_Jv_LookupInterfaceMethod

[Per Bothner]

Bryce McKinlay <bryce@albatross.co.nz> writes:

> I have mostly implemented (in the runtime) Per Bothner's constant-time
> dispatch and type checking algorithms, but it really needs this change
> to tie it all together. If someone do it (or give me explicit
> instructions on how ;-), then we'll get a *huge* performance increase on
> interface invocations.

Great.  While these are not "explicit instructions", these may be enough
to point you in the right direction.

First, in decl.c do:

Index: decl.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/java/decl.c,v
retrieving revision 1.41
diff -u -r1.41 decl.c
--- decl.c	1999/10/26 08:34:46	1.41
+++ decl.c	1999/12/01 18:53:00
@@ -766,7 +766,7 @@
 			0, NOT_BUILT_IN, NULL_PTR);
   t = tree_cons (NULL_TREE, ptr_type_node,
 		 tree_cons (NULL_TREE, ptr_type_node,
-			    tree_cons (NULL_TREE, ptr_type_node, endlink)));
+			    tree_cons (NULL_TREE, int_type_node, endlink)));
   soft_lookupinterfacemethod_node 
     = builtin_function ("_Jv_LookupInterfaceMethod",
 			build_function_type (ptr_type_node, t),

This changes the "prototype" of _Jv_LookupInterfaceMethod, as
seen by the compiler.

Then you need to change the code that generates the actual call.
This is build_invokeinterface in expr.c.  This is where the argument
list is constructed (right-to-left):
  lookup_arg = build_tree_list (NULL_TREE, 
                                (build_utf8_ref 
                                 (unmangle_classname
                                  (IDENTIFIER_POINTER(method_signature),
                                   IDENTIFIER_LENGTH(method_signature)))));
  lookup_arg = tree_cons (NULL_TREE, dtable,
                          tree_cons (NULL_TREE, build_utf8_ref (method_name),
                                     lookup_arg));

You can replace this by:
  lookup_arg = tree_cons (NULL_TREE, dtable,
                          tree_cons (NULL_TREE, IFACE,
                                     build_tree_list (NULL_TREE, IDX)));

Here IFACE and IDX are tree-nodes that evaluate to the iface and method_idx
parameters.  And here is where the next problem comes in:  Neither are
available in build_invokeinterface, so you have to change the parameter
list and *its* callers (in expr.c and parse.y).  Instead of passing
the method name, I suggest passing the value of `method' (in both
callers).  I *think* (i.e. I'm rusty and haven't tried it), then
back in build_invokeinterface you just replace IFACE by DECL_TYPE (method).

Figuring IDX is a litte trickier.  Since I don't know your implementation
in depth, I don't know the current value.  I'm guessing it's the index
in IFACE of the interface method we a trying to call.  I think you
need to loop through TYPE_METHODS (IFACE):

  tree meth;  int i = 0;
  for (meth = TYPE_METHODS (clas);  ;  meth = TREE_CHAIN (meth), i++)
    {
      if (meth == method)
        {
           IDX = build_int_2 (i, 0);
           break;
        }
      if (meth == NULL_TREE)
         fatal ("internal error");
    }

-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/~per/