This limits the size of each block (currently set to 1K), and gets us
closer to a canonical, more easily analysable bytecode format.
As a result of this, "Labels" are now simply entries to basic blocks.
Since there is no more 'conditional' jump (as all jumps are always
taken), JumpIf{True,False} are unified to JumpConditional, and
JumpIfNullish is renamed to JumpNullish.
Also fixes#7914 as a result of reimplementing the loop logic.
This change removes the mmap inside of Block in favor of a growing
vector of bytes. This is favorable for two reasons:
- We don't take more space than we need
- There is no limit to the growth of the vector (previously, if
the Block overstepped its 64kb boundary, it would just crash)
However, if that vector happens to resize, any pointer pointing into
that vector would become invalid. To avoid this, this commit adds an
InstructionHandle<Op> class which just stores a block and an offset
into that block.
This partially reverts c6ce7c9326.
The munmap part of that change was good, but we can't seal the blocks
since that breaks NewString and other ops that have String members.
After compiling bytecode, we should mark the memory read-only.
This currently does not work because it breaks instruction destruction.
I'm adding this anyway with a FIXME so we don't forget about it. :^)
This patch changes the LibJS bytecode to be a stream of instructions
packed one-after-the-other in contiguous memory, instead of a vector
of OwnPtr<Instruction>. This should be a lot more cache-friendly. :^)
Instructions are also devirtualized and instead have a type field
using a new Instruction::Type enum.
To iterate over a bytecode stream, one must now use
Bytecode::InstructionStreamIterator.
This patch begins the work of implementing JavaScript execution in a
bytecode VM instead of an AST tree-walk interpreter.
It's probably quite naive, but we have to start somewhere.
The basic idea is that you call Bytecode::Generator::generate() on an
AST node and it hands you back a Bytecode::Block filled with
instructions that can then be interpreted by a Bytecode::Interpreter.
This first version only implements two instructions: Load and Add. :^)
Each bytecode block has infinity registers, and the interpreter resizes
its register file to fit the block being executed.
Two new `js` options are added in this patch as well:
`-d` will dump the generated bytecode
`-b` will execute the generated bytecode
Note that unless `-d` and/or `-b` are specified, none of the bytecode
related stuff in LibJS runs at all. This is implemented in parallel
with the existing AST interpreter. :^)
