cvt.c

gcc-2.95.3 Linux下最常用的C编译器

/* Language-level data type conversion for GNU C++.
   Copyright (C) 1987, 88, 92-97, 1998 Free Software Foundation, Inc.
   Hacked by Michael Tiemann ([e-mail])

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, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */


/* This file contains the functions for converting C expressions
   to different data types.  The only entry point is `convert'.
   Every language front end must have a `convert' function
   but what kind of conversions it does will depend on the language.  */

#include "config.h"
#include "system.h"
#include "tree.h"
#include "flags.h"
#include "cp-tree.h"
#include "convert.h"
#include "toplev.h"
#include "decl.h"

static tree cp_convert_to_pointer PROTO((tree, tree));
static tree convert_to_pointer_force PROTO((tree, tree));
static tree build_up_reference PROTO((tree, tree, int));

/* Change of width--truncation and extension of integers or reals--
   is represented with NOP_EXPR.  Proper functioning of many things
   assumes that no other conversions can be NOP_EXPRs.

   Conversion between integer and pointer is represented with CONVERT_EXPR.
   Converting integer to real uses FLOAT_EXPR
   and real to integer uses FIX_TRUNC_EXPR.

   Here is a list of all the functions that assume that widening and
   narrowing is always done with a NOP_EXPR:
     In convert.c, convert_to_integer.
     In c-typeck.c, build_binary_op_nodefault (boolean ops),
        and truthvalue_conversion.
     In expr.c: expand_expr, for operands of a MULT_EXPR.
     In fold-const.c: fold.
     In tree.c: get_narrower and get_unwidened.

   C++: in multiple-inheritance, converting between pointers may involve
   adjusting them by a delta stored within the class definition.  */

/* Subroutines of `convert'.  */

/* if converting pointer to pointer
     if dealing with classes, check for derived->base or vice versa
     else if dealing with method pointers, delegate
     else convert blindly
   else if converting class, pass off to build_type_conversion
   else try C-style pointer conversion  */

static tree
cp_convert_to_pointer (type, expr)
     tree type, expr;
{
  register tree intype = TREE_TYPE (expr);
  register enum tree_code form;
  tree rval;

  if (IS_AGGR_TYPE (intype))
    {
      intype = complete_type (intype);
      if (TYPE_SIZE (intype) == NULL_TREE)
	{
	  cp_error ("can't convert from incomplete type `%T' to `%T'",
		    intype, type);
	  return error_mark_node;
	}

      rval = build_type_conversion (type, expr, 1);
      if (rval)
	{
	  if (rval == error_mark_node)
	    cp_error ("conversion of `%E' from `%T' to `%T' is ambiguous",
		      expr, intype, type);
	  return rval;
	}
    }

  /* Handle anachronistic conversions from (::*)() to cv void* or (*)().  */
  if (TREE_CODE (type) == POINTER_TYPE
      && (TREE_CODE (TREE_TYPE (type)) == FUNCTION_TYPE
	  || TYPE_MAIN_VARIANT (TREE_TYPE (type)) == void_type_node))
    {
      /* Allow an implicit this pointer for pointer to member
	 functions.  */
      if (TYPE_PTRMEMFUNC_P (intype))
	{
	  tree fntype = TREE_TYPE (TYPE_PTRMEMFUNC_FN_TYPE (intype));
	  tree decl = maybe_dummy_object (TYPE_METHOD_BASETYPE (fntype), 0);
	  expr = build (OFFSET_REF, fntype, decl, expr);
	}

      if (TREE_CODE (expr) == OFFSET_REF
	  && TREE_CODE (TREE_TYPE (expr)) == METHOD_TYPE)
	expr = resolve_offset_ref (expr);
      if (TREE_CODE (TREE_TYPE (expr)) == METHOD_TYPE)
	expr = build_addr_func (expr);
      if (TREE_CODE (TREE_TYPE (expr)) == POINTER_TYPE)
	{
	  if (TREE_CODE (TREE_TYPE (TREE_TYPE (expr))) == METHOD_TYPE)
	    if (pedantic || warn_pmf2ptr)
	      cp_pedwarn ("converting from `%T' to `%T'", TREE_TYPE (expr),
			  type);
	  return build1 (NOP_EXPR, type, expr);
	}
      intype = TREE_TYPE (expr);
    }

  form = TREE_CODE (intype);

  if (POINTER_TYPE_P (intype))
    {
      intype = TYPE_MAIN_VARIANT (intype);

      if (TYPE_MAIN_VARIANT (type) != intype
	  && TREE_CODE (type) == POINTER_TYPE
	  && TREE_CODE (TREE_TYPE (type)) == RECORD_TYPE
	  && IS_AGGR_TYPE (TREE_TYPE (type))
	  && IS_AGGR_TYPE (TREE_TYPE (intype))
	  && TREE_CODE (TREE_TYPE (intype)) == RECORD_TYPE
	  /* If EXPR is NULL, then we don't need to do any arithmetic
	     to convert it:

	       [conv.ptr]

	       The null pointer value is converted to the null pointer
	       value of the destination type.  */
	  && !integer_zerop (expr))
	{
	  enum tree_code code = PLUS_EXPR;
	  tree binfo = get_binfo (TREE_TYPE (type), TREE_TYPE (intype), 1);
	  if (binfo == error_mark_node)
	    return error_mark_node;
	  if (binfo == NULL_TREE)
	    {
	      binfo = get_binfo (TREE_TYPE (intype), TREE_TYPE (type), 1);
	      if (binfo == error_mark_node)
		return error_mark_node;
	      code = MINUS_EXPR;
	    }
	  if (binfo)
	    {
	      if (TYPE_USES_VIRTUAL_BASECLASSES (TREE_TYPE (type))
		  || TYPE_USES_VIRTUAL_BASECLASSES (TREE_TYPE (intype))
		  || ! BINFO_OFFSET_ZEROP (binfo))
		{
		  /* Need to get the path we took.  */
		  tree path;

		  if (code == PLUS_EXPR)
		    get_base_distance (TREE_TYPE (type), TREE_TYPE (intype),
				       0, &path);
		  else
		    get_base_distance (TREE_TYPE (intype), TREE_TYPE (type),
				       0, &path);
		  return build_vbase_path (code, type, expr, path, 0);
		}
	    }
	}

      if (TYPE_PTRMEM_P (type) && TYPE_PTRMEM_P (intype))
	{
	  tree b1 = TYPE_OFFSET_BASETYPE (TREE_TYPE (type));
	  tree b2 = TYPE_OFFSET_BASETYPE (TREE_TYPE (intype));
	  tree binfo = get_binfo (b2, b1, 1);
	  enum tree_code code = PLUS_EXPR;

	  if (binfo == NULL_TREE)
	    {
	      binfo = get_binfo (b1, b2, 1);
	      code = MINUS_EXPR;
	    }

	  if (binfo == error_mark_node)
	    return error_mark_node;
	  if (binfo && ! TREE_VIA_VIRTUAL (binfo))
	    expr = size_binop (code, expr, BINFO_OFFSET (binfo));
	}
      else if (TYPE_PTRMEMFUNC_P (type))
	{
	  cp_error ("cannot convert `%E' from type `%T' to type `%T'",
		    expr, intype, type);
	  return error_mark_node;
	}

      rval = build1 (NOP_EXPR, type, expr);
      TREE_CONSTANT (rval) = TREE_CONSTANT (expr);
      return rval;
    }
  else if (TYPE_PTRMEMFUNC_P (type) && TYPE_PTRMEMFUNC_P (intype))
    return build_ptrmemfunc (TYPE_PTRMEMFUNC_FN_TYPE (type), expr, 1);
  else if (TYPE_PTRMEMFUNC_P (intype))
    {
      cp_error ("cannot convert `%E' from type `%T' to type `%T'",
		expr, intype, type);
      return error_mark_node;
    }

  my_friendly_assert (form != OFFSET_TYPE, 186);

  if (TYPE_LANG_SPECIFIC (intype)
      && (IS_SIGNATURE_POINTER (intype) || IS_SIGNATURE_REFERENCE (intype)))
    return convert_to_pointer (type, build_optr_ref (expr));

  if (integer_zerop (expr))
    {
      if (TYPE_PTRMEMFUNC_P (type))
	return build_ptrmemfunc (TYPE_PTRMEMFUNC_FN_TYPE (type), expr, 0);
      expr = build_int_2 (0, 0);
      TREE_TYPE (expr) = type;
      return expr;
    }

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

  if (type_unknown_p (expr))
    return instantiate_type (type, expr, 1);

  cp_error ("cannot convert `%E' from type `%T' to type `%T'",
	    expr, intype, type);
  return error_mark_node;
}

/* Like convert, except permit conversions to take place which
   are not normally allowed due to access restrictions
   (such as conversion from sub-type to private super-type).  */

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

  /* Convert signature pointer/reference to `void *' first.  */
  if (form == RECORD_TYPE
      && (IS_SIGNATURE_POINTER (intype) || IS_SIGNATURE_REFERENCE (intype)))
    {
      expr = build_optr_ref (expr);
      intype = TREE_TYPE (expr);
      form = TREE_CODE (intype);
    }

  if (form == POINTER_TYPE)
    {
      intype = TYPE_MAIN_VARIANT (intype);

      if (TYPE_MAIN_VARIANT (type) != intype
	  && TREE_CODE (TREE_TYPE (type)) == RECORD_TYPE
	  && IS_AGGR_TYPE (TREE_TYPE (type))
	  && IS_AGGR_TYPE (TREE_TYPE (intype))
	  && TREE_CODE (TREE_TYPE (intype)) == RECORD_TYPE)
	{
	  enum tree_code code = PLUS_EXPR;
	  tree path;
	  int distance = get_base_distance (TREE_TYPE (type),
					    TREE_TYPE (intype), 0, &path);
	  if (distance == -2)
	    {
	    ambig:
	      cp_error ("type `%T' is ambiguous baseclass of `%s'",
			TREE_TYPE (type),
			TYPE_NAME_STRING (TREE_TYPE (intype)));
	      return error_mark_node;
	    }
	  if (distance == -1)
	    {
	      distance = get_base_distance (TREE_TYPE (intype),
					    TREE_TYPE (type), 0, &path);
	      if (distance == -2)
		goto ambig;
	      if (distance < 0)
		/* Doesn't need any special help from us.  */
		return build1 (NOP_EXPR, type, expr);

	      code = MINUS_EXPR;
	    }
	  return build_vbase_path (code, type, expr, path, 0);
	}
    }

  return cp_convert_to_pointer (type, expr);
}

/* We are passing something to a function which requires a reference.
   The type we are interested in is in TYPE. The initial
   value we have to begin with is in ARG.

   FLAGS controls how we manage access checking.
   DIRECT_BIND in FLAGS controls how any temporaries are generated.  */

static tree
build_up_reference (type, arg, flags)
     tree type, arg;
     int flags;
{
  tree rval;
  tree argtype = TREE_TYPE (arg);
  tree target_type = TREE_TYPE (type);

  my_friendly_assert (TREE_CODE (type) == REFERENCE_TYPE, 187);

  if ((flags & DIRECT_BIND) && ! real_lvalue_p (arg))
    {
      tree targ = arg;
      if (toplevel_bindings_p ())
	arg = get_temp_name (argtype, 1);
      else
	{
	  arg = pushdecl (build_decl (VAR_DECL, NULL_TREE, argtype));
	  DECL_ARTIFICIAL (arg) = 1;
	}
      DECL_INITIAL (arg) = targ;
      cp_finish_decl (arg, targ, NULL_TREE, 0,
		      LOOKUP_ONLYCONVERTING|DIRECT_BIND);
    }
  else if (!(flags & DIRECT_BIND) && ! lvalue_p (arg))
    {
      tree slot = build_decl (VAR_DECL, NULL_TREE, argtype);
      DECL_ARTIFICIAL (slot) = 1;
      arg = build (TARGET_EXPR, argtype, slot, arg, NULL_TREE, NULL_TREE);
      TREE_SIDE_EFFECTS (arg) = 1;
    }

  /* If we had a way to wrap this up, and say, if we ever needed it's
     address, transform all occurrences of the register, into a memory
     reference we could win better.  */
  rval = build_unary_op (ADDR_EXPR, arg, 1);
  if (rval == error_mark_node)
    return error_mark_node;

  if ((flags & LOOKUP_PROTECT)
      && TYPE_MAIN_VARIANT (argtype) != TYPE_MAIN_VARIANT (target_type)
      && IS_AGGR_TYPE (argtype)
      && IS_AGGR_TYPE (target_type))
    {
      /* We go through get_binfo for the access control.  */
      tree binfo = get_binfo (target_type, argtype, 1);
      if (binfo == error_mark_node)
	return error_mark_node;
      if (binfo == NULL_TREE)
	return error_not_base_type (target_type, argtype);
      rval = convert_pointer_to_real (binfo, rval);