RFR: 8273277: C2: Move conditional negation into rc_predicate [v3]

[Nils Eliasson]

> Hi,
> 
> I need some feedback on this patch. This was reported from Tencent and found in internal testing about the same time. This patch is based on a a patch provided by Tencent.
> 
> In some very specific circumstances we need to negate the range checks that we create in PhaseIdealLoop::loop_predication_impl_helper. This is done in three places, but that method also calls insert_initial_skeleton_predicate where this isn't taken into account. 
> 
> To simplify things I have moved the negation logic into rc_predicate. This should prevent us from missing this check again.
> 
> I do have a concern that negating the condition of the rangecheck in the skeleton predicate, since the skeleton predicate will be used as a clone template, and some rangechecks optimizations seems to assume that range checks always have LT as the condidtion. On the other hand - it is a really uncommon scenario since we haven't failed here before.
> 
> Feedback appreciated.
> 
> Best regards,
> Nils

Nils Eliasson has updated the pull request incrementally with one additional commit since the last revision:

  Add test

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5987/files
  - new: https://git.openjdk.java.net/jdk/pull/5987/files/21697bac..97e46ba9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5987&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5987&range=01-02

  Stats: 66 lines in 1 file changed: 66 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5987.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5987/head:pull/5987

PR: https://git.openjdk.java.net/jdk/pull/5987