AstGen: avoid emitting multiple `ret_type` instructions

This is a small optimization to generated ZIR. In any function where the
return type is not a trivial Ref, we know it is almost certainly not
`void` (unless the user aliased it or did something else weird to fool
AstGen), and thus the return type is very likely to be required for
return value RLS at some point. Thus, we can just emit one `ret_type` at
the start of the function and use it throughout.

This sees a very small improvement in overall ZIR bytes.

0 files changed, 0 insertions, 0 deletions