RE: [PATCH] Fix PR45878

["Nicola Pero" <nicola dot pero at meta-innovation dot com>]

Thanks Richard

it looks great. :-)

Btw, I looked at this bug for a while tonight, and I ended up with a question ... maybe you know the answer or can hint at it ... why are we using OBJ_TYPE_REFs in Objective-C ?

As far as I can see, OBJ_TYPE_REFs are normally used to represent C++ virtual method lookups.  The comment says that they represent "lookup in a virtual method table which is dependent on the runtime type of an object".

Objective-C method lookups/invocations seem considerably different - first of all, the result of any lookup is basically volatile and can change at any time [eg, it is valid for another thread to concurrently modify the "virtual method tables"], and second, the NeXT runtime doesn't even have a separate "lookup in a virtual method table" step - a single function call does everything (both lookup and invocation).

Do you know what is the advantage or reason for using OBJ_TYPE_REFs for Objective-C method lookups as opposed to doing them via standard C casts and function calls ?

It would be good to document the reason (if any) clearly. :-)

Thanks

-----Original Message-----
From: "Richard Guenther" <rguenther@suse.de>
Sent: Wednesday, 13 October, 2010 22:26
To: gcc-patches@gcc.gnu.org
Subject: [PATCH] Fix PR45878


This fixes another piece of that PR.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.

Richard.

2010-10-13  Richard Guenther  <rguenther@suse.de>

	PR objc/45878
	* gimple-fold.c (gimple_fold_obj_type_ref): Leave OBJ_TYPE_REFs
	alone if there are no virtual methods.

	* objc.dg/pr45878.m: New testcase.

Index: gcc/gimple-fold.c
===================================================================
*** gcc/gimple-fold.c	(revision 165430)
--- gcc/gimple-fold.c	(working copy)
*************** gimple_fold_obj_type_ref (tree ref, tree
*** 1524,1532 ****
    if (binfo)
      {
        HOST_WIDE_INT token = tree_low_cst (OBJ_TYPE_REF_TOKEN (ref), 1);
!       /* If there is no virtual methods fold this to an indirect call.  */
        if (!BINFO_VIRTUALS (binfo))
! 	return OBJ_TYPE_REF_EXPR (ref);
        return gimple_fold_obj_type_ref_known_binfo (token, binfo);
      }
    else
--- 1524,1532 ----
    if (binfo)
      {
        HOST_WIDE_INT token = tree_low_cst (OBJ_TYPE_REF_TOKEN (ref), 1);
!       /* If there is no virtual methods leave the OBJ_TYPE_REF alone.  */
        if (!BINFO_VIRTUALS (binfo))
! 	return NULL_TREE;
        return gimple_fold_obj_type_ref_known_binfo (token, binfo);
      }
    else
Index: gcc/testsuite/objc.dg/pr45878.m
===================================================================
*** gcc/testsuite/objc.dg/pr45878.m	(revision 0)
--- gcc/testsuite/objc.dg/pr45878.m	(revision 0)
***************
*** 0 ****
--- 1,28 ----
+ /* { dg-do compile } */
+ /* { dg-options "-O2 -fexceptions" } */
+ 
+ typedef struct objc_object { Class class_pointer; } *id;
+ typedef unsigned char  BOOL;
+ 
+ @interface Object
+ {
+   Class isa;
+ }
+ - (BOOL)isEqual:anObject;
+ @end
+ 
+ @interface NXConstantString: Object
+ {
+   char *c_string;
+   unsigned int len;
+ }
+ @end
+ 
+ void function (void)
+ {
+   if ([@"strings" isEqual: (id)0])
+     {
+       ;
+     }
+ }
+