825447 - IonMonkey: Populate safepoints directly in backtracking allocator

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Brian Hackett [Laid off!]]

Attachment: patch

Currently, the backtracking allocator uses the AllocationIntegrityState to compute the live registers and stack slots for each safepoint.  This was done for simplicity while developing the allocator, but slows down the allocator tremendously and needs to be fixed.  The backtracking allocator currently takes several times as long as LSRA (6x on v8-v7); cutting the use of AllocationIntegrityState reduces time so that backtracking is 1.5x to 2x slower than LSRA.

Comment 1

[Jan de Mooij [:jandem]]

Comment on attachment 696522 [details] [diff] [review]
patch

Review of attachment 696522 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/ion/BacktrackingAllocator.cpp
@@ +1046,5 @@
> +            break;
> +
> +        // Find the furthest endpoint.
> +        size_t lastInterval = reg->numIntervals() - 1;
> +        CodePosition end = reg->getInterval(lastInterval)->end();

Intervals used by the backtracking allocator can overlap right? Is the first interval still guaranteed to start before all other intervals, and the last interval ends after all other intervals? Maybe add a comment/assert.

Comment 2

[Brian Hackett [Laid off!]]

Good catch, yeah, that could cause safepoints to not be fully populated.

https://hg.mozilla.org/integration/mozilla-inbound/rev/663bfe4a4c2c

Comment 3

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/663bfe4a4c2c