RFR (S) 8135033: C1 should fast-path Object.class.isInstance(obj) to true

[Aleksey Shipilev]

Hi,

Continuing on VarHandles saga, more C1 quirks show up. Let's fix a
simple one: Object.class.isInstance(obj) should fold to "true". C2
handles this well, but not C1 (this is further exacerbated when tiered
policy decides Class.cast-holding method is trivial):
  https://bugs.openjdk.java.net/browse/JDK-8135033

Patch:
  http://cr.openjdk.java.net/~shade/8135033/webrev.00/

Testing:
  * JPRT
  * Targeted microbenchmarks, eyeballing assembly

Thanks,
-Aleksey

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