compiler.cfg.value-numbering: add slot addressing rewrite rule to eliminate a redundant ##add-imm from array-nth and set-array-nth

basis/compiler/cfg/value-numbering/slots/authors.txt

@@ -0,0 +1 @@
+Slava Pestov

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

@@ -0,0 +1,25 @@
+! Copyright (C) 2010 Slava Pestov.
+! See http://factorcode.org/license.txt for BSD license.
+USING: accessors combinators.short-circuit cpu.architecture fry
+kernel math
+compiler.cfg.instructions
+compiler.cfg.value-numbering.graph
+compiler.cfg.value-numbering.rewrite
+compiler.cfg.value-numbering.expressions ;
+IN: compiler.cfg.value-numbering.slots
+
+: simplify-slot-addressing? ( insn -- ? )
+    complex-addressing?
+    [ slot>> vreg>expr add-imm-expr? ] [ drop f ] if ;
+
+: simplify-slot-addressing ( insn -- insn/f )
+    dup simplify-slot-addressing? [
+        dup slot>> vreg>expr
+        [ src1>> vn>vreg >>slot ]
+        [ src2>> vn>integer over scale>> '[ _ _ shift - ] change-tag ]
+        bi
+    ] [ drop f ] if ;
+
+M: ##slot rewrite simplify-slot-addressing ;
+M: ##set-slot rewrite simplify-slot-addressing ;
+M: ##write-barrier rewrite simplify-slot-addressing ;

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

@@ -2209,6 +2209,25 @@ V{
 
 [ f ] [ 1 get instructions>> [ ##peek? ] any? ] unit-test
 
+! Slot addressing optimization
+cpu x86? [
+    [
+        V{
+            T{ ##peek f 0 D 0 }
+            T{ ##peek f 1 D 1 }
+            T{ ##add-imm f 2 1 2 }
+            T{ ##slot f 3 0 1 2 $[ 7 2 cells - ] }
+        }
+    ] [
+        V{
+            T{ ##peek f 0 D 0 }
+            T{ ##peek f 1 D 1 }
+            T{ ##add-imm f 2 1 2 }
+            T{ ##slot f 3 0 2 2 7 }
+        } value-numbering-step
+    ] unit-test
+] when
+
 ! Alien addressing optimization
 [
     V{

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

@@ -14,7 +14,8 @@ compiler.cfg.value-numbering.expressions
 compiler.cfg.value-numbering.graph
 compiler.cfg.value-numbering.math
 compiler.cfg.value-numbering.rewrite
-compiler.cfg.value-numbering.simplify ;
+compiler.cfg.value-numbering.simplify
+compiler.cfg.value-numbering.slots ;
 IN: compiler.cfg.value-numbering
 
 ! Local value numbering.