Enums that don't carry anything in their arms shouldn't use shape glue

[bblum]

enum fast { x, y, z, w } 
enum slow<T> { a(T), b(T), c(T), d(T) }

fn foo(yy: fast, xx: fast) -> bool {
    ret yy == xx; 
}
fn bar(yy: slow<bool>, xx: slow<bool>) -> bool {
    ret yy == xx; 
}

Both foo and bar generate calls to upcall_cmp_type. It'd be nice if, for performance, the compiler could recognise that fast can be represented by a primitive and skip the upcalls.

Related to #2132.

[eholk]

Oh sad, I was really hoping we handled at least this case.

[bblum]

I know, right?

Found during ICFP (#2928).

[catamorphism]

Obsolete, shape glue is dead.