If I encounter an error that looks like this:
  fn main: stmt copy: output 'm' not in a register

then I should do the following:
  - find the function mentioned (here `main`);
  - look for a statement that contains the mentioned output (here `m`) before
    the `<-`; and
  - replace the statement with a version of the same instruction that writes
    to an inout in memory. (Here, replace `m <- copy` with `copy-to m`.)

===

If I encounter an error that looks like this:
  label table: get-slice: key not found: copy-to

then I should do the following:
  - look for a statement with the same instruction (here `copy-to`) whose
    first inout is not a variable stored in memory; and
  - email Kartik (http://akkartik.name/contact) to ask why this message is so
    much less helpful then the previous one.