[Webkit-unassigned] [Bug 77855] New: ValueToNumber is redundant if it is pure and its user already knows how to perform the conversion

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=77855

           Summary: ValueToNumber is redundant if it is pure and its user
                    already knows how to perform the conversion
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: fpizlo at apple.com


If we have a and b both predicted number, then the following sequence:

1: ValueToNumber(a)
2: ValueToNumber(b)
3: ArithSub(@1, @2)

should be turned into:

1: ValueToNumberPure(a)  (skipped)
2: ValueToNumberPure(b)  (skipped)
3: ArithSub(a, b)

and hence we skip two moves and save a register.

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