Add compact-strings module: Compact Strings (JEP 254) measured with JOL on JDK 25, with and without -XX:-CompactStrings, and compact object headers on 25 vs 27

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01KqJyCidz3ZgRyHABv2GVJh

compact-strings/jmh/run-jmh.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+# Builds and runs StringBench on JDK 25 with the default and with -XX:-CompactStrings; writes ../output/30-jmh.txt (about 6 minutes).
+# JDK25=/path ./run-jmh.sh     (run ./fetch.sh once first)
+set -uo pipefail
+unset JAVA_TOOL_OPTIONS
+HERE="$(cd "$(dirname "$0")" && pwd)"; cd "$HERE"
+JDK25="${JDK25:-/opt/jdks/jdk-25.0.4.1+1}"
+CP="$(ls lib/*.jar | tr '\n' ':')"; B="$(mktemp -d)"; trap 'rm -rf "$B"' EXIT
+"$JDK25/bin/javac" -cp "$CP" -processorpath "$CP" -d "$B" src/bench/StringBench.java 2>&1 | grep -v '^Note:'
+{
+  echo "machine: $(nproc) CPUs, $(grep -m1 'model name' /proc/cpuinfo | sed 's/.*: //')"
+  for fl in "" "-XX:-CompactStrings"; do
+    echo; echo "\$ java $fl org.openjdk.jmh.Main -f 2 -wi 3 -w 1 -i 5 -r 1     ($("$JDK25/bin/java" -version 2>&1 | sed -n 2p | sed 's/.*(build \(.*\))/\1/'), JMH 1.37)"
+    "$JDK25/bin/java" -cp "$B:$CP" org.openjdk.jmh.Main -f 2 -wi 3 -w 1 -i 5 -r 1 -jvmArgs "$fl" 2>&1 | sed -n '/^Benchmark /,$p'
+  done
+} > "$HERE/../output/30-jmh.txt"
+cat "$HERE/../output/30-jmh.txt"