Requirements for function `return` calls

[dj2]

I can't find in the spec where it mentions when a function with a return value must call return. Playing around in godbot with glslang it appears that a single return is required but not all control paths must return, it injects an undef in those cases?

int foo() {
}

Produces an error that the function must return a value.

int foo() {
    if (true) {
        return 1;
    }
}

Compiles correctly with the end of the function return an OpUndef %int value.

int foo() {
    if (true) {
        return 1;
    } else {
        return 2;
    }
}

Injects an OpUnreachable at the end of the function since all control paths return.

It seems like, there must be a single return call at any nesting level inside a function to be valid (according to glslang) and any other paths out of the function will return an OpUndef value.

[gnl21]

I agree with what you've written with the exception that void functions don't need to have a 'return' statement. This kind of rule has always struck me as a bit silly (since we have to deal with not hitting the return anyway, requiring a single return is a bit pointless), but we should make sure that the spec says what we want it to.

I'll need to check what we want to have for when a function does not hit the return. It's possible that we might need something looser than undefined value.