RFR: 8341471: Reversed field layout caused by unstable sorting [v2]

[Fei Gao]

> For class Test:
> 
>     public class Test {
>         char a000;
>         char a001;
>         char a002;
>         char a003;
>         char a004;
>         char a005;
>         char a006;
>         char a007;
>         char a008;
>         char a009;
>         char a00a;
>         char a00b;
>     }
> 
> 
> We found its field layout on macOS was:
> 
> 
> Layout of class Test
>   Instance fields:
>    @0 12/- RESERVED
>    @12 "a00b" C 2/2 REGULAR
>    @14 "a001" C 2/2 REGULAR
>    @16 "a002" C 2/2 REGULAR
>    @18 "a003" C 2/2 REGULAR
>    @20 "a004" C 2/2 REGULAR
>    @22 "a005" C 2/2 REGULAR
>    @24 "a006" C 2/2 REGULAR
>    @26 "a007" C 2/2 REGULAR
>    @28 "a008" C 2/2 REGULAR
>    @30 "a009" C 2/2 REGULAR
>    @32 "a00a" C 2/2 REGULAR
>    @34 "a000" C 2/2 REGULAR
> 
> 
> `a000` was put in the end while `a00b` was put in the beginning.
> 
> Fields get sorted according to size in [1]. `qsort()` on macOS reverses the order of fields with the same size. We should extend the comparison function to preserve the order on macOS, as we did on Windows.
> 
> Tier 1-3 passed on macOS.
> 
> [1] https://github.com/openjdk/jdk/blob/3ee94e040a7395d11a294a6b660d707c97f188f8/src/hotspot/share/classfile/fieldLayoutBuilder.cpp#L102

Fei Gao 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 three additional commits since the last revision:

 - Extend the comparison function to all platforms
 - Merge branch 'master' into field_layout_fix
 - 8341471: [macOS_aarch64] Reversed field layout caused by unstable sorting
   
   For class Test:
   ```
       public class Test {
           char a000;
           char a001;
           char a002;
           char a003;
           char a004;
           char a005;
           char a006;
           char a007;
           char a008;
           char a009;
           char a00a;
           char a00b;
       }
   ```
   
   We found its field layout on macOS was:
   
   Layout of class Test
     Instance fields:
      @0 12/- RESERVED
      @12 "a00b" C 2/2 REGULAR
      @14 "a001" C 2/2 REGULAR
      @16 "a002" C 2/2 REGULAR
      @18 "a003" C 2/2 REGULAR
      @20 "a004" C 2/2 REGULAR
      @22 "a005" C 2/2 REGULAR
      @24 "a006" C 2/2 REGULAR
      @26 "a007" C 2/2 REGULAR
      @28 "a008" C 2/2 REGULAR
      @30 "a009" C 2/2 REGULAR
      @32 "a00a" C 2/2 REGULAR
      @34 "a000" C 2/2 REGULAR
   
   `a000` was put in the end while `a00b` was put in the beginning.
   
   Fields get sorted according to size in [1]. `qsort()` on macOS
   reverses the order of fields with the same size. We should extend
   the comparison function to preserve the order on macOS, as we
   did on Windows.
   
   Tier 1-3 passed on macOS.
   
   [1] https://github.com/openjdk/jdk/blob/3ee94e040a7395d11a294a6b660d707c97f188f8/src/hotspot/share/classfile/fieldLayoutBuilder.cpp#L102

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21382/files
  - new: https://git.openjdk.org/jdk/pull/21382/files/c19e07de..3034f28a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21382&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21382&range=00-01

  Stats: 7624 lines in 158 files changed: 6291 ins; 879 del; 454 mod
  Patch: https://git.openjdk.org/jdk/pull/21382.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21382/head:pull/21382

PR: https://git.openjdk.org/jdk/pull/21382