[Webkit-unassigned] [Bug 154725] New: [DFG] DFG ArithRound for non-zero-case is incorrect for negative numbers in x86

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=154725

            Bug ID: 154725
           Summary: [DFG] DFG ArithRound for non-zero-case is incorrect
                    for negative numbers in x86
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: utatane.tea at gmail.com

We use branchTruncateDoubleToInt32, it emits cvttsd2si_rr.
But its rounding mode is not floor.

The test case is the following.

function mathRoundDoesNotCareAboutMinusZero(value)
{
    return Math.round(value)|0;
}
noInline(mathRoundDoesNotCareAboutMinusZero);

for (var i = 0; i < 1e4; ++i) {
    var doubleMid = -9901 - 0.6;
    var roundedValue = mathRoundDoesNotCareAboutMinusZero(doubleMid);
    print(doubleMid, roundedValue);
    if (roundedValue !== -9902)
        throw "mathRoundDoesNotCareAboutMinusZero(" + doubleMid + ") = " + roundedValue;
}

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