bd3dcd313d
The relaxed-simd proposal for WebAssembly adds a fused-multiply-add operation for `v128` types so I was poking around at Cranelift's existing support for its `fma` instruction. I was also poking around at the x86_64 ISA's offerings for the FMA operation and ended up with this PR that improves the lowering of the `fma` instruction on the x64 backend in a number of ways: * A libcall-based fallback is now provided for `f32x4` and `f64x2` types in preparation for eventual support of the relaxed-simd proposal. These encodings are horribly slow, but it's expected that if FMA semantics must be guaranteed then it's the best that can be done without the `fma` feature. Otherwise it'll be up to producers (e.g. Wasmtime embedders) whether wasm-level FMA operations should be FMA or multiply-then-add. * In addition to the existing `vfmadd213*` instructions opcodes were added for `vfmadd132*`. The `132` variant is selected based on which argument can have a sinkable load. * Any argument in the `fma` CLIF instruction can now have a `sinkable_load` and it'll generate a single FMA instruction. * All `vfnmadd*` opcodes were added as well. These are pattern-matched where one of the arguments to the CLIF instruction is an `fneg`. I opted to not add a new CLIF instruction here since it seemed like pattern matching was easy enough but I'm also not intimately familiar with the semantics here so if that's the preferred approach I can do that too.
filetests
Filetests is a crate that contains multiple test suites for testing
various parts of cranelift. Each folder under cranelift/filetests/filetests is a different
test suite that tests different parts.
Adding a runtest
One of the available testsuites is the "runtest" testsuite. Its goal is to compile some piece of clif code, run it and ensure that what comes out is what we expect.
To build a run test you can add the following to a file:
test interpret
test run
target x86_64
target aarch64
target s390x
function %band_f32(f32, f32) -> f32 {
block0(v0: f32, v1: f32):
v2 = band v0, v1
return v2
}
; run: %band_f32(0x0.5, 0x1.0) == 0x1.5
Since this is a run test for band we can put it in: runtests/band.clif.
Once we have the file in the test suite we can run it by invoking: cargo run -- test filetests/filetests/runtests/band.clif from the cranelift directory.
The first lines tell clif-util what kind of tests we want to run on this file.
test interpret invokes the interpreter and checks if the conditions in the ; run comments pass. test run does the same, but compiles the file and runs it as a native binary.
For more information about testing see testing.md.