[Webkit-unassigned] [Bug 64573] New: DFG JIT is inconsistent about fusing branches and speculating integer comparisons for branches

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=64573

           Summary: DFG JIT is inconsistent about fusing branches and
                    speculating integer comparisons for branches
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: fpizlo at apple.com


The DFG speculative JIT typically speculates that compare operands are integers, except when they are fused branches; in which case it might always perform a slow call.  The DFG speculative JIT typically fuses compare/branch sequences, except for StringEqual.  The non-speculative JIT always first tries integer comparisons, and never goes straight to a C call for a comparison, but it never fuses branches.  It would be better if both JITs had a common strategy for compare/branch fusion, and if the speculative JIT always first attempted a fast comparison before going to slow calls.

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