1633736 - Warp: specialize OSR phis

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, task, P2)

Description

[Jan de Mooij [:jandem]]

After bug 1632757 we generate good code for an empty for-loop in a function in the non-OSR case, but OSR ends up with unboxing/boxing instructions in the loop body because the OSR entry block has (untyped) Values flowing in, polluting phi types.

To fix this we need to improve phi type analysis to add guards/unboxing to the OSR entry block if needed when WarpBuilder is enabled.

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Bug 1633736 part 1 - Use IsNullOrUndefined and IsMagicType helpers, handle MagicIsConstructing type in replaceRedundantPhi. r?iain!

The MagicIsConstructing case can happen with WarpBuilder with later patches.

Comment 2

[Jan de Mooij [:jandem]]

Attachment: Bug 1633736 part 2 - Add a helper method for draining phi worklist. r?iain!

A later patch will add a second caller.

Depends on D72880

Comment 3

[Jan de Mooij [:jandem]]

Attachment: Bug 1633736 part 3 - Add MGuardValue for guarding on a specific Value. r?iain!

A later patch will use this for null/undefined/magic Values: types that can't
be MUnbox'd.

Depends on D72881

Comment 4

[Jan de Mooij [:jandem]]

Attachment: Bug 1633736 part 4 - Specialize OSR phis as part of phi specialization when Warp is enabled. r?iain!

For WarpBuilder we need an alternative to the IonBuilder TI-based mechanism.
It's somewhat similar in spirit: determine types for each slot and then add
guard/unbox instructions to the OSR entry block to check this. See the big
SMDOC comment for details.

This does great on various loops I've been analyzing. We'll have to see how
it works out for the more complicated (nested) loops, but because this is
WarpBuilder-specific code we can hopefully easily change things later if needed.

Depends on D72882

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/21d7efbe77c8
part 1 - Use IsNullOrUndefined and IsMagicType helpers, handle MagicIsConstructing type in replaceRedundantPhi. r=iain
https://hg.mozilla.org/integration/autoland/rev/9358bf6499db
part 2 - Add a helper method for draining phi worklist. r=iain
https://hg.mozilla.org/integration/autoland/rev/b638015cdfd1
part 3 - Add MGuardValue for guarding on a specific Value. r=iain
https://hg.mozilla.org/integration/autoland/rev/78291462524e
part 4 - Specialize OSR phis as part of phi specialization when Warp is enabled. r=iain

Comment 6

[Cristian Brindusan [:cbrindusan]]

https://hg.mozilla.org/mozilla-central/rev/21d7efbe77c8
https://hg.mozilla.org/mozilla-central/rev/9358bf6499db
https://hg.mozilla.org/mozilla-central/rev/b638015cdfd1
https://hg.mozilla.org/mozilla-central/rev/78291462524e