Add unwinding and recover support for wasm using WebAssembly exception
handling. This still has a few gotchas:
* Many WASI systems don't support exception handling yet.
For example, see:
https://github.com/bytecodealliance/wasmtime/issues/2049
* Asyncify doesn't support wasm exception handling:
https://github.com/WebAssembly/binaryen/issues/4470
This means it's not possible to use goroutines together with
panic/recover.
* The current way that exceptions are implemented pretend to be C++
exceptions, but work slightly differently. If C++ code is called
(for example through CGo) that raises an exception, that exception
will be eaten by TinyGo and not be propagated. This is fixable, it
just hasn't been implemented (because we don't actually support C++
right now).
I hope that these issues will be resolved over time. At least for now,
people who need `recover()` have a way to use it.
This commit adds support for LLVM 16 and switches to it by default. That
means three LLVM versions are supported at the same time: LLVM 14, 15,
and 16.
This commit includes work by QuLogic:
* Part of this work was based on a PR by QuLogic:
https://github.com/tinygo-org/tinygo/pull/3649
But I also had parts of this already implemented in an old branch I
already made for LLVM 16.
* QuLogic also provided a CGo fix here, which is also incorporated in
this commit:
https://github.com/tinygo-org/tinygo/pull/3869
The difference with the original PR by QuLogic is that this commit is
more complete:
* It switches to LLVM 16 by default.
* It updates some things to also make it work with a self-built LLVM.
* It fixes the CGo bug in a slightly different way, and also fixes
another one not included in the original PR.
* It does not keep compiler tests passing on older LLVM versions. I
have found this to be quite burdensome and therefore don't generally
do this - the smoke tests should hopefully catch most regressions.
This gives a small improvement now, and is needed to be able to use the
Heap2Stack transform that's available in the Attributor pass. This
Heap2Stack transform could replace our custom OptimizeAllocs pass.
Most of the changes are just IR that changed, the actual change is
relatively small.
To give an example of why this is useful, here is the code size before
this change:
$ tinygo build -o test -size=short ./testdata/stdlib.go
code data bss | flash ram
95620 1812 968 | 97432 2780
$ tinygo build -o test -size=short ./testdata/stdlib.go
code data bss | flash ram
95380 1812 968 | 97192 2780
That's a 0.25% reduction. Not a whole lot, but nice for such a small
patch.
Ayke van Laethem
Elliott Sales de Andrade
Damian Gryski