ReFinalize in MergeBlocks so we can optimize unreachable instructions too (#6994)

In #6984 we optimized dropped blocks even if they had unreachable code. In #6988
that part was reverted, and blocks with unreachable code were ignored once more.
However, I realized that the check was not actually for unreachable code, but for
having an unreachable child, so it would miss things like this:

(block
  (block
    ..
    (br $somewhere) ;; unreachable type, but no unreachable code
  )
)

But it is useful to merge such blocks: we don't need the inner block here.

To fix this, just run ReFinalize if we change anything, which will propagate
unreachability as needed. I think MergeBlocks was written before we had
that utility, so it didn't use it...

This is not only useful for itself but will unblock an EH optimization in a
later PR, that has code in this form. It also simplifies the code by removing
the hasUnreachableChild checks.

0 files changed, 0 insertions, 0 deletions