By using separate struct we can avoid updating AST node and
ECMAScriptFunctionObject constructors every time there is a need to
add or remove some additional information colllected during parsing.
Allows to skip function environment allocation for non-arrow functions
if the only reason it is needed is to hold `this` binding.
The parser is changed to do following:
- If a function is an arrow function and uses `this` then all functions
in a scope chain are marked to allocate function environment for
`this` binding.
- If a function uses `new.target` then all functions in a scope chain
are marked to allocate function environment.
`ordinary_call_bind_this()` is changed to put `this` value in execution
context when function environment allocation is skipped.
35% improvement in Octane/typescript.js
50% improvement in Octane/deltablue.js
19% improvement in Octane/raytrace.js
This allows us to skip allocating a function environment in cases where
it was previously impossible because the arguments object needed a
binding.
This change does not bring visible improvement in Kraken or Octane
benchmarks but seems useful to have anyway.
By doing this, we can remove all the special-case checks for `length`
from the generic GetById and GetByIdWithThis code paths, making every
other property lookup a bit faster.
Small progressions on most benchmarks, and some larger progressions:
- 12% on Octane/crypto.js
- 6% on Kraken/ai-astar.js
The VERIFY assumed that we either have a finally block which we already
visited through a previous boundary or have no finally block what so
ever; But since 301a1fc763 we propagate
finalizers through unwind scopes breaking that assumption.
It wasn't safe to use addition_would_overflow(a, -b) to check if
subtraction (a - b) would overflow, since it doesn't cover this case.
I don't know why we didn't have subtraction_would_overflow(), so this
patch adds it. :^)
With this only `ContinuePendingUnwind` needs to dynamically check if a
scheduled return needs to go through a `finally` block, making the
interpreter loop a bit nicer
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.
The last completion value in a function is not exposed to the language,
since functions always either return something, or undefined.
Given this, we can avoid emitting code that propagates the completion
value from various statements, as long as we know we're generating code
for a context where the completion value is not accessible. In practical
terms, this means that function code gets to do less completion
shuffling, while global and eval code has to keep doing it.
This means that SetVariable instructions will now remember which
(relative) environment contains the targeted binding, letting it bypass
the full binding resolution machinery on subsequent accesses.
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.
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.
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.
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.
