compiler: bugfixes in dead code elimination

* stdlib/optimize (basic-blocks ling-graph): I'm reverting
an old design decision here. The decision is this:
the basic block of a close instruction points to the
first basic block of the closure as its next block,
but that next block does not point back: it doesn't list
the close instruction's basic block among the rlinks.
The idea was that the close instruction doesn't jump
to that block, and so it shouldn't be linked to it.
However, the next link was set purely so that the graph
is connected. Unfortunately, the inconsistency in the
graph structure which this causes is a problem in the
elim-dead-code method. A situation arises when that
first basic block after the close is removed. Because
pit has an empty rlinks list, the block remains listed
as the next block of the close block, even though it is
removed from the master list of blocks.
(basic-blocks check-bypass-empty): Fix one forgotten detail
in this function: the block being deleted must be removed
from the rlinks list of the next block.

1 files changed, 2 insertions, 2 deletions

diff --git a/stdlib/optimize.tl b/stdlib/optimize.tl
index 8e1e8182..914df5b3 100644
--- a/stdlib/optimize.tl
+++ b/stdlib/optimize.tl
@@ -135,8 +135,7 @@
          (set bl.links (list [bb.hash jlabel])))
         ((close @nil @nil @nil @jlabel . @nil)
          (set bl.links (list [bb.hash jlabel])
-              bl.next nxbl
-              link-next nil))
+              bl.next nxbl))
         ((swtch @nil . @jlabels)
          (set bl.links [mapcar bb.hash (uniq jlabels)]
               link-next nil))
@@ -502,6 +501,7 @@
 
 (defmeth basic-blocks check-bypass-empty (bb bl nx)
   (unless (cdr bl.insns)
+    (upd nx.rlinks (remq bl))
     (each ((pb bl.rlinks))
       (if (eq pb.next bl)
         (set pb.next nx))