RFR: 8300148: Consider using a StoreStore barrier instead of Release barrier on ctor exit [v9]

[Joshua Cao]

> The [JSR 133 cookbook](https://gee.cs.oswego.edu/dl/jmm/cookbook.html) has long recommended using a `StoreStore` barrier at the end of constructors that write to final fields. `StoreStore` barriers are much cheaper on arm machines as shown in benchmarks in this issue as well as https://bugs.openjdk.org/browse/JDK-8324186.
> 
> This change does not improve the case for constructors for objects with volatile fields because [MemBarRelease is emitted for volatile stores](https://github.com/openjdk/jdk/blob/8fc9097b3720314ef7efaf1f3ac31898c8d6ca19/src/hotspot/share/gc/shared/c2/barrierSetC2.cpp#L211). This is demonstrated in test case `classWithVolatile`, where this patch does not impact the IR.
> 
> I had to modify some code around escape analysis to make sure there are no regressions in eliminating allocations and `StoreStore`'s. The [current handling of StoreStore's in escape analysis](https://github.com/openjdk/jdk/blob/8fc9097b3720314ef7efaf1f3ac31898c8d6ca19/src/hotspot/share/opto/escape.cpp#L2590) makes the assumption that the barriers input is a `Proj` to an `Allocate` ([example](https://github.com/openjdk/jdk/blob/8fc9097b3720314ef7efaf1f3ac31898c8d6ca19/src/hotspot/share/opto/library_call.cpp#L1553)). This is contrary to the barriers in the end of the constructor where there the barrier directly takes in an `Allocate` without an in between `Proj`. I opted to instead eliminate `StoreStore`s in GVN, exactly how `MemBarRelease` is handled.
> 
> I had to add [checks for StoreStore in macro.cpp](https://github.com/openjdk/jdk/blob/8fc9097b3720314ef7efaf1f3ac31898c8d6ca19/src/hotspot/share/opto/macro.cpp#L636), or else we fail some [cases for reducing allocation merges](https://github.com/openjdk/jdk/blob/8fc9097b3720314ef7efaf1f3ac31898c8d6ca19/test/hotspot/jtreg/compiler/c2/irTests/scalarReplacement/AllocationMergesTests.java#L1233-L1256).
> 
> Passes hotspot tier1 locally on a Linux machine.
> 
> ### Benchmarks
> 
> Running Renaissance ParNnemonics on an Amazon Graviton (arm) instance.
> 
> Baseline:
> 
> Result "org.renaissance.jdk.streams.JmhParMnemonics.run":
>   N = 25
>   mean =   3309.611 ±(99.9%) 86.699 ms/op
> 
>   Histogram, ms/op:
>     [3000.000, 3050.000) = 0
>     [3050.000, 3100.000) = 4
>     [3100.000, 3150.000) = 1
>     [3150.000, 3200.000) = 0
>     [3200.000, 3250.000) = 0
>     [3250.000, 3300.000) = 0
>     [3300.000, 3350.000) = 9
>     [3350.000, 3400.000) = 6
>     [3400.000, 3450.000) = 5
> 
>   Percentiles, ms/op:
>       p(0.0000) =   3069.910 ms/op
>      p(50.0000) =   3348.140 ms/op
>      ...

Joshua Cao has updated the pull request incrementally with two additional commits since the last revision:

 - Guard everything by feature flag
 - Revert "Statistics for barriers generated/eliminated"
   
   This reverts commit 33d23635048afd3a1b40ae91e6fadf577742fa4f.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18505/files
  - new: https://git.openjdk.org/jdk/pull/18505/files/582848c7..5ff6bef5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18505&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18505&range=07-08

  Stats: 24 lines in 6 files changed: 2 ins; 17 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/18505.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18505/head:pull/18505

PR: https://git.openjdk.org/jdk/pull/18505