3c8cb7b908
This PR updates the "coloring" scheme that accounts for side-effects in the MachInst lowering logic. As a result, the new backends will now be able to merge effectful operations (such as memory loads) *into* other operations; previously, only the other way (pure ops merged into effectful ops) was possible. This will allow, for example, a load+ALU-op combination, as is common on x86. It should even allow a load + ALU-op + store sequence to merge into one lowered instruction. The scheme arose from many fruitful discussions with @julian-seward1 (thanks!); significant credit is due to him for the insights here. The first insight is that given the right basic conditions, i.e. that the root instruction is the only use of an effectful instruction's result, all we need is that the "color" of the effectful instruction is *one less* than the color of the current instruction. It's easier to think about colors on the program points between instructions: if the color coming *out* of the first (effectful def) instruction and *in* to the second (effectful or effect-free use) instruction are the same, then they can merge. Basically the color denotes a version of global state; if the same, then no other effectful ops happened in the meantime. The second insight is that we can keep state as we scan, tracking the "current color", and *update* this when we sink (merge) an op. Hence when we sink a load into another op, we effectively *re-color* every instruction it moved over; this may allow further sinks. Consider the example (and assume that we consider loads effectful in order to conservatively ensure a strong memory model; otherwise, replace with other effectful value-producing insts): ``` v0 = load x v1 = load y v2 = add v0, 1 v3 = add v1, 1 ``` Scanning from bottom to top, we first see the add producing `v3` and we can sink the load producing `v1` into it, producing a load + ALU-op machine instruction. This is legal because `v1` moves over only `v2`, which is a pure instruction. Consider, though, `v2`: under a simple scheme that has no other context, `v0` could not sink to `v2` because it would move over `v1`, another load. But because we already sunk `v1` down to `v3`, we are free to sink `v0` to `v2`; the update of the "current color" during the scan allows this. This PR also cleans up the `LowerCtx` interface a bit at the same time: whereas previously it always gave some subset of (constant, mergeable inst, register) directly from `LowerCtx::get_input()`, it now returns zero or more of (constant, mergable inst) from `LowerCtx::maybe_get_input_as_source_or_const()`, and returns the register only from `LowerCtx::put_input_in_reg()`. This removes the need to explicitly denote uses of the register, so it's a little safer. Note that this PR does not actually make use of the new ability to merge loads into other ops; that will come in future PRs, especially to optimize the `x64` backend by using direct-memory operands.
wasmtime
A standalone runtime for WebAssembly
A Bytecode Alliance project
Guide | Contributing | Website | Chat
Installation
The Wasmtime CLI can be installed on Linux and macOS with a small install script:
$ curl https://wasmtime.dev/install.sh -sSf | bash
Windows or otherwise interested users can download installers and binaries directly from the GitHub Releases page.
Example
If you've got the Rust compiler installed then you can take some Rust source code:
fn main() {
println!("Hello, world!");
}
and compile/run it with:
$ rustup target add wasm32-wasi
$ rustc hello.rs --target wasm32-wasi
$ wasmtime hello.wasm
Hello, world!
Features
-
Lightweight. Wasmtime is a standalone runtime for WebAssembly that scales with your needs. It fits on tiny chips as well as makes use of huge servers. Wasmtime can be embedded into almost any application too.
-
Fast. Wasmtime is built on the optimizing Cranelift code generator to quickly generate high-quality machine code at runtime.
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Configurable. Whether you need to precompile your wasm ahead of time, generate code blazingly fast with Lightbeam, or interpret it at runtime, Wasmtime has you covered for all your wasm-executing needs.
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WASI. Wasmtime supports a rich set of APIs for interacting with the host environment through the WASI standard.
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Standards Compliant. Wasmtime passes the official WebAssembly test suite, implements the official C API of wasm, and implements future proposals to WebAssembly as well. Wasmtime developers are intimately engaged with the WebAssembly standards process all along the way too.
Language Support
You can use Wasmtime from a variety of different languages through embeddings of the implementation:
- Rust - the
wasmtimecrate - C - the
wasm.h,wasi.h, andwasmtime.hheaders - Python - the
wasmtimePyPI package - .NET - the
WasmtimeNuGet package - Go - the
wasmtime-gorepository
Documentation
📚 Read the Wasmtime guide here! 📚
The wasmtime guide is the best starting point to learn about what Wasmtime can do for you or help answer your questions about Wasmtime. If you're curious in contributing to Wasmtime, it can also help you do that!.
It's Wasmtime.