[Webkit-unassigned] [Bug 209777] New: ASSERTION FAILED: m_cases[i - 1] < m_cases[I] due to DeleteIC.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=209777

            Bug ID: 209777
           Summary: ASSERTION FAILED: m_cases[i - 1] < m_cases[I] due to
                    DeleteIC.
           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: mark.lam at apple.com

We're seeing a ASSERTION FAILED: m_cases[i - 1] < m_cases[I] due to DeleteIC.  Here's the test case:

    function foo() {
        let j = 0;
        while (j++ < 2)
            delete this.x;
        Object.defineProperty(this, "x", {});
    }

    for (let i = 0; i < 5; i++)
        foo();

Run with --jitPolicyScale=0 --useDFGJIT=0 --useConcurrentJIT=0.

The duplicate cases are:
DeleteMiss:(Committed, ident = 'uid:(x)', structure = 0x10c4faee0:[0xf4c5, JSProxy, {}, NonArray, Proto:0x106dfa368, Leaf])
DeleteNonConfigurable:(Committed, ident = 'uid:(x)', structure = 0x10c4faee0:[0xf4c5, JSProxy, {}, NonArray, Proto:0x106dfa368, Leaf])

<rdar://problem/61051902>

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