Revert "make dead code elimination smarter and eliminate non-referenced "pure" nodes"

This reverts commit 4e87809ff904f170009418344d11772e6dec0e1b.

src/babel/transformation/transformers/utility/dead-code-elimination.js

@@ -21,38 +21,6 @@ export var metadata = {
   optional: true
 };
 
-export function Identifier(node, parent, scope) {
-  if (!this.isReferenced()) return;
-
-  var binding = scope.getBinding(node.name);
-  if (!binding || binding.references > 1 || !binding.constant) return;
-
-  var replacement = binding.path.node;
-  if (t.isVariableDeclarator(replacement)) {
-    replacement = replacement.init;
-  }
-  t.toExpression(replacement);
-
-  scope.removeBinding(node.name);
-
-  binding.path.remove();
-  return replacement;
-}
-
-export function FunctionDeclaration(node, parent, scope) {
-  var bindingInfo = scope.getBinding(node.id.name);
-  if (bindingInfo && !bindingInfo.referenced) {
-    this.remove();
-  }
-}
-
-export { FunctionDeclaration as ClassDeclaration };
-
-export function VariableDeclarator(node, parent, scope) {
-  if (!t.isIdentifier(node.id) || !scope.isPure(node.init)) return;
-  FunctionDeclaration.apply(this, arguments);
-}
-
 export function ConditionalExpression(node, parent, scope) {
   var evaluateTest = this.get("test").evaluateTruthy();
   if (evaluateTest === true) {

src/babel/traversal/binding.js

@@ -3,8 +3,6 @@ import * as t from "../types";
 export default class Binding {
   constructor({ identifier, scope, path, kind }) {
     this.identifier = identifier;
-    this.references = 0;
-    this.referenced = false;
     this.constant   = true;
     this.scope      = scope;
     this.path       = path;
@@ -60,15 +58,6 @@ export default class Binding {
     }
   }
 
-  /**
-   * Description
-   */
-
-  reference() {
-    this.referenced = true;
-    this.references++;
-  }
-
   /**
    * Description
    */

src/babel/traversal/path/index.js

@@ -319,12 +319,6 @@ export default class TraversalPath {
     var parent = this.parent;
     if (!parentPath) return;
 
-    // we've just removed the last declarator of a variable declaration so there's no point in
-    // keeping it
-    if (parentPath.isVariableDeclaration() && parent.declarations.length === 0) {
-      return parentPath.remove();
-    }
-
     // we're the child of an expression statement so we should remove the parent
     if (parentPath.isExpressionStatement()) {
       return parentPath.remove();
@@ -656,10 +650,6 @@ export default class TraversalPath {
     return this.shouldStop;
   }
 
-  /**
-   * Description
-   */
-
   getSibling(key) {
     return TraversalPath.get(this.parentPath, null, this.parent, this.container, key, this.file);
   }

src/babel/traversal/scope.js

@@ -40,12 +40,8 @@ var functionVariableVisitor = {
 
 var programReferenceVisitor = {
   enter(node, parent, scope, state) {
-    if (t.isReferencedIdentifier(node, parent)) {
-      var bindingInfo = scope.getBinding(node.name);
-      if (bindingInfo) {
-        state.addGlobal(node);
-        bindingInfo.reference();
-      }
+    if (t.isReferencedIdentifier(node, parent) && !scope.hasBinding(node.name)) {
+      state.addGlobal(node);
     } else if (t.isLabeledStatement(node)) {
       state.addGlobal(node);
     } else if (t.isAssignmentExpression(node)) {
@@ -486,19 +482,6 @@ export default class Scope {
     this.crawl();
   }
 
-  /**
-   * Description
-   */
-
-  isPure(node) {
-    if (t.isIdentifier(node)) {
-      var bindingInfo = this.getBinding(node.name);
-      return bindingInfo.constant;
-    } else {
-      return t.isPure(node);
-    }
-  }
-
   /**
    * Description
    */

src/babel/types/alias-keys.json

@@ -26,9 +26,9 @@
   "ExportNamedDeclaration":     ["Statement", "Declaration", "ModuleDeclaration", "ExportDeclaration"],
   "ImportDeclaration":          ["Statement", "Declaration", "ModuleDeclaration"],
 
-  "ArrowFunctionExpression": ["Scopable", "Function", "Expression", "Pure"],
-  "FunctionDeclaration":     ["Scopable", "Function", "Statement", "Pure", "Declaration"],
-  "FunctionExpression":      ["Scopable", "Function", "Expression", "Pure"],
+  "ArrowFunctionExpression": ["Scopable", "Function", "Expression"],
+  "FunctionDeclaration":     ["Scopable", "Function", "Statement", "Declaration"],
+  "FunctionExpression":      ["Scopable", "Function", "Expression"],
 
   "BlockStatement": ["Scopable", "Statement"],
   "Program":        ["Scopable"],
@@ -41,8 +41,8 @@
   "SpreadProperty":  ["UnaryLike"],
   "SpreadElement":   ["UnaryLike"],
 
-  "ClassDeclaration": ["Scopable", "Class", "Pure", "Statement", "Declaration"],
-  "ClassExpression":  ["Scopable", "Class", "Pure", "Expression"],
+  "ClassDeclaration": ["Scopable", "Class", "Statement", "Declaration"],
+  "ClassExpression":  ["Scopable", "Class", "Expression"],
 
   "ForOfStatement": ["Scopable", "Statement", "For", "Loop"],
   "ForInStatement": ["Scopable", "Statement", "For", "Loop"],
@@ -62,7 +62,7 @@
   "ConditionalExpression":     ["Expression"],
   "DoExpression":              ["Expression"],
   "Identifier":                ["Expression"],
-  "Literal":                   ["Expression", "Pure"],
+  "Literal":                   ["Expression"],
   "MemberExpression":          ["Expression"],
   "MetaProperty":              ["Expression"],
   "NewExpression":             ["Expression"],