[Webkit-unassigned] [Bug 37862] New: Use BLX and BX to keep happy the return stack predictor above ARMv4

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=37862

           Summary: Use BLX and BX to keep happy the return stack
                    predictor above ARMv4
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Other
        OS/Version: Other
            Status: NEW
          Severity: Enhancement
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: loki at webkit.org


The following kind of instruction sequences break the return stack predictor:
MOV LR, PC
MOV PC, Rx

We should avoid it above v4. The BLX instruction should be used for predicted
calls on ARMv5 and above.

The patch gives 2% performance progression.

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