Index: stor-layout.c
===================================================================
--- stor-layout.c	(revision 193837)
+++ stor-layout.c	(working copy)
@@ -2233,12 +2233,12 @@ layout_type (tree type)
 					      size_binop (MINUS_EXPR, ub, lb)));
 	      }
 
-	    /* If we arrived at a length of zero ignore any overflow
-	       that occurred as part of the calculation.  There exists
-	       an association of the plus one where that overflow would
-	       not happen.  */
+	    /* ??? We have no way to distinguish a null-sized array from an
+	       array spanning the whole sizetype range, so we arbitrarily
+	       decide that [0, -1] is the only valid representation.  */
 	    if (integer_zerop (length)
-		&& TREE_OVERFLOW (length))
+	        && TREE_OVERFLOW (length)
+		&& integer_zerop (lb))
 	      length = size_zero_node;
 
 	    TYPE_SIZE (type) = size_binop (MULT_EXPR, element_size,
Index: ada/gcc-interface/utils.c
===================================================================
--- ada/gcc-interface/utils.c	(revision 193837)
+++ ada/gcc-interface/utils.c	(working copy)
@@ -3024,59 +3024,67 @@ max_size (tree exp, bool max_p)
       return max_p ? size_one_node : size_zero_node;
 
     case tcc_unary:
+      if (code == NON_LVALUE_EXPR)
+	return max_size (TREE_OPERAND (exp, 0), max_p);
+ 
+      return fold_build1 (code, type,
+			  max_size (TREE_OPERAND (exp, 0),
+				    code == NEGATE_EXPR ? !max_p : max_p));
+
     case tcc_binary:
+      {
+	tree lhs = max_size (TREE_OPERAND (exp, 0), max_p);
+	tree rhs = max_size (TREE_OPERAND (exp, 1),
+			     code == MINUS_EXPR ? !max_p : max_p);
+
+	/* Special-case wanting the maximum value of a MIN_EXPR.
+	   In that case, if one side overflows, return the other.  */
+	if (max_p && code == MIN_EXPR)
+	  {
+	    if (TREE_CODE (rhs) == INTEGER_CST && TREE_OVERFLOW (rhs))
+	      return lhs;
+
+	    if (TREE_CODE (lhs) == INTEGER_CST && TREE_OVERFLOW (lhs))
+	      return rhs;
+	  }
+
+	/* Likewise, handle a MINUS_EXPR or PLUS_EXPR with the LHS
+	   overflowing and the RHS a variable.  */
+	if ((code == MINUS_EXPR || code == PLUS_EXPR)
+	    && TREE_CODE (lhs) == INTEGER_CST
+	    && TREE_OVERFLOW (lhs)
+	    && !TREE_CONSTANT (rhs))
+	  return lhs;
+
+	return size_binop (code, lhs, rhs);
+      }
+
     case tcc_expression:
       switch (TREE_CODE_LENGTH (code))
 	{
 	case 1:
 	  if (code == SAVE_EXPR)
 	    return exp;
-	  else if (code == NON_LVALUE_EXPR)
-	    return max_size (TREE_OPERAND (exp, 0), max_p);
-	  else
-	    return
-	      fold_build1 (code, type,
-			   max_size (TREE_OPERAND (exp, 0),
-				     code == NEGATE_EXPR ? !max_p : max_p));
+
+	  return fold_build1 (code, type,
+			      max_size (TREE_OPERAND (exp, 0), max_p));
 
 	case 2:
 	  if (code == COMPOUND_EXPR)
 	    return max_size (TREE_OPERAND (exp, 1), max_p);
 
-	  {
-	    tree lhs = max_size (TREE_OPERAND (exp, 0), max_p);
-	    tree rhs = max_size (TREE_OPERAND (exp, 1),
-				 code == MINUS_EXPR ? !max_p : max_p);
-
-	    /* Special-case wanting the maximum value of a MIN_EXPR.
-	       In that case, if one side overflows, return the other.
-	       sizetype is signed, but we know sizes are non-negative.
-	       Likewise, handle a MINUS_EXPR or PLUS_EXPR with the LHS
-	       overflowing and the RHS a variable.  */
-	    if (max_p
-		&& code == MIN_EXPR
-		&& TREE_CODE (rhs) == INTEGER_CST
-		&& TREE_OVERFLOW (rhs))
-	      return lhs;
-	    else if (max_p
-		     && code == MIN_EXPR
-		     && TREE_CODE (lhs) == INTEGER_CST
-		     && TREE_OVERFLOW (lhs))
-	      return rhs;
-	    else if ((code == MINUS_EXPR || code == PLUS_EXPR)
-		     && TREE_CODE (lhs) == INTEGER_CST
-		     && TREE_OVERFLOW (lhs)
-		     && !TREE_CONSTANT (rhs))
-	      return lhs;
-	    else
-	      return fold_build2 (code, type, lhs, rhs);
-	  }
+	  return fold_build2 (code, type,
+			      max_size (TREE_OPERAND (exp, 0), max_p),
+			      max_size (TREE_OPERAND (exp, 1), max_p));
 
 	case 3:
 	  if (code == COND_EXPR)
 	    return fold_build2 (max_p ? MAX_EXPR : MIN_EXPR, type,
 				max_size (TREE_OPERAND (exp, 1), max_p),
 				max_size (TREE_OPERAND (exp, 2), max_p));
+
+	default:
+	  break;
 	}
 
       /* Other tree classes cannot happen.  */
Index: ada/gcc-interface/decl.c
===================================================================
--- ada/gcc-interface/decl.c	(revision 193837)
+++ ada/gcc-interface/decl.c	(working copy)
@@ -1337,7 +1337,7 @@ gnat_to_gnu_entity (Entity_Id gnat_entit
 		  }
 
 		if (TREE_CODE (TYPE_SIZE_UNIT (gnu_alloc_type)) == INTEGER_CST
-		    && TREE_OVERFLOW (TYPE_SIZE_UNIT (gnu_alloc_type)))
+		    && !valid_constant_size_p (TYPE_SIZE_UNIT (gnu_alloc_type)))
 		  post_error ("?`Storage_Error` will be raised at run time!",
 			      gnat_entity);
 
@@ -4240,8 +4240,8 @@ gnat_to_gnu_entity (Entity_Id gnat_entit
 	       a function that returns that type.  This usage doesn't make
 	       sense anyway, so give an error here.  */
 	    if (TYPE_SIZE_UNIT (gnu_return_type)
-		&& TREE_CONSTANT (TYPE_SIZE_UNIT (gnu_return_type))
-		&& TREE_OVERFLOW (TYPE_SIZE_UNIT (gnu_return_type)))
+		&& TREE_CODE (TYPE_SIZE_UNIT (gnu_return_type)) == INTEGER_CST
+		&& !valid_constant_size_p (TYPE_SIZE_UNIT (gnu_return_type)))
 	      {
 		post_error ("cannot return type whose size overflows",
 			    gnat_entity);
@@ -5989,10 +5989,9 @@ elaborate_entity (Entity_Id gnat_entity)
 static bool
 allocatable_size_p (tree gnu_size, bool static_p)
 {
-  /* We can allocate a fixed size if it hasn't overflowed and can be handled
-     (efficiently) on the host.  */
+  /* We can allocate a fixed size if it is a valid for the middle-end.  */
   if (TREE_CODE (gnu_size) == INTEGER_CST)
-    return !TREE_OVERFLOW (gnu_size) && host_integerp (gnu_size, 1);
+    return valid_constant_size_p (gnu_size);
 
   /* We can allocate a variable size if this isn't a static allocation.  */
   else
@@ -7285,22 +7284,22 @@ annotate_value (tree gnu_size)
     case INTEGER_CST:
       if (TREE_OVERFLOW (gnu_size))
 	return No_Uint;
-
-      /* This may come from a conversion from some smaller type, so ensure
-	 this is in bitsizetype.  */
-      gnu_size = convert (bitsizetype, gnu_size);
-
-      /* For a negative value, build NEGATE_EXPR of the opposite.  Such values
-	 appear in expressions containing aligning patterns.  Note that, since
-	 sizetype is sign-extended but nonetheless unsigned, we don't directly
-	 use tree_int_cst_sgn.  */
-      if (TREE_INT_CST_HIGH (gnu_size) < 0)
+      else
 	{
-	  tree op_size = fold_build1 (NEGATE_EXPR, bitsizetype, gnu_size);
-	  return annotate_value (build1 (NEGATE_EXPR, bitsizetype, op_size));
-	}
+	  /* For negative values, build NEGATE_EXPR of the opposite.  Such
+	     values appear in expressions containing aligning patterns.  Note
+	     that, since sizetype is unsigned, we jump through some hoops.  */
+	  double_int signed_size
+	    = tree_to_double_int (gnu_size).sext (TYPE_PRECISION (sizetype));
+	  if (signed_size.is_negative ())
+	    {
+	      tree op_size = double_int_to_tree (sizetype, -signed_size);
+	      if (op_size != gnu_size)
+		return annotate_value (build1 (NEGATE_EXPR, sizetype, op_size));
+	    }
 
-      return UI_From_gnu (gnu_size);
+	  return UI_From_gnu (gnu_size);
+	}
 
     case COMPONENT_REF:
       /* The only case we handle here is a simple discriminant reference.  */
Index: ada/gcc-interface/utils2.c
===================================================================
--- ada/gcc-interface/utils2.c	(revision 193837)
+++ ada/gcc-interface/utils2.c	(working copy)
@@ -2286,7 +2286,7 @@ build_allocator (tree type, tree init, t
 					     init);
 
       /* If the size overflows, pass -1 so Storage_Error will be raised.  */
-      if (TREE_CODE (size) == INTEGER_CST && TREE_OVERFLOW (size))
+      if (TREE_CODE (size) == INTEGER_CST && !valid_constant_size_p (size))
 	size = size_int (-1);
 
       storage = build_call_alloc_dealloc (NULL_TREE, size, storage_type,
@@ -2345,7 +2345,7 @@ build_allocator (tree type, tree init, t
     }
 
   /* If the size overflows, pass -1 so Storage_Error will be raised.  */
-  if (TREE_CODE (size) == INTEGER_CST && TREE_OVERFLOW (size))
+  if (TREE_CODE (size) == INTEGER_CST && !valid_constant_size_p (size))
     size = size_int (-1);
 
   storage = convert (result_type,
Index: ada/gcc-interface/trans.c
===================================================================
--- ada/gcc-interface/trans.c	(revision 193837)
+++ ada/gcc-interface/trans.c	(working copy)
@@ -6115,7 +6115,7 @@ gnat_to_gnu (Node_Id gnat_node)
       /* If the type has a size that overflows, convert this into raise of
 	 Storage_Error: execution shouldn't have gotten here anyway.  */
       if (TREE_CODE (TYPE_SIZE_UNIT (TREE_TYPE (gnu_lhs))) == INTEGER_CST
-	   && TREE_OVERFLOW (TYPE_SIZE_UNIT (TREE_TYPE (gnu_lhs))))
+	   && !valid_constant_size_p (TYPE_SIZE_UNIT (TREE_TYPE (gnu_lhs))))
 	gnu_result = build_call_raise (SE_Object_Too_Large, gnat_node,
 				       N_Raise_Storage_Error);
       else if (Nkind (Expression (gnat_node)) == N_Function_Call)
Index: ada/gcc-interface/misc.c
===================================================================
--- ada/gcc-interface/misc.c	(revision 193837)
+++ ada/gcc-interface/misc.c	(working copy)
@@ -604,8 +604,8 @@ gnat_get_subrange_bounds (const_tree gnu
 bool
 default_pass_by_ref (tree gnu_type)
 {
-  /* We pass aggregates by reference if they are sufficiently large.  The
-     choice of constant here is somewhat arbitrary.  We also pass by
+  /* We pass aggregates by reference if they are sufficiently large for
+     their alignment.  The ratio is somewhat arbitrary.  We also pass by
      reference if the target machine would either pass or return by
      reference.  Strictly speaking, we need only check the return if this
      is an In Out parameter, but it's probably best to err on the side of
@@ -618,9 +618,9 @@ default_pass_by_ref (tree gnu_type)
     return true;
 
   if (AGGREGATE_TYPE_P (gnu_type)
-      && (!host_integerp (TYPE_SIZE (gnu_type), 1)
-	  || 0 < compare_tree_int (TYPE_SIZE (gnu_type),
-				   8 * TYPE_ALIGN (gnu_type))))
+      && (!valid_constant_size_p (TYPE_SIZE_UNIT (gnu_type))
+	  || 0 < compare_tree_int (TYPE_SIZE_UNIT (gnu_type),
+				   TYPE_ALIGN (gnu_type))))
     return true;
 
   return false;
@@ -639,8 +639,8 @@ must_pass_by_ref (tree gnu_type)
      not have such objects.  */
   return (TREE_CODE (gnu_type) == UNCONSTRAINED_ARRAY_TYPE
 	  || TYPE_IS_BY_REFERENCE_P (gnu_type)
-	  || (TYPE_SIZE (gnu_type)
-	      && TREE_CODE (TYPE_SIZE (gnu_type)) != INTEGER_CST));
+	  || (TYPE_SIZE_UNIT (gnu_type)
+	      && TREE_CODE (TYPE_SIZE_UNIT (gnu_type)) != INTEGER_CST));
 }
 
 /* This function is called by the front-end to enumerate all the supported