435b6894d7
I noticed recently that for the `ImmRegRegShift` addressing mode Cranelift will unconditionally emit at least a 1-byte immediate for the offset to be added to the register addition computation, even when the offset is zero. In this case though the instruction encoding can be slightly more compact and remove a byte. This commit started off by applying this optimization, which resulted in the `*.clif` test changes in this commit. Further reading this code, however, I personally found it quite hard to follow what was happening with all the various branches and ModRM/SIB bits. I reviewed these encodings in the x64 architecture manual and attempted to improve the logic for encoding here. The new version in this commit is intended to be functionally equivalent to the prior version where dropping a zero-offset from the `ImmRegRegShift` variant is the only change.
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.