RFR: 8370454: C2 SuperWord: unsigned comparison information is lost for VectorMaskCmp [v2]

[Hamlin Li]

> Hi,
> Can you help to review the patch? @eme64 
> 
> Currently, in SLP if we support transformation from (Bool + CmpU + CMove) to (VectorMaskCmp + VectorBlend), the unsigned comparison information is lost, it's in CmpU, but current code only check Bool for the information. For details please check code at `SuperWordVTransformBuilder::make_vector_vtnode_for_pack` and `PackSet::get_bool_test`.
> 
> This loss of unsigned comparison information blocks the optimization proposed in https://github.com/openjdk/jdk/pull/25336 and https://github.com/openjdk/jdk/pull/25341.
> 
> Currently, `BoolTest` does not support an unsigned construction (`BoolTest( mask btm ) : _test(btm) { assert((btm & unsigned_compare) == 0, "unsupported");}`), seems to me a feasible solution would be get the unsigned information from CmpU (which could be an input of Bool) and pass it to VectorMaskCmp.
> 
> Thanks

Hamlin Li has updated the pull request incrementally with two additional commits since the last revision:

 - tests
 - switch

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27942/files
  - new: https://git.openjdk.org/jdk/pull/27942/files/6271a8e7..eee8acd8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27942&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27942&range=00-01

  Stats: 202 lines in 2 files changed: 194 ins; 4 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/27942.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27942/head:pull/27942

PR: https://git.openjdk.org/jdk/pull/27942