RFR(S) : 8029381 : assert(is_method_type()) failed: bad cast

[David Chase]

bug: https://bugs.openjdk.java.net/browse/JDK-8029381
webrev: http://cr.openjdk.java.net/~drchase/8029381/webrev.00/

Problem: about once per month this assertion would fail in SQE testing,
usually running one of the streams-related tests with -Xcomp.

  ciMethodType* as_method_type() {
    assert(is_method_type(), "bad cast");
    return (ciMethodType*)this;
  }

The cause was a failure to check "f1" before accessing constant pool
cache entries, and when competing threads raced, junk would be observed.
This would only matter for invokedynamic -- the combo of needing both
invokedynamic and multiple threads racing in the cpcache meant that 
it was observed in the streams tests (even a test hand-crafted to make this
failure occur would only fire about once ever 5000 times, and with -Xcomp that
meant this was painfully slow).

The fix is to insert the check into the access macros themselves
(for both method_type and appendix -- same problem for invokedynamic)
and to remove the now-redundant checks from those places where it had
been done right already.

Testing:

that bug was fixed: distilled the bug trigger out of the streams tests into something that
did nothing by fork-joins into bug triggers.  Then modified hotspot to repeat one side of
the race 1000 times in the event of an invokedynamic.  Observed failures once per 50 runs
in this case, applied fix, observed no failures in 2600 runs.

that no harm was done:
jtreg of hotspot/compiler
jtreg of jdk/{jdk,vm}, no flags and -Xcomp
jprt of hotspot

Question -- should test test case be added?  It practically never fails even when the
bug is unfixed; without tweaking hotspot, it tells you practically nothing at all.  Checking
the fix took all night.
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