Created attachment 525489 [details]
I get this assert when using Gmail.
It looks from the stack and pointer values like we are triggering recompilation immediately after having pushed a new, empty stack segment for an ExternalInvoke, which StackSpace::containingSegment doesn't like. This makes containingSegment work in such cases. I don't think calling containingSegment is possible in the TM branch between when the segment gets pushed and the associated invoke frame gets pushed, but this still might want to go on TM.