RFR: 8270848: Redundant unsafe opmask register allocation in some instruction patterns. [v2]

[Jatin Bhateja]

> - Some string compare/array equality patters in x86_[32/64].ad files accept the temporary opmark register operands, instructions using these registers are guarded by target feature checks.
> - Even if control path leading to these instructions is not chosen, RA will still allocate physical registers to these temporary operands.
> - Pulling out the feature checks upto the instruction level can save redundant allocations which may effect spilling decisions.
> - Also existing platform dependent routine Matcher::has_predicated_vector() check the existence of AVX512VL feature which is not required.

Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:

  8270848: Review comments resolution.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4813/files
  - new: https://git.openjdk.java.net/jdk/pull/4813/files/865cfbd1..1e242978

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4813&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4813&range=00-01

  Stats: 5 lines in 1 file changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4813.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4813/head:pull/4813

PR: https://git.openjdk.java.net/jdk/pull/4813