RFR: 8331341: secondary_super_cache does not scale well: C1 and interpreter [v6]

[Vladimir Ivanov]

On Wed, 24 Jul 2024 16:14:47 GMT, Andrew Haley <aph at openjdk.org> wrote:

>>> I suspect that Klass::search_secondary_supers() won't be inlinined in such case.
>> 
>> That's true, but it's true of every other function in that file. Is it not deliberate?
>
> FYI, somewhat related: AArch64 GCC inlines `lookup_secondary_supers_table()` 237 times (it's only a few instructions.)
> x86-64 GCC, because it doesn't use a popcount intrinsic, decides that `lookup_secondary_supers_table()` is too big to be worth inlining in all but 3 cases. So the right thing happens, I think: where we can profit from fast lookups without bloating the runtime, we do.

> That's true, but it's true of every other function in that file. Is it not deliberate?

IMO the fact that `Klass::search_secondary_supers()` is used in `klass.hpp` makes a difference here. 

After thinking more about it, I did a small experiment [1] and observed a build failure on AArch64 [2]. 
I think we don't see any more failures simply because `klass.inline.hpp` is included pervasively.

What do you think about moving `Klass::is_subtype_of()` to `klass.inline.hpp`? 

[1]

diff --git a/test/hotspot/gtest/oops/test_klass.cpp b/test/hotspot/gtest/oops/test_klass.cpp
new file mode 100644
index 00000000000..326a70f1f54
--- /dev/null
+++ b/test/hotspot/gtest/oops/test_klass.cpp
@@ -0,0 +1,9 @@
+#include "precompiled.hpp"
+#include "oops/klass.hpp"
+#include "unittest.hpp"
+
+TEST_VM(Klass, is_subtype_of) {
+  Klass* k = vmClasses::Object_klass();
+  ASSERT_TRUE(k->is_subtype_of(k));
+}


[2] 

Undefined symbols for architecture arm64:
  "Klass::search_secondary_supers(Klass*) const", referenced from:
      Klass_is_subtype_of_vm_Test::TestBody() in test_klass.o

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/19989#discussion_r1690472489