1781242 - Simplify JitContext a bit

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, task, P3)

Description

[Jan de Mooij [:jandem]]

JitContext has some complexity, for example multiple contexts can be nested.

Last week I wrote some patches to simplify this to prepare for bug 1774178, but then went with a different approach for that bug. We should still land the JitContext parts though.

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 1 - Remove support for nested JitContexts. r?iain!

A long time ago, JitContext was also used for entering JIT code, but now we only
use it for the compiler backend where we don't need to support nesting.

This requires some minor changes to avoid having multiple active contexts on the
stack, but makes it easier to reason about.

Comment 2

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 2 - Remove MacroAssembler::jitContext. r?iain!

One of the MacroAssembler constructors instantiates a JitContext lazily, but
it's simpler to require the callers to create a JitContext.

Depends on D152762

Comment 3

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 3 - Ensure JitContext always has an allocator. r?iain!

With this patch we always pass a non-null allocator to the JitContext constructor,
and then never change it. Use references instead of pointers to make this clearer.

This lets us clean up more code: AutoJitContextAlloc can be removed and the
MacroAssembler no longer needs the constructor to optionally instantiate that
class.

Depends on D152763

Comment 4

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 4 - Remove AutoJitContextAlloc.h and some references. r?iain!

Depends on D152765

Comment 5

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 5 - Cache JitContext* in the MacroAssembler. r?iain!

The MacroAssembler is the main place where we still do TLS lookups for JitContext.
We can avoid that by caching the JitContext in the MacroAssembler.

This works because we now always instantiate the JitContext before we create the assembler.
Exceptions are Wasm compilations where we currently don't need the JitContext, and off-thread
JIT compilations where we can reset the context manually.

Depends on D152766

Comment 6

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 6 - Use jitContext_ instead of doing a TLS lookup in the MacroAssembler. r?iain!

Depends on D152767

Comment 7

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 5 - Remove arm32/arm64 assembler buffer id. r?iain!

This removes some old code to tag debug spew with an ID per assembler, based on a
counter stored in JitContext. Usually there's only one assembler per JitContext and
we were also not using this for Wasm compilations (it always used id 0), so this
patch removes it.

Depends on D152766

Comment 8

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 6 - Always pass TempAllocator to MacroAssembler. r?iain!

This follows the Wasm code and prepares for (a) removing the second MacroAssembler
constructor and (b) removing the allocator from JitContext.

Depends on D152846

Comment 9

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 7 - Remove Wasm-specific MacroAssembler constructor. r?iain!

MacroAssembler now has a single constructor, instead of three different ones
before this patch stack.

Depends on D152847

Comment 10

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 8 - Remove allocator from JitContext. r?iain!

Depends on D152848

Comment 11

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 9 - Store CompileRealm and CompileRuntime in the MacroAssembler. r?iain!

This lets us replace relatively slow TLS lookups with a simple dereference.

This also removes the realm from JitContext. The runtime still has a few uses
in the MIR backend.

Depends on D152849

Comment 12

[Jan de Mooij [:jandem]]

Attachment: Bug 1781242 part 10 - Mark JitContext MOZ_RAII, update a comment. r?iain!

Depends on D152850

Comment 13

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/80977afb9edc
part 1 - Remove support for nested JitContexts. r=iain
https://hg.mozilla.org/integration/autoland/rev/bbf8fe85e541
part 2 - Remove MacroAssembler::jitContext. r=iain
https://hg.mozilla.org/integration/autoland/rev/090af82e2597
part 3 - Ensure JitContext always has an allocator. r=iain
https://hg.mozilla.org/integration/autoland/rev/8de9467effb2
part 4 - Remove AutoJitContextAlloc.h and some references. r=iain
https://hg.mozilla.org/integration/autoland/rev/83749da6cc3c
part 5 - Remove arm32/arm64 assembler buffer id. r=iain
https://hg.mozilla.org/integration/autoland/rev/175d3849180d
part 6 - Always pass TempAllocator to MacroAssembler. r=iain
https://hg.mozilla.org/integration/autoland/rev/322cae63ed26
part 7 - Remove Wasm-specific MacroAssembler constructor. r=iain
https://hg.mozilla.org/integration/autoland/rev/28f6e56b0ebb
part 8 - Remove allocator from JitContext. r=iain
https://hg.mozilla.org/integration/autoland/rev/371648da494c
part 9 - Store CompileRealm and CompileRuntime in the MacroAssembler. r=iain
https://hg.mozilla.org/integration/autoland/rev/b1526450d444
part 10 - Mark JitContext MOZ_RAII, update a comment. r=iain

Comment 14

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/80977afb9edc
https://hg.mozilla.org/mozilla-central/rev/bbf8fe85e541
https://hg.mozilla.org/mozilla-central/rev/090af82e2597
https://hg.mozilla.org/mozilla-central/rev/8de9467effb2
https://hg.mozilla.org/mozilla-central/rev/83749da6cc3c
https://hg.mozilla.org/mozilla-central/rev/175d3849180d
https://hg.mozilla.org/mozilla-central/rev/322cae63ed26
https://hg.mozilla.org/mozilla-central/rev/28f6e56b0ebb
https://hg.mozilla.org/mozilla-central/rev/371648da494c
https://hg.mozilla.org/mozilla-central/rev/b1526450d444