RFR: 8284848: C2: Compiler blackhole arguments should be treated as globally escaping

[Vladimir Kozlov]

On Wed, 13 Apr 2022 17:18:43 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> WIP so far, but I would appreciate early review of someone savvy in C2 EA code. I'll try to whip up the test with IR Framework too.
> 
> See more discussion in the bug.
> 
> Additional testing:
>  - [x] Linux x86_64 fastdebug `tier1`
>  - [x] Linux x86_64 fastdebug `tier2`
>  - [x] OpenJDK microbenchmark corpus sanity run

src/hotspot/share/opto/escape.cpp line 825:

> 823:           set_escape_state(ptn, PointsToNode::GlobalEscape NOT_PRODUCT(COMMA "blackhole"));
> 824:         }
> 825:         add_edge(n_ptn, ptn);

Why not use `add_local_var_and_edge()` here?

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PR: https://git.openjdk.java.net/jdk/pull/8228