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 :^)
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.
This is just something I spotted looking around the code, previously
the PassPipelineExecutable was passed by value to
generate_cfg_for_block, which generated the CFG then just dropped it on
the floor. Making this a reference results in the CFG actually getting
generated.
We were missing some unwind related control flow paths, and followed
some in improper ways, leading us to access a dead unwind frame in some
cases, as well as generating a technically wrong CFG.
This reorders the ways EnterUnwindContext works and alleviates those
errors.
This uses a newly added instruction `ScheduleJump`
This instruction tells the finally proceeding it, that instead of
jumping to it's next block it should jump to the designated block.
To achieve this it now uses recursive descend, to make the state
managements easier.
With this we now correctly handle try-catch-finally blocks correctly,
modeling all possible controll flows between these blocks, which allows
analysis and optimization passes to make more accurate descisions about
accessibility of the enclosed blocks
This commit adds a bunch of passes, the most interesting of which is a
pass that merges blocks together, and a pass that places blocks that
flow into each other next to each other, and a very simply pass that
removes duplicate basic blocks.
Note that this does not remove the jump at the end of each block in that
pass to avoid scope creep in the passes.
