1602681 - Disambiguate OSR pc arguments in a few places

Status: RESOLVED DUPLICATE of bug 1602390

(Core :: JavaScript Engine: JIT, task, P1)

Description

[Jan de Mooij [:jandem]]

Some functions take a jsbytecode* pc argument: if it's a JSOP_LOOPHEAD they treat it as OSR and else it must be script->code(). However this is ambiguous as scripts can start with JSOP_LOOPHEAD for while-loops.

We could change to jsbytecode* osrPc and use nullptr for the non-OSR case so there's never any confusion.

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Bug 1602681 - Disambiguate prologue vs OSR pc arguments. r?tcampbell!

Some functions took a pc argument: if it's a JSOP_LOOPHEAD they treated it as
OSR and else it must be script->code() indicating prologue code. However this
is ambiguous as scripts can start with JSOP_LOOPHEAD for while-loops.

This patch changes the code to pass an osrPc instead: if nullptr it's for the
prologue and else it must be a JSOP_LOOPHEAD pc. This avoids any ambiguity and
is similar to what we already do elsewhere.

Comment 2

[Jan de Mooij [:jandem]]

This patch exposes a bailout issue with --ion-eager when JSOP_LOOPHEAD is the first op in a script. IsPrologueBailout thinks we're doing a prologue bailout when we resume at the LOOPHEAD op so we end up with an enter-Ion => bailout-to-prologue => enter-Ion loop.

Until we improve the prologue logic I think we should just emit a JSOP_NOP for now. That fixes this bug + bug 1602390.

Comment 3

[Jan de Mooij [:jandem]]

Fixing this differently in bug 1602390.