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git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@247 138bc75d-0d04-0410-961f-82ee72b054a4

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diff --git a/gcc/c-convert.c b/gcc/c-convert.c
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+/* Language-level data type conversion for GNU C.
+   Copyright (C) 1987, 1988, 1991 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.  */
+
+
+/* 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 "tree.h"
+#include "flags.h"
+
+/* 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 c-convert.c, convert_to_integer.
+     In c-typeck.c, build_binary_op (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.  */
+
+/* Subroutines of `convert'.  */
+
+static tree
+convert_to_pointer (type, expr)
+     tree type, expr;
+{
+  register tree intype = TREE_TYPE (expr);
+  register enum tree_code form = TREE_CODE (intype);
+  
+  if (integer_zerop (expr))
+    {
+      if (type == TREE_TYPE (null_pointer_node))
+	return null_pointer_node;
+      expr = build_int_2 (0, 0);
+      TREE_TYPE (expr) = type;
+      return expr;
+    }
+
+  if (form == POINTER_TYPE)
+    return build1 (NOP_EXPR, type, expr);
+
+
+  if (form == INTEGER_TYPE || form == ENUMERAL_TYPE)
+    {
+      if (type_precision (intype) == POINTER_SIZE)
+	return build1 (CONVERT_EXPR, type, expr);
+      expr = convert (type_for_size (POINTER_SIZE, 0), expr);
+      if (TYPE_MODE (TREE_TYPE (expr)) != 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);
+    }
+
+  error ("cannot convert to a pointer type");
+
+  return null_pointer_node;
+}
+
+static tree
+convert_to_real (type, expr)
+     tree type, expr;
+{
+  register enum tree_code form = TREE_CODE (TREE_TYPE (expr));
+
+  if (form == REAL_TYPE)
+    return build1 (flag_float_store ? CONVERT_EXPR : NOP_EXPR,
+		   type, expr);
+
+  if (form == INTEGER_TYPE || form == ENUMERAL_TYPE)
+    return build1 (FLOAT_EXPR, type, expr);
+
+  if (form == POINTER_TYPE)
+    error ("pointer value used where a float was expected");
+  else
+    error ("aggregate value used where a float was expected");
+
+  {
+    register tree tem = make_node (REAL_CST);
+    TREE_TYPE (tem) = type;
+    TREE_REAL_CST (tem) = REAL_VALUE_ATOF ("0.0");
+    return tem;
+  }
+}
+
+/* The result of this is always supposed to be a newly created tree node
+   not in use in any existing structure.  */
+
+static tree
+convert_to_integer (type, expr)
+     tree type, expr;
+{
+  register tree intype = TREE_TYPE (expr);
+  register enum tree_code form = TREE_CODE (intype);
+
+  if (form == POINTER_TYPE)
+    {
+      if (integer_zerop (expr))
+	expr = integer_zero_node;
+      else
+	expr = fold (build1 (CONVERT_EXPR,
+			     type_for_size (POINTER_SIZE, 0), expr));
+      intype = TREE_TYPE (expr);
+      form = TREE_CODE (intype);
+      if (intype == type)
+	return expr;
+    }
+
+  if (form == INTEGER_TYPE || form == ENUMERAL_TYPE)
+    {
+      register unsigned outprec = TYPE_PRECISION (type);
+      register unsigned inprec = TYPE_PRECISION (intype);
+      register enum tree_code ex_form = TREE_CODE (expr);
+
+      if (outprec >= inprec)
+	return build1 (NOP_EXPR, 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 negative constant.  */
+	  if (TREE_CODE (TREE_OPERAND (expr, 1)) != INTEGER_CST
+	      || TREE_INT_CST_LOW (TREE_OPERAND (expr, 1)) > 0)
+	    break;
+	  goto trunc1;
+
+	case LSHIFT_EXPR:
+	  /* We can pass truncation down through left shifting
+	     when the shift count is a positive constant.  */
+	  if (TREE_CODE (TREE_OPERAND (expr, 1)) != INTEGER_CST
+	      || TREE_INT_CST_LOW (TREE_OPERAND (expr, 1)) < 0)
+	    break;
+	  /* In this case, shifting is like multiplication.  */
+	  goto trunc1;
+
+	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.  */
+		&& (TREE_UNSIGNED (TREE_TYPE (arg0))
+		    == TREE_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:
+	case BIT_ANDTC_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.  */
+		register 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 = type_for_size (TYPE_PRECISION (typex),
+					 TREE_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 either of the original operands were
+		       unsigned then can safely do the work as unsigned.
+		       And we may need to do it as unsigned
+		       if we truncate to the original size.  */
+		    typex = ((TREE_UNSIGNED (TREE_TYPE (expr))
+			      || TREE_UNSIGNED (TREE_TYPE (arg0))
+			      || TREE_UNSIGNED (TREE_TYPE (arg1)))
+			     ? unsigned_type (typex) : signed_type (typex));
+		    return convert (type,
+				    build_binary_op (ex_form,
+						     convert (typex, arg0),
+						     convert (typex, arg1),
+						     0));
+		  }
+	      }
+	  }
+	  break;
+
+	case EQ_EXPR:
+	case NE_EXPR:
+	case GT_EXPR:
+	case GE_EXPR:
+	case LT_EXPR:
+	case LE_EXPR:
+	case TRUTH_AND_EXPR:
+	case TRUTH_ANDIF_EXPR:
+	case TRUTH_OR_EXPR:
+	case TRUTH_ORIF_EXPR:
+	case TRUTH_NOT_EXPR:
+	  /* If we want result of comparison converted to a byte,
+	     we can just regard it as a byte, since it is 0 or 1.  */
+	  TREE_TYPE (expr) = type;
+	  return expr;
+
+	case NEGATE_EXPR:
+	case BIT_NOT_EXPR:
+	case ABS_EXPR:
+	  {
+	    register 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 = type_for_size (TYPE_PRECISION (typex),
+				     TREE_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.  */
+		typex = (TREE_UNSIGNED (TREE_TYPE (expr))
+			 ? unsigned_type (typex) : signed_type (typex));
+		return convert (type,
+				build_unary_op (ex_form,
+						convert (typex, TREE_OPERAND (expr, 0)),
+						1));
+	      }
+	  }
+
+	case NOP_EXPR:
+	  /* 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:
+	  /* Can treat the two alternative values like the operands
+	     of an arithmetic expression.  */
+	  {
+	    tree arg1 = get_unwidened (TREE_OPERAND (expr, 1), type);
+	    tree arg2 = get_unwidened (TREE_OPERAND (expr, 2), type);
+
+	    if (outprec >= BITS_PER_WORD
+		|| TRULY_NOOP_TRUNCATION (outprec, inprec)
+		|| inprec > TYPE_PRECISION (TREE_TYPE (arg1))
+		|| inprec > TYPE_PRECISION (TREE_TYPE (arg2)))
+	      {
+		/* Do the arithmetic in type TYPEX,
+		   then convert result to TYPE.  */
+		register 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 = type_for_size (TYPE_PRECISION (typex),
+					 TREE_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.  */
+		    typex = (TREE_UNSIGNED (TREE_TYPE (expr))
+			     ? unsigned_type (typex) : signed_type (typex));
+		    return convert (type,
+				    fold (build (COND_EXPR, typex,
+						 TREE_OPERAND (expr, 0),
+						 convert (typex, arg1),
+						 convert (typex, arg2))));
+		  }
+	      }
+	  }
+	}
+
+      return build1 (NOP_EXPR, type, expr);
+    }
+
+  if (form == REAL_TYPE)
+    return build1 (FIX_TRUNC_EXPR, type, expr);
+
+  error ("aggregate value used where an integer was expected");
+
+  {
+    register tree tem = build_int_2 (0, 0);
+    TREE_TYPE (tem) = type;
+    return tem;
+  }
+}
+
+/* Create an expression whose value is that of EXPR,
+   converted to type TYPE.  The TREE_TYPE of the value
+   is always TYPE.  This function implements all reasonable
+   conversions; callers should filter out those that are
+   not permitted by the language being compiled.  */
+
+tree
+convert (type, expr)
+     tree type, expr;
+{
+  register tree e = expr;
+  register enum tree_code code = TREE_CODE (type);
+
+  if (type == TREE_TYPE (expr) || TREE_CODE (expr) == ERROR_MARK)
+    return expr;
+  if (TREE_CODE (TREE_TYPE (expr)) == ERROR_MARK)
+    return error_mark_node;
+  if (TREE_CODE (TREE_TYPE (expr)) == VOID_TYPE)
+    {
+      error ("void value not ignored as it ought to be");
+      return error_mark_node;
+    }
+  if (code == VOID_TYPE)
+    return build1 (CONVERT_EXPR, type, e);
+#if 0
+  /* This is incorrect.  A truncation can't be stripped this way.
+     Extensions will be stripped by the use of get_unwidened.  */
+  if (TREE_CODE (expr) == NOP_EXPR)
+    return convert (type, TREE_OPERAND (expr, 0));
+#endif
+  if (code == INTEGER_TYPE || code == ENUMERAL_TYPE)
+    return fold (convert_to_integer (type, e));
+  if (code == POINTER_TYPE)
+    return fold (convert_to_pointer (type, e));
+  if (code == REAL_TYPE)
+    return fold (convert_to_real (type, e));
+
+  error ("conversion to non-scalar type requested");
+  return error_mark_node;
+}