Cannot perform pointer arithmetic in complex assignment

[jyn514]

int main() {
        int i, *p;
        p += i;
}
<stdin>:3:8: error: invalid program: cannot implicitly convert 'int' to 'int *'. help: use an explicit cast: (int *)

[jyn514]

This is actually because of the +=, we currently don't handle binary assignment very well (see #25). I'm considering removing this from the AST altogether and just adding a is_assign boolean to operations that could be an assignment.

[jyn514]

We can't desugar this to p = p + i because p could be the result of an arbitrary expression and the standard requires that we only evaluate it once:

int *a[10];
int main() {    
        int i;
        *a = &i;
        *a += 1;     
}

[jyn514]

I mean ... we could desugar it and just violate the standard ...

[jyn514]

That doesn't work for function calls though:

int x;
int *f() {
    // mutates global state!
    x += 5;
    return &x;
}
int main() {
    *f() += 5;
}

[jyn514]

Oh! I can just desugar to tmp = f(x); *tmp = *tmp + 5;

[jyn514]

That involves a needless load and store though ... maybe I should finally implement the register keyword in the backend?

[jyn514]

Even simpler: emit a declaration of the variable that gets sent to the backend, then register is just an optimization instead of a requirement

[jyn514]

I have a start on this in the compound-assignment branch, but it requires separating out parsing from semantic analysis. I've always meant to do this, it's just a little earlier than I planned. I think I'll make separate analysis a different branch and merge that before I merge compound assignment.

[jyn514]

Waiting on #151