On Wed, 16 Apr 2025 00:01:18 GMT, Chen Liang <li...@openjdk.org> wrote:
>> This PR proposes to add the `@Stable` annotation to `j.l.String.hash` and >> `j.l.String.hashIsZero`. This means the VM can trust these fields to never >> change which enables constant folding optimizations. >> >> This PR is tested in tier1, tier2, tier3, and tier4 which all pass. > > src/java.base/share/classes/java/lang/String.java line 183: > >> 181: * us to avoid recalculating this. >> 182: */ >> 183: @Stable > > Suggestion: > > // Marking hashIsZero stable is meaningless, as a read of `0` on hash > blocks > // constant folding of reading hashIsZero > > A compromise. A stable on the hash field is a net improvement; we can > investigate constant folding the zero hashes later. yes ! I would write "given the current implementation of hashCode(), marking hasIsZero @Stable is not useful for constant folding, as the field `hash` of value '0' is read first." ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/24625#discussion_r2046079733
