[11] RFR(S): 8202949: C2: assert(false) failed: Bad graph detected in build_loop_late

[Roland Westrelin]

Hi Tobias,

> We crash during loop opts verification because memory from a non-dominating path is consumed by a
> MemBarReleaseNode. The problem is that a range check dependent CastII is removed because the type of
> the input value is always in bounds. The corresponding ConvI2L floats up during loop optimizations
> and becomes TOP because the loop induction variable of the unrolled loop is out of bounds. As a
> result, the memory graph is corrupted with memory consuming nodes still being reachable because the
> dead loop is not (yet) removed (Opaque1 nodes are still guarding the bounds). See comment in test
> for details.
>
> Range check dependent CastIIs were introduced to fix JDK-6675699 and should not be removed. The
> offending code was introduced by JDK-8139771.

Isn't it the case that the CastII and the ConvI2L have the same type i.e
0..9? So if you leave the CastII in, why doesn't it become top?

Roland.