[Webkit-unassigned] [Bug 142966] New: Optimize typed array access with a masked index

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=142966

            Bug ID: 142966
           Summary: Optimize typed array access with a masked index
    Classification: Unclassified
           Product: WebKit
           Version: 528+ (Nightly build)
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: dtc-llvm at scieneer.com

Emscripten now has an experimental mode that emits heap accesses as a[(i & mask) + c >> n] which keeps the index within bounds and is easy for the JS compiler to match and to optimize away bounds checks. The technique is also used in the asm.js jump tables as a[i&mask]. The technique is not asm.js specific and can be used in general JS code. The masked index can often be hoisted using Value Numbering etc, and a small constant offset can be emitted in the load or store instruction addressing mode.

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