[13] RFR (S): 8192001: C2: inlining through dispatching MH linkers ignores speculative type of the receiver
Vladimir Ivanov
vladimir.x.ivanov at oracle.com
Fri Jan 25 01:56:39 UTC 2019
http://cr.openjdk.java.net/~vlivanov/8192001/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8192001
When inlining through MethodHandle calls, C2 can improve inlining
decisions by taking speculative types into account (availability of type
information is addressed by JDK-8191998 [1]).
There's no profiling performed at method handle linker call sites
(MethodHandle::linkTo*), but type info can flow from other sources.
As an example, consider the following case:
class A { void m() { ... } }
class B extends A { void m() { ... } }
MH = LOOKUP.findVirtual(A.class, "m", ...);
void test(A o) throws Throwable {
MH.invokeExact(o);
}
test(new B());
Before (no inlining):
251 12 !b TestMH::test (21 bytes)
...
@ 16 TestMH1$A::m (1 bytes) virtual call
After (guarded inlining):
251 12 !b TestMH::test (21 bytes)
...
@ 16 TestMH1$B1::m (1 bytes) inline (hot)
\-> TypeProfile (-1/6701 counts) = TestMH1$B1
Testing: hs-precheckin-comp, hs-tier1, hs-tier2.
Best regards,
Vladimir Ivanov
[1] https://bugs.openjdk.java.net/browse/JDK-8192001
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