RFR: 8321620: Optimize JImage decompressors

[Per Minborg]

On Wed, 8 Nov 2023 11:55:22 GMT, Glavo <duke at openjdk.org> wrote:

> 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).

src/java.base/share/classes/jdk/internal/jimage/BasicImageReader.java line 349:

> 347: 
> 348:     int getStringMUTF8(int offset, byte[] bytesOut, int bytesOutOffset) {
> 349:         if (offset < 0 || offset >= strings.limit()) {

Can we use `Objects::checkIndex` here instead?

src/java.base/share/classes/jdk/internal/jimage/decompressor/StringSharingDecompressor.java line 94:

> 92:                                    int offset, long originalSize) throws IOException {
> 93:         if (originalSize > Integer.MAX_VALUE) {
> 94:             throw new OutOfMemoryError("Required array size too large");

Is this the correct exception type?

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

PR Review Comment: https://git.openjdk.org/jdk/pull/16556#discussion_r1399517646
PR Review Comment: https://git.openjdk.org/jdk/pull/16556#discussion_r1399518707