This CL fixes a crash when we build the scope chain after re-parsing
for Debugger.evaluateOnCallFrame.
The following script causes the crash:
class A {
test(){
debugger;
}
f = (x) => {}
}
let a = new A()
a.test()
The current scope search tries to be smart and descends deeper
into the scope tree based on source position. That is not a sound
approach as V8 doesn't guarantee that sibling scopes don't overlap.
In the above case V8 creates an instance initializer scope where
f is assigned (and the initializer scope is the parent scope for
the arrow function). The problem is that the initializer scope
uses the same source range as the class `A` itself, so when we
look for the scope for `test`, we descend wrongly into the
initializer scope and can't recover.
The solution is to not try and be too smart:
- First, find the closure scope with a straight-up DFS.
- Once we have that, descend from there and try to find the
closest fitting scope around the break position.
R=bmeurer@chromium.org, jarin@chromium.org
Bug: chromium:1348186
Change-Id: Ic5e20c4d12b3d768f76a17367dc0f87bcc73763b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3807594
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82216}
This is a reland of commit 491de34bcc
co-authors: Ji Qiu <qiuji@iscas.ac.cn>
Alvise De Faveri Tron <elvisilde@gmail.com>
Usman Zain <uszain@gmail.com>
Zheng Quan <vitalyankh@gmail.com>
Original change's description:
> [riscv32] Add RISCV32 backend
>
> This very large changeset adds support for RISCV32.
>
> Bug: v8:13025
> Change-Id: Ieacc857131e6620f0fcfd7daa88a0f8d77056aa9
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3736732
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Commit-Queue: Yahan Lu <yahan@iscas.ac.cn>
> Reviewed-by: ji qiu <qiuji@iscas.ac.cn>
> Reviewed-by: Andreas Haas <ahaas@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82053}
Bug: v8:13025
Change-Id: I220fae4b8e2679bdc111724e08817b079b373bd5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3807124
Commit-Queue: Yahan Lu <yahan@iscas.ac.cn>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: ji qiu <qiuji@iscas.ac.cn>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82198}
v8::TracedReference is supposed to be used from objects allocated on
CppHeap. Such objects can be in construction during garbage
collection, meaning that they are unable to invoke
Trace(v8::TraceReference) as they have not been properly set up.
It is thus necessary to use conservative tracing to find
v8::TracedReference (backed by TracedNode in GlobalHandle) in
in-construction objects.
Change-Id: I5b4ac6e7805ff7ded33f63a405db65ea08d809ad
Bug: v8:13141, chromium:1322114
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3806439
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82188}
Implement the WebAssembly.Function-based API.
With the old API, wrapping an import and export with JS Promise
Integration looked like:
WebAssembly.returnPromiseOnSuspend(<wasm_export>);
WebAssembly.suspendOnReturnedPromise(
new WebAssembly.Function(<sig>, <js_import>));
With the new API:
new WebAssembly.Function(<sig>, <wasm_export>, {promising: 'first'})
new WebAssembly.Function(<sig>, <js_import>, {suspending: 'first'})
For details, see
https://github.com/WebAssembly/js-promise-integration/pull/8/filesR=ahaas@chromium.org
Bug: v8:12191
Change-Id: Iaefaac5304a038fc39283db165b637af7e48b009
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3804669
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82183}
With streaming compilation we delay the generation of errors until after
all bytes are received, so that potentially better error messages get
generated. With this CL we also delay the generation of errors in the
combination of lazy compilation and streaming compilation.
In particular, this CL does the following:
* It avoids the creation of a `DecodeFail` task in
`FinishAsyncCompileJobWithError`, which would create an error immediately before a potential name section arrived.
* It calls `CompilationStateImpl::SetError()` so that an error is
created once the stream finishes.
* It removes the return value of `ProcessFunctionBody` so that wire
bytes continue to be received even after a validation error.
* It adds an early exit to `ProcessFunctionBody` if
`CompilationStateImpl::failed()` is true, so that we don't continue
validation after the first detected error.
R=clemensb@chromium.org
Bug: v8:12852
Change-Id: Ie8c6be243a257ef62cbb29fea6b8e0c205060680
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3802691
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82181}
Async compilation with lazy compilation generated an error message that
did not include the function name. With this CL the function name now
gets included.
R=clemensb@chromium.org
Bug: v8:12852
Change-Id: Ia8aed83a2114a2c9da1367045404b20fa8554c8a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3804863
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82172}
The serialized module contains information for each function whether the
serialized code for the function exists, and whether the function has
been executed before serialization. The latter information is used to
decide if the function should get compiled eagerly after deserialization
(in case the function has been executed before serialization), or if the
function should get compiled lazily because it will probably not be
executed anytime soon.
So far this code only worked for eager compilation. When lazy compilation
was enabled, all functions would get compiled lazily after
deserialization. With this CL the behavior described above is extended to
lazy compilation.
R=clemensb@chromium.org
Bug: v8:12926
Change-Id: Ifd6f400396222105feffa472c2e8787e1358220e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3807583
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82171}
This is a reland of commit a1392fa113
The original change was reverted due to v8:13135, which was fixed
separately.
Original change's description:
> Enable background merging when --stress-background-compile
>
> This change adds new functions to BackgroundCompileTask which closely
> match those in BackgroundDeserializeTask. These functions allow a caller
> to manage background merging of newly compiled content into an existing
> Script from the Isolate compilation cache. These functions are not yet
> exposed via the API; instead, StressBackgroundCompileThread uses them to
> increase test coverage of the merging logic.
>
> Bug: v8:12808
> Change-Id: I4d2f429164223785169fe447ce2bdd8beaee00d4
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3793959
> Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82121}
Bug: v8:12808
Change-Id: I530c6e87bbad11e178ef4abfdc25fa98530f0224
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3806590
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#82165}
Some tests assume that liftoff code is available immediately after
compilation. Add the `--no-wasm-lazy-compilation` flag to these tests
so that they work even after shipping lazy compilation.
R=clemensb@chromium.org
Bug: v8:12926
Change-Id: I839610221390822b90b25e1bef3ae727fa33d1ca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3804862
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82162}
This reverts commit a1392fa113.
Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20GC%20Stress%20-%20custom%20snapshot/43149/overview
Original change's description:
> Enable background merging when --stress-background-compile
>
> This change adds new functions to BackgroundCompileTask which closely
> match those in BackgroundDeserializeTask. These functions allow a caller
> to manage background merging of newly compiled content into an existing
> Script from the Isolate compilation cache. These functions are not yet
> exposed via the API; instead, StressBackgroundCompileThread uses them to
> increase test coverage of the merging logic.
>
> Bug: v8:12808
> Change-Id: I4d2f429164223785169fe447ce2bdd8beaee00d4
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3793959
> Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82121}
Bug: v8:12808
Change-Id: Ibb0bc2adb79e4655b39a8a6ac33d8c8ffc5ebdb9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3804602
Owners-Override: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Nico Hartmann <nicohartmann@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#82137}
This reverts commit 872b7faa32.
Reason for revert: Somewhat speculative revert because of https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux%20-%20gc%20stress/39673/overview (reverting locally resolved the issue for me)
Original change's description:
> Fix Context PromiseHook behaviour with debugger enabled
>
> This is a solution for https://github.com/nodejs/node/issues/43148.
>
> Due to differences in behaviour between code with and without the debugger enabled, some promise lifecycle events were being missed and some extra ones were being added. This change resolves this and verifies the event sequence is consistent between code with and without the debugger.
>
> Change-Id: I3dabf1dceb14233226b1752083d659f1c2f97966
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3779922
> Reviewed-by: Victor Gomes <victorgomes@chromium.org>
> Commit-Queue: Camillo Bruni <cbruni@chromium.org>
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82132}
Change-Id: I3e05adead5d8033906055e0741854da68aade2ac
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3804859
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Owners-Override: Nico Hartmann <nicohartmann@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82136}
This is a solution for https://github.com/nodejs/node/issues/43148.
Due to differences in behaviour between code with and without the debugger enabled, some promise lifecycle events were being missed and some extra ones were being added. This change resolves this and verifies the event sequence is consistent between code with and without the debugger.
Change-Id: I3dabf1dceb14233226b1752083d659f1c2f97966
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3779922
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82132}
This change adds new functions to BackgroundCompileTask which closely
match those in BackgroundDeserializeTask. These functions allow a caller
to manage background merging of newly compiled content into an existing
Script from the Isolate compilation cache. These functions are not yet
exposed via the API; instead, StressBackgroundCompileThread uses them to
increase test coverage of the merging logic.
Bug: v8:12808
Change-Id: I4d2f429164223785169fe447ce2bdd8beaee00d4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3793959
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82121}
struct.new_default may not be called for immutable structs.
Follow-up to d2c75d321e.
Change-Id: I7b682938ca5da00ef6c9bec29856133301beb6b4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3802688
Auto-Submit: Matthias Liedtke <mliedtke@chromium.org>
Commit-Queue: Matthias Liedtke <mliedtke@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82108}
Introduce RootVisitor and related class hierarchy to just handle
roots. This avoids the awkard definitions for roots visiation in all
the cases they are not needed.
Change-Id: Ib0912e4bf543db2ecf68caead6929c68d6afdda6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3782794
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82107}
Bump the memory size limit of memory64 memories from 4GB to 16GB. Tests
are added for larger sizes (5GB, 16GB).
Drive-by: Improve two decoder errors to properly include the unit,
tested by the new tests.
R=jkummerow@chromium.org
Bug: v8:10949
Change-Id: I99dfc216b9213838784214c0b65ba863831d5884
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3789507
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82105}
It's difficult to say which structs might in the future have deprecated
fields, so this CL adds tests for two more for now.
Once we add deprecated fields, we then need to define copy/move
constructs and assignment operators via
{ALLOW_COPY_AND_MOVE_WITH_DEPRECATED_FIELDS} (same as for other structs
which are not tested yet).
R=mlippautz@chromium.org
Bug: v8:13092
Change-Id: I89a330661a02d86d3d48e216b69cb6f77f02cff2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3789508
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82098}
This is a reland of commit 07e11a64e4.
The original change removed the fill_thehole_and_call_runtime bailout
in StringBuiltinsAssembler::StringToArray() so when the string
is external and cannot be unpacked, the FixedArray won't be filled
with holes before we call into the runtime, thus failing a
heap verification if a GC happens before the array is filled. This
reland adds back the bailout for this case.
Bug: v8:12718, chromium:1330410
Original change's description:
> [heap] pre-populate the single_character_string_cache
>
> This simplifies the code and removes the runtime overhead of
> spontaneously adding strings to the cache.
>
> Bug: v8:12718
> Change-Id: I2ed49bd82e3baf2563eeb8f463be72c0308c52c5
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3616553
> Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
> Commit-Queue: Joyee Cheung <joyee@igalia.com>
> Cr-Commit-Position: refs/heads/main@{#80803}
Change-Id: I25e8724d511a8d0d971fa2a9b6ba8a0eafce4413
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3793525
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82082}
If we grow memory (out-of-place, so only without trap handling and only
if the maximum is >1GB) and the previous size is close to the maximum,
then the minimum growth we calculate can be bigger than the allowed
maximum. In this situation, the {std::clamp} has undefined behaviour,
since the provided lower limit is bigger then the upper limit.
Thus apply {std::min} and {std::max} in an order such that {max_pages}
has precedence over {min_growth}.
R=thibaudm@chromium.org
Bug: chromium:1348335
Change-Id: I4f9e9ce10a0685892248eaf0e06ffd2e84b9a069
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3793396
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82081}
Due to popular demand.
As a necessary byproduct, this drops our former experimental in-progress
support for accessing struct fields from JS as `.field0` etc. If we need
something similar in the future, we'll have to build a new mechanism for
it that scales to >1020 fields.
Bug: v8:7748
Change-Id: I08b2051bd9f76cf7128f3d4c74910ca891c38130
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3793616
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82079}
Call test functions immediately, and make them print their name before
execution.
R=thibaudm@chromium.org
Change-Id: I2057e2b3c2032c342a86705dbda8992aa54493e5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3793612
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82077}
Table<any> is not allowed any more and may therefore not be generated by
the fuzzer. Instead, the new type is table<externref>.
Bug: chromium:1348437
Change-Id: Ibf788222fc777508e59178db48e6497a18b250d8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3793610
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Auto-Submit: Matthias Liedtke <mliedtke@chromium.org>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82073}
This is required by the MVP spec. In the future, it might be possible
to pass values for any immutable fields.
Bug: v8:7748
Change-Id: Ie7705b48e9d6ebb87d5e1b0a2a10556302395db6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3793383
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82072}
Currently, we canonicalize types for call_indirect by looking in the
current module for a signature of the same shape. This is not enough
as of wasm-gc. Instead, the canonical identifier representing a type
has to be computed via isorecursive canonicalization.
This change is implemented behind a flag for now.
Future work: Also integrate export wrappers with isorecursive
canonical types. We need to store wrappers in instance-independent
storage.
Drive-by:
- Always emit type check for call_indirect. We did not emit a check
only when typed-function-references was enabled, but not gc. This
is not something that will be possible long-term.
- Fix some wasm cctests.
Bug: v8:7748
Change-Id: I7cced187009ac148c833dff5e720a8bb9a717e68
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3784600
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82064}
This very large changeset adds support for RISCV32.
Bug: v8:13025
Change-Id: Ieacc857131e6620f0fcfd7daa88a0f8d77056aa9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3736732
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Yahan Lu <yahan@iscas.ac.cn>
Reviewed-by: ji qiu <qiuji@iscas.ac.cn>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82053}
It was delegating to GetDerivedMap but not handling the possible
error coming from it.
Bug: v8:11111,chromium:1347722
Change-Id: I348ed721281d8edd324f0e364d8ed45602cb9f54
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3791063
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Auto-Submit: Marja Hölttä <marja@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82046}
This is a reland of commit e895b7af73
The unit test has been updated to work correctly when
--stress-incremental-marking is enabled.
Original change's description:
> Background merging of deserialized scripts
>
> Recently, https://crrev.com/c/v8/v8/+/3681880 added new API functions
> with which an embedder could request that V8 merge newly deserialized
> script data into an existing Script from the Isolate's compilation
> cache. This change implements those new functions. This functionality is
> still disabled by default due to the flag
> merge_background_deserialized_script_with_compilation_cache.
>
> The goal of this new functionality is to reduce memory usage when
> multiple frames load the same script with a long delay between (long
> enough for the script to have been evicted from Blink's in-memory cache
> and for the top-level SharedFunctionInfo to be flushed). In that case,
> there are two Script objects for the same script: one which was found in
> the Isolate compilation cache (the "old" script), and one which was
> recently deserialized (the "new" script). The new script's object graph
> is essentially standalone: it may point to internalized strings and
> readonly objects such as the empty feedback metadata, but otherwise
> it is unconnected to the rest of the heap. The merging logic takes any
> useful data from the new script's object graph and attaches it into the
> old script's object graph, so that the new Script object and any other
> duplicated objects can be discarded. More specifically:
>
> 1. If the new Script has a SharedFunctionInfo for a particular function
> literal, and the old Script does not, then the old Script is updated
> to refer to the new SharedFunctionInfo.
> 2. If the new Script has a compiled SharedFunctionInfo for a particular
> function literal, and the old Script has an uncompiled
> SharedFunctionInfo, then the old SharedFunctionInfo is updated to
> point to the function_data and feedback_metadata from the new
> SharedFunctionInfo.
> 3. If any used object from the new object graph points to a
> SharedFunctionInfo, where the old object graph contains a matching
> SharedFunctionInfo for the same function literal, then that pointer
> is updated to point to the old SharedFunctionInfo.
>
> The document at [0] includes diagrams showing an example merge on a very
> small script.
>
> Steps 1 and 2 above are pretty simple, but step 3 requires walking a
> possibly large set of objects, so this new API lets the embedder run
> step 3 from a background thread. Steps 1 and 2 are performed later, on
> the main thread.
>
> The next important question is: in what ways can the old script's object
> graph be modified during the background execution of step 3, or during
> the time after step 3 but before steps 1 and 2?
>
> A. SharedFunctionInfos can go from compiled to uncompiled due to
> flushing. This is okay; the worst outcome is that the function would
> need to be compiled again later. Such a risk is already present,
> since V8 doesn't keep IsCompiledScopes for every compiled function in
> a background-deserialized script.
> B. SharedFunctionInfos can go from uncompiled to compiled due to lazy
> compilation. This is also okay; the merge completion logic on the
> main thread will just keep this lazily compiled data rather than
> inserting compiled data from the newly deserialized object graph.
> C. SharedFunctionInfos can be cleared from the Script's weak array if
> they are no longer referenced. This is mostly okay, because any
> SharedFunctionInfo that is needed by the background merge is strongly
> referenced and therefore can't be cleared. The only problem arises if
> the top-level SharedFunctionInfo gets cleared, so the merge task must
> deliberately keep a reference to that one.
> D. SharedFunctionInfos can be created if they are needed due to lazy
> compilation of a parent function. This change is somewhat troublesome
> because it invalidates the background thread's work and requires a
> re-traversal on the main thread to update any pointers that should
> point to this lazily compiled SharedFunctionInfo.
>
> At a high level, this change implements three previously unimplemented
> functions in BackgroundDeserializeTask (in compiler.cc) and updates one:
>
> - BackgroundDeserializeTask::SourceTextAvailable, run on the main
> thread, checks whether there is a matching Script in the Isolate
> compilation cache which doesn't already have a top-level
> SharedFunctionInfo. If so, it saves that Script in a persistent
> handle.
> - BackgroundDeserializeTask::ShouldMergeWithExistingScript checks
> whether the persistent handle from the first step exists (a fast
> operation which can be called from any thread).
> - BackgroundDeserializeTask::MergeWithExistingScript, run on a
> background thread, performs step 3 of the merge described above and
> generates lists of persistent data describing how the main thread can
> complete the merge.
> - BackgroundDeserializeTask::Finish is updated to perform the merge
> steps 1 and 2 listed above, as well as a possible re-traversal of the
> graph if required due to newly created SharedFunctionInfos in the old
> Script.
>
> The merge logic has nothing to do with deserialization, and indeed I
> hope to reuse it for background compilation tasks as well, so it is all
> contained within a new class BackgroundMergeTask (in compiler.h,cc). It
> uses a second class, ForwardPointersVisitor (in compiler.cc) to perform
> the object visitation that updates pointers to SharedFunctionInfos.
>
> [0] https://docs.google.com/document/d/1UksB5Vm7TT1-f3S9W1dK_rP9jKn_ly0WVm_UDPpWuBw/edit
>
> Bug: v8:12808
> Change-Id: Id405869e9d5b106ca7afd9c4b08cb5813e6852c6
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3739232
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
> Cr-Commit-Position: refs/heads/main@{#81941}
Bug: v8:12808
Change-Id: Id2036dfa4eba8670cac899773d7a906825fa2c50
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3787266
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#82045}
