compiler.cfg.gvn.redundancy-elimination: rough draft

extra/compiler/cfg/gvn/redundancy-elimination/authors.txt

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+Alex Vondrak

extra/compiler/cfg/gvn/redundancy-elimination/redundancy-elimination.factor

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+! Copyright (C) 2011 Alex Vondrak.
+! See http://factorcode.org/license.txt for BSD license.
+USING: ;
+IN: compiler.cfg.gvn.redundancy-elimination
+
+! ! ! Available expressions analysis
+
+FORWARD-ANALYSIS: avail
+
+M: avail-analysis transfer-set drop defined assoc-union ;
+
+: available? ( vn -- ? )
+    basic-block get avail-ins get at key? ;
+
+! ! ! Copy propagation
+
+RENAMING: propagate [ vreg>avail-vn ] [ vreg>avail-vn ] [ drop next-vreg ]
+
+! ! ! Redundancy elimination
+
+! Returns f if insn should be removed
+GENERIC: process-instruction ( insn -- insn'/f )
+
+: redundant-instruction ( insn vn -- f ) 2drop f ; inline
+
+: make-available ( vn -- )
+    dup basic-block get avail-ins get [ ?set-at ] change-at ;
+
+:: useful-instruction ( insn expr -- insn' )
+    insn dst>> :> vn
+    vn make-available
+    insn propagate-insn-uses ! I think that's right?
+    insn ;
+
+: check-redundancy ( insn -- insn'/f )
+    dup >expr dup exrs>vns get at
+    [ redundant-instruction ] [ useful-instruction ] ?if ;
+
+: check-redundancy? ( insn -- ? )
+    defs-vregs {
+        [ length 1 = ]
+        [ first dup vreg>vn = not ] ! avoid ##copy x x
+    } 1&& ;
+
+M: insn process-instruction
+    dup rewrite
+    [ process-instruction ]
+    [ dup check-redundancy? [ check-redundancy ] when ] ?if ;
+
+M: ##copy process-instruction drop f ;
+
+M: array process-instruction [ process-instruction ] map ;
+
+: redundancy-elimination-step ( insns -- insns' )
+    [ process-instruction ] map flatten sift ;
+
+: eliminate-redunancies ( cfg -- )
+    final-iteration? on ! if vreg>vn uses this to obey avail-ins
+    dup compute-avail-sets
+    [ redundancy-elimination-step ] simple-optimization ;