Add release barriers when allocating objects with concurrent collection

[Andrew Haley]

8165808 (Add release barriers when allocating objects with concurrent
collection) added release barriers to object allocation paths. But it
only added them in shared code, not in the fast-path code.

I find a comment I added to AArch64 in 2013:

 void MacroAssembler::store_klass(Register dst, Register src) {
+  // FIXME: Should this be a store release?  concurrent gcs assumes
+  // klass length is valid if klass field is not null.

PPC doesn't have release barriers here either:

void MacroAssembler::store_klass(Register dst_oop, Register klass, Register ck) {
  if (UseCompressedClassPointers) {
    encode_klass_not_null(ck, klass);
    stw(ck, oopDesc::klass_offset_in_bytes(), dst_oop);
  } else {
    std(klass, oopDesc::klass_offset_in_bytes(), dst_oop);
  }
}

So what's up? What should we be doing here? Surely if the slow path
code needs the barriers, the fast path does too.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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