Experiments with literal stack

Author: theBF

COMPILER/Optimizers/POPPUSH-OPT.FTH

@@ -0,0 +1,30 @@
+\ poppush optimizer
+\ This idea failed because the logic is not correct for all
+\ cases. More work needed.
+
+C136 CONSTANT 'DROP'   \ 9900 machine code for DROP (*SP+ R4 MOV,)
+VARIABLE DROPS         \ count when DROP, is executed
+VARIABLE #OPTS         \ # of optimizations made
+VARIABLE #DUPS         \ # of DUPS made
+
+: DUP,     ( n -- n n)  TOS DPUSH, #DUPS 1+! ;  \ normal dup
+: DROP,    TOS DPOP,  DROPS 1+! ; \ count each drop
+
+: LOOKBACK ( -- u)  THERE 2- @ ; \ fetch previous instruction code
+
+: OPT-DUP, ( n -- n ?n)
+  #DUPS @ 2 <  ( this is PFM )
+  IF  \ not enough DUPS were done so we must do one
+     DUP,
+  ELSE
+      LOOKBACK 'DROP' =     \ look back for DROP
+      IF
+         -2 TALLOT          \ move target dictionary ie: erase DROP
+         #OPTS 1+!
+      ELSE
+          DUP,
+      THEN
+  THEN
+;
+
+DEFER SMARTDUP,     ' DUP, IS SMARTDUP,   \ default is unoptimized