Being an arguments alias just means that your OSR exit recovery should attempt arguments creation. This is true of arguments locals. We had special cases that tried to make it not true of arguments locals. The only consequence of those special cases was to cause crashes in case of arguments that are also captured variables (i.e. we have SlowArguments).
Created attachment 227824 [details]
Comment on attachment 227824 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=227824&action=review
> + arguments aliases, and non-captured variables get completely SSAified - i.e. no Setocals
Setocals -> SetLocals
Landed in http://trac.webkit.org/changeset/166281