Do not indicate location with this on unsafe field access to work around potential compiler bug

There seems to be a Graal compiler bug, at least that's what a ZipPy commit indicates. And this change here also seems to fix the issues with the Bounce benchmark.

Signed-off-by: Stefan Marr <git@stefan-marr.de>

Author: smarr

src/som/interpreter/nodes/FieldAccessor.java

@@ -49,13 +49,15 @@ private static final class DirectStoreAccessor extends FieldAccessor {
 
     @Override
     public Object read(final SObject self) {
-      return CompilerDirectives.unsafeGetObject(self, fieldOffset, true, this);
+      //return CompilerDirectives.unsafeGetObject(self, fieldOffset, true, this);
+      return CompilerDirectives.unsafeGetObject(self, fieldOffset, true, null);
     }
 
 
     @Override
     public void write(final SObject self, final Object value) {
-      CompilerDirectives.unsafePutObject(self, fieldOffset, value, this);
+      // CompilerDirectives.unsafePutObject(self, fieldOffset, value, this);
+      CompilerDirectives.unsafePutObject(self, fieldOffset, value, null);
     }
   }
 }