RFR: 8291555: Implement alternative fast-locking scheme [v29]

[Thomas Stuefe]

On Fri, 24 Mar 2023 11:36:24 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Merge remote-tracking branch 'origin/JDK-8291555-v2' into JDK-8291555-v2
>>  - Set condition flags correctly after fast-lock call on aarch64
>
> src/hotspot/share/runtime/lockStack.cpp line 42:
> 
>> 40: 
>> 41: #ifndef PRODUCT
>> 42: void LockStack::validate(const char* msg) const {
> 
> Would you also like to check there are no `nullptr` elements on stack here?

Please also verify against over- and underflow, and better than just null checks check that every oop really is an oop. I added this to my code:

  assert((_offset <=  end_offset()), "lockstack overflow: _offset %d end_offset %d", _offset, end_offset());
  assert((_offset >= start_offset()), "lockstack underflow: _offset %d end_offset %d", _offset, start_offset());
  int end = to_index(_offset);
  for (int i = 0; i < end; i++) {
    assert(oopDesc::is_oop(_base[i]), "index %i: not an oop (" PTR_FORMAT ")", i, p2i(_base[i]));
...

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PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1147841666