
      (*pos) += 3;
      return value_from_long (exp->elts[pc + 1].type,
			      exp->elts[pc + 2].longconst);

    case OP_DOUBLE:
      (*pos) += 3;
      return value_from_double (exp->elts[pc + 1].type,
				exp->elts[pc + 2].doubleconst);

    case OP_VAR_VALUE:
      (*pos) += 2;
      if (noside == EVAL_SKIP)
	goto nosideret;
      return value_of_variable (exp->elts[pc + 1].symbol);

    case OP_LAST:
      (*pos) += 2;
      return access_value_history ((int) exp->elts[pc + 1].longconst);

    case OP_REGISTER:
      (*pos) += 2;
      return value_of_register ((int) exp->elts[pc + 1].longconst);

    case OP_INTERNALVAR:
      (*pos) += 2;
      return value_of_internalvar (exp->elts[pc + 1].internalvar);

    case OP_STRING:
      tem = strlen (&exp->elts[pc + 1].string);
      (*pos) += 2 + (tem + sizeof (union exp_element)) / sizeof (union exp_element);
      if (noside == EVAL_SKIP)
	goto nosideret;
      return value_string (&exp->elts[pc + 1].string, tem);

    case TERNOP_COND:
      /* Skip third and second args to evaluate the first one.  */
      arg1 = evaluate_subexp (0, exp, pos, noside);
      if (value_zerop (arg1))
	{
	  evaluate_subexp (0, exp, pos, EVAL_SKIP);
	  return evaluate_subexp (0, exp, pos, noside);
	}
      else
	{
	  arg2 = evaluate_subexp (0, exp, pos, noside);
	  evaluate_subexp (0, exp, pos, EVAL_SKIP);
	  return arg2;
	}

    case OP_FUNCALL:
      (*pos) += 2;
      op = exp->elts[*pos].opcode;
      if (op == STRUCTOP_MEMBER || op == STRUCTOP_MPTR)
	{
	  int fnptr;
	  int tem2;

	  nargs = (int) exp->elts[pc + 1].longconst + 1;
	  /* First, evaluate the structure into arg2 */
	  pc2 = (*pos)++;

	  if (noside == EVAL_SKIP)
	    goto nosideret;

	  if (op == STRUCTOP_MEMBER)
	    {
	      arg2 = evaluate_subexp_for_address (exp, pos, noside);
	    }
	  else
	    {
	      arg2 = evaluate_subexp (0, exp, pos, noside);
	    }

	  /* If the function is a virtual function, then the
	     aggregate value (providing the structure) plays
	     its part by providing the vtable.  Otherwise,
	     it is just along for the ride: call the function
	     directly.  */

	  arg1 = evaluate_subexp (0, exp, pos, noside);

	  fnptr = (int) value_as_long (arg1);
	  if (fnptr < 128)
	    {
	      struct type *basetype;
	      int i, j;
	      basetype = TYPE_TARGET_TYPE (VALUE_TYPE (arg2));
	      basetype = TYPE_VPTR_BASETYPE (basetype);
	      for (i = TYPE_NFN_FIELDS (basetype) - 1; i >= 0; i--)
		{
		  struct fn_field *f = TYPE_FN_FIELDLIST1 (basetype, i);
		  /* If one is virtual, then all are virtual.  */
		  if (TYPE_FN_FIELD_VIRTUAL_P (f, 0))
		    for (j = TYPE_FN_FIELDLIST_LENGTH (basetype, i) - 1; j >= 0; --j)
		      if (TYPE_FN_FIELD_VOFFSET (f, j) == fnptr)
			{
			  value vtbl;
			  value base = value_ind (arg2);
			  struct type *fntype = lookup_pointer_type (TYPE_FN_FIELD_TYPE (f, j));

			  if (TYPE_VPTR_FIELDNO (basetype) < 0)
			    TYPE_VPTR_FIELDNO (basetype)
			      = fill_in_vptr_fieldno (basetype);

			  VALUE_TYPE (base) = basetype;
			  vtbl = value_field (base, TYPE_VPTR_FIELDNO (basetype));
			  VALUE_TYPE (vtbl) = lookup_pointer_type (fntype);
			  VALUE_TYPE (arg1) = builtin_type_int;
			  arg1 = value_subscript (vtbl, arg1);
			  VALUE_TYPE (arg1) = fntype;
			  goto got_it;
			}
		}
	      if (i < 0)
		error ("virtual function at index %d not found", fnptr);
	    }
	  else
	    {
	      VALUE_TYPE (arg1) = lookup_pointer_type (TYPE_TARGET_TYPE (VALUE_TYPE (arg1)));
	    }
	got_it:

	  /* Now, say which argument to start evaluating from */
	  tem = 2;
	}
      else if (op == STRUCTOP_STRUCT || op == STRUCTOP_PTR)
	{
	  /* Hair for method invocations */
	  int tem2;

	  nargs = (int) exp->elts[pc + 1].longconst + 1;
	  /* First, evaluate the structure into arg2 */
	  pc2 = (*pos)++;
	  tem2 = strlen (&exp->elts[pc2 + 1].string);
	  *pos += 2 + (tem2 + sizeof (union exp_element)) / sizeof (union exp_element);
	  if (noside == EVAL_SKIP)
	    goto nosideret;

	  if (op == STRUCTOP_STRUCT)
	    {
	      arg2 = evaluate_subexp_for_address (exp, pos, noside);
	    }
	  else
	    {
	      arg2 = evaluate_subexp (0, exp, pos, noside);
	    }
	  /* Now, say which argument to start evaluating from */
	  tem = 2;
	}
      else
	{
	  nargs = (int) exp->elts[pc + 1].longconst;
	  tem = 0;
	}
      argvec = (value *) alloca (sizeof (value) * (nargs + 2));
      for (; tem <= nargs; tem++)
	/* Ensure that array expressions are coerced into pointer objects. */
	argvec[tem] = evaluate_subexp_with_coercion (exp, pos, noside);

      /* signal end of arglist */
      argvec[tem] = 0;

      if (op == STRUCTOP_STRUCT || op == STRUCTOP_PTR)
	{
	  argvec[1] = arg2;
	  argvec[0] =
	    value_struct_elt (arg2, argvec+1, &exp->elts[pc2 + 1].string,
			      op == STRUCTOP_STRUCT
			      ? "structure" : "structure pointer");
	}
      else if (op == STRUCTOP_MEMBER || op == STRUCTOP_MPTR)
	{
	  argvec[1] = arg2;
	  argvec[0] = arg1;
	}

      if (noside == EVAL_SKIP)
	goto nosideret;
      if (noside == EVAL_AVOID_SIDE_EFFECTS)
	{
	  /* If the return type doesn't look like a function type, call an
	     error.  This can happen if somebody tries to turn a variable into
	     a function call. This is here because people often want to
	     call, eg, strcmp, which gdb doesn't know is a function.  If
	     gdb isn't asked for it's opinion (ie. through "whatis"),
	     it won't offer it. */

	  struct type *ftype =
	    TYPE_TARGET_TYPE (VALUE_TYPE (argvec[0]));

	  if (ftype)
	    return allocate_value (TYPE_TARGET_TYPE (VALUE_TYPE (argvec[0])));
	  else
	    error ("Expression of type other than \"Function returning ...\" used as function");
	}
      return call_function (argvec[0], nargs, argvec + 1);

    case STRUCTOP_STRUCT:
      tem = strlen (&exp->elts[pc + 1].string);
      (*pos) += 2 + (tem + sizeof (union exp_element)) / sizeof (union exp_element);
      arg1 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      return value_struct_elt (arg1, 0, &exp->elts[pc + 1].string,
			       "structure");

    case STRUCTOP_PTR:
      tem = strlen (&exp->elts[pc + 1].string);
      (*pos) += 2 + (tem + sizeof (union exp_element)) / sizeof (union exp_element);
      arg1 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      return value_struct_elt (arg1, 0, &exp->elts[pc + 1].string,
			       "structure pointer");

    case STRUCTOP_MEMBER:
      arg1 = evaluate_subexp_for_address (exp, pos, noside);
      arg2 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      /* Now, convert these values to an address.  */
      arg3 = value_from_long (builtin_type_long,
			      value_as_long (arg1) + value_as_long (arg2));
      VALUE_TYPE (arg3) = lookup_pointer_type (TYPE_TARGET_TYPE (VALUE_TYPE (arg2)));
      return value_ind (arg3);

    case STRUCTOP_MPTR:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      /* Now, convert these values to an address.  */
      arg3 = value_from_long (builtin_type_long,
			      value_as_long (arg1) + value_as_long (arg2));
      VALUE_TYPE (arg3) = lookup_pointer_type (TYPE_TARGET_TYPE (VALUE_TYPE (arg2)));
      return value_ind (arg3);

    case BINOP_ASSIGN:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (VALUE_TYPE (arg1), exp, pos, noside);
      if (noside == EVAL_SKIP || noside == EVAL_AVOID_SIDE_EFFECTS)
	return arg1;
      if (binop_user_defined_p (op, arg1, arg2))
	return value_x_binop (arg1, arg2, op, 0);
      else
	return value_assign (arg1, arg2);

    case BINOP_ASSIGN_MODIFY:
      (*pos) += 2;
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (VALUE_TYPE (arg1), exp, pos, noside);
      if (noside == EVAL_SKIP || noside == EVAL_AVOID_SIDE_EFFECTS)
	return arg1;
      op = exp->elts[pc + 1].opcode;
      if (binop_user_defined_p (op, arg1, arg2))
	return value_x_binop (arg1, arg2, BINOP_ASSIGN_MODIFY, op);
      else if (op == BINOP_ADD)
	arg2 = value_add (arg1, arg2);
      else if (op == BINOP_SUB)
	arg2 = value_sub (arg1, arg2);
      else
	arg2 = value_binop (arg1, arg2, op);
      return value_assign (arg1, arg2);

    case BINOP_ADD:
      arg1 = evaluate_subexp_with_coercion (exp, pos, noside);
      arg2 = evaluate_subexp_with_coercion (exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	return value_x_binop (arg1, arg2, op, 0);
      else
	return value_add (arg1, arg2);

    case BINOP_SUB:
      arg1 = evaluate_subexp_with_coercion (exp, pos, noside);
      arg2 = evaluate_subexp_with_coercion (exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	return value_x_binop (arg1, arg2, op, 0);
      else
	return value_sub (arg1, arg2);

    case BINOP_MUL:
    case BINOP_DIV:
    case BINOP_REM:
    case BINOP_LSH:
    case BINOP_RSH:
    case BINOP_LOGAND:
    case BINOP_LOGIOR:
    case BINOP_LOGXOR:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	return value_x_binop (arg1, arg2, op, 0);
      else
	return value_binop (arg1, arg2, op);

    case BINOP_SUBSCRIPT:
      arg1 = evaluate_subexp_with_coercion (exp, pos, noside);
      arg2 = evaluate_subexp_with_coercion (exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	return value_x_binop (arg1, arg2, op, 0);
      else
	return value_subscript (arg1, arg2, op);
      
    case BINOP_AND:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	{
	  arg2 = evaluate_subexp (0, exp, pos, noside);
	  goto nosideret;
	}
      
      oldpos = *pos;
      arg2 = evaluate_subexp (0, exp, pos, EVAL_AVOID_SIDE_EFFECTS);
      *pos = oldpos;
      
      if (binop_user_defined_p (op, arg1, arg2)) 
	{
	  arg2 = evaluate_subexp (0, exp, pos, noside);
	  return value_x_binop (arg1, arg2, op, 0);
	}
      else
	{
	  tem = value_zerop (arg1);
	  arg2 = evaluate_subexp (0, exp, pos,
				  (tem ? EVAL_SKIP : noside));
	  return value_from_long (builtin_type_int,
				  (LONGEST) (!tem && !value_zerop (arg2)));
	}

    case BINOP_OR:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	{
	  arg2 = evaluate_subexp (0, exp, pos, noside);
	  goto nosideret;
	}
      
      oldpos = *pos;
      arg2 = evaluate_subexp (0, exp, pos, EVAL_AVOID_SIDE_EFFECTS);
      *pos = oldpos;
      
      if (binop_user_defined_p (op, arg1, arg2)) 
	{
	  arg2 = evaluate_subexp (0, exp, pos, noside);
	  return value_x_binop (arg1, arg2, op, 0);
	}
      else
	{
	  tem = value_zerop (arg1);
	  arg2 = evaluate_subexp (0, exp, pos,
				  (!tem ? EVAL_SKIP : noside));
	  return value_from_long (builtin_type_int,
				  (LONGEST) (!tem || !value_zerop (arg2)));
	}

    case BINOP_EQUAL:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (VALUE_TYPE (arg1), exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	{
	  return value_x_binop (arg1, arg2, op, 0);
	}
      else
	{
	  tem = value_equal (arg1, arg2);
	  return value_from_long (builtin_type_int, (LONGEST) tem);
	}

    case BINOP_NOTEQUAL:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (VALUE_TYPE (arg1), exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	{
	  return value_x_binop (arg1, arg2, op, 0);
	}
      else
	{
	  tem = value_equal (arg1, arg2);
	  return value_from_long (builtin_type_int, (LONGEST) ! tem);
	}

    case BINOP_LESS:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (VALUE_TYPE (arg1), exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	{
	  return value_x_binop (arg1, arg2, op, 0);
	}
      else
	{
	  tem = value_less (arg1, arg2);
	  return value_from_long (builtin_type_int, (LONGEST) tem);
	}

    case BINOP_GTR:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (VALUE_TYPE (arg1), exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	{
	  return value_x_binop (arg1, arg2, op, 0);
	}
      else
	{
	  tem = value_less (arg2, arg1);
	  return value_from_long (builtin_type_int, (LONGEST) tem);
	}

    case BINOP_GEQ:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (VALUE_TYPE (arg1), exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	{
	  return value_x_binop (arg1, arg2, op, 0);
	}
      else
	{
	  tem = value_less (arg1, arg2);
	  return value_from_long (builtin_type_int, (LONGEST) ! tem);
	}

    case BINOP_LEQ:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (VALUE_TYPE (arg1), exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (binop_user_defined_p (op, arg1, arg2))
	{
	  return value_x_binop (arg1, arg2, op, 0);
	}
      else 
	{
	  tem = value_less (arg2, arg1);
	  return value_from_long (builtin_type_int, (LONGEST) ! tem);
	}

    case BINOP_REPEAT:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      arg2 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      return value_repeat (arg1, (int) value_as_long (arg2));

    case BINOP_COMMA:
      evaluate_subexp (0, exp, pos, noside);
      return evaluate_subexp (0, exp, pos, noside);

    case UNOP_NEG:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (unop_user_defined_p (op, arg1))
	return value_x_unop (arg1, op, 0);
      else
	return value_neg (arg1);

    case UNOP_LOGNOT:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (unop_user_defined_p (op, arg1))
	return value_x_unop (arg1, op, 0);
      else
	return value_lognot (arg1);

    case UNOP_ZEROP:
      arg1 = evaluate_subexp (0, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      if (unop_user_defined_p (op, arg1))
	return value_x_unop (arg1, op, 0);
      else
	return value_from_long (builtin_type_int,
				(LONGEST) value_zerop (arg1));

    case UNOP_IND:
      if (expect_type && TYPE_CODE (expect_type) == TYPE_CODE_PTR)
        expect_type = TYPE_TARGET_TYPE (expect_type);
      arg1 = evaluate_subexp (expect_type, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      return value_ind (arg1);

    case UNOP_ADDR:
      /* C++: check for and handle pointer to members.  */
      
      op = exp->elts[*pos].opcode;

      if (noside == EVAL_SKIP)
	{
	  if (op == OP_SCOPE)
	    {
	      char *name = &exp->elts[pc+3].string;
	      int tem = strlen (name);
	      (*pos) += 2 + (tem + sizeof (union exp_element)) / sizeof (union exp_element);
	    }
	  else
	    evaluate_subexp (expect_type, exp, pos, EVAL_SKIP);
	  goto nosideret;
	}

      if (op == OP_SCOPE)
	{
	  char *name = &exp->elts[pc+3].string;
	  int tem = strlen (name);
	  struct type *domain = exp->elts[pc+2].type;
	  (*pos) += 2 + (tem + sizeof (union exp_element)) / sizeof (union exp_element);
	  arg1 = value_struct_elt_for_address (domain, expect_type, name);
	  if (arg1)
	    return arg1;
	  error ("no field `%s' in structure", name);
	}
      else
	return evaluate_subexp_for_address (exp, pos, noside);

    case UNOP_SIZEOF:
      if (noside == EVAL_SKIP)
	{
	  evaluate_subexp (0, exp, pos, EVAL_SKIP);
	  goto nosideret;
	}
      return evaluate_subexp_for_sizeof (exp, pos);

    case UNOP_CAST:
      (*pos) += 2;
      arg1 = evaluate_subexp (expect_type, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      return value_cast (exp->elts[pc + 1].type, arg1);

    case UNOP_MEMVAL:
      (*pos) += 2;
      arg1 = evaluate_subexp (expect_type, exp, pos, noside);
      if (noside == EVAL_SKIP)
	goto nosideret;
      return value_at (exp->elts[pc + 1].type,
		       (CORE_ADDR) value_as_long (arg1));

    case UNOP_PREINCREMENT:
      arg1 = evaluate_subexp (expect_type, exp, pos, noside);
      if (noside == EVAL_SKIP || noside == EVAL_AVOID_SIDE_EFFECTS)
	return arg1;
      else if (unop_user_defined_p (op, arg1))
	{
	  return value_x_unop (arg1, op, 0);
	}
      else
	{
	  arg2 = value_add (arg1, value_from_long (builtin_type_char, 
						   (LONGEST) 1));
	  return value_assign (arg1, arg2);
	}

    case UNOP_PREDECREMENT:
      arg1 = evaluate_subexp (expect_type, exp, pos, noside);
      if (noside == EVAL_SKIP || noside == EVAL_AVOID_SIDE_EFFECTS)
	return arg1;
      else if (unop_user_defined_p (op, arg1))
	{
	  return value_x_unop (arg1, op, 0);
	}
      else
	{
	  arg2 = value_sub (arg1, value_from_long (builtin_type_char, 
						   (LONGEST) 1));
	  return value_assign (arg1, arg2);
	}

    case UNOP_POSTINCREMENT:
      arg1 = evaluate_subexp (expect_type, exp, pos, noside);
      if (noside == EVAL_SKIP || noside == EVAL_AVOID_SIDE_EFFECTS)
	return arg1;
      else if (unop_user_defined_p (op, arg1))
	{
	  return value_x_unop (arg1, op, 0);
	}
      else
	{
	  arg2 = value_add (arg1, value_from_long (builtin_type_char, 
						   (LONGEST) 1));
	  value_assign (arg1, arg2);
	  return arg1;
	}

    case UNOP_POSTDECREMENT:
      arg1 = evaluate_subexp (expect_type, exp, pos, noside);
      if (noside == EVAL_SKIP || noside == EVAL_AVOID_SIDE_EFFECTS)
	return arg1;
      else if (unop_user_defined_p (op, arg1))
	{
	  return value_x_unop (arg1, op, 0);
	}
      else
	{
	  arg2 = value_sub (arg1, value_from_long (builtin_type_char, 
						   (LONGEST) 1));
	  value_assign (arg1, arg2);
	  return arg1;
	}
	
    case OP_THIS:
      (*pos) += 1;
      return value_of_this (1);

    default:
      error ("internal error: I do not know how to evaluate what you gave me");
    }

 nosideret:
  return value_from_long (builtin_type_long, (LONGEST) 1);
}

/* Evaluate a subexpression of EXP, at index *POS,
   and return the address of that subexpression.
   Advance *POS over the subexpression.
   If the subexpression isn't an lvalue, get an error.
   NOSIDE may be EVAL_AVOID_SIDE_EFFECTS;
   then only the type of the result need be correct.  */

static value
evaluate_subexp_for_address (exp, pos, noside)
     register struct expression *exp;
     register int *pos;
     enum noside noside;
{
  enum exp_opcode op;
  register int pc;

  pc = (*pos);
  op = exp->elts[pc].opcode;

  switch (op)
    {
    case UNOP_IND:
      (*pos)++;
      return evaluate_subexp (0, exp, pos, noside);

    case UNOP_MEMVAL:
      (*pos) += 3;
      return value_cast (lookup_pointer_type (exp->elts[pc + 1].type),
			 evaluate_subexp (0, exp, pos, noside));

    case OP_VAR_VALUE:
      (*pos) += 3;
      return locate_var_value (exp->elts[pc + 1].symbol, (CORE_ADDR) 0);

    default:
      return value_addr (evaluate_subexp (0, exp, pos, noside));
    }
}

/* Evaluate like `evaluate_subexp' except coercing arrays to pointers.
   When used in contexts where arrays will be coerced anyway,
   this is equivalent to `evaluate_subexp'
   but much faster because it avoids actually fetching array contents.  */

static value
evaluate_subexp_with_coercion (exp, pos, noside)
     register struct expression *exp;
     register int *pos;
     enum noside noside;
{
  register enum exp_opcode op;
  register int pc;
  register value val;

  pc = (*pos);
  op = exp->elts[pc].opcode;

  switch (op)
    {
    case OP_VAR_VALUE:
      if (TYPE_CODE (SYMBOL_TYPE (exp->elts[pc + 1].symbol)) == TYPE_CODE_ARRAY)
	{
	  (*pos) += 3;
	  val = locate_var_value (exp->elts[pc + 1].symbol, (CORE_ADDR) 0);
	  return value_cast (lookup_pointer_type (TYPE_TARGET_TYPE (SYMBOL_TYPE (exp->elts[pc + 1].symbol))),
			     val);
	}
    }

  return evaluate_subexp (0, exp, pos, noside);
}

/* Evaluate a subexpression of EXP, at index *POS,
   and return a value for the size of that subexpression.
   Advance *POS over the subexpression.  */

static value
evaluate_subexp_for_sizeof (exp, pos)
     register struct expression *exp;
     register int *pos;
{
  enum exp_opcode op;
  register int pc;
  value val;

  pc = (*pos);
  op = exp->elts[pc].opcode;

  switch (op)
    {
      /* This case is handled specially
	 so that we avoid creating a value for the result type.
	 If the result type is very big, it's desirable not to
	 create a value unnecessarily.  */
    case UNOP_IND:
      (*pos)++;
      val = evaluate_subexp (0, exp, pos, EVAL_AVOID_SIDE_EFFECTS);
      return value_from_long (builtin_type_int, (LONGEST)
		      TYPE_LENGTH (TYPE_TARGET_TYPE (VALUE_TYPE (val))));

    case UNOP_MEMVAL:
      (*pos) += 3;
      return value_from_long (builtin_type_int, 
			      (LONGEST) TYPE_LENGTH (exp->elts[pc + 1].type));

    case OP_VAR_VALUE:
      (*pos) += 3;
      return value_from_long (builtin_type_int,
	 (LONGEST) TYPE_LENGTH (SYMBOL_TYPE (exp->elts[pc + 1].symbol)));

    default:
      val = evaluate_subexp (0, exp, pos, EVAL_AVOID_SIDE_EFFECTS);
      return value_from_long (builtin_type_int,
			      (LONGEST) TYPE_LENGTH (VALUE_TYPE (val)));
    }
}