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.
Filling a typed array with an integer shouldn't have to go through the
generic Set for every element.
This knocks a 7% item down to <1% in profiles of Another World JS at
https://cyxx.github.io/another_js/
When comparing two numbers, we can avoid a lot of implicit type
conversion nonsense and go straight to comparison, saving time in the
most common case.
These were out-of-line because we had some ideas about marking
instruction streams PROT_READ only, but that seems pretty arbitrary and
there's a lot of performance to be gained by putting these inline.
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
This patch stops emitting the BlockDeclarationInstantiation instruction
when there are no locals, and no function declarations in the scope.
We were spending 20% of CPU time on https://ventrella.com/Clusters/ just
creating empty environments for no reason.
Instead of relying on native stack overflows to kick us out of circular
proxy chains, we now keep track of the recursion depth and kick
ourselves out if it exceeds 10'000.
This fixes an issue where compiler tail/sibling call optimizations would
turn infinite recursion into infinite loops, and thus never hit a stack
overflow to kick itself out.
For whatever reason, we've only seen the issue on SerenityOS with UBSAN,
but it could theoretically happen on any platform.
If the minimal amount of required bindings is known in advance, it could
be used to ensure capacity to avoid resizing the internal vector that
holds bindings.
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.
Instead of storing a full JS::Completion for the "throw completion"
case, we now store a simple JS::Value (wrapped in ErrorValue for the
type system).
This shrinks TCO<void> and TCO<Value> (the most common TCOs) by 8 bytes,
which has a non-trivial impact on performance.
If the callee is already a temporary register, we don't need to copy it
to *another* temporary before evaluating arguments. None of the
arguments will clobber the existing temporary anyway.
We only need to make copies of locals here, in case the locals are
modified by something like increment/decrement expressions.
Registers and constants can slip right through, without being Mov'ed
into a temporary first.
We know that `undefined` in the global scope is always the proper
undefined value. This commit takes advantage of that by simply emitting
a constant undefined value instead.
Unfortunately we can't be so sure in other scopes.
This helps some of the Cloudflare Turnstile stuff run faster, since they
are deliberately screwing with JS engines by asking us to do a bunch of
bitwise operations on e.g 65535.56
By rounding such values in bytecode generation, the interpreter can stay
on the happy path while executing, and finish quite a bit faster.
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.
Before this change, switch codegen would interleave bytecode like this:
(test for case 1)
(code for case 1)
(test for case 2)
(code for case 2)
This meant that we often had to make many large jumps while looking for
the matching case, since code for each case can be huge.
It now looks like this instead:
(test for case 1)
(test for case 2)
(code for case 1)
(code for case 2)
This way, we can just fall through the tests until we hit one that fits,
without having to make any large jumps.
This removes a layer of indirection in the bytecode where we had to make
sure all the initializer elements were laid out in sequential registers.
Array expressions no longer clobber registers permanently, and they can
be reused immediately afterwards.
This patch adds a register freelist to Bytecode::Generator and switches
all operands inside the generator to a new ScopedOperand type that is
ref-counted and automatically frees the register when nothing uses it.
This dramatically reduces the size of bytecode executable register
windows, which were often in the several thousands of registers for
large functions. Most functions now use less than 100 registers.
The first block in every executable will always execute first, so if it
ends up doing a ResolveThisBinding, it's fine for all other blocks
within the same executable to use the same `this` value.
In the common case, parseInt() is being called with strings that don't
have leading whitespace. By checking for that first, we can avoid the
cost of trimming and multiple malloc/GC allocations.
Once executed, this instruction will always produce the same result
in subsequent executions, so it's okay to cache it.
Unfortunately it may throw, so we can't just hoist it to the top of
every executable, since that would break observable execution order.
