784702 - remove cx->fp/maybefp/regs/maybeRegs footguns

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, defect)

Description

[Luke Wagner [:luke]]

Why are they footguns?  Several reasons:
 1. with JM inlining and all IM code, cx->fp might not be the innermost frame and cx->regs.pc might not be the current pc
 2. with dummy frames removed (bug 625199), cx->fp might point to a StackFrame in a different compartment than cx->compartment
 3. when VM code is reached by a direct JSAPI call (e.g., JSNative via JS_CallFunctionValue or native getter via JS_GetProperty), cx->fp will be completely unrelated (or non-existant)

Alternatives are ScriptFrameIter, StackIter, currentScript, currentScriptedScopeChain or making new semantically better-defined queries that we can place on ContextStack.

Comment 1

[Luke Wagner [:luke]]

n/m, most of the current uses just get turned into cx->stack.fp(), so this is needless churn