RFR: JDK-8316756: C2 EA fails with "missing memory path" when encountering unsafe_arraycopy stub call

[Tobias Holenstein]

Before https://github.com/openjdk/jdk/pull/5259 the graph of the following program looked like this during Escape Analysis:


static int test() {
    MyClass obj = new MyClass(); // Non-escaping to trigger Escape Analysis
    UNSAFE.copyMemory(null, SRC_BASE, null, DST_BASE, 4);
    obj.x = 42;
    return obj.x;
}

With MemBarCPUOrder:
<img width="395" alt="working" src="https://github.com/openjdk/jdk/assets/71546117/63a82554-49ff-4373-8567-4457b094093f">

Setting `RC_NARROW_MEM` flag in `LibraryCallKit::inline_unsafe_copyMemory()` removes the `428 MergeMem` node. Without a `MergeMem` node after `432 StoreB` EA failes in Phase 2 of `ConnectionGraph::split_unique_types(...)` when trying to push the allocation's users on the appropriate worklist - `429 CallLeafNoFP` is not an expected user of `428 StoreB`. Therefore the assert `"EA: missing memory path"` is hit. 
Without MemBarCPUOrdera and after setting `RC_NARROW_MEM`:
<img width="370" alt="failing" src="https://github.com/openjdk/jdk/assets/71546117/5d98c38c-d404-4ac4-bd11-bc1e1b7b481f">


### Proposed Fix
Dropping the `RC_NARROW_MEM` flag in `LibraryCallKit::inline_unsafe_copyMemory()` causes the introduction of a `MergeMem` between `StoreB` and `CallLeafNoFP`, so the corresponding code in EA doesn't encounter a `CallLeafNoFP` anymore:
<img width="336" alt="fixed" src="https://github.com/openjdk/jdk/assets/71546117/c538c199-6676-49a4-aaac-a2b3b8f11694">

Testing: Tier1-4 passed

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

Commit messages:
 - JDK-8316756: C2 EA fails with "missing memory path" when encountering unsafe_arraycopy stub call

Changes: https://git.openjdk.org/jdk/pull/17347/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17347&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316756
  Stats: 106 lines in 2 files changed: 67 ins; 37 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/17347.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17347/head:pull/17347

PR: https://git.openjdk.org/jdk/pull/17347