Removing variable indirection for simple steps

Author: jashkenas

lib/coffee-script/nodes.js

@@ -2566,7 +2566,7 @@
     For.prototype.children = ['body', 'source', 'guard', 'step'];
 
     For.prototype.compileNode = function(o) {
-      var body, defPart, forPart, forVarPart, guardPart, idt1, index, ivar, kvar, kvarAssign, lastJumps, lvar, name, namePart, ref, resultPart, returnResult, rvar, scope, source, stepPart, stepvar, svar, varPart, _ref2;
+      var body, defPart, forPart, forVarPart, guardPart, idt1, index, ivar, kvar, kvarAssign, lastJumps, lvar, name, namePart, ref, resultPart, returnResult, rvar, scope, source, stepPart, stepvar, svar, varPart, _base, _ref2;
       body = Block.wrap([this.body]);
       lastJumps = (_ref2 = last(body.expressions)) != null ? _ref2.jumps() : void 0;
       if (lastJumps && lastJumps instanceof Return) {
@@ -2589,7 +2589,8 @@
       kvar = (this.range && name) || index || ivar;
       kvarAssign = kvar !== ivar ? "" + kvar + " = " : "";
       if (this.step && !this.range) {
-        stepvar = scope.freeVariable("step");
+        this.complexStep = !(typeof (_base = this.step).isSimpleNumber === "function" ? _base.isSimpleNumber() : void 0);
+        stepvar = this.complexStep ? scope.freeVariable("step") : this.step.compile(o, LEVEL_OP);
       }
       if (this.pattern) {
         name = ivar;
@@ -2616,7 +2617,7 @@
         if (!this.object) {
           lvar = scope.freeVariable('len');
           forVarPart = "" + kvarAssign + ivar + " = 0, " + lvar + " = " + svar + ".length";
-          if (this.step) {
+          if (this.complexStep) {
             forVarPart += ", " + stepvar + " = " + (this.step.compile(o, LEVEL_OP));
           }
           stepPart = "" + kvarAssign + (this.step ? "" + ivar + " += " + stepvar : (kvar !== ivar ? "++" + ivar : "" + ivar + "++"));

src/nodes.coffee

@@ -1742,7 +1742,9 @@ exports.For = class For extends While
     kvar      = (@range and name) or index or ivar
     kvarAssign = if kvar isnt ivar then "#{kvar} = " else ""
     # the `_by` variable is created twice in `Range`s if we don't prevent it from being declared here
-    stepvar   = scope.freeVariable "step" if @step and not @range
+    if @step and not @range
+      @complexStep = not @step.isSimpleNumber?()
+      stepvar = if @complexStep then scope.freeVariable "step" else @step.compile(o, LEVEL_OP)
     name      = ivar if @pattern
     varPart   = ''
     guardPart = ''
@@ -1760,7 +1762,7 @@ exports.For = class For extends While
       unless @object
         lvar       = scope.freeVariable 'len'
         forVarPart = "#{kvarAssign}#{ivar} = 0, #{lvar} = #{svar}.length"
-        forVarPart += ", #{stepvar} = #{@step.compile o, LEVEL_OP}" if @step
+        forVarPart += ", #{stepvar} = #{@step.compile o, LEVEL_OP}" if @complexStep
         stepPart   = "#{kvarAssign}#{if @step then "#{ivar} += #{stepvar}" else (if kvar isnt ivar then "++#{ivar}" else "#{ivar}++")}"
         forPart    = "#{forVarPart}; #{ivar} < #{lvar}; #{stepPart}"
     if @returns