[9] RFR [XS] 8054492: Casting can result in redundant null checks in generated code

[Vladimir Kozlov]

On 10/22/14 2:29 AM, Paul Sandoz wrote:
> On Oct 22, 2014, at 10:54 AM, Roland Westrelin <roland.westrelin at oracle.com> wrote:
>>> Here is intrinsic implementation:
>>>
>>> http://cr.openjdk.java.net/~kvn/8054492/webrev.01/
>>
>> That looks good to me.
>>
> Same here.
>
> On Oct 22, 2014, at 2:02 AM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>> Paul, is it enough for you?
>>
>
> Yes, many thanks. I verified in a number of scenarios.
>
> With Class.cast intrinsified can we can replace uses of following method in j.l.i.MethodHandleImpl with Class.cast?

Intrinsic is not enough. That code was added because we do not inline Class.cast() for deep call stacks. C2 has inline 
depth limit 9. But we can workaround using next changes:

--- a/src/share/vm/opto/bytecodeInfo.cpp	Fri Aug 22 09:55:49 2014 -0700
+++ b/src/share/vm/opto/bytecodeInfo.cpp	Wed Oct 22 22:07:21 2014 -0700
@@ -161,6 +161,7 @@
    if ((freq >= InlineFrequencyRatio) ||
        (call_site_count >= InlineFrequencyCount) ||
        is_unboxing_method(callee_method, C) ||
+      (callee_method->intrinsic_id() == vmIntrinsics::_class_cast) ||
        is_init_with_ea(callee_method, caller_method, C)) {

      max_inline_size = C->freq_inline_size();
@@ -262,6 +263,11 @@
      return false;
    }

+  if (callee_method->intrinsic_id() == vmIntrinsics::_class_cast) {
+    // Inline Class.cast() method.
+    return false;
+  }
+
    if (callee_method->has_compiled_code() &&
        callee_method->instructions_size() > InlineSmallCode) {
      set_msg("already compiled into a big method");


Thanks,
Vladimir

>
>      @ForceInline
>      @SuppressWarnings("unchecked")
>      static <T,U> T castReference(Class<? extends T> t, U x) {
>          // inlined Class.cast because we can't ForceInline it
>          if (x != null && !t.isInstance(x))
>              throw newClassCastException(t, x);
>          return (T) x;
>      }
>
> Paul.
>