This PR significantly speeds up decompressing resources in Jimage while significantly reducing temporary memory allocations in the process.
This will improve startup speed for runtime images generated using `jlink --compress 1` and `jlink --compress 2` . I generated a runtime image containing javac using `jlink --compress 1 --add-modules jdk.compiler` and tested the time it took to compile a simple HelloWorld program 20 times using `perf stat -r20 javac /dev/shm/HelloWorld.java`, this PR reduces the total time taken from 17830ms to 13598ms (31.12% faster). ------------- Commit messages: - getStringMUTF8 - Small optimization - use Byte.toUnsignedInt - opt decompressFlow - Delete CompressIndexes.readInt(DataInputStream) - opt StringSharingDecompressor - opt ZipDecompressor Changes: https://git.openjdk.org/jdk/pull/16556/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16556&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8321620 Stats: 210 lines in 7 files changed: 70 ins; 60 del; 80 mod Patch: https://git.openjdk.org/jdk/pull/16556.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/16556/head:pull/16556 PR: https://git.openjdk.org/jdk/pull/16556
