[Webkit-unassigned] [Bug 162349] New: Add acquire/release flags to B3::MemoryValue

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=162349

            Bug ID: 162349
           Summary: Add acquire/release flags to B3::MemoryValue
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: fpizlo at apple.com

On ARM, we can mark loads and stores as having acquire or release semantics.  B3 should know about this.

I believe that this means that a load-acquire will have a write heap range.  This range must be non-empty.  This achieves both goals of acquire: it means that this load itself is not hoistable, and it means that other loads cannot be hoisted above this load, if they overlap with the write range.

I believe that this means that a store-release will have a read heap range.  This range must be non-empty.  The read range prevents other stores from being sunk below this one.  Also, the write range must be expanded to include anything that we don't want this store to be sunk to.

Maybe we can model acq/rel by just giving MemoryValue a second range?  That would be weird but it seems like it would work.  Alternatively, we would have a B3FencedMemoryValue, which includes the second range.  This second range would behave either as the read range or the write range depending on whether this was a load or a store.

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