RFR: 8333258: C2: high memory usage in PhaseCFG::insert_anti_dependences()

[Roland Westrelin]

In a debug build, `PhaseCFG::insert_anti_dependences()` is called
twice for a single node: once for actual processing, once for
verification.

In TestAntiDependenciesHighMemUsage, the test has a `Region` that
merges 337 incoming path. It also has one `Phi` per memory slice that
are stored to: 1000 `Phi` nodes. Each `Phi` node has 337 inputs that
are identical except for one. The common input is the memory state on
method entry. The test has 60 `Load` that needs to be processed for
anti dependences. All `Load` share the same memory input: the memory
state on method entry. For each `Load`, all `Phi` nodes are pushed 336
times on the work lists for anti dependence processing because all of
them appear multiple times as uses of each `Load`s memory state: `Phi`s
are pushed 336 000 on 2 work lists. Memory is not reclaimed on exit
from `PhaseCFG::insert_anti_dependences()` so memory usage grows as
`Load` nodes are processed:

336000 * 2 work lists * 60 loads * 8 bytes pointer = 322 MB. 

The fix I propose for this is to not push `Phi` nodes more than once
when they have the same inputs multiple times.

In TestAntiDependenciesHighMemUsage2, the test has 4000 loads. For
each of them, when processed for anti dependences, all 4000 loads are
pushed on the work lists because they share the same memory
input. Then when they are popped from the work list, they are
discarded because only stores are of interest:

4000 loads processed * 4000 loads pushed * 2 work lists * 8 bytes pointer = 256 MB. 

The fix I propose for this is to test before pushing on the work list
whether a node is a store or not.

Finally, I propose adding a `ResourceMark` so memory doesn't
accumulate over calls to `PhaseCFG::insert_anti_dependences()`.

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Commit messages:
 - whitespaces
 - tests & fix

Changes: https://git.openjdk.org/jdk/pull/19791/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19791&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333258
  Stats: 10912 lines in 3 files changed: 10911 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19791.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19791/head:pull/19791

PR: https://git.openjdk.org/jdk/pull/19791