Instead of SetVariable having 2x2 modes for variable/lexical and
initialize/set, those 4 modes are now separate instructions, which
makes each instruction much less branchy.
Merging registers, constants and locals into single vector means:
- Better data locality
- No need to check type in Interpreter::get() and Interpreter::set()
which are very hot functions
Performance improvement is visible in almost all Octane and Kraken
tests.
Instead, generate bytecode to execute their AST nodes and save the
resulting operands inside the NewClass instruction.
Moving property expression evaluation to happen before NewClass
execution also moves along creation of new private environment and
its population with private members (private members should be visible
during property evaluation).
Before:
- NewClass
After:
- CreatePrivateEnvironment
- AddPrivateName
- ...
- AddPrivateName
- NewClass
- LeavePrivateEnvironment
By doing that all instructions required for instantiation are emitted
once in compilation and then reused for subsequent calls, instead of
running generic instantiation process for each call.
We now fuse sequences like [LessThan, JumpIf] to JumpLessThan.
This is only allowed for temporaries (i.e VM registers) with no other
references to them.
Now that the interpreter is unrolled, we can advance the program counter
manually based on the current instruction type.
This makes most instructions a bit smaller. :^)
This commit adds a HANDLE_INSTRUCTION macro that expands to everything
needed to handle a single instruction (invoking the handler function,
checking for exceptions, and advancing the program counter).
This gives a ~15% speed-up on a for loop microbenchmark, and makes
basically everything faster.
Instead of storing source offsets with each instruction, we now keep
them in a side table in Executable.
This shrinks each instruction by 8 bytes, further improving locality.
Instead of keeping bytecode as a set of disjoint basic blocks on the
malloc heap, bytecode is now a contiguous sequence of bytes(!)
The transformation happens at the end of Bytecode::Generator::generate()
and the only really hairy part is rerouting jump labels.
This required solving a few problems:
- The interpreter execution loop had to change quite a bit, since we
were storing BasicBlock pointers all over the place, and control
transfer was done by redirecting the interpreter's current block.
- Exception handlers & finalizers are now stored per-bytecode-range
in a side table in Executable.
- The interpreter now has a plain program counter instead of a stream
iterator. This actually makes error stack generation a bit nicer
since we just have to deal with a number instead of reaching into
the iterator.
This yields a 25% performance improvement on this microbenchmark:
for (let i = 0; i < 1_000_000; ++i) { }
But basically everything gets faster. :^)
This does two things:
* Clear exceptions when transferring control out of a finalizer
Otherwise they would resurface at the end of the next finalizer
(see test the new test case), or at the end of a function
* Pop one scheduled jump when transferring control out of a finalizer
This removes one old FIXME
This patch adds a new "Peephole" pass for performing small, local
optimizations to bytecode.
We also introduce the first such optimization, fusing a sequence of
some comparison instruction FooCompare followed by a JumpIf into a
new set of JumpFooCompare instructions.
This gives a ~50% speed-up on the following microbenchmark:
for (let i = 0; i < 10_000_000; ++i) {
}
But more traditional benchmarks see a pretty sizable speed-up as well,
for example 15% on Kraken/ai-astar.js and 16% on Kraken/audio-dft.js :^)
Instead of emitting a NewBigInt instruction to construct a primitive
bigint from a parsed literal, we now instantiate the BigInt on the heap
during codegen.
Instead of emitting a NewString instruction to construct a primitive
string from a parsed literal, we now instantiate the PrimitiveString on
the heap during codegen.
Instead of splitting the postfix variants into ToNumeric + Inc/Dec,
we now have dedicated PostfixIncrement and PostfixDecrement instructions
that handle both outputs in one go.
This patch moves us away from the accumulator-based bytecode format to
one with explicit source and destination registers.
The new format has multiple benefits:
- ~25% faster on the Kraken and Octane benchmarks :^)
- Fewer instructions to accomplish the same thing
- Much easier for humans to read(!)
Because this change requires a fundamental shift in how bytecode is
generated, it is quite comprehensive.
Main implementation mechanism: generate_bytecode() virtual function now
takes an optional "preferred dst" operand, which allows callers to
communicate when they have an operand that would be optimal for the
result to go into. It also returns an optional "actual dst" operand,
which is where the completion value (if any) of the AST node is stored
after the node has "executed".
One thing of note that's new: because instructions can now take locals
as operands, this means we got rid of the GetLocal instruction.
A side-effect of that is we have to think about the temporal deadzone
(TDZ) a bit differently for locals (GetLocal would previously check
for empty values and interpret that as a TDZ access and throw).
We now insert special ThrowIfTDZ instructions in places where a local
access may be in the TDZ, to maintain the correct behavior.
There are a number of progressions and regressions from this test:
A number of async generator tests have been accidentally fixed while
converting the implementation to the new bytecode format. It didn't
seem useful to preserve bugs in the original code when converting it.
Some "does eval() return the correct completion value" tests have
regressed, in particular ones related to propagating the appropriate
completion after control flow statements like continue and break.
These are all fairly obscure issues, and I believe we can continue
working on them separately.
The net test262 result is a progression though. :^)
This commit un-deprecates DeprecatedString, and repurposes it as a byte
string.
As the null state has already been removed, there are no other
particularly hairy blockers in repurposing this type as a byte string
(what it _really_ is).
This commit is auto-generated:
$ xs=$(ack -l \bDeprecatedString\b\|deprecated_string AK Userland \
Meta Ports Ladybird Tests Kernel)
$ perl -pie 's/\bDeprecatedString\b/ByteString/g;
s/deprecated_string/byte_string/g' $xs
$ clang-format --style=file -i \
$(git diff --name-only | grep \.cpp\|\.h)
$ gn format $(git ls-files '*.gn' '*.gni')
When iterating over an iterable, we get back a JS object with the fields
"value" and "done".
Before this change, we've had two dedicated instructions for retrieving
the two fields: IteratorResultValue and IteratorResultDone. These had no
fast path whatsoever and just did a generic [[Get]] access to fetch the
corresponding property values.
By replacing the instructions with GetById("value") and GetById("done"),
they instantly get caching and JIT fast paths for free, making iterating
over iterables much faster. :^)
26% speed-up on this microbenchmark:
function go(a) {
for (const p of a) {
}
}
const a = [];
a.length = 1_000_000;
go(a);
This patch makes IteratorRecord an Object. Although it's not exposed to
author code, this does allow us to store it in a VM register.
Now that we can store it in a VM register, we don't need to convert it
back and forth between IteratorRecord and Object when accessing it from
bytecode.
The big win here is avoiding 3 [[Get]] accesses on every iteration step
of for..of loops. There are also a bunch of smaller efficiencies gained.
20% speed-up on this microbenchmark:
function go(a) {
for (const p of a) {
}
}
const a = [];
a.length = 1_000_000;
go(a);
This will not meaningfully affect short array literals, but it does
give us a bit of extra perf when evaluating huge array expressions like
in Kraken/imaging-darkroom.js
Until now, the unwind context stack has not been maintained by jitted
code, which meant we were unable to support the `with` statement.
This is a first step towards supporting that by making jitted code
call out to C++ to update the unwind context stack when entering/leaving
unwind contexts.
We also introduce a new "Catch" bytecode instruction that moves the
current exception into the accumulator. It's always emitted at the start
of a "catch" block.
This works by walking a backtrace until the currently executing
native executable is found, and then mapping the native address
to its bytecode instruction.
Nuke all the per-instruction bounds checking when iterating instructions
by using raw pointers instead of indexing into a ReadonlyBytes.
The interpreter loop already checks that we're in-bounds anyway.
Instead of running a big switch statement on the opcode when checking
how long an instruction is, we now simply store that in a member
variable at construction time for instant access.
This yields a 10.2% speed-up on Kraken/ai-astar :^)
This works by adding source start/end offset to every bytecode
instruction. In the future we can make this more efficient by keeping
a map of bytecode ranges to source ranges in the Executable instead,
but let's just get traces working first.
Co-Authored-By: Andrew Kaster <akaster@serenityos.org>
If we're inside of a `with` statement scope, we have to take care to
extract the correct `this` value for use in calls when calling a method
on the binding object via an Identifier instead of a MemberExpression.
This makes Vue.js work way better in the bytecode VM. :^)
Also, 1 new pass on test262.
These passes have not been shown to actually optimize any JS, and tests
have become very flaky with optimizations enabled. Until some measurable
benefit is shown, remove the optimization passes to reduce overhead of
maintaining bytecode operations and to reduce CI churn. The framework
for optimizations will live on in git history, and can be restored once
proven useful.
Using a special instruction to access global variables allows skipping
the environment chain traversal for them and going directly to the
module/global environment. Currently, this instruction only caches the
offset for bindings that belong to the global object environment.
However, there is also an opportunity to cache the offset in the global
declarative record.
This change results in a 57% increase in speed for
imaging-gaussian-blur.js in Kraken.
- Update ECMAScriptFunctionObject::function_declaration_instantiation
to initialize local variables
- Introduce GetLocal, SetLocal, TypeofLocal that will be used to
operate on local variables.
- Update bytecode generator to emit instructions for local variables
