Return the result of the discriminant from trans_alt,
rather than nil, in the _|_ case. This was breaking the
enclosed test case (alt-bot-2) when optimization was disabled.
Closes#769
This was at least partially responsible for Issue 777.
The only solution I can think of is for trans to just not generate
code for a comparison if one or both sides has type _|_. Since
that means evaluating that subexpression diverges, it should be ok
to never do the comparison. Actually generating code for the
comparison would trip an LLVM assertion failure.
This is required so that assigning to these locals doesn't clobber
the content of the box.
(A possible optimization would be to only do this copying for
locals that actually are assigned to.)
You can now say
let {bcx, val} = some_result_returner();
Similar for loop variables. Assigning to such variables is not safe
yet. Function arguments also remain a TODO.
Probably more should be moved or split off into other files. My algorithm
was something along the lines of: move the contexts and their transitive
dependencies along with some functions to work with them. I stopped when
I was going to have to start pulling glue generation, which really
should go into a trans_glue file.
