[lworld] RFR: 8354981: [lworld] Atomic flat stores need preceding CPUMemBar

[Quan Anh Mai]

Hi,

Atomic flat stores cover many memory slices. As a result, it needs a preceding CPUMemBar or else it only takes the slice of the first field as its memory input, which is incorrect.

I don't know how to make a regression test for this. I encounter this crash while working on JDK-8335256. The crash was due to the memory input of the flat store gets split during escape analysis. The compiler then tries looking at the flat stores, which is vastly different from what it expects.

Please take a look and leave your reviews, thanks a lot.

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Commit messages:
 - Atomic flat store needs a preceding barrier

Changes: https://git.openjdk.org/valhalla/pull/1437/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1437&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354981
  Stats: 38 lines in 1 file changed: 15 ins; 16 del; 7 mod
  Patch: https://git.openjdk.org/valhalla/pull/1437.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1437/head:pull/1437

PR: https://git.openjdk.org/valhalla/pull/1437