Sema: catch invalid asm input operands

[wooster0]

$ zig-out/bin/zig test test/cases/compile_errors/non_sized_asm_input_operand.zig
test/cases/compile_errors/non_sized_asm_input_operand.zig:4:23: error: input operand of type 'type' is not sized
        : [_] "{al}" (u8),
                      ^~
test/cases/compile_errors/non_sized_asm_input_operand.zig:12:22: error: input operand of type 'type' is not sized
          [_] "{x}" (void),
                     ^~~~
test/cases/compile_errors/non_sized_asm_input_operand.zig:19:22: error: input operand of type 'type' is not sized
        : [_] "{x}" (enum {}),
                     ^~~~~~~

I don't know if disallowing non-sized types is the best solution because for example RISC-V has a zero register that is hardwired to zero so : [x0] "{x0}" (@as(u0, 0)), in a way could be valid but u0 is non-sized so it won't work.
At the same time though you can argue that anything that isn't sized can't actually be in a register.

Fixes #7843 (wasn't an issue with just stage1 btw, stage2 too segfaults without this patch)

[wooster0]

updated

[wooster0]

tests pass

[andrewrk]

Needs a rebase but after that I think it can be merged. Thanks.

[mlugg]

I seem to recall something about the SPIR-V backend using types as asm inputs... yeah, here we are, #20550 covers it. @Snektron, I'm a little unclear from that proposal -- does this need to work today to avoid regressing stuff? If so, we'll need to add a special case here for SPIR-V.

[wooster0]

It's still a proposal so I assume it's not implemented yet so this can be changed when that proposal gets implemented? Well let's wait for an answer from @Snektron.

[alichraghi]

SPIR-V is a typed language so regardless of the status of that proposal, We still need to be able to pass types through asm inputs/outputs.

[wooster0]

So would I do this?

                if (try sema.typeRequiresComptime(uncasted_arg_ty)) {
                    const target = pt.zcu.getTarget();
                    const arch = target.cpu.arch;
                    const is_spirv = arch.isSpirV();
                    if (uncasted_arg_ty.zigTypeTag(zcu) != .Type and !is_spirv) {
                        return sema.fail(
                            block,
                            input_op_src,
                            "type '{}' is comptime-only and cannot be used for an assembly input operand",
                            .{uncasted_arg_ty.fmt(pt)},
                        );
                    }
                }

[mlugg]

s/and/or/. Aside from that, looks good.

[Snektron]

Its not properly implemented in SPIR-V yet in any case, feel free to do whatever for now. We'll make the necessary changes when its required.

Sorry for the late reply 😅