RFR: 8313402: C1: Incorrect LoadIndexed value numbering [v2]

[Aleksey Shipilev]

> See the bug for more investigation. 
> 
> This manifests in current tests, if you run them with C1. The root cause for the failure is that we fold two `LoadIndexed` nodes, when one of them reads `char` from `byte[]` via `_getCharStringU` intrinsic, and another one reads `byte` normally. So we can fold the "char"-reading load with "byte" reading load, effectively reading the wrong thing. New regression test shows it: it would read "42" instead of full char.
> 
> 
> $ build/macosx-aarch64-server-fastdebug/images/jdk/bin/java -XX:TieredStopAtLevel=1 -XX:CICompilerCount=1 -XX:+PrintCompilation -XX:+PrintIR0 -XX:+PrintValueNumbering Test8313402.java
> 
> . 8 0 i152 a141[i110](i144) (B) [rc]
> ...
> . 7 0 i180 a162[i110] (C)
> ...
> Value Numbering: LoadIndexed i180 equal to i152 (size 47, entries 27, nesting-diff 0)
> ``` 
> 
> GVN hash discriminates on `type()->tag()`, but that `ValueType` maps to the same `T_INT` for both `char` and `byte`! Instead of hashing on that, let's hash on the original element type instead.
> 
> Testing:
>  - [x] New regression test fails without the fix, passes after the fix
>  - [x] Linux AArch64 fastdebug, `tier1 tier2 tier3`
>  - [x] Linux x86_64 fastdebug, `tier1 tier2 tier3`

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into JDK-8313402-c1-gvn-loadindexed
 - Initial fix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15091/files
  - new: https://git.openjdk.org/jdk/pull/15091/files/02827351..d9c210b5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15091&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15091&range=00-01

  Stats: 4522 lines in 92 files changed: 2213 ins; 1029 del; 1280 mod
  Patch: https://git.openjdk.org/jdk/pull/15091.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15091/head:pull/15091

PR: https://git.openjdk.org/jdk/pull/15091