On Thu, 4 Apr 2024 09:45:58 GMT, Stefan Karlsson <stef...@openjdk.org> wrote:
> We have a few places that uses the terms `KlassObj` and `klassOop` when > referring to Klasses. This is old code from before the PermGen removal, when > Klasses also were Java objects. > > These names tripped me up when I was reading the heap heapInspection.cpp and > first though we were mixing the klass *mirror* objects and klass pointers in > the hash code calculation: > > // An aligned reference address (typically the least > // address in the perm gen) used for hashing klass > // objects. > HeapWord* _ref; > ... > _ref = (HeapWord*) Universe::boolArrayKlassObj(); > ... > uint KlassInfoTable::hash(const Klass* p) { > return (uint)(((uintptr_t)p - (uintptr_t)_ref) >> 2); > } > > > I propose that we rename these functions (and stop casting the Klass* to a > (HeapWord*)). > > Tested with serviceability/dcmd/gc/ClassHistogramTest.java but will run this > through our lower tiers. This is a useful change, it has tripped me up a couple of times, too. Change mostly looks good, just a few minor suggestions. src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 1202: > 1200: ldrw(scan_temp, Address(recv_klass, Klass::vtable_length_offset())); > 1201: > 1202: // %%% Could store the aligned, prescaled offset in the klassoop. Unrelated, but what's the point of the %%% in all those comments? Might want to remove that, while you're there. src/hotspot/share/memory/heapInspection.cpp line 173: > 171: KlassInfoTable::KlassInfoTable(bool add_all_classes) { > 172: _size_of_instances_in_words = 0; > 173: _ref = (uintptr_t) Universe::boolArrayKlass(); It seems weird (non-obvious) to cast to uintptr_t here. I see it is only used in KlassInfoTable::hash(), which is weird, too. I am not sure that this even does a useful hashing. Might be worth to get rid of the whole thing and use the [fastHash](https://github.com/rkennke/jdk/blob/JDK-8305896/src/hotspot/share/utilities/fastHash.hpp) stuff that @rose00 proposed for Lilliput. Perhaps in a follow-up. I'd probably either cast to void* or Klass*, or cast to uintptr_t as you did and remove the unnecessary cast in ::hash(). ------------- Changes requested by rkennke (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/18618#pullrequestreview-1979371014 PR Review Comment: https://git.openjdk.org/jdk/pull/18618#discussion_r1551366745 PR Review Comment: https://git.openjdk.org/jdk/pull/18618#discussion_r1551384583