Introduces several new runtime mechanics for defining private fields,
including:
- Bytecode StaKeyedPropertyAsDefine
- Builtins StoreOwnIC{Trampoline|Baseline|_NoFeedback}
- Builtins KeyedDefineOwnIC{Trampoline|Baseline|_Megamorphic}
- TurboFan IR opcode JSDefineProperty
These new operations can reduce a runtime call per class field into a
more traditional Store equivalent. In the microbenchmarks, this
results in a substantial win over the status quo (~8x benchmark score
for single fields with the changes, ~20x with multiple fields).
The TurboFan JSDefineProperty op is lowered in
JSNativeContextSpecialization, however this required some hacks.
Because private fields are defined as DONT_ENUM when added to the
object, we can't find a suitable transition using the typical data
property (NONE) flags. I've added a mechanism to specify the required
PropertyAttributes for the transition we want to look up.
Details:
New bytecodes:
- StaKeyedPropertyAsDefine, which is essentially StaKeyedProperty
but with a different IC builtin (KeyedDefineOwnIC). This is a
bytecode rather than a flag for the existing StaKeyedProperty in
order to avoid impacting typical keyed stores in any way due to
additional branching and testing.
New builtins:
- StoreOwnIC{TTrampoline|Baseline|_NoFeedback} is now used for
StaNamedOwnProperty. Unlike the regular StoreIC, this variant will
no longer look up the property name in the prototype.
In adddition, this CL changes an assumption that
StoreNamedOwnProperty can't result in a map transition, as we
can't rely on the property already being present in the Map due
to an object literal boilerplate.
In the context of class features, this replaces the runtime
function %CreateDataProperty().
- KeyedDefineOwnIC{Trampoline|Baseline|_Megamorphic} is used by the
new StaKeyedPropertyAsDefine bytecode. This is similar to an
ordinary KeyedStoreIC, but will not check the prototype for
setters, and for private fields, will take the slow path if the
field already exists.
In the context of class features, this replaces the runtime
function %AddPrivateField().
TurboFan IR:
- JSDefineProperty is introduced to represent a situation where we
need to use "Define" semantics, in particular, it codifies that we
do not consult the prototype chain, and the semantics relating to
private fields are implied as well.
R=leszeks@chromium.org, syg@chromium.org, rmcilroy@chromium.org
Bug: v8:9888
Change-Id: Idcc947585c0e612f9e8533aa4e2e0f8f0df8875d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2795831
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Cr-Commit-Position: refs/heads/main@{#77377}
713ebae3b4