compiler.cfg.empty-blocks: new pass to delete empty blocks, runs after phi elimination

basis/compiler/cfg/empty-blocks/empty-blocks.factor

@@ -0,0 +1,38 @@
+! Copyright (C) 2008, 2009 Slava Pestov.
+! See http://factorcode.org/license.txt for BSD license.
+USING: kernel accessors sequences combinators combinators.short-circuit
+classes vectors compiler.cfg compiler.cfg.instructions compiler.cfg.rpo ;
+IN: compiler.cfg.empty-blocks
+ 
+: update-predecessor ( bb -- )
+    ! We have to replace occurrences of bb with bb's successor
+    ! in bb's predecessor's list of successors.
+    dup predecessors>> first [
+        [
+            2dup eq? [ drop successors>> first ] [ nip ] if
+        ] with map
+    ] change-successors drop ;
+ 
+: update-successor ( bb -- )
+    ! We have to replace occurrences of bb with bb's predecessor
+    ! in bb's sucessor's list of predecessors.
+    dup successors>> first [
+        [
+            2dup eq? [ drop predecessors>> first ] [ nip ] if
+        ] with map
+    ] change-predecessors drop ;
+ 
+: delete-basic-block ( bb -- )
+    [ update-predecessor ] [ update-successor ] bi ;
+ 
+: delete-basic-block? ( bb -- ? )
+    {
+        [ instructions>> length 1 = ]
+        [ predecessors>> length 1 = ]
+        [ successors>> length 1 = ]
+        [ instructions>> first ##branch? ]
+    } 1&& ;
+ 
+: delete-empty-blocks ( cfg -- cfg' )
+    dup [ dup delete-basic-block? [ delete-basic-block ] [ drop ] if ] each-basic-block
+    cfg-changed ;

basis/compiler/cfg/optimizer/optimizer.factor

@@ -14,6 +14,7 @@ compiler.cfg.dce
 compiler.cfg.write-barrier
 compiler.cfg.rpo
 compiler.cfg.phi-elimination
+compiler.cfg.empty-blocks
 compiler.cfg.checker ;
 IN: compiler.cfg.optimizer
 
@@ -42,5 +43,6 @@ SYMBOL: check-optimizer?
         eliminate-dead-code
         eliminate-write-barriers
         eliminate-phis
+        delete-empty-blocks
         ?check
     ] with-scope ;