compiler.cfg.copy-prop: remove ##phi nodes where all inputs are copy-equivalent

basis/compiler/cfg/copy-prop/copy-prop.factor

@@ -1,6 +1,6 @@
 ! Copyright (C) 2008, 2009 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: kernel namespaces assocs accessors sequences
+USING: kernel namespaces assocs accessors sequences grouping
 compiler.cfg.rpo compiler.cfg.renaming compiler.cfg.instructions ;
 IN: compiler.cfg.copy-prop
 
@@ -8,10 +8,13 @@ IN: compiler.cfg.copy-prop
 SYMBOL: copies
 
 : resolve ( vreg -- vreg )
-    [ copies get at ] keep or ;
+    copies get ?at drop ;
+
+: (record-copy) ( dst src -- )
+    swap copies get set-at ; inline
 
 : record-copy ( ##copy -- )
-    [ src>> resolve ] [ dst>> ] bi copies get set-at ; inline
+    [ dst>> ] [ src>> resolve ] bi (record-copy) ; inline
 
 <PRIVATE
 
@@ -19,7 +22,9 @@ GENERIC: visit-insn ( insn -- )
 
 M: ##copy visit-insn record-copy ;
 
-M: ##phi visit-insn inputs>> values [ resolve ] map all-equal? [ "BLAH!" print ] when ;
+M: ##phi visit-insn
+    [ dst>> ] [ inputs>> values [ resolve ] map ] bi
+    dup all-equal? [ first (record-copy) ] [ 2drop ] if ;
 
 M: insn visit-insn drop ;
 
@@ -34,6 +39,9 @@ GENERIC: update-insn ( insn -- keep? )
 
 M: ##copy update-insn drop f ;
 
+M: ##phi update-insn
+    dup dst>> copies get key? [ drop f ] [ call-next-method ] if ;
+
 M: insn update-insn rename-insn-uses t ;
 
 : rename-copies ( cfg -- )