From 03d1e633026d1141418d31bae4590d4ffde3c869 Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Mon, 7 Aug 2017 21:56:25 +0200
Subject: [PATCH 1/8] Helper evaluate Path

---
 .../babel-helper-evaluate-path/src/index.js   | 146 ++++++++++++++++++
 .../package.json                              |   5 +-
 .../src/index.js                              |  35 +----
 3 files changed, 150 insertions(+), 36 deletions(-)

diff --git a/packages/babel-helper-evaluate-path/src/index.js b/packages/babel-helper-evaluate-path/src/index.js
index 55bfb892a..e529b4eec 100644
--- a/packages/babel-helper-evaluate-path/src/index.js
+++ b/packages/babel-helper-evaluate-path/src/index.js
@@ -1,4 +1,36 @@
+"use strict";
+
 module.exports = function evaluate(path) {
+  if (path.isIdentifier()) {
+    return evaluateIdentifier(path);
+  }
+
+  const state = {
+    deoptPath: null,
+    confident: false
+  };
+
+  // prepare
+  path.traverse({
+    Scope(scopePath) {
+      scopePath.skip();
+    },
+    ReferencedIdentifier(idPath) {
+      const evalResult = evaluateIdentifier(idPath);
+      if (evalResult.confident) {
+        idPath.replaceWith(evalResult.value);
+        deref(idPath);
+      } else {
+        state.confident = evalResult.confident;
+        state.deoptPath = evalResult.deoptPath;
+      }
+    }
+  });
+
+  if (!state.confident) {
+    return state;
+  }
+
   try {
     return path.evaluate();
   } catch (e) {
@@ -8,3 +40,117 @@ module.exports = function evaluate(path) {
     };
   }
 };
+
+// Original Source:
+// https://github.com/babel/babel/blob/master/packages/babel-traverse/src/path/evaluation.js
+// modified for Babili use
+function evaluateIdentifier(path) {
+  if (!path.isReferencedIdentifier()) {
+    throw new Error(`Expected ReferencedIdentifier. Got ${path.type}`);
+  }
+
+  const { node } = path;
+
+  const binding = path.scope.getBinding(node.name);
+
+  if (!binding) {
+    return deopt(path);
+  }
+
+  if (binding.constantViolations.length > 0) {
+    return deopt(binding.path);
+  }
+
+  // let/var/const referenced before init
+  // or "var" referenced in an outer scope
+  if (shouldDeoptBasedOnFlow(binding, path)) {
+    return deopt(path);
+  }
+
+  return path.evaluate();
+}
+
+function shouldDeoptBasedOnFlow(binding, refPath) {
+  const decl = binding.path;
+  const refs = binding.referencePaths;
+
+  if (binding.kind === "var") {
+    // early-exit
+    const declaration = binding.path.parentPath;
+    if (
+      declaration.parentPath.isIfStatement() ||
+      declaration.parentPath.isLoop()
+    ) {
+      return true;
+    }
+
+    let blockParent = binding.path.scope.getBlockParent().path;
+    const fnParent = binding.path.getFunctionParent();
+
+    if (blockParent === fnParent) {
+      blockParent = blockParent.get("body");
+    }
+
+    detectUsageOutsideInitScope: {
+      if (!blockParent.get("body").some(stmt => stmt.isAncestor(refPath))) {
+        return true;
+      }
+    }
+
+    detectUsageBeforeInit: {
+      const stmts = fnParent.get("body").get("body");
+
+      const state = stmts.map(stmt => {
+        if (stmt.isAncestor(binding.path)) {
+          return { type: "binding" };
+        } else {
+          for (const ref of binding.referencePaths) {
+            if (stmt.isAncestor(ref)) {
+              return {
+                type: "ref"
+              };
+            }
+          }
+          return { type: "neither" };
+        }
+      });
+
+      if (state[0].type === "ref") {
+        return true;
+      }
+    }
+  } else if (binding.kind === "let" || binding.kind === "const") {
+    throw "not implemented";
+  }
+
+  return false;
+}
+
+function deopt(deoptPath) {
+  return {
+    confident: false,
+    deoptPath
+  };
+}
+
+function deref(refPath) {
+  if (!refPath.isReferencedIdentifier()) {
+    throw new Error(`Expected ReferencedIdentifier. Got ${refPath.type}`);
+  }
+
+  const binding = refPath.scope.getBinding(refPath.node.name);
+
+  if (binding.references > 0) {
+    binding.references--;
+  }
+  if (binding.references === 0) {
+    binding.referenced = false;
+  }
+  const idx = binding.referencePaths.indexOf(refPath);
+
+  if (idx < 0) {
+    throw new Error("Unexpected Error. Scope not updated properly");
+  }
+
+  binding.referecePaths.splice(idx, 1);
+}
diff --git a/packages/babel-plugin-minify-dead-code-elimination/package.json b/packages/babel-plugin-minify-dead-code-elimination/package.json
index 332301d99..8b97fd4d3 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/package.json
+++ b/packages/babel-plugin-minify-dead-code-elimination/package.json
@@ -8,10 +8,9 @@
   "author": "amasad",
   "license": "MIT",
   "main": "lib/index.js",
-  "keywords": [
-    "babel-plugin"
-  ],
+  "keywords": ["babel-plugin"],
   "dependencies": {
+    "babel-helper-evaluate-path": "^0.1.0",
     "babel-helper-mark-eval-scopes": "^0.1.1",
     "babel-helper-remove-or-void": "^0.1.1",
     "lodash.some": "^4.6.0"
diff --git a/packages/babel-plugin-minify-dead-code-elimination/src/index.js b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
index 73c3abf77..31f0264d1 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/src/index.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
@@ -3,6 +3,7 @@
 const some = require("lodash.some");
 const { markEvalScopes, hasEval } = require("babel-helper-mark-eval-scopes");
 const removeUseStrict = require("./remove-use-strict");
+const evaluate = require("babel-helper-evaluate-path");
 
 function prevSiblings(path) {
   const parentPath = path.parentPath;
@@ -771,41 +772,9 @@ module.exports = ({ types: t, traverse }) => {
           const alternate = path.get("alternate");
           const test = path.get("test");
 
-          const evalResult = test.evaluate();
+          const evalResult = evaluate(test);
           const isPure = test.isPure();
 
-          const binding = path.scope.getBinding(test.node.name);
-
-          // Ref - https://github.com/babel/babili/issues/574
-          // deopt if var is declared in other scope
-          // if (a) { var b = blahl;} if (b) { //something }
-          if (
-            binding &&
-            binding.path.parentPath.isVariableDeclaration({ kind: "var" })
-          ) {
-            let ifStatementParent = null;
-
-            const fnParent =
-              binding.path.getFunctionParent() ||
-              binding.path.getProgramParent();
-
-            forEachAncestor(binding.path.parentPath, parent => {
-              if (fnParent === parent) return;
-              if (parent.isIfStatement()) {
-                ifStatementParent = parent;
-              }
-            });
-
-            if (
-              ifStatementParent &&
-              binding.referencePaths.some(
-                ref => !ref.isDescendant(ifStatementParent)
-              )
-            ) {
-              return;
-            }
-          }
-
           const replacements = [];
           if (evalResult.confident && !isPure && test.isSequenceExpression()) {
             replacements.push(

From 8998845bb7788e171d220a72c03636b9abc296e6 Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Tue, 8 Aug 2017 16:00:01 +0200
Subject: [PATCH 2/8] mutative evaluate

---
 .../babel-helper-evaluate-path/src/index.js   | 146 +++++++++++++-----
 .../babel-plugin-minify-builtins/src/index.js |   2 +-
 .../src/index.js                              |   2 +-
 .../__tests__/dead-code-elimination-test.js   |  84 +++++-----
 .../src/index.js                              |   2 +-
 5 files changed, 156 insertions(+), 80 deletions(-)

diff --git a/packages/babel-helper-evaluate-path/src/index.js b/packages/babel-helper-evaluate-path/src/index.js
index e529b4eec..d0b8256fa 100644
--- a/packages/babel-helper-evaluate-path/src/index.js
+++ b/packages/babel-helper-evaluate-path/src/index.js
@@ -1,13 +1,15 @@
 "use strict";
 
-module.exports = function evaluate(path) {
-  if (path.isIdentifier()) {
+module.exports = function evaluate(path, t) {
+  if (!t) {
+    throw new Error("Expected babel-types");
+  }
+  if (path.isReferencedIdentifier()) {
     return evaluateIdentifier(path);
   }
 
   const state = {
-    deoptPath: null,
-    confident: false
+    confident: true
   };
 
   // prepare
@@ -16,10 +18,15 @@ module.exports = function evaluate(path) {
       scopePath.skip();
     },
     ReferencedIdentifier(idPath) {
+      const binding = idPath.scope.getBinding(idPath.node.name);
+      // don't deopt globals
+      // let babel take care of it
+      if (!binding) return;
+
       const evalResult = evaluateIdentifier(idPath);
       if (evalResult.confident) {
-        idPath.replaceWith(evalResult.value);
-        deref(idPath);
+        idPath.replaceWith(t.valueToNode(evalResult.value));
+        deref(idPath, binding);
       } else {
         state.confident = evalResult.confident;
         state.deoptPath = evalResult.deoptPath;
@@ -61,19 +68,38 @@ function evaluateIdentifier(path) {
     return deopt(binding.path);
   }
 
+  // referenced in a different scope - deopt
+  if (shouldDeoptBasedOnScope(binding, path)) {
+    return deopt(path);
+  }
+
   // let/var/const referenced before init
   // or "var" referenced in an outer scope
-  if (shouldDeoptBasedOnFlow(binding, path)) {
+  const flowEvalResult = evaluateBasedOnControlFlow(binding, path);
+
+  if (flowEvalResult.confident) {
+    return flowEvalResult;
+  }
+
+  if (flowEvalResult.shouldDeopt) {
     return deopt(path);
   }
 
   return path.evaluate();
 }
 
-function shouldDeoptBasedOnFlow(binding, refPath) {
-  const decl = binding.path;
-  const refs = binding.referencePaths;
+// check if referenced in a different fn scope
+// we can't determine if this function is called sync or async
+// if the binding is in program scope
+// all it's references inside a different function should be deopted
+function shouldDeoptBasedOnScope(binding, refPath) {
+  if (binding.scope.path.isProgram() && refPath.scope !== binding.scope) {
+    return true;
+  }
+  return false;
+}
 
+function evaluateBasedOnControlFlow(binding, refPath) {
   if (binding.kind === "var") {
     // early-exit
     const declaration = binding.path.parentPath;
@@ -81,49 +107,91 @@ function shouldDeoptBasedOnFlow(binding, refPath) {
       declaration.parentPath.isIfStatement() ||
       declaration.parentPath.isLoop()
     ) {
-      return true;
+      return { shouldDeopt: true };
     }
 
     let blockParent = binding.path.scope.getBlockParent().path;
     const fnParent = binding.path.getFunctionParent();
 
     if (blockParent === fnParent) {
-      blockParent = blockParent.get("body");
+      if (!fnParent.isProgram()) blockParent = blockParent.get("body");
+    }
+
+    //detect Usage Outside Init Scope
+    if (!blockParent.get("body").some(stmt => stmt.isAncestor(refPath))) {
+      return { shouldDeopt: true };
     }
 
-    detectUsageOutsideInitScope: {
-      if (!blockParent.get("body").some(stmt => stmt.isAncestor(refPath))) {
-        return true;
+    // Detect usage before init
+    const stmts = fnParent.isProgram()
+      ? fnParent.get("body")
+      : fnParent.get("body").get("body");
+
+    const state = stmts.map(stmt => {
+      if (stmt.isAncestor(binding.path)) {
+        return { type: "binding" };
+      }
+      for (const ref of binding.referencePaths) {
+        if (stmt.isAncestor(ref)) {
+          return {
+            type: ref === refPath ? "current-ref" : "other-ref"
+          };
+        }
       }
+      return { type: "neither" };
+    });
+
+    const types = state.map(s => s.type);
+
+    if (types.indexOf("current-ref") < types.indexOf("binding")) {
+      return { shouldDeopt: true };
+    }
+  } else if (binding.kind === "let" || binding.kind === "const") {
+    // binding.path is the declarator
+    const declarator = binding.path;
+
+    let scopePath = declarator.scope.path;
+
+    if (scopePath.isFunction()) {
+      scopePath = scopePath.get("body");
     }
 
-    detectUsageBeforeInit: {
-      const stmts = fnParent.get("body").get("body");
-
-      const state = stmts.map(stmt => {
-        if (stmt.isAncestor(binding.path)) {
-          return { type: "binding" };
-        } else {
-          for (const ref of binding.referencePaths) {
-            if (stmt.isAncestor(ref)) {
-              return {
-                type: "ref"
-              };
-            }
-          }
-          return { type: "neither" };
+    // Detect Usage before Init
+    const stmts = scopePath.get("body");
+
+    const state = {
+      binding: null,
+      reference: null
+    };
+
+    for (const [idx, stmt] of stmts.entries()) {
+      if (stmt.isAncestor(binding.path)) {
+        state.binding = { idx };
+      }
+      for (const ref of binding.referencePaths) {
+        if (ref === refPath && stmt.isAncestor(ref)) {
+          state.reference = {
+            idx,
+            scope: binding.path.scope === ref.scope ? "current" : "other"
+          };
+          break;
         }
-      });
+      }
+    }
 
-      if (state[0].type === "ref") {
-        return true;
+    if (state.reference && state.binding) {
+      if (
+        state.reference.scope === "current" &&
+        state.reference.idx < state.binding.idx
+      ) {
+        return { confident: true, value: void 0 };
       }
+
+      return { shouldDeopt: true };
     }
-  } else if (binding.kind === "let" || binding.kind === "const") {
-    throw "not implemented";
   }
 
-  return false;
+  return { confident: false, shouldDeopt: false };
 }
 
 function deopt(deoptPath) {
@@ -133,13 +201,11 @@ function deopt(deoptPath) {
   };
 }
 
-function deref(refPath) {
+function deref(refPath, binding) {
   if (!refPath.isReferencedIdentifier()) {
     throw new Error(`Expected ReferencedIdentifier. Got ${refPath.type}`);
   }
 
-  const binding = refPath.scope.getBinding(refPath.node.name);
-
   if (binding.references > 0) {
     binding.references--;
   }
@@ -152,5 +218,5 @@ function deref(refPath) {
     throw new Error("Unexpected Error. Scope not updated properly");
   }
 
-  binding.referecePaths.splice(idx, 1);
+  binding.referencePaths.splice(idx, 1);
 }
diff --git a/packages/babel-plugin-minify-builtins/src/index.js b/packages/babel-plugin-minify-builtins/src/index.js
index 5f1119e01..5dd205b66 100644
--- a/packages/babel-plugin-minify-builtins/src/index.js
+++ b/packages/babel-plugin-minify-builtins/src/index.js
@@ -48,7 +48,7 @@ module.exports = function({ types: t }) {
             // computed property should be not optimized
             // Math[max]() -> Math.max()
             if (!isComputed(callee) && isBuiltin(callee)) {
-              const result = evaluate(path);
+              const result = evaluate(path, t);
               // deopt when we have side effecty evaluate-able arguments
               // Math.max(foo(), 1) --> untouched
               // Math.floor(1) --> 1
diff --git a/packages/babel-plugin-minify-constant-folding/src/index.js b/packages/babel-plugin-minify-constant-folding/src/index.js
index 5e591a4f2..4cce64d2d 100644
--- a/packages/babel-plugin-minify-constant-folding/src/index.js
+++ b/packages/babel-plugin-minify-constant-folding/src/index.js
@@ -143,7 +143,7 @@ module.exports = babel => {
           return;
         }
 
-        const res = evaluate(path);
+        const res = evaluate(path, t);
         if (res.confident) {
           // Avoid fractions because they can be longer than the original expression.
           // There is also issues with number percision?
diff --git a/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js b/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
index c4b5ab9e3..d01ccac94 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
@@ -518,59 +518,41 @@ describe("dce-plugin", () => {
   );
 
   thePlugin(
-    "should handle orpahaned returns",
+    "should handle orphaned returns",
     `
-    var a = true;
-    function foo() {
-      if (a) return;
-      x();
-    }
-  `,
+      var a = true;
+      function foo() {
+        if (a) return;
+        x();
+      }
     `
-    var a = true;
-    function foo() {}
-  `
   );
 
   thePlugin(
     "should handle orpahaned returns with a value",
     `
-    var a = true;
-    function foo() {
-      if (a) return 1;
-      x();
-    }
-  `,
+      var a = true;
+      function foo() {
+        if (a) return 1;
+        x();
+      }
     `
-    var a = true;
-    function foo() {
-      return 1;
-    }
-  `
   );
 
   thePlugin(
     "should handle orphaned, redundant returns",
     `
-    var x = true;
-    function foo() {
-      if (b) {
-        if (x) {
-          z();
-          return;
+      var x = true;
+      function foo() {
+        if (b) {
+          if (x) {
+            z();
+            return;
+          }
+          y();
         }
-        y();
       }
-    }
-  `,
     `
-    var x = true;
-    function foo() {
-      if (b) {
-        z();
-      }
-    }
-  `
   );
 
   thePlugin(
@@ -2472,4 +2454,32 @@ describe("dce-plugin", () => {
       }
     `
   );
+
+  thePlugin(
+    "should optimize to void 0 for lets referenced before init declarations",
+    `
+      function foo() {
+        bar(a);
+        let a = 1;
+      }
+    `,
+    `
+      function foo() {
+        bar(void 0);
+      }
+    `
+  );
+
+  thePlugin(
+    "should optimize lets referenced before init declarations - 2",
+    `
+      function foo() {
+        if (a) console.log(a);
+        let a = 1;
+      }
+    `,
+    `
+      function foo() {}
+    `
+  );
 });
diff --git a/packages/babel-plugin-minify-dead-code-elimination/src/index.js b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
index 31f0264d1..badc08314 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/src/index.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
@@ -772,7 +772,7 @@ module.exports = ({ types: t, traverse }) => {
           const alternate = path.get("alternate");
           const test = path.get("test");
 
-          const evalResult = evaluate(test);
+          const evalResult = evaluate(test, t);
           const isPure = test.isPure();
 
           const replacements = [];

From 0002669e6f6e9d979dc00d1b21e441a3ddd643c5 Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Tue, 8 Aug 2017 17:59:08 +0200
Subject: [PATCH 3/8] Fix let and var

---
 .../babel-helper-evaluate-path/src/index.js   | 41 +++++++++++++------
 .../__tests__/dead-code-elimination-test.js   | 12 +++++-
 .../src/index.js                              | 10 ++---
 3 files changed, 43 insertions(+), 20 deletions(-)

diff --git a/packages/babel-helper-evaluate-path/src/index.js b/packages/babel-helper-evaluate-path/src/index.js
index d0b8256fa..b99f2ebf0 100644
--- a/packages/babel-helper-evaluate-path/src/index.js
+++ b/packages/babel-helper-evaluate-path/src/index.js
@@ -117,7 +117,7 @@ function evaluateBasedOnControlFlow(binding, refPath) {
       if (!fnParent.isProgram()) blockParent = blockParent.get("body");
     }
 
-    //detect Usage Outside Init Scope
+    // detect Usage Outside Init Scope
     if (!blockParent.get("body").some(stmt => stmt.isAncestor(refPath))) {
       return { shouldDeopt: true };
     }
@@ -127,23 +127,34 @@ function evaluateBasedOnControlFlow(binding, refPath) {
       ? fnParent.get("body")
       : fnParent.get("body").get("body");
 
-    const state = stmts.map(stmt => {
+    const state = {
+      binding: null,
+      reference: null
+    };
+
+    for (const [idx, stmt] of stmts.entries()) {
       if (stmt.isAncestor(binding.path)) {
-        return { type: "binding" };
+        state.binding = { idx };
       }
       for (const ref of binding.referencePaths) {
-        if (stmt.isAncestor(ref)) {
-          return {
-            type: ref === refPath ? "current-ref" : "other-ref"
+        if (ref === refPath && stmt.isAncestor(ref)) {
+          state.reference = {
+            idx,
+            scope: binding.path.scope === ref.scope ? "current" : "other"
           };
+          break;
         }
       }
-      return { type: "neither" };
-    });
+    }
 
-    const types = state.map(s => s.type);
+    if (state.reference && state.binding) {
+      if (
+        state.reference.scope === "current" &&
+        state.reference.idx < state.binding.idx
+      ) {
+        return { confident: true, value: void 0 };
+      }
 
-    if (types.indexOf("current-ref") < types.indexOf("binding")) {
       return { shouldDeopt: true };
     }
   } else if (binding.kind === "let" || binding.kind === "const") {
@@ -184,10 +195,14 @@ function evaluateBasedOnControlFlow(binding, refPath) {
         state.reference.scope === "current" &&
         state.reference.idx < state.binding.idx
       ) {
-        return { confident: true, value: void 0 };
+        throw new Error(
+          `ReferenceError: Used ${refPath.node.name}: ` +
+            `${binding.kind} binding before declaration`
+        );
+      }
+      if (state.reference.scope === "other") {
+        return { shouldDeopt: true };
       }
-
-      return { shouldDeopt: true };
     }
   }
 
diff --git a/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js b/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
index d01ccac94..51d95086a 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
@@ -2474,12 +2474,20 @@ describe("dce-plugin", () => {
     "should optimize lets referenced before init declarations - 2",
     `
       function foo() {
-        if (a) console.log(a);
+        function bar() {
+          if (a) console.log(a);
+        }
         let a = 1;
+        return bar;
       }
     `,
     `
-      function foo() {}
+      function foo() {
+        let a = 1;
+        return function () {
+          if (a) console.log(a);
+        };
+      }
     `
   );
 });
diff --git a/packages/babel-plugin-minify-dead-code-elimination/src/index.js b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
index badc08314..fd851bcfa 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/src/index.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
@@ -509,7 +509,7 @@ module.exports = ({ types: t, traverse }) => {
 
     SwitchStatement: {
       exit(path) {
-        const evaluated = path.get("discriminant").evaluate();
+        const evaluated = evaluate(path.get("discriminant"), t);
 
         if (!evaluated.confident) return;
 
@@ -528,7 +528,7 @@ module.exports = ({ types: t, traverse }) => {
             continue;
           }
 
-          const testResult = test.evaluate();
+          const testResult = evaluate(test, t);
 
           // if we are not able to deternine a test during
           // compile time, we terminate immediately
@@ -614,7 +614,7 @@ module.exports = ({ types: t, traverse }) => {
 
     WhileStatement(path) {
       const test = path.get("test");
-      const result = test.evaluate();
+      const result = evaluate(test, t);
       if (result.confident && test.isPure() && !result.value) {
         path.remove();
       }
@@ -624,7 +624,7 @@ module.exports = ({ types: t, traverse }) => {
       const test = path.get("test");
       if (!test.isPure()) return;
 
-      const result = test.evaluate();
+      const result = evaluate(test, t);
       if (result.confident) {
         if (result.value) {
           test.remove();
@@ -636,7 +636,7 @@ module.exports = ({ types: t, traverse }) => {
 
     DoWhileStatement(path) {
       const test = path.get("test");
-      const result = test.evaluate();
+      const result = evaluate(test, t);
       if (result.confident && test.isPure() && !result.value) {
         const body = path.get("body");
 

From 110a1ecbc575e0667be0fe2e13bf4005d962cfdb Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Tue, 8 Aug 2017 18:02:10 +0200
Subject: [PATCH 4/8] Fix minify builtins testcases

---
 packages/babel-helper-evaluate-path/src/index.js   |  2 +-
 .../__snapshots__/minify-builtins.js.snap          | 14 +++++++-------
 .../__tests__/minify-builtins.js                   |  6 +++---
 3 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/packages/babel-helper-evaluate-path/src/index.js b/packages/babel-helper-evaluate-path/src/index.js
index b99f2ebf0..ec65c8739 100644
--- a/packages/babel-helper-evaluate-path/src/index.js
+++ b/packages/babel-helper-evaluate-path/src/index.js
@@ -25,8 +25,8 @@ module.exports = function evaluate(path, t) {
 
       const evalResult = evaluateIdentifier(idPath);
       if (evalResult.confident) {
-        idPath.replaceWith(t.valueToNode(evalResult.value));
         deref(idPath, binding);
+        idPath.replaceWith(t.valueToNode(evalResult.value));
       } else {
         state.confident = evalResult.confident;
         state.deoptPath = evalResult.deoptPath;
diff --git a/packages/babel-plugin-minify-builtins/__tests__/__snapshots__/minify-builtins.js.snap b/packages/babel-plugin-minify-builtins/__tests__/__snapshots__/minify-builtins.js.snap
index 444173407..ffe207d50 100644
--- a/packages/babel-plugin-minify-builtins/__tests__/__snapshots__/minify-builtins.js.snap
+++ b/packages/babel-plugin-minify-builtins/__tests__/__snapshots__/minify-builtins.js.snap
@@ -85,7 +85,7 @@ new A();",
 exports[`minify-builtins should collect and minify no matter any depth 1`] = `
 Object {
   "_source": "function a (){
-  Math.max(b, a);
+  Math.max(c, a);
   const b = () => {
     const a = Math.floor(c);
     Math.min(b, a) * Math.floor(b);
@@ -95,7 +95,7 @@ Object {
   }
 }",
   "expected": "function a() {
-  Math.max(b, a);
+  Math.max(c, a);
   const b = () => {
     var _Mathmin = Math.min;
     var _Mathfloor = Math.floor;
@@ -170,8 +170,8 @@ exports[`minify-builtins should minify builtins to method scope for class declar
 Object {
   "_source": "class Test {
   foo() {
-    Math.max(c, d)
-    Math.max(c, d)
+    Math.max(a, d)
+    Math.max(a, d)
     const c = function() {
       Math.max(c, d)
       Math.floor(m);
@@ -187,8 +187,8 @@ Object {
   foo() {
     var _Mathmax = Math.max;
 
-    _Mathmax(c, d);
-    _Mathmax(c, d);
+    _Mathmax(a, d);
+    _Mathmax(a, d);
     const c = function () {
       var _Mathfloor = Math.floor;
 
@@ -220,7 +220,7 @@ Object {
 
   let a = 10;
   const d = false;
-  _Mathmax(a, b) + _Mathmax(b, a);
+  _Mathmax(10, b) + _Mathmax(b, 10);
   return d && true;
 }",
 }
diff --git a/packages/babel-plugin-minify-builtins/__tests__/minify-builtins.js b/packages/babel-plugin-minify-builtins/__tests__/minify-builtins.js
index 344396c78..7837a6e47 100644
--- a/packages/babel-plugin-minify-builtins/__tests__/minify-builtins.js
+++ b/packages/babel-plugin-minify-builtins/__tests__/minify-builtins.js
@@ -40,7 +40,7 @@ describe("minify-builtins", () => {
     "should collect and minify no matter any depth",
     `
     function a (){
-      Math.max(b, a);
+      Math.max(c, a);
       const b = () => {
         const a = Math.floor(c);
         Math.min(b, a) * Math.floor(b);
@@ -68,8 +68,8 @@ describe("minify-builtins", () => {
     `
     class Test {
       foo() {
-        Math.max(c, d)
-        Math.max(c, d)
+        Math.max(a, d)
+        Math.max(a, d)
         const c = function() {
           Math.max(c, d)
           Math.floor(m);

From b51b904ad4d5eabc80e3690d95ddcd4e786e811c Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Tue, 8 Aug 2017 18:22:40 +0200
Subject: [PATCH 5/8] Fix for switchcase parent

---
 packages/babel-helper-evaluate-path/src/index.js          | 8 +++-----
 .../__tests__/__snapshots__/minify-builtins.js.snap       | 2 +-
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/packages/babel-helper-evaluate-path/src/index.js b/packages/babel-helper-evaluate-path/src/index.js
index ec65c8739..6a43e4ecd 100644
--- a/packages/babel-helper-evaluate-path/src/index.js
+++ b/packages/babel-helper-evaluate-path/src/index.js
@@ -24,10 +24,7 @@ module.exports = function evaluate(path, t) {
       if (!binding) return;
 
       const evalResult = evaluateIdentifier(idPath);
-      if (evalResult.confident) {
-        deref(idPath, binding);
-        idPath.replaceWith(t.valueToNode(evalResult.value));
-      } else {
+      if (!evalResult.confident) {
         state.confident = evalResult.confident;
         state.deoptPath = evalResult.deoptPath;
       }
@@ -105,7 +102,8 @@ function evaluateBasedOnControlFlow(binding, refPath) {
     const declaration = binding.path.parentPath;
     if (
       declaration.parentPath.isIfStatement() ||
-      declaration.parentPath.isLoop()
+      declaration.parentPath.isLoop() ||
+      declaration.parentPath.isSwitchCase()
     ) {
       return { shouldDeopt: true };
     }
diff --git a/packages/babel-plugin-minify-builtins/__tests__/__snapshots__/minify-builtins.js.snap b/packages/babel-plugin-minify-builtins/__tests__/__snapshots__/minify-builtins.js.snap
index ffe207d50..2873bc632 100644
--- a/packages/babel-plugin-minify-builtins/__tests__/__snapshots__/minify-builtins.js.snap
+++ b/packages/babel-plugin-minify-builtins/__tests__/__snapshots__/minify-builtins.js.snap
@@ -220,7 +220,7 @@ Object {
 
   let a = 10;
   const d = false;
-  _Mathmax(10, b) + _Mathmax(b, 10);
+  _Mathmax(a, b) + _Mathmax(b, a);
   return d && true;
 }",
 }

From ad9be49288048d74b99169800ea76c55d3b15f15 Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Tue, 8 Aug 2017 18:26:10 +0200
Subject: [PATCH 6/8] Remove deadcode

---
 .../babel-helper-evaluate-path/src/index.js   | 25 +------------------
 .../babel-plugin-minify-builtins/src/index.js |  2 +-
 .../src/index.js                              |  2 +-
 .../src/index.js                              | 12 ++++-----
 4 files changed, 9 insertions(+), 32 deletions(-)

diff --git a/packages/babel-helper-evaluate-path/src/index.js b/packages/babel-helper-evaluate-path/src/index.js
index 6a43e4ecd..cea47a1b0 100644
--- a/packages/babel-helper-evaluate-path/src/index.js
+++ b/packages/babel-helper-evaluate-path/src/index.js
@@ -1,9 +1,6 @@
 "use strict";
 
-module.exports = function evaluate(path, t) {
-  if (!t) {
-    throw new Error("Expected babel-types");
-  }
+module.exports = function evaluate(path) {
   if (path.isReferencedIdentifier()) {
     return evaluateIdentifier(path);
   }
@@ -213,23 +210,3 @@ function deopt(deoptPath) {
     deoptPath
   };
 }
-
-function deref(refPath, binding) {
-  if (!refPath.isReferencedIdentifier()) {
-    throw new Error(`Expected ReferencedIdentifier. Got ${refPath.type}`);
-  }
-
-  if (binding.references > 0) {
-    binding.references--;
-  }
-  if (binding.references === 0) {
-    binding.referenced = false;
-  }
-  const idx = binding.referencePaths.indexOf(refPath);
-
-  if (idx < 0) {
-    throw new Error("Unexpected Error. Scope not updated properly");
-  }
-
-  binding.referencePaths.splice(idx, 1);
-}
diff --git a/packages/babel-plugin-minify-builtins/src/index.js b/packages/babel-plugin-minify-builtins/src/index.js
index 5dd205b66..5f1119e01 100644
--- a/packages/babel-plugin-minify-builtins/src/index.js
+++ b/packages/babel-plugin-minify-builtins/src/index.js
@@ -48,7 +48,7 @@ module.exports = function({ types: t }) {
             // computed property should be not optimized
             // Math[max]() -> Math.max()
             if (!isComputed(callee) && isBuiltin(callee)) {
-              const result = evaluate(path, t);
+              const result = evaluate(path);
               // deopt when we have side effecty evaluate-able arguments
               // Math.max(foo(), 1) --> untouched
               // Math.floor(1) --> 1
diff --git a/packages/babel-plugin-minify-constant-folding/src/index.js b/packages/babel-plugin-minify-constant-folding/src/index.js
index 4cce64d2d..5e591a4f2 100644
--- a/packages/babel-plugin-minify-constant-folding/src/index.js
+++ b/packages/babel-plugin-minify-constant-folding/src/index.js
@@ -143,7 +143,7 @@ module.exports = babel => {
           return;
         }
 
-        const res = evaluate(path, t);
+        const res = evaluate(path);
         if (res.confident) {
           // Avoid fractions because they can be longer than the original expression.
           // There is also issues with number percision?
diff --git a/packages/babel-plugin-minify-dead-code-elimination/src/index.js b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
index fd851bcfa..e882b7b94 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/src/index.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
@@ -509,7 +509,7 @@ module.exports = ({ types: t, traverse }) => {
 
     SwitchStatement: {
       exit(path) {
-        const evaluated = evaluate(path.get("discriminant"), t);
+        const evaluated = evaluate(path.get("discriminant"));
 
         if (!evaluated.confident) return;
 
@@ -528,7 +528,7 @@ module.exports = ({ types: t, traverse }) => {
             continue;
           }
 
-          const testResult = evaluate(test, t);
+          const testResult = evaluate(test);
 
           // if we are not able to deternine a test during
           // compile time, we terminate immediately
@@ -614,7 +614,7 @@ module.exports = ({ types: t, traverse }) => {
 
     WhileStatement(path) {
       const test = path.get("test");
-      const result = evaluate(test, t);
+      const result = evaluate(test);
       if (result.confident && test.isPure() && !result.value) {
         path.remove();
       }
@@ -624,7 +624,7 @@ module.exports = ({ types: t, traverse }) => {
       const test = path.get("test");
       if (!test.isPure()) return;
 
-      const result = evaluate(test, t);
+      const result = evaluate(test);
       if (result.confident) {
         if (result.value) {
           test.remove();
@@ -636,7 +636,7 @@ module.exports = ({ types: t, traverse }) => {
 
     DoWhileStatement(path) {
       const test = path.get("test");
-      const result = evaluate(test, t);
+      const result = evaluate(test);
       if (result.confident && test.isPure() && !result.value) {
         const body = path.get("body");
 
@@ -772,7 +772,7 @@ module.exports = ({ types: t, traverse }) => {
           const alternate = path.get("alternate");
           const test = path.get("test");
 
-          const evalResult = evaluate(test, t);
+          const evalResult = evaluate(test);
           const isPure = test.isPure();
 
           const replacements = [];

From 81e364ac43aa534124f4d9d8ac166aee4438d127 Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Tue, 8 Aug 2017 23:28:05 +0200
Subject: [PATCH 7/8] Extract compare function

---
 .../babel-helper-evaluate-path/src/index.js   | 88 +++++++++----------
 1 file changed, 41 insertions(+), 47 deletions(-)

diff --git a/packages/babel-helper-evaluate-path/src/index.js b/packages/babel-helper-evaluate-path/src/index.js
index cea47a1b0..4247d3f4d 100644
--- a/packages/babel-helper-evaluate-path/src/index.js
+++ b/packages/babel-helper-evaluate-path/src/index.js
@@ -122,30 +122,16 @@ function evaluateBasedOnControlFlow(binding, refPath) {
       ? fnParent.get("body")
       : fnParent.get("body").get("body");
 
-    const state = {
-      binding: null,
-      reference: null
-    };
-
-    for (const [idx, stmt] of stmts.entries()) {
-      if (stmt.isAncestor(binding.path)) {
-        state.binding = { idx };
-      }
-      for (const ref of binding.referencePaths) {
-        if (ref === refPath && stmt.isAncestor(ref)) {
-          state.reference = {
-            idx,
-            scope: binding.path.scope === ref.scope ? "current" : "other"
-          };
-          break;
-        }
-      }
-    }
+    const compareResult = compareBindingAndReference({
+      binding,
+      refPath,
+      stmts
+    });
 
-    if (state.reference && state.binding) {
+    if (compareResult.reference && compareResult.binding) {
       if (
-        state.reference.scope === "current" &&
-        state.reference.idx < state.binding.idx
+        compareResult.reference.scope === "current" &&
+        compareResult.reference.idx < compareResult.binding.idx
       ) {
         return { confident: true, value: void 0 };
       }
@@ -155,9 +141,7 @@ function evaluateBasedOnControlFlow(binding, refPath) {
   } else if (binding.kind === "let" || binding.kind === "const") {
     // binding.path is the declarator
     const declarator = binding.path;
-
     let scopePath = declarator.scope.path;
-
     if (scopePath.isFunction()) {
       scopePath = scopePath.get("body");
     }
@@ -165,37 +149,23 @@ function evaluateBasedOnControlFlow(binding, refPath) {
     // Detect Usage before Init
     const stmts = scopePath.get("body");
 
-    const state = {
-      binding: null,
-      reference: null
-    };
-
-    for (const [idx, stmt] of stmts.entries()) {
-      if (stmt.isAncestor(binding.path)) {
-        state.binding = { idx };
-      }
-      for (const ref of binding.referencePaths) {
-        if (ref === refPath && stmt.isAncestor(ref)) {
-          state.reference = {
-            idx,
-            scope: binding.path.scope === ref.scope ? "current" : "other"
-          };
-          break;
-        }
-      }
-    }
+    const compareResult = compareBindingAndReference({
+      binding,
+      refPath,
+      stmts
+    });
 
-    if (state.reference && state.binding) {
+    if (compareResult.reference && compareResult.binding) {
       if (
-        state.reference.scope === "current" &&
-        state.reference.idx < state.binding.idx
+        compareResult.reference.scope === "current" &&
+        compareResult.reference.idx < compareResult.binding.idx
       ) {
         throw new Error(
           `ReferenceError: Used ${refPath.node.name}: ` +
             `${binding.kind} binding before declaration`
         );
       }
-      if (state.reference.scope === "other") {
+      if (compareResult.reference.scope === "other") {
         return { shouldDeopt: true };
       }
     }
@@ -204,6 +174,30 @@ function evaluateBasedOnControlFlow(binding, refPath) {
   return { confident: false, shouldDeopt: false };
 }
 
+function compareBindingAndReference({ binding, refPath, stmts }) {
+  const state = {
+    binding: null,
+    reference: null
+  };
+
+  for (const [idx, stmt] of stmts.entries()) {
+    if (stmt.isAncestor(binding.path)) {
+      state.binding = { idx };
+    }
+    for (const ref of binding.referencePaths) {
+      if (ref === refPath && stmt.isAncestor(ref)) {
+        state.reference = {
+          idx,
+          scope: binding.path.scope === ref.scope ? "current" : "other"
+        };
+        break;
+      }
+    }
+  }
+
+  return state;
+}
+
 function deopt(deoptPath) {
   return {
     confident: false,

From c9a8059c603b337de31e7f83e8ff110f2e95a05b Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Tue, 8 Aug 2017 23:33:13 +0200
Subject: [PATCH 8/8] Skip test

---
 .../__tests__/dead-code-elimination-test.js              | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js b/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
index 51d95086a..26d0ef427 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
@@ -2455,18 +2455,13 @@ describe("dce-plugin", () => {
     `
   );
 
-  thePlugin(
+  thePlugin.skip(
     "should optimize to void 0 for lets referenced before init declarations",
     `
       function foo() {
-        bar(a);
+        bar(a); // Should be a ReferenceError
         let a = 1;
       }
-    `,
-    `
-      function foo() {
-        bar(void 0);
-      }
     `
   );