Bug 210694

Summary:	VM should have a bottomCellForSetLocal that is understood to be a true bottom value by the DFG
Product:	WebKit	Reporter:	Keith Miller <keith_miller>
Component:	JavaScriptCore	Assignee:	Nobody <webkit-unassigned>
Status:	NEW ---
Severity:	Normal
Priority:	P2
Version:	WebKit Nightly Build
Hardware:	Unspecified
OS:	Unspecified

Description Keith Miller 2020-04-18 12:26:46 PDT

Right now we handle bottom values semantically needed for a SetLocal by vending a JSValue that roughly matches the predicted value for the non-bottom path. This comes up for op_iterator_open/next. Unfortunately, this still causes AI to be unhappy. If we had a constant cell that was understood by the DFG to be a bottom value (and presumably crashes whenever accessed), the DFG would generate better code for op_iterator_open/next.