[14] RFR(S): 8234616: assert(0 <= i && i < _len) failed: illegal index in PhaseMacroExpand::expand_macro_nodes()

[Vladimir Ivanov]

> http://cr.openjdk.java.net/~thartmann/8234616/webrev.00/

Looks good.

Best regards,
Vladimir Ivanov

> 
> We assert in PhaseMacroExpand::expand_macro_nodes() when accessing the macro_node array because
> 'macro_idx' is out of the upper bound:
> https://hg.openjdk.java.net/jdk/jdk/file/43c4fb8ba96b/src/hotspot/share/opto/macro.cpp#l2591
> 
> The problem is that in the previous iteration, we hit the following code path which removes an
> unreachable macro node but does not decrement 'macro_idx':
> https://hg.openjdk.java.net/jdk/jdk/file/43c4fb8ba96b/src/hotspot/share/opto/macro.cpp#l2594
> 
> The problem was introduced in JDK 14 by the fix for JDK-8227384:
> https://hg.openjdk.java.net/jdk/jdk/rev/43c4fb8ba96b#l3.25
> 
> I've changed the loop to a for-loop to make sure the index is always decremented and also
> strengthened the asserts. I was not able to create a regression test but the issue reproduces
> intermittently with Lucene.
> 
> Thanks,
> Tobias
>