[Webkit-unassigned] [Bug 143937] New: ByteCodeParser::m_currentSemanticOrigin is incorrect for multiple setLocals in a single bytecode instruction

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=143937

            Bug ID: 143937
           Summary: ByteCodeParser::m_currentSemanticOrigin is incorrect
                    for multiple setLocals in a single bytecode
                    instruction
    Classification: Unclassified
           Product: WebKit
           Version: 528+ (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

The DFG bytecode parser has a bunch of machinery to handle the possibility that a single bytecode instruction will have multiple SetLocals.  At some point we added a m_currentSemanticOrigin thing for making the semantic origin of a SetLocal look "right".  But, that functionality assumes that there will be just one SetLocal per bytecode instruction.

We probably don't have bytecode instructions with multiple SetLocals right now, but that is by no means a rule of bytecode.

So, this should either be fixed, or the m_currentSemanticOrigin feature should be removed. There is probably no harm in a SetLocal having the semantic origin of the following instruction.

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