df923f18ca
* aarch64: constant generation cleanup Add support for MOVZ and MOVN generation via ISLE. Handle f32const, f64const, and nop instructions via ISLE. No longer call Inst::gen_constant from lower.rs. * riscv64: constant generation cleanup Handle f32const, f64const, and nop instructions via ISLE. * s390x: constant generation cleanup Fix rule priorities for "imm" term. Only handle 32-bit stack offsets; no longer use load_constant64. * x64: constant generation cleanup No longer call Inst::gen_constant from lower.rs or abi.rs. * Refactor LowerBackend::lower to return InstOutput No longer write to the per-insn output registers; instead, return an InstOutput vector of temp registers holding the outputs. This will allow calling LowerBackend::lower multiple times for the same instruction, e.g. to rematerialize constants. When emitting the primary copy of the instruction during lowering, writing to the per-insn registers is now done in lower_clif_block. As a result, the ISLE lower_common routine is no longer needed. In addition, the InsnOutput type and all code related to it can be removed as well. * Refactor IsleContext to hold a LowerBackend reference Remove the "triple", "flags", and "isa_flags" fields that are copied from LowerBackend to each IsleContext, and instead just hold a reference to LowerBackend in IsleContext. This will allow calling LowerBackend::lower from within callbacks in src/machinst/isle.rs, e.g. to rematerialize constants. To avoid having to pass LowerBackend references through multiple functions, eliminate the lower_insn_to_regs subroutines in those targets that still have them, and just inline into the main lower routine. This also eliminates lower_inst.rs on aarch64 and riscv64. Replace all accesses to the removed IsleContext fields by going through the LowerBackend reference. * Remove MachInst::gen_constant This addresses the problem described in issue https://github.com/bytecodealliance/wasmtime/issues/4426 that targets currently have to duplicate code to emit constants between the ISLE logic and the gen_constant callback. After the various cleanups in earlier patches in this series, the only remaining user of get_constant is put_value_in_regs in Lower. This can now be removed, and instead constant rematerialization can be performed in the put_in_regs ISLE callback by simply directly calling LowerBackend::lower on the instruction defining the constant (using a different output register). Since the check for egraph mode is now no longer performed in put_value_in_regs, the Lower::flags member becomes obsolete. Care needs to be taken that other calls directly to the Lower::put_value_in_regs routine now handle the fact that no more rematerialization is performed. All such calls in target code already historically handle constants themselves. The remaining call site in the ISLE gen_call_common helper can be redirected to the ISLE put_in_regs callback. The existing target implementations of gen_constant are then unused and can be removed. (In some target there may still be further opportunities to remove duplication between ISLE and some local Rust code - this can be left to future patches.)
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 and various extensions like SIMD), although it needs to be used within an external WebAssembly embedding such as Wasmtime to be part of a complete WebAssembly implementation. It is also usable as a backend for non-WebAssembly use cases: for example, there is an effort to build a Rust compiler backend using Cranelift.
Cranelift is production-ready, and is used in production in several places, all within the context of Wasmtime. It is carefully fuzzed as part of Wasmtime with differential comparison against V8 and the executable Wasm spec, and the register allocator is separately fuzzed with symbolic verification. There is an active effort to formally verify Cranelift's instruction-selection backends. We take security seriously and have a security policy as a part of Bytecode Alliance.
Cranelift has three backends: x86-64, aarch64 (aka ARM64), and s390x (aka IBM Z). All three backends fully support enough functionality for Wasm MVP, and x86-64 and aarch64 fully support SIMD as well. On x86-64, Cranelift supports both the System V AMD64 ABI calling convention used on many platforms and the Windows x64 calling convention. On aarch64, Cranelift supports the standard Linux calling convention and also has specific support for macOS (i.e., M1 / Apple Silicon).
Cranelift's code quality is within range of competitiveness to browser JIT engines' optimizing tiers. A recent paper includes third-party benchmarks of Cranelift, driven by Wasmtime, against V8 and an LLVM-based Wasm engine, WAVM (Fig 22). The speed of Cranelift's generated code is ~2% slower than that of V8 (TurboFan), and ~14% slower than WAVM (LLVM). Its compilation speed, in the same paper, is measured as approximately an order of magnitude faster than WAVM (LLVM). We continue to work to improve both measures.
The core codegen crates have minimal dependencies and are carefully written to handle malicious or arbitrary compiler input: in particular, they do not use callstack recursion.
Cranelift performs some basic mitigations for Spectre attacks on heap bounds checks, table bounds checks, and indirect branch bounds checks; see #1032 for more.
Cranelift's APIs are not yet considered stable, though we do follow semantic-versioning (semver) with minor-version patch releases.
Cranelift generally requires the latest stable Rust to build as a policy, and is tested as such, but we can incorporate fixes for compilation with older Rust versions on a best-effort basis.
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 were:
- Wasmtime non-Web wasm engine.
- Debug build backend for the Rust compiler.
- WebAssembly compiler for the SpiderMonkey engine in Firefox (currently not planned anymore; SpiderMonkey team may re-assess in the future).
- Backend for the IonMonkey JavaScript JIT compiler in Firefox (currently not planned anymore; SpiderMonkey team may re-assess in the future).
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.
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: