add riscv64 backend for cranelift.

[yuyang-ok]

I am been trying to add riscv64 backend for cranelift these days.
right now I have pass all run test in filetests.

some features not implemented right now.
i128 mul div rem, all simd type and compare overflow.

some test need platform support.
like bitrev need qemu-riscv64 support bitmanip and zbkb extension (don't know how to enable it.).

[yuyang-ok]

@cfallin I think we are ready.
maybe some part not appropriate like https://github.com/yuyang-ok/wasmtime/blob/risc-v/crates/wasmtime/src/engine.rs#L493 .
maybe you can help me a little??

[a1phyr]

I think you could do the same that for s390x, i.e. calling getauxval by yourself.

You can find a RISC-V example in std_detect (the implementation of is_riscv64_feature_detected!) here.

[yuyang-ok]

I think you could do the same that for s390x, i.e. calling getauxval by yourself.

still look a little hard to use to me. look like need use C???

[yuyang-ok]

@cfallin what do you think appropriate to solve is_riscv64_feature_detected???

[cfallin]

@cfallin what do you think appropriate to solve is_riscv64_feature_detected???

If we want to wait for stabilization of the feature-detection macro in the standard library, I don't see anything wrong with assuming a baseline RISC-V ISA level for now (in other words, running with no features ever detected). Does this seem reasonable or would it result in important optimizations going missing?

[cfallin]

@yuyang-ok -- I went over the rest of the code and I think this looks generally fine. At least, passing all Wasm core tests indicates that this is of sufficient quality to merge, and can be refined and improved more in-tree.

I do have one minor comment below; and there's my answer to the getauxval question above. I'm not opposed to ignoring the getauxval issue for now (and simply not detecting features), if baseline RISC-V without extra ISA features is good enough to get started. And re: the below, a comment and factoring out the logic to a helper should be enough I think. Let me know once you've done this and then we can merge.

Thanks so much for the patience and hard work as we've reviewed this; I'm really excited to see it merge soon!

[yuyang-ok]

Does this seem reasonable or would it result in important optimizations going missing?

popcnt,ctz,rev8,brev8 will fallback to loop implementation, seen reasonable to me, I think these instructions are used rare to me.

[cfallin]

Updates look good to me -- thanks!

I'm going to go ahead and merge this now. Thanks again @yuyang-ok -- this was a huge amount of work.

More improvements are always welcome of course, from you and others -- anyone who wants to talk about further improvements to the RISC-V backend, please feel free to join our project meeting or file issues!

[yuyang-ok]

@cfallin ok,thanks. :-)

[rice7th]

@cfallin ok,thanks. :-)

Congratulations!

[martasp]

How can I use this feature, is there documentation?
How can I set a target risc5 and produce Linux risc5 elf binary?
I would want to use it like that:

wasmtime exampleProgram.wasm --target risc5 

[archanox]

This work is for RISC-V not risc5.
You'll likely need to use riscv64gc as per the changes in this PR.

[martasp]

I see that we have binaries riscv64gc here: https://github.com/bytecodealliance/wasmtime/releases/tag/v2.0.2 therefore It should probably work on riscv64 Linux. So I tried to install wasmtime in riscv64 Linux but without success.
Probably there is a difference between riscv64 and riscv64gc but I'm kinda new to these things, where can I learn it, any good resources?

[root@localhost ~]# curl https://wasmtime.dev/install.sh -sSf | bash
Error: Sorry! Wasmtime currently only provides pre-built binaries for x86_64 (Linux, macOS, Windows), aa
rch64 (Linux, macOS), and s390x (Linux).
 
[root@localhost ~]# uname
Linux
[root@localhost ~]# uname -p
riscv64

[bjorn3]

The script at https://wasmtime.dev/install.sh hasn't been updated yet for riscv64 support. You should probably directly download the binary from https://github.com/bytecodealliance/wasmtime/releases/tag/v2.0.2.