Matching enums generates unused variables

[franziskuskiefer]

In different cases where enums are used, unused variables are generated in C.
Here is one example I could isolate.

enum E {
    A = 1,
    B = 2,
}

fn fun_a(_x: &[u8]) {}
fn fun_b(_x: &[u8]) {}

fn use_enum(e: E, x: &[u8]) {
    match e {
        E::A => fun_a(x),
        E::B => fun_b(x),
    }
}

This generates the following C code.
Note that the function calls are dropped because they don't do anything. When they do something, they are called. But the uu____0 sticks around.

void eurydice_tests_use_enum(eurydice_tests_E e, Eurydice_slice x)
{
  void *uu____0 = (void *)0U;
  if (!(e == eurydice_tests_E_A))
  {
    return;
  }
}

[msprotz]

this is an easy fix I'm running regressions on everest right now -- just need to inline away variables that are internal and that are trivially values

[msprotz]

the easy fix breaks HACL*

[msprotz]

FStarLang/karamel#522