RFR: 8351414: C2: MergeStores must happen after RangeCheck smearing [v2]

[Emanuel Peter]

> With [JDK-8348959](https://bugs.openjdk.org/browse/JDK-8348959) we see that there can be some issues when RangeCheck smearing happens in the same IGVN phase as MergeStores. It means that some RangeChecks are still around as we do MergeStores, and then we cannot merge as many stores as we would like. We should ensure that RangeCheck smearing happens during post-loop-opts, and then MergeStores happens in a separate dedicated IGVN round afterwards.

Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:

  For Christian, add comment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23944/files
  - new: https://git.openjdk.org/jdk/pull/23944/files/4667e4bc..41292a65

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23944&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23944&range=00-01

  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23944.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23944/head:pull/23944

PR: https://git.openjdk.org/jdk/pull/23944