1770509 - Use an IC when closing for-of iterators

Status: RESOLVED FIXED

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

Description

[Iain Ireland [:iain]]

We generate a lot of bytecode for for-of loops. A lot of that bytecode is dedicated to closing iterators on the way out. Many/most for-of loops are iterating over arrays or other collections that don't even have a return method. We can reduce bytecode size by folding the iterator closure code up in an IC.

Comment 1

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Add JSOp::CloseIter r=jandem

This initial implementation doesn't handle throw completions. Support for those is added in a later patch.

Comment 2

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Add baseline IC for CloseIter r=jandem

Depends on D147344

Comment 3

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Add CacheIR generator for CloseIter r=jandem

tryAttachNoReturnMethod covers built-in collections (arrays, maps, and sets), and any custom iterator that doesn't have a return method.

Depends on D147345

Comment 4

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Add Warp support r=jandem

Depends on D147346

Comment 5

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Add LoadFixedSlot to CacheIR r=jandem

We had LoadDynamicSlot, but not LoadFixedSlot.

Depends on D147347

Comment 6

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Rename prepareVMCall to enterStubFrame r=jandem

Entering a stub frame is the same whether we're doing a callVM or a callJit. This aligns better with baseline and simplifies the getter/setter code.

At some point we could consider rewriting the Ion code to use AutoStubFrame.

Depends on D147348

Comment 7

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Support GuardFunctionScript in IonCacheIRCompiler r=jandem

Depends on D147349

Comment 8

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Add CloseIterScriptedResult r=jandem

This supports custom iterators with return methods. It is also necessary to support generators (which call the self-hosted GeneratorReturn function), although those won't work until a subsequent patch adds support for rectifier frames.

Depends on D147350

Comment 9

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Transpile CloseIterScriptedResult r=jandem

Depends on D147351

Comment 10

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Don't overwrite stack slot with undefined r=jandem

When closing a for-of iterator, we overwrite the iterator on the stack with undefined. Comments / commit messages say it's so the iterator doesn't get closed again in the catch block. But there's a for-of-iterclose trynote covering this code, so we never end up in the catch block, and this code is dead.

Depends on D147352

Comment 11

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Support CompletionKind::Throw r=jandem

The spec handles IteratorClose specially when the completion kind is 'throw' so that the original exception isn't overwritten by an exception that happens while closing the iterator. See https://tc39.es/ecma262/#sec-iteratorclose.

Depends on D147353

Comment 12

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Support return methods with nargs > 0 r=jandem

We guard on the specific function/script, so nargs is constant for a particular IC stub. Generating a rectifier frame is overkill.

The main use case for this is generators: GeneratorReturn takes one argument.

Depends on D147354

Comment 13

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Add tests r=jandem

Depends on D147355

Comment 14

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Update bailoutKind earlier r=jandem

In the next patch, we want to change the bailout kind in BaselineStackBuilder. This patch sets the initial bailout kind earlier, so that we don't clobber the update.

Depends on D147356

Comment 15

[Iain Ireland [:iain]]

Attachment: Bug 1770509: Add ResumeMode::ResumeAfterCheckIsObject r=jandem

If we throw an exception while building the stack frame in BailoutIonToBaseline, we will skip try/catch blocks in that frame. Throwing in FinishBailoutToBaseline ensures that we unwind correctly.

Depends on D148332

Comment 16

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/0f94133f476e
Add JSOp::CloseIter r=jandem
https://hg.mozilla.org/integration/autoland/rev/6c908030c328
Add baseline IC for CloseIter r=jandem
https://hg.mozilla.org/integration/autoland/rev/bbfedd0e08ce
Add CacheIR generator for CloseIter r=jandem
https://hg.mozilla.org/integration/autoland/rev/9d37be10da8f
Add Warp support r=jandem
https://hg.mozilla.org/integration/autoland/rev/874a4adcb3bf
Add LoadFixedSlot to CacheIR r=jandem
https://hg.mozilla.org/integration/autoland/rev/d20dcc34e87c
Rename prepareVMCall to enterStubFrame r=jandem
https://hg.mozilla.org/integration/autoland/rev/4235a298993a
Support GuardFunctionScript in IonCacheIRCompiler r=jandem
https://hg.mozilla.org/integration/autoland/rev/1d912ad801b0
Add CloseIterScriptedResult r=jandem
https://hg.mozilla.org/integration/autoland/rev/7d425224ec84
Transpile CloseIterScriptedResult r=jandem
https://hg.mozilla.org/integration/autoland/rev/cc2d84593658
Don't overwrite stack slot with undefined r=arai
https://hg.mozilla.org/integration/autoland/rev/7ad24b936f3b
Support CompletionKind::Throw r=jandem
https://hg.mozilla.org/integration/autoland/rev/347c2d2b6751
Support return methods with nargs > 0 r=jandem
https://hg.mozilla.org/integration/autoland/rev/d26c5eb9eb33
Add tests r=jandem
https://hg.mozilla.org/integration/autoland/rev/0c4b84f3d824
Update bailoutKind earlier r=jandem
https://hg.mozilla.org/integration/autoland/rev/0b909b1ebdf8
Add ResumeMode::ResumeAfterCheckIsObject r=jandem

Comment 17

[bszekely]

https://hg.mozilla.org/mozilla-central/rev/0f94133f476e
https://hg.mozilla.org/mozilla-central/rev/6c908030c328
https://hg.mozilla.org/mozilla-central/rev/bbfedd0e08ce
https://hg.mozilla.org/mozilla-central/rev/9d37be10da8f
https://hg.mozilla.org/mozilla-central/rev/874a4adcb3bf
https://hg.mozilla.org/mozilla-central/rev/d20dcc34e87c
https://hg.mozilla.org/mozilla-central/rev/4235a298993a
https://hg.mozilla.org/mozilla-central/rev/1d912ad801b0
https://hg.mozilla.org/mozilla-central/rev/7d425224ec84
https://hg.mozilla.org/mozilla-central/rev/cc2d84593658
https://hg.mozilla.org/mozilla-central/rev/7ad24b936f3b
https://hg.mozilla.org/mozilla-central/rev/347c2d2b6751
https://hg.mozilla.org/mozilla-central/rev/d26c5eb9eb33
https://hg.mozilla.org/mozilla-central/rev/0c4b84f3d824
https://hg.mozilla.org/mozilla-central/rev/0b909b1ebdf8