In #3721, we have been discussing what to do about the ARM32 backend in
Cranelift. Currently, this backend supports only 32-bit types, which is
insufficient for full Wasm-MVP; it's missing other critical bits, like
floating-point support; and it has only ever been exercised, AFAIK, via
the filetests for the individual CLIF instructions that are implemented.
We were very very thankful for the original contribution of this
backend, even in its partial state, and we had hoped at the time that we
could eventually mature it in-tree until it supported e.g. Wasm and
other use-cases. But that hasn't yet happened -- to the blame of no-one,
to be clear, we just haven't had a contributor with sufficient time.
Unfortunately, the existence of the backend and lack of active
maintainer now potentially pose a bit of a burden as we hope to make
continuing changes to the backend framework. For example, the ISLE
migration, and the use of regalloc2 that it will allow, would need all
of the existing lowering patterns in the hand-written ARM32 backend to
be rewritten as ISLE rules.
Given that we don't currently have the resources to do this, we think
it's probably best if we, sadly, for now remove this partial backend.
This is not in any way a statement of what we might accept in the
future, though. If, in the future, an ARM32 backend updated to our
latest codebase with an active maintainer were to appear, we'd be happy
to merge it (and likewise for any other architecture!). But for now,
this is probably the best path. Thanks again to the original contributor
@jmkrauz and we hope that this work can eventually be brought back and
reused if someone has the time to do so!
This adds support for the IBM z/Architecture (s390x-ibm-linux).
The status of the s390x backend in its current form is:
- Wasmtime is fully functional and passes all tests on s390x.
- All back-end features supported, with the exception of SIMD.
- There is still a lot of potential for performance improvements.
- Currently the only supported processor type is z15.
Before this patch, running the x64 new backend would require both
compiling with --features experimental_x64 and running with
`use_new_backend`.
This patches changes this behavior so that the runtime flag is not
needed anymore: using the feature flag will enforce usage of the new
backend everywhere, making using and testing it much simpler:
cargo run --features experimental_x64 ;; other CLI options/flags
This also gives a hint at what the meta language generation would look
like after switching to the new backend.
Compiling only with the x64 codegen flag gives a nice compile time speedup.
