[Webkit-unassigned] [Bug 150656] New: B3::reduceStrength() should do DCE

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=150656

            Bug ID: 150656
           Summary: B3::reduceStrength() should do DCE
    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

Here's what my rough DCE can do:

B3 after initial, before reduceStrength:
BB#0: ; frequency = nan
    Int64 @0 = ArgumentReg(%rdi)
    Int64 @1 = Const64(0)
    Int64 @2 = Add(@0, @1)
    Int32 @3 = Load(@2, ControlDependent|Reads:Top)
    Int64 @4 = Const64(4)
    Int64 @5 = Add(@0, @4)
    Int32 @6 = Load(@5, ControlDependent|Reads:Top)
    Int32 @7 = Add(@3, @6)
    Void @8 = Return(@7, Terminal)
B3 after reduceStrength, before lowerToAir:
BB#0: ; frequency = nan
    Int64 @0 = ArgumentReg(%rdi)
    Int32 @3 = Load(@0, ControlDependent|Reads:Top)
    Int32 @6 = Load(@0, offset = 4, ControlDependent|Reads:Top)
    Int32 @7 = Add(@3, @6)
    Void @8 = Return(@7, Terminal)

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