RFR: 8284848: C2: Compiler blackhole arguments should be treated as globally escaping [v2]

[Aleksey Shipilev]

> 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

Aleksey Shipilev has updated the pull request incrementally with two additional commits since the last revision:

 - IR tests
 - Handle only pointer arguments

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8228/files
  - new: https://git.openjdk.java.net/jdk/pull/8228/files/c3e82437..3e0a2c28

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8228&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8228&range=00-01

  Stats: 171 lines in 4 files changed: 160 ins; 2 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8228.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8228/head:pull/8228

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