1467384 - Split prologue into 2 sections (DEFVAR etc vs others) and compose them later

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, enhancement, P3)

Description

[Tooru Fujisawa [:arai]]

Currently prologue contains the following bytecode:
  * JSOP_DEFVAR/JSOP_DEFLET/JSOP_DEFCONST
  * JSOP_PUSHVARENV (eval in strict mode)
  * JSOP_RUNONCE for run-once function
  * JSOP_ARGUMENTS+JSOP_SETLOCAL+JSOP_POP for `arguments` in function
  * JSOP_FUNCTIONTHIS+JSOP_SETLOCAL+JSOP_POP for `this` in function
  * JSOP_LAMBDA+(|JSOP_TOASYNC|JSOP_TOASYNCGEN)+JSOP_DEFFUN for top-level functions

this is problematic for BinAST streaming compilation, because whether to emit JSOP_DEFVAR or JSOP_DEFFUN for "var" bindings is unknown at the point of parsing Asserted*Scope.
what we can do here is split prologue into 2 sections (JSOP_DEFVAR/JSOP_DEFLET/JSOP_DEFCONST, and others),
and emit JSOP_DEFVAR/JSOP_DEFLET/JSOP_DEFCONST section at the end of emitting whole script, instead of the beginning,
so that it's known which "var" binding is actually "function" at that point.
we can compose them once bug 1464311 gets fixed, to get the same prologue bytecode.

Comment 1

[Tooru Fujisawa [:arai]]

we might be able to handle it in JSScript::fullyInitFromEmitter instead of composition, if the bytecode is simple enough,
so that the number of copy can be reduced.

Comment 2

[Tooru Fujisawa [:arai]]

DefVar etc are removed by bug 1677580