c-decl.c (grokdeclarator): Special case the creation of an index for a zero-length array.

        * c-decl.c (grokdeclarator): Special case the creation of an
        index for a zero-length array.
        * tree.c (build_index_type): Revert Oct 20 change.

From-SVN: r37558

gcc/ChangeLog

+2000-11-18  Richard Henderson  <rth@redhat.com>
+
+	* c-decl.c (grokdeclarator): Special case the creation of an
+	index for a zero-length array.
+	* tree.c (build_index_type): Revert Oct 20 change.
+
 2000-11-18  Marek Michalkiewicz  <marekm@linux.org.pl>
 
 	* config/avr/avr-protos.h (avr_output_addr_vec_elt): Prototype.

gcc/c-decl.c

@@ -4494,27 +4494,41 @@ grokdeclarator (declarator, declspecs, decl_context, initialized)
 		    }
 		}
 
-	      /* Convert size to index_type, so that if it is a variable
-		 the computations will be done in the proper mode.  */
-	      itype = fold (build (MINUS_EXPR, index_type,
-				   convert (index_type, size),
-				   convert (index_type, size_one_node)));
-
-	      /* If that overflowed, the array is too big.
-		 ??? While a size of INT_MAX+1 technically shouldn't cause
-		 an overflow (because we subtract 1), the overflow is recorded
-		 during the conversion to index_type, before the subtraction.
-		 Handling this case seems like an unnecessary complication.  */
-	      if (TREE_OVERFLOW (itype))
+	      if (integer_zerop (size))
 		{
-		  error ("size of array `%s' is too large", name);
-		  type = error_mark_node;
-		  continue;
+		  /* A zero-length array cannot be represented with an
+		     unsigned index type, which is what we'll get with
+		     build_index_type.  Create a signed range instead.  */
+		  itype = build_range_type (index_type, size,
+					    build_int_2 (-1, -1));
 		}
+	      else
+		{
+		  /* Compute the maximum valid index, that is, size - 1.
+		     Do the calculation in index_type, so that if it is
+		     a variable the computations will be done in the
+		     proper mode.  */
+	          itype = fold (build (MINUS_EXPR, index_type,
+				       convert (index_type, size),
+				       convert (index_type, size_one_node)));
+
+	          /* If that overflowed, the array is too big.
+		     ??? While a size of INT_MAX+1 technically shouldn't
+		     cause an overflow (because we subtract 1), the overflow
+		     is recorded during the conversion to index_type, before
+		     the subtraction.  Handling this case seems like an
+		     unnecessary complication.  */
+		  if (TREE_OVERFLOW (itype))
+		    {
+		      error ("size of array `%s' is too large", name);
+		      type = error_mark_node;
+		      continue;
+		    }
 
-	      if (size_varies)
-		itype = variable_size (itype);
-	      itype = build_index_type (itype);
+		  if (size_varies)
+		    itype = variable_size (itype);
+		  itype = build_index_type (itype);
+		}
 	    }
 
 #if 0

gcc/tree.c

@@ -3676,33 +3676,18 @@ build_index_type (maxval)
      tree maxval;
 {
   register tree itype = make_node (INTEGER_TYPE);
-  int no_hash = 0;
 
   TREE_TYPE (itype) = sizetype;
   TYPE_PRECISION (itype) = TYPE_PRECISION (sizetype);
-
-  /* If sizetype is unsigned and the upper bound is negative, use a
-     lower bound of one and an upper bound of zero.  */
-  if (TREE_UNSIGNED (sizetype) && TREE_CODE (maxval) == INTEGER_CST
-      && tree_int_cst_sgn (maxval) < 0)
-    {
-      TYPE_MIN_VALUE (itype) = size_one_node;
-      TYPE_MAX_VALUE (itype) = size_zero_node;
-      no_hash = 1;
-    }
-  else
-    {
-      TYPE_MIN_VALUE (itype) = size_zero_node;
-      TYPE_MAX_VALUE (itype) = convert (sizetype, maxval);
-    }
-
+  TYPE_MIN_VALUE (itype) = size_zero_node;
+  TYPE_MAX_VALUE (itype) = convert (sizetype, maxval);
   TYPE_MODE (itype) = TYPE_MODE (sizetype);
   TYPE_SIZE (itype) = TYPE_SIZE (sizetype);
   TYPE_SIZE_UNIT (itype) = TYPE_SIZE_UNIT (sizetype);
   TYPE_ALIGN (itype) = TYPE_ALIGN (sizetype);
   TYPE_USER_ALIGN (itype) = TYPE_USER_ALIGN (sizetype);
 
-  if (!no_hash && host_integerp (maxval, 1))
+  if (host_integerp (maxval, 1))
     return type_hash_canon (tree_low_cst (maxval, 1), itype);
   else
     return itype;