AArch64: suppress false positive GCC -Wnonnull warning Suppress the known GCC false positive around read(2) using the same diagnostic guard as current upstream. This allows fastdebug builds with warnings-as-errors without changing runtime behavior.
aarch64: add optimization path hit diagnostics Add the diagnostic PrintAArch64OptimizationHits flag to print the first entry into selected AArch64 optimization paths. Use a shared 64-bit hit mask and an atomic first-hit reporter so each path is printed once while later entries skip the reporter. Preserve r16 and the link register before entering the shared reporter, then preserve the complete live GPR, vector, predicate, and NZCV state around the native call. This keeps the diagnostic safe for stubs with narrow C2 clobber contracts. Track NEON and SVE2 vectorized hashCode stubs, forward arraycopy prefetch, SVE small-block zeroing, String case conversion, vectorizedMismatch, and String.equalsIgnoreCase. Add a jtreg driver covering disabled, enabled, and single-report behavior.