NoTailCall option

[daurnimator]

Originally from #2598

I just recalled something from https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66826

Now dlsym (and other dl-functions) secretly take shadow parameter - return address on stack

We need a way to ensure that a given call is not a tail call.

LLVM does have a notail option

[daurnimator]

To avoid proliferation of @inlineCall/@noInlineCall/@newStackCall/@noTailCall, etc.
I propose a @call builtin that takes a structure of options:

const Maybe = enum {
    Default,
    Always,
    Never,
};
@call(comptime options: struct {
    tailCall: Maybe = .Default,
    inlineCall: Maybe = .Default,
    newStack: ?[]align(target_stack_align) u8 = null,
}, function: var, args: ...);

[emekoi]

perhaps asyncCall could be merged with this?

[ghost]

Your code example is missing the handle to the function itself, and if we are getting rid of var args (#208) then the args argument should be a var which is filled using anonymous literal syntax. That would end up looking like this:

const result = @call(myFunc, .{ .tailCall = false }, .{ false, 1, "three" });

[fengb]

How about just 1 argument?

 @call(.{
    .tailCall = false,
    .func = myFunc,
    .args = .{ false, 1, "three" })
});

[daurnimator]

How about just 1 argument?

I think this looks harder to use. Also the call type needs to be comptime known, while the function and arguments can be runtime known.

[daurnimator]

Your code example is missing the handle to the function itself,

Fixed.

and if we are getting rid of var args (#208) then the args argument should be a var which is filled using anonymous literal syntax. That would end up looking like this:

const result = @call(myFunc, .{ .tailCall = false }, .{ false, 1, "three" });

Builtins don't need to follow the rest of the language like this: they aren't normal functions. see e.g. @field