Finally :) My coworker back in 2017 implemented the WebAssembly backend for the Go compiler[0], and noted at the time that WASM doesn't have any equivalent to setjmp/longjmp. As a result, Go's WebAssembly implementation actually emulates a register machine on top of the WASM stack machine. Quoting him (some parts omitted):
> For example its architecture is a stack machine instead of a register machine. This means that it isn't immediately suitable as simply yet another target at the last stage of the Go compiler next to x86 and friends.
> There might be an alternative: Emulate what we need. We may use the stack machine to emulate a register machine and hopefully do so in a reasonably performant way.
> WebAssembly has linear memory with load and store instructions, which is good. We would not use WebAssembly's call instruction at all and instead roll our own stack management and call mechanism. Stacks would live on that linear memory and be managed by the Go runtime. The stackpointer would be a global variable. All code would live in a single WebAssembly function. The toplevel would be a giant switch statement (or WebAssembly's br_table based equivalent) with one branch for each function. Each function would have another switch statement with one branch per SSA basic block.
> There are some details that I'm omitting here, but in the big picture this looks like a decent register machine to me. Of course the performance of this heavily depends on how well WebAssembly can transform these constructs into actual machine code.
LLVM and other compilers that use SSA but target a stack machine can run a stackification phase. Even without reordering instructions, it seems to work well in practice.
In Virgil I implemented this for both the JVM and Wasm. Here's the algorithm used for Wasm:
> For example its architecture is a stack machine instead of a register machine. This means that it isn't immediately suitable as simply yet another target at the last stage of the Go compiler next to x86 and friends.
> There might be an alternative: Emulate what we need. We may use the stack machine to emulate a register machine and hopefully do so in a reasonably performant way.
> WebAssembly has linear memory with load and store instructions, which is good. We would not use WebAssembly's call instruction at all and instead roll our own stack management and call mechanism. Stacks would live on that linear memory and be managed by the Go runtime. The stackpointer would be a global variable. All code would live in a single WebAssembly function. The toplevel would be a giant switch statement (or WebAssembly's br_table based equivalent) with one branch for each function. Each function would have another switch statement with one branch per SSA basic block.
> There are some details that I'm omitting here, but in the big picture this looks like a decent register machine to me. Of course the performance of this heavily depends on how well WebAssembly can transform these constructs into actual machine code.
[0] https://github.com/golang/go/issues/18892#issuecomment-30931...