Initial revision

[gcc.git] / gcc / c-common.c

/* Subroutines shared by all languages that are variants of C.
   Copyright (C) 1992 Free Software Foundation, Inc.

This file is part of GNU CC.

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, 675 Mass Ave, Cambridge, MA 02139, USA.  */

#include "config.h"
#include "tree.h"
#include "c-lex.h"
#include "c-tree.h"
#include "flags.h"
#include <stdio.h>

#undef NULL
#define NULL 0

/* Given a chain of STRING_CST nodes,
   concatenate them into one STRING_CST
   and give it a suitable array-of-chars data type.  */

tree
combine_strings (strings)
     tree strings;
{
  register tree value, t;
  register int length = 1;
  int wide_length = 0;
  int wide_flag = 0;
  int wchar_bytes = TYPE_PRECISION (wchar_type_node) / BITS_PER_UNIT;
  int nchars;

  if (TREE_CHAIN (strings))
    {
      /* More than one in the chain, so concatenate.  */
      register char *p, *q;

      /* Don't include the \0 at the end of each substring,
	 except for the last one.
	 Count wide strings and ordinary strings separately.  */
      for (t = strings; t; t = TREE_CHAIN (t))
	{
	  if (TREE_TYPE (t) == wchar_array_type_node)
	    {
	      wide_length += (TREE_STRING_LENGTH (t) - wchar_bytes);
	      wide_flag = 1;
	    }
	  else
	    length += (TREE_STRING_LENGTH (t) - 1);
	}

      /* If anything is wide, the non-wides will be converted,
	 which makes them take more space.  */
      if (wide_flag)
	length = length * wchar_bytes + wide_length;

      p = savealloc (length);

      /* Copy the individual strings into the new combined string.
	 If the combined string is wide, convert the chars to ints
	 for any individual strings that are not wide.  */

      q = p;
      for (t = strings; t; t = TREE_CHAIN (t))
	{
	  int len = (TREE_STRING_LENGTH (t)
		     - ((TREE_TYPE (t) == wchar_array_type_node)
			? wchar_bytes : 1));
	  if ((TREE_TYPE (t) == wchar_array_type_node) == wide_flag)
	    {
	      bcopy (TREE_STRING_POINTER (t), q, len);
	      q += len;
	    }
	  else
	    {
	      int i;
	      for (i = 0; i < len; i++)
		((int *) q)[i] = TREE_STRING_POINTER (t)[i];
	      q += len * wchar_bytes;
	    }
	}
      if (wide_flag)
	{
	  int i;
	  for (i = 0; i < wchar_bytes; i++)
	    *q++ = 0;
	}
      else
	*q = 0;

      value = make_node (STRING_CST);
      TREE_STRING_POINTER (value) = p;
      TREE_STRING_LENGTH (value) = length;
      TREE_CONSTANT (value) = 1;
    }
  else
    {
      value = strings;
      length = TREE_STRING_LENGTH (value);
      if (TREE_TYPE (value) == wchar_array_type_node)
	wide_flag = 1;
    }

  /* Compute the number of elements, for the array type.  */ 
  nchars = wide_flag ? length / wchar_bytes : length;

  /* Create the array type for the string constant.
     -Wwrite-strings says make the string constant an array of const char
     so that copying it to a non-const pointer will get a warning.  */
  if (warn_write_strings
      && (! flag_traditional  && ! flag_writable_strings))
    {
      tree elements
	= build_type_variant (wide_flag ? wchar_type_node : char_type_node,
			      1, 0);
      TREE_TYPE (value)
	= build_array_type (elements,
			    build_index_type (build_int_2 (nchars - 1, 0)));
    }
  else
    TREE_TYPE (value)
      = build_array_type (wide_flag ? wchar_type_node : char_type_node,
			  build_index_type (build_int_2 (nchars - 1, 0)));
  TREE_CONSTANT (value) = 1;
  TREE_STATIC (value) = 1;
  return value;
}
\f
/* Process the attributes listed in ATTRIBUTES
   and install them in DECL.  */

void
decl_attributes (decl, attributes)
     tree decl, attributes;
{
  tree a;
  for (a = attributes; a; a = TREE_CHAIN (a))
    if (TREE_VALUE (a) != 0
	&& TREE_CODE (TREE_VALUE (a)) == TREE_LIST
	&& TREE_PURPOSE (TREE_VALUE (a)) == get_identifier ("aligned"))
      {
	int align = TREE_INT_CST_LOW (TREE_VALUE (TREE_VALUE (a)))
		    * BITS_PER_UNIT;
	
	if (exact_log2 (align) == -1)
	  warning_with_decl (decl,
			"requested alignment of `%s' is not a power of 2");
	else if (TREE_CODE (decl) != VAR_DECL
		 && TREE_CODE (decl) != FIELD_DECL)
	  warning_with_decl (decl,
		"alignment specified for `%s' which is not a variable");

	/* ??? The maximum alignment gcc can currently handle is 16 bytes!
	   We should change the representation to be the log of the
	   actual alignment since we only handle powers of 2 anyway.  */
	else if (align > 255)
	  warning_with_decl (decl,
		"requested alignment of `%s' exceeds compiler limits");
	else
	  DECL_ALIGN (decl) = align;
      }
    else if (TREE_VALUE (a) != 0
	     && TREE_CODE (TREE_VALUE (a)) == TREE_LIST
	     && TREE_PURPOSE (TREE_VALUE (a)) == get_identifier ("packed"))
      {
	if (TREE_CODE (decl) == FIELD_DECL)
	  DECL_PACKED (decl) = 1;
      }
    else if (TREE_VALUE (a) != 0
	&& TREE_CODE (TREE_VALUE (a)) == TREE_LIST
	&& TREE_PURPOSE (TREE_VALUE (a)) == get_identifier ("format"))
      {
        tree list = TREE_VALUE (TREE_VALUE (a));
        tree format_type = TREE_PURPOSE (list);
	int format_num = TREE_INT_CST_LOW (TREE_PURPOSE (TREE_VALUE (list)));
	int first_arg_num = TREE_INT_CST_LOW (TREE_VALUE (TREE_VALUE (list)));
	int is_scan;
	
	if (TREE_CODE (decl) != FUNCTION_DECL)
	  {
	    warning_with_decl (decl,
		"argument format specified for non-function `%s'");
	    return;
	  }
	
	if (format_type == get_identifier ("printf"))
	  is_scan = 0;
	else if (format_type == get_identifier ("scanf"))
	  is_scan = 1;
	else
	  {
	    warning_with_decl (decl,"unrecognized format specifier for `%s'");
	    return;
	  }
	
	if (first_arg_num != 0 && first_arg_num <= format_num)
	  {
	    warning_with_decl (decl,
		"format string arg follows the args to be formatted, for `%s'");
	    return;
	  }
	
	record_format_info (DECL_NAME (decl), is_scan, format_num,
			    first_arg_num);
      }
}
\f
void
c_expand_expr_stmt (expr)
     tree expr;
{
  /* Do default conversion if safe and possibly important,
     in case within ({...}).  */
  if ((TREE_CODE (TREE_TYPE (expr)) == ARRAY_TYPE && lvalue_p (expr))
      || TREE_CODE (TREE_TYPE (expr)) == FUNCTION_TYPE)
    expr = default_conversion (expr);

  if (TREE_TYPE (expr) != error_mark_node
      && TYPE_SIZE (TREE_TYPE (expr)) == 0
      && TREE_CODE (TREE_TYPE (expr)) != ARRAY_TYPE)
    error ("expression statement has incomplete type");

  expand_expr_stmt (expr);
}
\f
/* Validate the expression after `case' and apply default promotions.  */

tree
check_case_value (value)
     tree value;
{
  if (value == NULL_TREE)
    return value;

  /* Strip NON_LVALUE_EXPRs since we aren't using as an lvalue.  */
  if (TREE_CODE (value) == NON_LVALUE_EXPR)
    value = TREE_OPERAND (value, 0);

  if (TREE_CODE (value) != INTEGER_CST
      && value != error_mark_node)
    {
      error ("case label does not reduce to an integer constant");
      value = error_mark_node;
    }
  else
    /* Promote char or short to int.  */
    value = default_conversion (value);

  return value;
}
\f
/* Return an integer type with BITS bits of precision,
   that is unsigned if UNSIGNEDP is nonzero, otherwise signed.  */

tree
type_for_size (bits, unsignedp)
     unsigned bits;
     int unsignedp;
{
  if (bits <= TYPE_PRECISION (signed_char_type_node))
    return unsignedp ? unsigned_char_type_node : signed_char_type_node;

  if (bits <= TYPE_PRECISION (short_integer_type_node))
    return unsignedp ? short_unsigned_type_node : short_integer_type_node;

  if (bits <= TYPE_PRECISION (integer_type_node))
    return unsignedp ? unsigned_type_node : integer_type_node;

  if (bits <= TYPE_PRECISION (long_integer_type_node))
    return unsignedp ? long_unsigned_type_node : long_integer_type_node;

  if (bits <= TYPE_PRECISION (long_long_integer_type_node))
    return (unsignedp ? long_long_unsigned_type_node
	    : long_long_integer_type_node);

  return 0;
}

/* Return a data type that has machine mode MODE.
   If the mode is an integer,
   then UNSIGNEDP selects between signed and unsigned types.  */

tree
type_for_mode (mode, unsignedp)
     enum machine_mode mode;
     int unsignedp;
{
  if (mode == TYPE_MODE (signed_char_type_node))
    return unsignedp ? unsigned_char_type_node : signed_char_type_node;

  if (mode == TYPE_MODE (short_integer_type_node))
    return unsignedp ? short_unsigned_type_node : short_integer_type_node;

  if (mode == TYPE_MODE (integer_type_node))
    return unsignedp ? unsigned_type_node : integer_type_node;

  if (mode == TYPE_MODE (long_integer_type_node))
    return unsignedp ? long_unsigned_type_node : long_integer_type_node;

  if (mode == TYPE_MODE (long_long_integer_type_node))
    return unsignedp ? long_long_unsigned_type_node : long_long_integer_type_node;

  if (mode == TYPE_MODE (float_type_node))
    return float_type_node;

  if (mode == TYPE_MODE (double_type_node))
    return double_type_node;

  if (mode == TYPE_MODE (long_double_type_node))
    return long_double_type_node;

  if (mode == TYPE_MODE (build_pointer_type (char_type_node)))
    return build_pointer_type (char_type_node);

  if (mode == TYPE_MODE (build_pointer_type (integer_type_node)))
    return build_pointer_type (integer_type_node);

  return 0;
}
\f
/* Print an error message for invalid operands to arith operation CODE.
   NOP_EXPR is used as a special case (see truthvalue_conversion).  */

void
binary_op_error (code)
     enum tree_code code;
{
  register char *opname;
  switch (code)
    {
    case NOP_EXPR:
      error ("invalid truth-value expression");
      return;

    case PLUS_EXPR:
      opname = "+"; break;
    case MINUS_EXPR:
      opname = "-"; break;
    case MULT_EXPR:
      opname = "*"; break;
    case MAX_EXPR:
      opname = "max"; break;
    case MIN_EXPR:
      opname = "min"; break;
    case EQ_EXPR:
      opname = "=="; break;
    case NE_EXPR:
      opname = "!="; break;
    case LE_EXPR:
      opname = "<="; break;
    case GE_EXPR:
      opname = ">="; break;
    case LT_EXPR:
      opname = "<"; break;
    case GT_EXPR:
      opname = ">"; break;
    case LSHIFT_EXPR:
      opname = "<<"; break;
    case RSHIFT_EXPR:
      opname = ">>"; break;
    case TRUNC_MOD_EXPR:
      opname = "%"; break;
    case TRUNC_DIV_EXPR:
      opname = "/"; break;
    case BIT_AND_EXPR:
      opname = "&"; break;
    case BIT_IOR_EXPR:
      opname = "|"; break;
    case TRUTH_ANDIF_EXPR:
      opname = "&&"; break;
    case TRUTH_ORIF_EXPR:
      opname = "||"; break;
    case BIT_XOR_EXPR:
      opname = "^"; break;
    }
  error ("invalid operands to binary %s", opname);
}
\f
/* Subroutine of build_binary_op, used for comparison operations.
   See if the operands have both been converted from subword integer types
   and, if so, perhaps change them both back to their original type.

   The arguments of this function are all pointers to local variables
   of build_binary_op: OP0_PTR is &OP0, OP1_PTR is &OP1,
   RESTYPE_PTR is &RESULT_TYPE and RESCODE_PTR is &RESULTCODE.

   If this function returns nonzero, it means that the comparison has
   a constant value.  What this function returns is an expression for
   that value.  */

tree
shorten_compare (op0_ptr, op1_ptr, restype_ptr, rescode_ptr)
     tree *op0_ptr, *op1_ptr;
     tree *restype_ptr;
     enum tree_code *rescode_ptr;
{
  register tree type;
  tree op0 = *op0_ptr;
  tree op1 = *op1_ptr;
  int unsignedp0, unsignedp1;
  int real1, real2;
  tree primop0, primop1;
  enum tree_code code = *rescode_ptr;

  /* Throw away any conversions to wider types
     already present in the operands.  */

  primop0 = get_narrower (op0, &unsignedp0);
  primop1 = get_narrower (op1, &unsignedp1);

  /* Handle the case that OP0 does not *contain* a conversion
     but it *requires* conversion to FINAL_TYPE.  */

  if (op0 == primop0 && TREE_TYPE (op0) != *restype_ptr)
    unsignedp0 = TREE_UNSIGNED (TREE_TYPE (op0));
  if (op1 == primop1 && TREE_TYPE (op1) != *restype_ptr)
    unsignedp1 = TREE_UNSIGNED (TREE_TYPE (op1));

  /* If one of the operands must be floated, we cannot optimize.  */
  real1 = TREE_CODE (TREE_TYPE (primop0)) == REAL_TYPE;
  real2 = TREE_CODE (TREE_TYPE (primop1)) == REAL_TYPE;

  /* If first arg is constant, swap the args (changing operation
     so value is preserved), for canonicalization.  */

  if (TREE_CONSTANT (primop0))
    {
      register tree tem = primop0;
      register int temi = unsignedp0;
      primop0 = primop1;
      primop1 = tem;
      tem = op0;
      op0 = op1;
      op1 = tem;
      *op0_ptr = op0;
      *op1_ptr = op1;
      unsignedp0 = unsignedp1;
      unsignedp1 = temi;
      temi = real1;
      real1 = real2;
      real2 = temi;

      switch (code)
	{
	case LT_EXPR:
	  code = GT_EXPR;
	  break;
	case GT_EXPR:
	  code = LT_EXPR;
	  break;
	case LE_EXPR:
	  code = GE_EXPR;
	  break;
	case GE_EXPR:
	  code = LE_EXPR;
	  break;
	}
      *rescode_ptr = code;
    }

  /* If comparing an integer against a constant more bits wide,
     maybe we can deduce a value of 1 or 0 independent of the data.
     Or else truncate the constant now
     rather than extend the variable at run time.

     This is only interesting if the constant is the wider arg.
     Also, it is not safe if the constant is unsigned and the
     variable arg is signed, since in this case the variable
     would be sign-extended and then regarded as unsigned.
     Our technique fails in this case because the lowest/highest
     possible unsigned results don't follow naturally from the
     lowest/highest possible values of the variable operand.
     For just EQ_EXPR and NE_EXPR there is another technique that
     could be used: see if the constant can be faithfully represented
     in the other operand's type, by truncating it and reextending it
     and see if that preserves the constant's value.  */

  if (!real1 && !real2
      && TREE_CODE (primop1) == INTEGER_CST
      && TYPE_PRECISION (TREE_TYPE (primop0)) < TYPE_PRECISION (*restype_ptr))
    {
      int min_gt, max_gt, min_lt, max_lt;
      tree maxval, minval;
      /* 1 if comparison is nominally unsigned.  */
      int unsignedp = TREE_UNSIGNED (*restype_ptr);
      tree val;

      type = signed_or_unsigned_type (unsignedp0, TREE_TYPE (primop0));

      maxval = TYPE_MAX_VALUE (type);
      minval = TYPE_MIN_VALUE (type);

      if (unsignedp && !unsignedp0)
	*restype_ptr = signed_type (*restype_ptr);

      if (TREE_TYPE (primop1) != *restype_ptr)
	primop1 = convert (*restype_ptr, primop1);
      if (type != *restype_ptr)
	{
	  minval = convert (*restype_ptr, minval);
	  maxval = convert (*restype_ptr, maxval);
	}

      if (unsignedp && unsignedp0)
	{
	  min_gt = INT_CST_LT_UNSIGNED (primop1, minval);
	  max_gt = INT_CST_LT_UNSIGNED (primop1, maxval);
	  min_lt = INT_CST_LT_UNSIGNED (minval, primop1);
	  max_lt = INT_CST_LT_UNSIGNED (maxval, primop1);
	}
      else
	{
	  min_gt = INT_CST_LT (primop1, minval);
	  max_gt = INT_CST_LT (primop1, maxval);
	  min_lt = INT_CST_LT (minval, primop1);
	  max_lt = INT_CST_LT (maxval, primop1);
	}

      val = 0;
      /* This used to be a switch, but Genix compiler can't handle that.  */
      if (code == NE_EXPR)
	{
	  if (max_lt || min_gt)
	    val = integer_one_node;
	}
      else if (code == EQ_EXPR)
	{
	  if (max_lt || min_gt)
	    val = integer_zero_node;
	}
      else if (code == LT_EXPR)
	{
	  if (max_lt)
	    val = integer_one_node;
	  if (!min_lt)
	    val = integer_zero_node;
	}
      else if (code == GT_EXPR)
	{
	  if (min_gt)
	    val = integer_one_node;
	  if (!max_gt)
	    val = integer_zero_node;
	}
      else if (code == LE_EXPR)
	{
	  if (!max_gt)
	    val = integer_one_node;
	  if (min_gt)
	    val = integer_zero_node;
	}
      else if (code == GE_EXPR)
	{
	  if (!min_lt)
	    val = integer_one_node;
	  if (max_lt)
	    val = integer_zero_node;
	}

      /* If primop0 was sign-extended and unsigned comparison specd,
	 we did a signed comparison above using the signed type bounds.
	 But the comparison we output must be unsigned.

	 Also, for inequalities, VAL is no good; but if the signed
	 comparison had *any* fixed result, it follows that the
	 unsigned comparison just tests the sign in reverse
	 (positive values are LE, negative ones GE).
	 So we can generate an unsigned comparison
	 against an extreme value of the signed type.  */

      if (unsignedp && !unsignedp0)
	{
	  if (val != 0)
	    switch (code)
	      {
	      case LT_EXPR:
	      case GE_EXPR:
		primop1 = TYPE_MIN_VALUE (type);
		val = 0;
		break;

	      case LE_EXPR:
	      case GT_EXPR:
		primop1 = TYPE_MAX_VALUE (type);
		val = 0;
		break;
	      }
	  type = unsigned_type (type);
	}

      if (max_lt && !unsignedp0)
	{
	  /* This is the case of (char)x >?< 0x80, which people used to use
	     expecting old C compilers to change the 0x80 into -0x80.  */
	  if (val == integer_zero_node)
	    warning ("comparison is always 0 due to limited range of data type");
	  if (val == integer_one_node)
	    warning ("comparison is always 1 due to limited range of data type");
	}

      if (min_gt && unsignedp0)
	{
	  /* This is the case of (unsigned char)x >?< -1.  */
	  if (val == integer_zero_node)
	    warning ("comparison is always 0 due to limited range of data type");
	  if (val == integer_one_node)
	    warning ("comparison is always 1 due to limited range of data type");
	}

      if (val != 0)
	{
	  /* Don't forget to evaluate PRIMOP0 if it has side effects.  */
	  if (TREE_SIDE_EFFECTS (primop0))
	    return build (COMPOUND_EXPR, TREE_TYPE (val), primop0, val);
	  return val;
	}

      /* Value is not predetermined, but do the comparison
	 in the type of the operand that is not constant.
	 TYPE is already properly set.  */
    }
  else if (real1 && real2
	   && TYPE_PRECISION (TREE_TYPE (primop0)) == TYPE_PRECISION (TREE_TYPE (primop1)))
    type = TREE_TYPE (primop0);

  /* If args' natural types are both narrower than nominal type
     and both extend in the same manner, compare them
     in the type of the wider arg.
     Otherwise must actually extend both to the nominal
     common type lest different ways of extending
     alter the result.
     (eg, (short)-1 == (unsigned short)-1  should be 0.)  */

  else if (unsignedp0 == unsignedp1 && real1 == real2
	   && TYPE_PRECISION (TREE_TYPE (primop0)) < TYPE_PRECISION (*restype_ptr)
	   && TYPE_PRECISION (TREE_TYPE (primop1)) < TYPE_PRECISION (*restype_ptr))
    {
      type = common_type (TREE_TYPE (primop0), TREE_TYPE (primop1));
      type = signed_or_unsigned_type (unsignedp0
				      || TREE_UNSIGNED (*restype_ptr),
				      type);
      /* Make sure shorter operand is extended the right way
	 to match the longer operand.  */
      primop0 = convert (signed_or_unsigned_type (unsignedp0, TREE_TYPE (primop0)),
			 primop0);
      primop1 = convert (signed_or_unsigned_type (unsignedp1, TREE_TYPE (primop1)),
			 primop1);
    }
  else
    {
      /* Here we must do the comparison on the nominal type
	 using the args exactly as we received them.  */
      type = *restype_ptr;
      primop0 = op0;
      primop1 = op1;

      if (!real1 && !real2 && integer_zerop (primop1)
	  && TREE_UNSIGNED (TREE_TYPE (primop0)))
	{
	  tree value = 0;
	  switch (code)
	    {
	    case GE_EXPR:
	      if (extra_warnings)
		warning ("unsigned value >= 0 is always 1");
	      value = integer_one_node;
	      break;

	    case LT_EXPR:
	      if (extra_warnings)
		warning ("unsigned value < 0 is always 0");
	      value = integer_zero_node;
	    }

	  if (value != 0)
	    {
	      /* Don't forget to evaluate PRIMOP0 if it has side effects.  */
	      if (TREE_SIDE_EFFECTS (primop0))
		return build (COMPOUND_EXPR, TREE_TYPE (value),
			      primop0, value);
	      return value;
	    }
	}
    }

  *op0_ptr = convert (type, primop0);
  *op1_ptr = convert (type, primop1);

  *restype_ptr = integer_type_node;

  return 0;
}
\f
/* Prepare expr to be an argument of a TRUTH_NOT_EXPR,
   or validate its data type for an `if' or `while' statement or ?..: exp.

   This preparation consists of taking the ordinary
   representation of an expression expr and producing a valid tree
   boolean expression describing whether expr is nonzero.  We could
   simply always do build_binary_op (NE_EXPR, expr, integer_zero_node, 1),
   but we optimize comparisons, &&, ||, and !.

   The resulting type should always be `integer_type_node'.  */

tree
truthvalue_conversion (expr)
     tree expr;
{
  register enum tree_code code;

  switch (TREE_CODE (expr))
    {
      /* It is simpler and generates better code to have only TRUTH_*_EXPR
	 or comparison expressions as truth values at this level.  */
#if 0
    case COMPONENT_REF:
      /* A one-bit unsigned bit-field is already acceptable.  */
      if (1 == TREE_INT_CST_LOW (DECL_SIZE (TREE_OPERAND (expr, 1)))
	  && TREE_UNSIGNED (TREE_OPERAND (expr, 1)))
	return expr;
      break;
#endif

    case EQ_EXPR:
      /* It is simpler and generates better code to have only TRUTH_*_EXPR
	 or comparison expressions as truth values at this level.  */
#if 0
      if (integer_zerop (TREE_OPERAND (expr, 1)))
	return build_unary_op (TRUTH_NOT_EXPR, TREE_OPERAND (expr, 0), 0);
#endif
    case NE_EXPR: case LE_EXPR: case GE_EXPR: case LT_EXPR: case GT_EXPR:
    case TRUTH_ANDIF_EXPR:
    case TRUTH_ORIF_EXPR:
    case TRUTH_AND_EXPR:
    case TRUTH_OR_EXPR:
    case ERROR_MARK:
      return expr;

    case INTEGER_CST:
      return integer_zerop (expr) ? integer_zero_node : integer_one_node;

    case REAL_CST:
      return real_zerop (expr) ? integer_zero_node : integer_one_node;

    case ADDR_EXPR:
      if (TREE_SIDE_EFFECTS (TREE_OPERAND (expr, 0)))
	return build (COMPOUND_EXPR, integer_type_node,
		      TREE_OPERAND (expr, 0), integer_one_node);
      else
	return integer_one_node;

    case NEGATE_EXPR:
    case ABS_EXPR:
    case FLOAT_EXPR:
    case FFS_EXPR:
      /* These don't change whether an object is non-zero or zero.  */
      return truthvalue_conversion (TREE_OPERAND (expr, 0));

    case LROTATE_EXPR:
    case RROTATE_EXPR:
      /* These don't change whether an object is zero or non-zero, but
	 we can't ignore them if their second arg has side-effects.  */
      if (TREE_SIDE_EFFECTS (TREE_OPERAND (expr, 1)))
	return build (COMPOUND_EXPR, integer_type_node, TREE_OPERAND (expr, 1),
		      truthvalue_conversion (TREE_OPERAND (expr, 0)));
      else
	return truthvalue_conversion (TREE_OPERAND (expr, 0));
      
    case COND_EXPR:
      /* Distribute the conversion into the arms of a COND_EXPR.  */
      return fold (build (COND_EXPR, integer_type_node, TREE_OPERAND (expr, 0),
			  truthvalue_conversion (TREE_OPERAND (expr, 1)),
			  truthvalue_conversion (TREE_OPERAND (expr, 2))));

    case CONVERT_EXPR:
      /* Don't cancel the effect of a CONVERT_EXPR from a REFERENCE_TYPE,
	 since that affects how `default_conversion' will behave.  */
      if (TREE_CODE (TREE_TYPE (expr)) == REFERENCE_TYPE
	  || TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0))) == REFERENCE_TYPE)
	break;
      /* fall through... */
    case NOP_EXPR:
      /* If this is widening the argument, we can ignore it.  */
      if (TYPE_PRECISION (TREE_TYPE (expr))
	  >= TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (expr, 0))))
	return truthvalue_conversion (TREE_OPERAND (expr, 0));
      break;

    case BIT_XOR_EXPR:
    case MINUS_EXPR:
      /* These can be changed into a comparison of the two objects.  */
      if (TREE_TYPE (TREE_OPERAND (expr, 0))
	  == TREE_TYPE (TREE_OPERAND (expr, 1)))
	return build_binary_op (NE_EXPR, TREE_OPERAND (expr, 0),
				TREE_OPERAND (expr, 1), 1);
      return build_binary_op (NE_EXPR, TREE_OPERAND (expr, 0),
			      fold (build1 (NOP_EXPR,
					    TREE_TYPE (TREE_OPERAND (expr, 0)),
					    TREE_OPERAND (expr, 1))), 1);
    }

  return build_binary_op (NE_EXPR, expr, integer_zero_node, 1);
}
\f
/* Read the rest of a #-directive from input stream FINPUT.
   In normal use, the directive name and the white space after it
   have already been read, so they won't be included in the result.
   We allow for the fact that the directive line may contain
   a newline embedded within a character or string literal which forms
   a part of the directive.

   The value is a string in a reusable buffer.  It remains valid
   only until the next time this function is called.  */

char *
get_directive_line (finput)
     register FILE *finput;
{
  static char *directive_buffer = NULL;
  static unsigned buffer_length = 0;
  register char *p;
  register char *buffer_limit;
  register int looking_for = 0;
  register int char_escaped = 0;

  if (buffer_length == 0)
    {
      directive_buffer = (char *)xmalloc (128);
      buffer_length = 128;
    }

  buffer_limit = &directive_buffer[buffer_length];

  for (p = directive_buffer; ; )
    {
      int c;

      /* Make buffer bigger if it is full.  */
      if (p >= buffer_limit)
        {
	  register unsigned bytes_used = (p - directive_buffer);

	  buffer_length *= 2;
	  directive_buffer
	    = (char *)xrealloc (directive_buffer, buffer_length);
	  p = &directive_buffer[bytes_used];
	  buffer_limit = &directive_buffer[buffer_length];
        }

      c = getc (finput);

      /* Discard initial whitespace.  */
      if ((c == ' ' || c == '\t') && p == directive_buffer)
	continue;

      /* Detect the end of the directive.  */
      if (c == '\n' && looking_for == 0)
	{
          ungetc (c, finput);
	  c = '\0';
	}

      *p++ = c;

      if (c == 0)
	return directive_buffer;

      /* Handle string and character constant syntax.  */
      if (looking_for)
	{
	  if (looking_for == c && !char_escaped)
	    looking_for = 0;	/* Found terminator... stop looking.  */
	}
      else
        if (c == '\'' || c == '"')
	  looking_for = c;	/* Don't stop buffering until we see another
				   another one of these (or an EOF).  */

      /* Handle backslash.  */
      char_escaped = (c == '\\' && ! char_escaped);
    }
}