RFR: 8277508: need to check has_predicated_vectors before calling scalable_predicate_reg_slots [v2]

[Yadong Wang]

> Hi, Team,
> A separate set of predicate registers is not mandatory for an implementation of scalable vectors. It will cause a failure in some platform which supports scalable vectors without explicit predicated registers, like riscv. All code about RegVectMask should be covered by has_predicated_vectors here in Matcher::init_first_stack_mask().
> 
> Yadong

Yadong Wang has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8277508: need to check has_predicated_vectors before calling scalable_predicate_reg_slots

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6492/files
  - new: https://git.openjdk.java.net/jdk/pull/6492/files/b3171c26..5f54b7fc

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6492&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6492&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6492.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6492/head:pull/6492

PR: https://git.openjdk.java.net/jdk/pull/6492