On Thu, 3 Oct 2024 12:14:08 GMT, Erik Österlund <eosterl...@openjdk.org> wrote:
>> Aleksey Shipilev has updated the pull request incrementally with one >> additional commit since the last revision: >> >> Also dispatch to slow-path on other arches > > src/hotspot/share/opto/library_call.cpp line 7002: > >> 7000: // Add memory barrier to prevent commoning the accesses in this code, >> 7001: // since GC can change the value of referent at any time. >> 7002: insert_mem_bar(Op_MemBarCPUOrder); > > I think this CPU memory barrier and comment above are confusing and obviously > just taken from the referent loading intrinsics. The commoning it is talking > about is to short circuit a second load with the result of a first load of > the referent field, since the compiler "knows" the first load would give the > "same" answer unless "something happened" (GC clearing it). > In this case the mutator just cleared it, so what the compiler thinks is that > null is stored in that field. And that's completely accurate, and the GC is > not going to transition the field from null to some random other object. > Let's remove this CPU memory barrier and the misleading comments. Right. I removed it in my local patch queue. Now I have to reconcile this PR with late barrier expansion in G1, I'll push the update once that is done. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/20139#discussion_r1786549120
