557375 - remove JSStackFrame::thisv

Status: RESOLVED DUPLICATE of bug 539144

(Core :: JavaScript Engine, defect)

Description

[Luke Wagner [:luke]]

If fp->argv == null (global code), thisv caches the computed 'this' value.  If fp->argv != null (function code), thisv holds a copy of argv[-1].  thisv also roots the 'obj' parameter to slow natives (in case the slow native overwrites argv[-1].  We could remove this JSStackFrame member by (1) always having argv[-1] refer to a valid jsval and (2) using a AutoValueRooter to root the 'obj' parameter to slow natives.  This would save one jsval which, with bug 549143, is getting much fatter.

Comment 1

[Luke Wagner [:luke]]

There is also the case where stack frames share the same argv because of an obj_eval.  However, bug 539144 aims at cloning arguments in this case.