8349772: C2 hits MemLimit during incremental inlining

[dafedafe]

The issue was very intermittent but an old run that reproduced (for the crash with -XX:-TieredCompilation -XX:+AlwaysIncrementalInline) suggested the following was happening:
The test builds a very long MH adapter chain (in some runs up to ~10,000 transformations). Many small MH adapters are late-inlined, and C2 performs repeated incremental-inline/prune/IGVN rounds.
In each round, parser/IR/support data is allocated from compile arenas. Even when pruning removes dead nodes (live node count seems to remain moderate, e.g. ~13k), arena usage appears to be reclaimed only when the compilation ends.
So, for runs with long/complex chains, peak arena usage seems to cross MemLimit, which triggers a crash in debug (or a compilation bailout in product/non-crash mode).
Disabling/stopping late inlining at that point would probably only postpone the resource failure to a later phase.
JDK-8349820 disabled the explicit test-level MemLimit override. This change keeps a safeguard by using a larger explicit limit (2G) in debug builds.

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Issue

• JDK-8349772: C2 hits MemLimit during incremental inlining (Bug - P4)

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