RFR: 8301869: Regression ~14% in J2dBench-bimg_misc-* in 21-b5 only on linux-aarch64 [v3]

[Jayathirth D V]

> Under https://bugs.openjdk.org/browse/JDK-8264846 we moved to -O3 level of gcc optimizations from -O1 level for libawt build. This improved our J2DBench performance numbers in some options considerably.
> 
> Recent changes done under https://bugs.openjdk.org/browse/JDK-8299337 causes difference in generated code by gcc and this is resulting in performance regression for bimg_misc-* J2DBench options in our performance servers. Under https://bugs.openjdk.org/browse/JDK-8299337 we have just removed unused variables and it is a cleanup task.
> 
> We can force gcc to generate position independent code by using -fpic option.Also i have removed -fgcse-after-reload option for gcc, because this is by default covered under -O3 level of optimization introduced under https://bugs.openjdk.org/browse/JDK-8264846.
> 
> With this change bimg_misc-* J2DBench option performance regression is resolved and there are no regression in other options of J2DBench or SwingMark and it is verified in our performance servers.

Jayathirth D V has updated the pull request incrementally with one additional commit since the last revision:

  Shift comment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12761/files
  - new: https://git.openjdk.org/jdk/pull/12761/files/e8d25674..135883db

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12761&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12761&range=01-02

  Stats: 8 lines in 1 file changed: 4 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12761.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12761/head:pull/12761

PR: https://git.openjdk.org/jdk/pull/12761