explicit default values for a leaner codegen, .cursor variables for optimization

compiler/dfa.nim

@@ -686,42 +686,3 @@ proc constructCfg*(s: PSym; body: PNode): ControlFlowGraph =
   gen(c, body)
   genImplicitReturn(c)
   shallowCopy(result, c.code)
-
-proc interpret(code: ControlFlowGraph; pc: int, state: seq[PSym], comesFrom: int; threadId: int): (seq[PSym], int) =
-  var res = state
-  var pc = pc
-  while pc < code.len:
-    #echo threadId, " ", code[pc].kind
-    case code[pc].kind
-    of goto:
-      pc = pc + code[pc].dest
-    of fork:
-      let target = pc + code[pc].dest
-      let (branchA, pcA) = interpret(code, pc+1, res, pc, threadId+1)
-      let (branchB, _) = interpret(code, target, res, pc, threadId+2)
-      # we add vars if they are in both branches:
-      for v in branchB:
-        if v in branchA:
-          if v notin res:
-            res.add v
-      pc = pcA+1
-    of join:
-      let target = pc + code[pc].dest
-      if comesFrom == target: return (res, pc)
-      inc pc
-    of use:
-      let v = code[pc].sym
-      if v notin res and v.kind != skParam:
-        echo "attempt to read uninitialized variable ", v.name.s
-      inc pc
-    of def:
-      let v = code[pc].sym
-      if v notin res:
-        res.add v
-      inc pc
-  return (res, pc)
-
-proc dataflowAnalysis*(s: PSym; body: PNode) =
-  let c = constructCfg(s, body)
-  #echoCfg c
-  discard interpret(c, 0, @[], -1, 1)