compiler.cfg.value-numbering: identify VNs with their representative vregs, eliminating the vn>vreg hash

basis/compiler/cfg/value-numbering/expressions/expressions.factor

@@ -77,13 +77,7 @@ M: reference-expr equal?
 M: reference-expr hashcode*
     nip value>> dup float? [ double>bits ] [ identity-hashcode ] if ;
 
-! Expressions whose values are inputs to the basic block.
-TUPLE: input-expr n ;
-
-: next-input-expr ( -- expr )
-    input-expr-counter counter input-expr boa ;
-
-M: insn >expr drop next-input-expr ;
+M: insn >expr drop input-expr-counter counter neg ;
 
 M: ##copy >expr "Fail" throw ;
 

basis/compiler/cfg/value-numbering/graph/graph.factor

@@ -1,14 +1,13 @@
 ! Copyright (C) 2008, 2010 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: accessors kernel math namespaces assocs biassocs ;
+USING: accessors kernel math namespaces assocs ;
 IN: compiler.cfg.value-numbering.graph
 
-! Value numbers are negative, to catch confusion with vregs
-SYMBOL: vn-counter
-
 SYMBOL: input-expr-counter
 
-: next-vn ( -- vn ) vn-counter [ 1 - dup ] change ;
+! assoc mapping vregs to value numbers
+! this is the identity on canonical representatives
+SYMBOL: vregs>vns
 
 ! assoc mapping expressions to value numbers
 SYMBOL: exprs>vns
@@ -18,21 +17,14 @@ SYMBOL: vns>insns
 
 : vn>insn ( vn -- insn ) vns>insns get at ;
 
-! biassocs mapping vregs to value numbers, and value numbers to
-! their primary vregs
-SYMBOL: vregs>vns
-
-: vreg>vn ( vreg -- vn ) vregs>vns get [ drop next-vn ] cache ;
-
-: vn>vreg ( vn -- vreg ) vregs>vns get value-at ;
+: vreg>vn ( vreg -- vn ) vregs>vns get [ ] cache ;
 
 : set-vn ( vn vreg -- ) vregs>vns get set-at ;
 
-: vreg>insn ( vreg -- insn ) vreg>vn vn>insn ; inline
+: vreg>insn ( vreg -- insn ) vreg>vn vn>insn ;
 
 : init-value-graph ( -- )
-    0 vn-counter set
     0 input-expr-counter set
-    <bihash> vregs>vns set
+    H{ } clone vregs>vns set
     H{ } clone exprs>vns set
     H{ } clone vns>insns set ;

basis/compiler/cfg/value-numbering/value-numbering.factor

@@ -21,11 +21,11 @@ IN: compiler.cfg.value-numbering
 GENERIC: process-instruction ( insn -- insn' )
 
 : redundant-instruction ( insn vn -- insn' )
-    [ dst>> ] dip [ swap set-vn ] [ vn>vreg <copy> ] 2bi ;
+    [ dst>> ] dip [ swap set-vn ] [ <copy> ] 2bi ;
 
 :: useful-instruction ( insn expr -- insn' )
-    next-vn :> vn
-    vn insn dst>> vregs>vns get set-at
+    insn dst>> :> vn
+    vn vn vregs>vns get set-at
     vn expr exprs>vns get set-at
     insn vn vns>insns get set-at
     insn ;