gigi.h (enum standard_datatypes): Add new values ADT_sbitsize_one_node and ADT_sbitsize_unit_node.

	* gcc-interface/gigi.h (enum standard_datatypes): Add new values
	ADT_sbitsize_one_node and ADT_sbitsize_unit_node.
	(sbitsize_one_node): New macro.
	(sbitsize_unit_node): Likewise.
	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Array_Subtype>: Fix
	latent bug in the computation of subrange_p.  Fold wider_p predicate.
	(cannot_be_superflat_p): Use an explicitly signed 64-bit type to do
	the final comparison.
	(make_aligning_type): Build real negation and use sizetype throughout
	the offset computation.
	(maybe_pad_type): Do not issue the warning when the new size expression
	is too complex.
	(annotate_value) <INTEGER_CST>: Simplify code handling negative values.
	* gcc-interface/misc.c (gnat_init): Initialize sbitsize_one_node and
	sbitsize_unit_node.
	* gcc-interface/trans.c (Attribute_to_gnu) <Attr_Pool_Address>: Fold
	double negation.
	(gnat_to_gnu) <N_Free_Statement>: Likewise.
	* gcc-interface/utils.c (convert): Use sbitsize_unit_node.
	* gcc-interface/utils2.c (compare_arrays): Compute real lengths and use
	constants in sizetype.  Remove dead code and tweak comments.  Generate
	equality instead of inequality comparisons for zero length tests.

From-SVN: r158461

7 files changed, 105 insertions, 101 deletions

diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index 2612635..21800d8 100644
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,28 @@
+2010-04-17  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* gcc-interface/gigi.h (enum standard_datatypes): Add new values
+	ADT_sbitsize_one_node and ADT_sbitsize_unit_node.
+	(sbitsize_one_node): New macro.
+	(sbitsize_unit_node): Likewise.
+	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Array_Subtype>: Fix
+	latent bug in the computation of subrange_p.  Fold wider_p predicate.
+	(cannot_be_superflat_p): Use an explicitly signed 64-bit type to do
+	the final comparison.
+	(make_aligning_type): Build real negation and use sizetype throughout
+	the offset computation.
+	(maybe_pad_type): Do not issue the warning when the new size expression
+	is too complex.
+	(annotate_value) <INTEGER_CST>: Simplify code handling negative values.
+	* gcc-interface/misc.c (gnat_init): Initialize sbitsize_one_node and
+	sbitsize_unit_node.
+	* gcc-interface/trans.c (Attribute_to_gnu) <Attr_Pool_Address>: Fold
+	double negation.
+	(gnat_to_gnu) <N_Free_Statement>: Likewise.
+	* gcc-interface/utils.c (convert): Use sbitsize_unit_node.
+	* gcc-interface/utils2.c (compare_arrays): Compute real lengths and use
+	constants in sizetype.  Remove dead code and tweak comments.  Generate
+	equality instead of inequality comparisons for zero length tests.
+
 2010-04-16  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gcc-interface/gigi.h (gnat_init_decl_processing): Delete.
diff --git a/gcc/ada/gcc-interface/decl.c b/gcc/ada/gcc-interface/decl.c
index 02d7296..b7fd331 100644
--- a/gcc/ada/gcc-interface/decl.c
+++ b/gcc/ada/gcc-interface/decl.c
@@ -2115,11 +2115,12 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, int definition)
 	      const int prec_comp
 		= compare_tree_int (TYPE_RM_SIZE (gnu_index_type),
 				    TYPE_PRECISION (sizetype));
-	      const bool subrange_p = (prec_comp < 0)
-				      || (prec_comp == 0
-					  && TYPE_UNSIGNED (gnu_index_type)
-					     == TYPE_UNSIGNED (sizetype));
-	      const bool wider_p = (prec_comp > 0);
+	      const bool subrange_p = (prec_comp < 0
+				       && (TYPE_UNSIGNED (gnu_index_type)
+					   || !TYPE_UNSIGNED (sizetype)))
+ 				      || (prec_comp == 0
+ 					  && TYPE_UNSIGNED (gnu_index_type)
+ 					     == TYPE_UNSIGNED (sizetype));
 	      tree gnu_orig_min = TYPE_MIN_VALUE (gnu_index_type);
 	      tree gnu_orig_max = TYPE_MAX_VALUE (gnu_index_type);
 	      tree gnu_min = convert (sizetype, gnu_orig_min);
@@ -2298,7 +2299,7 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, int definition)
 		      && TREE_CODE (TREE_TYPE (gnu_index_type))
 			 != INTEGER_TYPE)
 		  || TYPE_BIASED_REPRESENTATION_P (gnu_index_type)
-		  || wider_p)
+		  || prec_comp > 0)
 		need_index_type_struct = true;
 	    }
 
@@ -5381,7 +5382,7 @@ cannot_be_superflat_p (Node_Id gnat_range)
 {
   Node_Id gnat_lb = Low_Bound (gnat_range), gnat_hb = High_Bound (gnat_range);
   Node_Id scalar_range;
-  tree gnu_lb, gnu_hb;
+  tree gnu_lb, gnu_hb, gnu_lb_minus_one;
 
   /* If the low bound is not constant, try to find an upper bound.  */
   while (Nkind (gnat_lb) != N_Integer_Literal
@@ -5401,19 +5402,23 @@ cannot_be_superflat_p (Node_Id gnat_range)
 	     || Nkind (scalar_range) == N_Range))
     gnat_hb = Low_Bound (scalar_range);
 
-  if (!(Nkind (gnat_lb) == N_Integer_Literal
-	&& Nkind (gnat_hb) == N_Integer_Literal))
+  /* If we have failed to find constant bounds, punt.  */
+  if (Nkind (gnat_lb) != N_Integer_Literal
+      || Nkind (gnat_hb) != N_Integer_Literal)
     return false;
 
-  gnu_lb = UI_To_gnu (Intval (gnat_lb), bitsizetype);
-  gnu_hb = UI_To_gnu (Intval (gnat_hb), bitsizetype);
+  /* We need at least a signed 64-bit type to catch most cases.  */
+  gnu_lb = UI_To_gnu (Intval (gnat_lb), sbitsizetype);
+  gnu_hb = UI_To_gnu (Intval (gnat_hb), sbitsizetype);
+  if (TREE_OVERFLOW (gnu_lb) || TREE_OVERFLOW (gnu_hb))
+    return false;
 
   /* If the low bound is the smallest integer, nothing can be smaller.  */
-  gnu_lb = size_binop (MINUS_EXPR, gnu_lb, bitsize_one_node);
-  if (TREE_OVERFLOW (gnu_lb))
+  gnu_lb_minus_one = size_binop (MINUS_EXPR, gnu_lb, sbitsize_one_node);
+  if (TREE_OVERFLOW (gnu_lb_minus_one))
     return true;
 
-  return (tree_int_cst_lt (gnu_hb, gnu_lb) == 0);
+  return !tree_int_cst_lt (gnu_hb, gnu_lb_minus_one);
 }
 
 /* Return true if GNU_EXPR is (essentially) the address of a CONSTRUCTOR.  */
@@ -5876,7 +5881,6 @@ make_aligning_type (tree type, unsigned int align, tree size,
   /* We will be crafting a record type with one field at a position set to be
      the next multiple of ALIGN past record'address + room bytes.  We use a
      record placeholder to express record'address.  */
-
   tree record_type = make_node (RECORD_TYPE);
   tree record = build0 (PLACEHOLDER_EXPR, record_type);
 
@@ -5896,7 +5900,6 @@ make_aligning_type (tree type, unsigned int align, tree size,
 
      Every length is in sizetype bytes there, except "pos" which has to be
      set as a bit position in the GCC tree for the record.  */
-
   tree room_st = size_int (room);
   tree vblock_addr_st = size_binop (PLUS_EXPR, record_addr_st, room_st);
   tree voffset_st, pos, field;
@@ -5911,13 +5914,11 @@ make_aligning_type (tree type, unsigned int align, tree size,
   /* Compute VOFFSET and then POS.  The next byte position multiple of some
      alignment after some address is obtained by "and"ing the alignment minus
      1 with the two's complement of the address.   */
-
   voffset_st = size_binop (BIT_AND_EXPR,
-			   size_diffop (size_zero_node, vblock_addr_st),
-			   ssize_int ((align / BITS_PER_UNIT) - 1));
+			   fold_build1 (NEGATE_EXPR, sizetype, vblock_addr_st),
+			   size_int ((align / BITS_PER_UNIT) - 1));
 
   /* POS = (ROOM + VOFFSET) * BIT_PER_UNIT, in bitsizetype.  */
-
   pos = size_binop (MULT_EXPR,
 		    convert (bitsizetype,
 			     size_binop (PLUS_EXPR, room_st, voffset_st)),
@@ -5936,7 +5937,6 @@ make_aligning_type (tree type, unsigned int align, tree size,
      consequences on the alignment computation, and create_field_decl would
      make one without this special argument, for instance because of the
      complex position expression.  */
-
   field = create_field_decl (get_identifier ("F"), type, record_type,
                              1, size, pos, -1);
   TYPE_FIELDS (record_type) = field;
@@ -6287,6 +6287,7 @@ maybe_pad_type (tree type, tree size, unsigned int align,
   if (Present (gnat_entity)
       && size
       && TREE_CODE (size) != MAX_EXPR
+      && TREE_CODE (size) != COND_EXPR
       && !operand_equal_p (size, orig_size, 0)
       && !(TREE_CODE (size) == INTEGER_CST
 	   && TREE_CODE (orig_size) == INTEGER_CST
@@ -7123,33 +7124,16 @@ annotate_value (tree gnu_size)
       if (TREE_OVERFLOW (gnu_size))
 	return No_Uint;
 
-      /* This may have come from a conversion from some smaller type,
-	 so ensure this is in bitsizetype.  */
+      /* This may come from a conversion from some smaller type, so ensure
+	 this is in bitsizetype.  */
       gnu_size = convert (bitsizetype, gnu_size);
 
-      /* For negative values, use NEGATE_EXPR of the supplied value.  */
+      /* For a negative value, use NEGATE_EXPR of the opposite.  Such values
+	 appear in expressions containing aligning patterns.  */
       if (tree_int_cst_sgn (gnu_size) < 0)
 	{
-	  /* The ridiculous code below is to handle the case of the largest
-	     negative integer.  */
-	  tree negative_size = size_diffop (bitsize_zero_node, gnu_size);
-	  bool adjust = false;
-	  tree temp;
-
-	  if (TREE_OVERFLOW (negative_size))
-	    {
-	      negative_size
-		= size_binop (MINUS_EXPR, bitsize_zero_node,
-			      size_binop (PLUS_EXPR, gnu_size,
-					  bitsize_one_node));
-	      adjust = true;
-	    }
-
-	  temp = build1 (NEGATE_EXPR, bitsizetype, negative_size);
-	  if (adjust)
-	    temp = build2 (MINUS_EXPR, bitsizetype, temp, bitsize_one_node);
-
-	  return annotate_value (temp);
+	  tree op_size = fold_build1 (NEGATE_EXPR, bitsizetype, gnu_size);
+	  return annotate_value (build1 (NEGATE_EXPR, bitsizetype, op_size));
 	}
 
       return UI_From_gnu (gnu_size);
diff --git a/gcc/ada/gcc-interface/gigi.h b/gcc/ada/gcc-interface/gigi.h
index 61baf34..224abe8 100644
--- a/gcc/ada/gcc-interface/gigi.h
+++ b/gcc/ada/gcc-interface/gigi.h
@@ -356,9 +356,15 @@ enum standard_datatypes
   /* Type declaration node  <==> typedef virtual void *T() */
   ADT_fdesc_type,
 
-  /* Null pointer for above type */
+  /* Null pointer for above type.  */
   ADT_null_fdesc,
 
+  /* Value 1 in signed bitsizetype.  */
+  ADT_sbitsize_one_node,
+
+  /* Value BITS_PER_UNIT in signed bitsizetype.  */
+  ADT_sbitsize_unit_node,
+
   /* Function declaration nodes for run-time functions for allocating memory.
      Ada allocators cause calls to these functions to be generated.  Malloc32
      is used only on 64bit systems needing to allocate 32bit memory.  */
@@ -401,6 +407,8 @@ extern GTY(()) tree gnat_raise_decls[(int) LAST_REASON_CODE + 1];
 #define ptr_void_ftype gnat_std_decls[(int) ADT_ptr_void_ftype]
 #define fdesc_type_node gnat_std_decls[(int) ADT_fdesc_type]
 #define null_fdesc_node gnat_std_decls[(int) ADT_null_fdesc]
+#define sbitsize_one_node gnat_std_decls[(int) ADT_sbitsize_one_node]
+#define sbitsize_unit_node gnat_std_decls[(int) ADT_sbitsize_unit_node]
 #define malloc_decl gnat_std_decls[(int) ADT_malloc_decl]
 #define malloc32_decl gnat_std_decls[(int) ADT_malloc32_decl]
 #define free_decl gnat_std_decls[(int) ADT_free_decl]
diff --git a/gcc/ada/gcc-interface/misc.c b/gcc/ada/gcc-interface/misc.c
index 1b31890..52fe65a 100644
--- a/gcc/ada/gcc-interface/misc.c
+++ b/gcc/ada/gcc-interface/misc.c
@@ -407,6 +407,8 @@ gnat_init (void)
   SET_TYPE_RM_SIZE (boolean_type_node, bitsize_int (1));
 
   build_common_tree_nodes_2 (0);
+  sbitsize_one_node = sbitsize_int (1);
+  sbitsize_unit_node = sbitsize_int (BITS_PER_UNIT);
   boolean_true_node = TYPE_MAX_VALUE (boolean_type_node);
 
   ptr_void_type_node = build_pointer_type (void_type_node);
diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
index 7f35bc2..4b7946c 100644
--- a/gcc/ada/gcc-interface/trans.c
+++ b/gcc/ada/gcc-interface/trans.c
@@ -1356,15 +1356,9 @@ Attribute_to_gnu (Node_Id gnat_node, tree *gnu_result_type_p, int attribute)
 	  {
 	    tree gnu_char_ptr_type = build_pointer_type (char_type_node);
 	    tree gnu_pos = byte_position (TYPE_FIELDS (gnu_obj_type));
-	    tree gnu_byte_offset
-	      = convert (sizetype,
-			 size_diffop (size_zero_node, gnu_pos));
-	    gnu_byte_offset
-	      = fold_build1 (NEGATE_EXPR, sizetype, gnu_byte_offset);
-
 	    gnu_ptr = convert (gnu_char_ptr_type, gnu_ptr);
 	    gnu_ptr = build_binary_op (POINTER_PLUS_EXPR, gnu_char_ptr_type,
-				       gnu_ptr, gnu_byte_offset);
+				       gnu_ptr, gnu_pos);
 	  }
 
 	gnu_result = convert (gnu_result_type, gnu_ptr);
@@ -5399,15 +5393,9 @@ gnat_to_gnu (Node_Id gnat_node)
 	    {
 	      tree gnu_char_ptr_type = build_pointer_type (char_type_node);
 	      tree gnu_pos = byte_position (TYPE_FIELDS (gnu_obj_type));
-	      tree gnu_byte_offset
-		= convert (sizetype,
-			   size_diffop (size_zero_node, gnu_pos));
-	      gnu_byte_offset
-		= fold_build1 (NEGATE_EXPR, sizetype, gnu_byte_offset);
-
 	      gnu_ptr = convert (gnu_char_ptr_type, gnu_ptr);
 	      gnu_ptr = build_binary_op (POINTER_PLUS_EXPR, gnu_char_ptr_type,
-					 gnu_ptr, gnu_byte_offset);
+					 gnu_ptr, gnu_pos);
 	    }
 
 	  gnu_result
diff --git a/gcc/ada/gcc-interface/utils.c b/gcc/ada/gcc-interface/utils.c
index e110ef5..668226b 100644
--- a/gcc/ada/gcc-interface/utils.c
+++ b/gcc/ada/gcc-interface/utils.c
@@ -4066,9 +4066,8 @@ convert (tree type, tree expr)
 	  tree bit_diff
 	    = size_diffop (bit_position (TYPE_FIELDS (TREE_TYPE (etype))),
 			   bit_position (TYPE_FIELDS (TREE_TYPE (type))));
-	  tree byte_diff = size_binop (CEIL_DIV_EXPR, bit_diff,
-				       sbitsize_int (BITS_PER_UNIT));
-
+	  tree byte_diff
+	    = size_binop (CEIL_DIV_EXPR, bit_diff, sbitsize_unit_node);
 	  expr = build1 (NOP_EXPR, type, expr);
 	  TREE_CONSTANT (expr) = TREE_CONSTANT (TREE_OPERAND (expr, 0));
 	  if (integer_zerop (byte_diff))
diff --git a/gcc/ada/gcc-interface/utils2.c b/gcc/ada/gcc-interface/utils2.c
index 33f3a61..ca35cc7 100644
--- a/gcc/ada/gcc-interface/utils2.c
+++ b/gcc/ada/gcc-interface/utils2.c
@@ -260,28 +260,27 @@ compare_arrays (tree result_type, tree a1, tree a2)
     a2 = gnat_protect_expr (a2);
 
   /* Process each dimension separately and compare the lengths.  If any
-     dimension has a size known to be zero, set SIZE_ZERO_P to 1 to
-     suppress the comparison of the data.  */
+     dimension has a length known to be zero, set LENGTH_ZERO_P to true
+     in order to suppress the comparison of the data at the end.  */
   while (TREE_CODE (t1) == ARRAY_TYPE && TREE_CODE (t2) == ARRAY_TYPE)
     {
       tree lb1 = TYPE_MIN_VALUE (TYPE_DOMAIN (t1));
       tree ub1 = TYPE_MAX_VALUE (TYPE_DOMAIN (t1));
       tree lb2 = TYPE_MIN_VALUE (TYPE_DOMAIN (t2));
       tree ub2 = TYPE_MAX_VALUE (TYPE_DOMAIN (t2));
-      tree bt = get_base_type (TREE_TYPE (lb1));
-      tree length1 = fold_build2 (MINUS_EXPR, bt, ub1, lb1);
-      tree length2 = fold_build2 (MINUS_EXPR, bt, ub2, lb2);
+      tree length1 = size_binop (PLUS_EXPR, size_binop (MINUS_EXPR, ub1, lb1),
+				 size_one_node);
+      tree length2 = size_binop (PLUS_EXPR, size_binop (MINUS_EXPR, ub2, lb2),
+				 size_one_node);
       tree comparison, this_a1_is_null, this_a2_is_null;
-      tree nbt, tem;
-      bool btem;
 
       /* If the length of the first array is a constant, swap our operands
-	 unless the length of the second array is the constant zero.
-	 Note that we have set the `length' values to the length - 1.  */
-      if (TREE_CODE (length1) == INTEGER_CST
-	  && !integer_zerop (fold_build2 (PLUS_EXPR, bt, length2,
-					  convert (bt, integer_one_node))))
+	 unless the length of the second array is the constant zero.  */
+      if (TREE_CODE (length1) == INTEGER_CST && !integer_zerop (length2))
 	{
+	  tree tem;
+	  bool btem;
+
 	  tem = a1, a1 = a2, a2 = tem;
 	  tem = t1, t1 = t2, t2 = tem;
 	  tem = lb1, lb1 = lb2, lb2 = tem;
@@ -292,57 +291,56 @@ compare_arrays (tree result_type, tree a1, tree a2)
 	  a2_side_effects_p = btem;
 	}
 
-      /* If the length of this dimension in the second array is the constant
-	 zero, we can just go inside the original bounds for the first
-	 array and see if last < first.  */
-      if (integer_zerop (fold_build2 (PLUS_EXPR, bt, length2,
-				      convert (bt, integer_one_node))))
+      /* If the length of the second array is the constant zero, we can just
+	 use the original stored bounds for the first array and see whether
+	 last < first holds.  */
+      if (integer_zerop (length2))
 	{
-	  tree ub = TYPE_MAX_VALUE (TYPE_INDEX_TYPE (TYPE_DOMAIN (t1)));
-	  tree lb = TYPE_MIN_VALUE (TYPE_INDEX_TYPE (TYPE_DOMAIN (t1)));
+	  length_zero_p = true;
 
-	  comparison = build_binary_op (LT_EXPR, result_type, ub, lb);
+	  ub1 = TYPE_MAX_VALUE (TYPE_INDEX_TYPE (TYPE_DOMAIN (t1)));
+	  lb1 = TYPE_MIN_VALUE (TYPE_INDEX_TYPE (TYPE_DOMAIN (t1)));
+
+	  comparison = build_binary_op (LT_EXPR, result_type, ub1, lb1);
 	  comparison = SUBSTITUTE_PLACEHOLDER_IN_EXPR (comparison, a1);
 	  if (EXPR_P (comparison))
 	    SET_EXPR_LOCATION (comparison, input_location);
 
-	  length1 = SUBSTITUTE_PLACEHOLDER_IN_EXPR (length1, a1);
-
-	  length_zero_p = true;
 	  this_a1_is_null = comparison;
 	  this_a2_is_null = convert (result_type, boolean_true_node);
 	}
 
-      /* If the length is some other constant value, we know that the
-	 this dimension in the first array cannot be superflat, so we
-	 can just use its length from the actual stored bounds.  */
+      /* Otherwise, if the length is some other constant value, we know that
+	 this dimension in the second array cannot be superflat, so we can
+	 just use its length computed from the actual stored bounds.  */
       else if (TREE_CODE (length2) == INTEGER_CST)
 	{
+	  tree bt;
+
 	  ub1 = TYPE_MAX_VALUE (TYPE_INDEX_TYPE (TYPE_DOMAIN (t1)));
 	  lb1 = TYPE_MIN_VALUE (TYPE_INDEX_TYPE (TYPE_DOMAIN (t1)));
 	  /* Note that we know that UB2 and LB2 are constant and hence
 	     cannot contain a PLACEHOLDER_EXPR.  */
 	  ub2 = TYPE_MAX_VALUE (TYPE_INDEX_TYPE (TYPE_DOMAIN (t2)));
 	  lb2 = TYPE_MIN_VALUE (TYPE_INDEX_TYPE (TYPE_DOMAIN (t2)));
-	  nbt = get_base_type (TREE_TYPE (ub1));
+	  bt = get_base_type (TREE_TYPE (ub1));
 
 	  comparison
 	    = build_binary_op (EQ_EXPR, result_type,
-			       build_binary_op (MINUS_EXPR, nbt, ub1, lb1),
-			       build_binary_op (MINUS_EXPR, nbt, ub2, lb2));
+			       build_binary_op (MINUS_EXPR, bt, ub1, lb1),
+			       build_binary_op (MINUS_EXPR, bt, ub2, lb2));
 	  comparison = SUBSTITUTE_PLACEHOLDER_IN_EXPR (comparison, a1);
 	  if (EXPR_P (comparison))
 	    SET_EXPR_LOCATION (comparison, input_location);
 
-	  length1 = SUBSTITUTE_PLACEHOLDER_IN_EXPR (length1, a1);
-
 	  this_a1_is_null = build_binary_op (LT_EXPR, result_type, ub1, lb1);
 	  if (EXPR_P (this_a1_is_null))
 	    SET_EXPR_LOCATION (this_a1_is_null, input_location);
+
 	  this_a2_is_null = convert (result_type, boolean_false_node);
 	}
 
-      /* Otherwise compare the computed lengths.  */
+      /* Otherwise, compare the computed lengths.  */
       else
 	{
 	  length1 = SUBSTITUTE_PLACEHOLDER_IN_EXPR (length1, a1);
@@ -353,24 +351,24 @@ compare_arrays (tree result_type, tree a1, tree a2)
 	  if (EXPR_P (comparison))
 	    SET_EXPR_LOCATION (comparison, input_location);
 
-	  this_a1_is_null
-	    = build_binary_op (LT_EXPR, result_type, length1,
-			       convert (bt, integer_zero_node));
+	  this_a1_is_null = build_binary_op (EQ_EXPR, result_type, length1,
+					     size_zero_node);
 	  if (EXPR_P (this_a1_is_null))
 	    SET_EXPR_LOCATION (this_a1_is_null, input_location);
 
-	  this_a2_is_null
-	    = build_binary_op (LT_EXPR, result_type, length2,
-			       convert (bt, integer_zero_node));
+	  this_a2_is_null = build_binary_op (EQ_EXPR, result_type, length2,
+					     size_zero_node);
 	  if (EXPR_P (this_a2_is_null))
 	    SET_EXPR_LOCATION (this_a2_is_null, input_location);
 	}
 
+      /* Append expressions for this dimension to the final expressions.  */
       result = build_binary_op (TRUTH_ANDIF_EXPR, result_type,
 				result, comparison);
 
       a1_is_null = build_binary_op (TRUTH_ORIF_EXPR, result_type,
 				    this_a1_is_null, a1_is_null);
+
       a2_is_null = build_binary_op (TRUTH_ORIF_EXPR, result_type,
 				    this_a2_is_null, a2_is_null);
 
@@ -378,7 +376,7 @@ compare_arrays (tree result_type, tree a1, tree a2)
       t2 = TREE_TYPE (t2);
     }
 
-  /* Unless the size of some bound is known to be zero, compare the
+  /* Unless the length of some dimension is known to be zero, compare the
      data in the array.  */
   if (!length_zero_p)
     {