[Webkit-unassigned] [Bug 93080] New: 64-bit JSValues can be hold in an XMM register on X86

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=93080

           Summary: 64-bit JSValues can be hold in an XMM register on X86
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: yuqiang.xian at intel.com
                CC: fpizlo at apple.com


On X86 we have limited number of general purpose registers and only 5 of them are left for allocation. In JSC a 64-bit JSValue will occupy 2 GPRs. Instead of simply spilling the GPRs into memory, we could pack the pair of GPRs holding a JSValue into an XMM register which has smaller usage pressure. The SSE (especially SSE4.1) support makes the packing and extraction of the data cheaper than storing to and reading from memory.

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