RFR: 8255579: x86: Use cmpq(Register, Address) in safepoint_poll [v2]

[Aleksey Shipilev]

> JDK-8253180 added a new block in `safepoint_poll` that uses broken `cmpq` (JDK-8255550): it effectively does the comparison with operands swapped. It makes sense to use the non-broken `cmpq`, as to avoid changing the condition code and thus making the code less understandable. See the discussion in #910. 
> 
> Testing:
>   - [x] `tier1` with Z (some SA tests fail, and some other fail with OOME -- seem to be expected/problem-listed)

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into JDK-8255579-safepoint-poll
 - 8255579: x86: Use cmpq(Register,Address) in safepoint_poll

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/924/files
  - new: https://git.openjdk.java.net/jdk/pull/924/files/1f156d72..cc98eaae

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=924&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=924&range=00-01

  Stats: 1637 lines in 27 files changed: 139 ins; 1454 del; 44 mod
  Patch: https://git.openjdk.java.net/jdk/pull/924.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/924/head:pull/924

PR: https://git.openjdk.java.net/jdk/pull/924