RFR (L) 8154580: Save mirror in interpreter frame to enable cleanups of CLDClosure

[Christian Thalinger]

> On Apr 19, 2016, at 9:50 AM, Coleen Phillimore <coleen.phillimore at oracle.com> wrote:
> 
> Summary: GC walks the mirror using OopClosure rather than using CLDClosure in oops_interpreted_do()
> 
> See bug for more description and justification.  The changes are large but very redundant.  The main change is in TemplateInterpreterGenerator::generate_fixed_frame().

+  // Save oop Mirror (with padding)
+  __ load_mirror(rscratch1, rmethod);

+  // get mirror and store it in the frame so that this Method* is never
+  // reclaimed while it's running.
+  Register mirror = LcpoolCache;
+  __ load_mirror(mirror, Method);

+  // Push the mirror so this method isn't collected
+  __ load_mirror(rdx, rbi);

Please use the same comment on all platforms.

> 
> open webrev at http://cr.openjdk.java.net/~coleenp/8154580.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8154580

src/share/vm/runtime/frame.cpp

     // The method pointer in the frame might be the only path to the method's
     // klass, and the klass needs to be kept alive while executing. The GCs
     // don't trace through method pointers, so typically in similar situations
     // the mirror or the class loader of the klass are installed as a GC root.

-    // To minimize the overhead of doing that here, we ask the GC to pass down a
-    // closure that knows how to keep klasses alive given a ClassLoaderData.
-    cld_f->do_cld(m->method_holder()->class_loader_data());
-  }
-
-  if (m->is_native() PPC32_ONLY(&& m->is_static())) {
-    f->do_oop(interpreter_frame_temp_oop_addr());
-  }
+  // And it is here too.
+  f->do_oop(interpreter_frame_mirror_addr());

That comment is kinda funny now.  It still hints at the old-way of doing things but “it is here too”.

> 
> Tested with hotspot-runtime-nightly and gc-nightly tests.
> 
> Need testing with ppc and aarch64 open code.  I implemented the changes but I can't test them.

One obvious bug is that you copied the __ as well:

+void MacroAssembler::load_mirror(Register dst, Register method) {
+  const int mirror_offset = in_bytes(Klass::java_mirror_offset());
+  __ ldr(dst, Address(rmethod, Method::const_offset()));
+  __ ldr(dst, Address(dst, ConstMethod::constants_offset()));
+  __ ldr(dst, Address(dst, ConstantPool::pool_holder_offset_in_bytes()));
+  __ ldr(dst, Address(dst, mirror_offset));
+}

Other than that it looks fine to me.  Nothing obvious stood out.

> 
> Thanks,
> Coleen