579104 - JM: Investigate unrolling bytecode for low trip-count loops

Status: RESOLVED INVALID

(Core :: JavaScript Engine, defect)

Description

[Chris Leary [:cdleary] (not checking bugmail)]

To avoid unnecessary frame state information dropping across back edges we may be able to unroll low trip-count loops in the font end.

Branchy or call-oriented code will have less benefit since it has to drop frame state info above branch targets and sync before a call (respectively), so maybe there's an easy heuristic we can flag on conditionals/invocations in the AST.

The induction variable has to be effectively scoped to the loop body and, to make it easy, require all defs to be scoped to the loop header.

Comment 1

[Till Schneidereit [:till]]

Is this still relevant? Certainly doesn't sounds like it's JM-specific, but it might have been obsoleted by other changes in the meantime.

Comment 2

[Brian Hackett [Laid off!]]

I don't think this has been relevant since before JM+TI came around, as JM+TI could carry registers across loop backdges.