RFR: 8367692: RISC-V: Align post call nop [v6]

[Robbin Ehn]

> Hi please, consider.
> 
> As ziccif require instructions to natural aligned to be atomic the 4 byte post call nop must be aligned.
> But I don't want to add a c.nop(2b) to align the nop(4b) which means the jal(r) must also be algined.
> As we have no utility to aligned the end of an instruction sequence the call it self is aligned and uses only 4 byte instructions. Only in the case where we could use an two c-instruction we may loose space.
> 
> Thanks, Robbin

Robbin Ehn 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 seven additional commits since the last revision:

 - Merge branch 'master' into align_post_nops
 - Use relocation spec as marker.
 - Revert "Removed relocate for post call nops"
   
   This reverts commit 033ecd4ab3d62c1ccc7845d8bc9e62fc6574e05d.
 - Removed relocate for post call nops
 - Merge branch 'master' into align_post_nops
 - Review comments
 - init

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27467/files
  - new: https://git.openjdk.org/jdk/pull/27467/files/1438c380..76c4f861

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27467&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27467&range=04-05

  Stats: 8627 lines in 220 files changed: 5167 ins; 2402 del; 1058 mod
  Patch: https://git.openjdk.org/jdk/pull/27467.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27467/head:pull/27467

PR: https://git.openjdk.org/jdk/pull/27467