RFR: 8267098: AArch64: C1 StubFrames end confusingly [v2]

[Alan Hayward]

> For many of the stub frames, a leave/ret is generated after the stub has
> already branched or returned. This is confusing. For these cases, replace
> the superfluous code with a should_not_reach_here
> 
> For handle excception, instead of storing return from the exception
> handler on the stack, it can be moved directly into lr, replacing a store and
> load with a single move. (If/when PAC support is implemented, then this store
> would also have to be signed).

Alan Hayward has updated the pull request incrementally with two additional commits since the last revision:

 - Restore save to stack code
   
   Change-Id: I20c9d04d372c2da3fceb6921a3696074561666d9
 - Add return_state_t enum
   
   Change-Id: If4472d3230466ac4409e9b63dedfdb54013c6e3d

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4030/files
  - new: https://git.openjdk.java.net/jdk/pull/4030/files/6f060c59..9d6a057a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4030&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4030&range=00-01

  Stats: 33 lines in 1 file changed: 14 ins; 10 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4030.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4030/head:pull/4030

PR: https://git.openjdk.java.net/jdk/pull/4030