71ead6e31d
This implements all of the ops on I128 that are implemented by the legacy x86 backend, and includes all that are required by at least one major use-case (cg_clif rustc backend). The sequences are open-coded where necessary; for e.g. the bit operations, this can be somewhat complex, but these sequences have been tested carefully. This PR also includes a drive-by fix of clz/ctz for 8- and 16-bit cases where they were incorrect previously. Also includes ridealong fixes developed while bringing up cg_clif support, because they are difficult to completely separate due to other refactors that occurred in this PR: - fix REX prefix logic for some 8-bit instructions. When using an 8-bit register in 64-bit mode on x86-64, the REX prefix semantics are somewhat subtle: without the REX prefix, register numbers 4--7 correspond to the second-to-lowest byte of the first four registers (AH, CH, BH, DH), whereas with the REX prefix, these register numbers correspond to the usual encoding (SPL, BPL, SIL, DIL). We could always emit a REX byte for instructions with 8-bit cases (this is harmless even if unneeded), but this would unnecessarily inflate code size; instead, the usual approach is to emit it only for these registers. This logic was present in some cases but missing for some other instructions: divide, not, negate, shifts. Fixes #2508. - avoid unaligned SSE loads on some f64 ops. The implementations of several FP ops, such as fabs/fneg, used SSE instructions. This is not a problem per-se, except that load-op merging did not take *alignment* into account. Specifically, if an op on an f64 loaded from memory happened to merge that load, and the instruction into which it was merged was an SSE instruction, then the SSE instruction imposes stricter (128-bit) alignment requirements than the load.f64 did. This PR simply forces any instruction lowerings that could use SSE instructions to implement non-SIMD operations to take inputs in registers only, and avoid load-op merging. Fixes #2507. - two bugfixes exposed by cg_clif: urem/srem.i8, select.b1. - urem/srem.i8: the 8-bit form of the DIV instruction on x86-64 places the remainder in AH, not RDX, different from all the other width-forms of this instruction. - select.b1: we were not recognizing selects of boolean values as integer-typed operations, so we were generating XMM moves instead (!).
Cranelift Code Generator
A Bytecode Alliance project
Cranelift is a low-level retargetable code generator. It translates a target-independent intermediate representation into executable machine code.
For more information, see the documentation.
For an example of how to use the JIT, see the JIT Demo, which implements a toy language.
For an example of how to use Cranelift to run WebAssembly code, see Wasmtime, which implements a standalone, embeddable, VM using Cranelift.
Status
Cranelift currently supports enough functionality to run a wide variety of programs, including all the functionality needed to execute WebAssembly MVP functions, although it needs to be used within an external WebAssembly embedding to be part of a complete WebAssembly implementation.
The x86-64 backend is currently the most complete and stable; other architectures are in various stages of development. Cranelift currently supports both the System V AMD64 ABI calling convention used on many platforms and the Windows x64 calling convention. The performance of code produced by Cranelift is not yet impressive, though we have plans to fix that.
The core codegen crates have minimal dependencies, support no_std mode (see below), and do not require any host floating-point support, and do not use callstack recursion.
Cranelift does not yet perform mitigations for Spectre or related security issues, though it may do so in the future. It does not currently make any security-relevant instruction timing guarantees. It has seen a fair amount of testing and fuzzing, although more work is needed before it would be ready for a production use case.
Cranelift's APIs are not yet stable.
Cranelift currently requires Rust 1.37 or later to build.
Contributing
If you're interested in contributing to Cranelift: thank you! We have a contributing guide which will help you getting involved in the Cranelift project.
Planned uses
Cranelift is designed to be a code generator for WebAssembly, but it is general enough to be useful elsewhere too. The initial planned uses that affected its design are:
- WebAssembly compiler for the SpiderMonkey engine in Firefox.
- Backend for the IonMonkey JavaScript JIT compiler in Firefox.
- Debug build backend for the Rust compiler.
- Wasmtime non-Web wasm engine.
Building Cranelift
Cranelift uses a conventional Cargo build process.
Cranelift consists of a collection of crates, and uses a Cargo
Workspace,
so for some cargo commands, such as cargo test, the --all is needed
to tell cargo to visit all of the crates.
test-all.sh at the top level is a script which runs all the cargo
tests and also performs code format, lint, and documentation checks.
Building with no_std
The following crates support `no_std`, although they do depend on liballoc:
- cranelift-entity
- cranelift-bforest
- cranelift-codegen
- cranelift-frontend
- cranelift-native
- cranelift-wasm
- cranelift-module
- cranelift-preopt
- cranelift
To use no_std mode, disable the std feature and enable the core feature. This currently requires nightly rust.
For example, to build `cranelift-codegen`:
cd cranelift-codegen
cargo build --no-default-features --features core
Or, when using cranelift-codegen as a dependency (in Cargo.toml):
[dependency.cranelift-codegen]
...
default-features = false
features = ["core"]
no_std support is currently "best effort". We won't try to break it, and we'll accept patches fixing problems, however we don't expect all developers to build and test no_std when submitting patches. Accordingly, the ./test-all.sh script does not test no_std.
There is a separate ./test-no_std.sh script that tests the no_std support in packages which support it.
It's important to note that cranelift still needs liballoc to compile. Thus, whatever environment is used must implement an allocator.
Also, to allow the use of HashMaps with no_std, an external crate called hashmap_core is pulled in (via the core feature). This is mostly the same as std::collections::HashMap, except that it doesn't have DOS protection. Just something to think about.
Log configuration
Cranelift uses the log crate to log messages at various levels. It doesn't
specify any maximal logging level, so embedders can choose what it should be;
however, this can have an impact of Cranelift's code size. You can use log
features to reduce the maximum logging level. For instance if you want to limit
the level of logging to warn messages and above in release mode:
[dependency.log]
...
features = ["release_max_level_warn"]
Editor Support
Editor support for working with Cranelift IR (clif) files: