[Webkit-unassigned] [Bug 154685] New: B3 should have a DoubleToInt that takes a list of exceptional values

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Thu Feb 25 10:58:16 PST 2016


https://bugs.webkit.org/show_bug.cgi?id=154685

            Bug ID: 154685
           Summary: B3 should have a DoubleToInt that takes a list of
                    exceptional values
    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

Different hardware returns different results for double-to-int failure.  Because of that, we avoided adding DoubleToInt as an opcode in B3.

But we could add a DoubleToInt opcode that has this syntax:

@result = DoubleToInt(@input, @negOverflow, @posOverflow, @negNaN, @posNaN)

Where:

- @negOverflow is the value we return if @input is smaller than INT_MIN.
- @posOverflow is the value we return if @input is larger than INT_MAX.
- @negNaN is the value we return if @input is negative NaN.
- @posNaN is the value we return if @input is positive NaN.

Collectively these are the failure codes.  This means that the client could request that B3 emulates any kind of hardware doubleToInt operation.  If you want X86 behavior, you pass INT_MIN for all of the failure codes.  On ARM64, we would pass either INT_MIN or INT_MAX depending on whether it's positive or negative.

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