fix unsafe on evaluate of reduce_vars (#1870)

Determine if variables with non-constant values can escape and be modified.

fixes #1865

test/compress/reduce_vars.js

@@ -297,7 +297,7 @@ unsafe_evaluate_array: {
     }
 }
 
-unsafe_evaluate_equality: {
+unsafe_evaluate_equality_1: {
     options = {
         evaluate     : true,
         reduce_vars  : true,
@@ -305,47 +305,62 @@ unsafe_evaluate_equality: {
         unused       : true
     }
     input: {
-        function f0(){
+        function f0() {
             var a = {};
-            console.log(a === a);
+            return a === a;
         }
-
-        function f1(){
+        function f1() {
             var a = [];
-            console.log(a === a);
+            return a === a;
         }
+        console.log(f0(), f1());
+    }
+    expect: {
+        function f0() {
+            return true;
+        }
+        function f1() {
+            return true;
+        }
+        console.log(f0(), f1());
+    }
+    expect_stdout: true
+}
 
-        function f2(){
+unsafe_evaluate_equality_2: {
+    options = {
+        collapse_vars: true,
+        evaluate     : true,
+        passes       : 2,
+        reduce_vars  : true,
+        unsafe       : true,
+        unused       : true
+    }
+    input: {
+        function f2() {
             var a = {a:1, b:2};
             var b = a;
             var c = a;
-            console.log(b === c);
+            return b === c;
         }
-
-        function f3(){
+        function f3() {
             var a = [1, 2, 3];
             var b = a;
             var c = a;
-            console.log(b === c);
+            return b === c;
         }
+        console.log(f2(), f3());
     }
     expect: {
-        function f0(){
-            console.log(true);
+        function f2() {
+            return true;
         }
-
-        function f1(){
-            console.log(true);
-        }
-
-        function f2(){
-            console.log(true);
-        }
-
-        function f3(){
-            console.log(true);
+        function f3() {
+            return true;
         }
+        console.log(f2(), f3());
     }
+    expect_stdout: true
 }
 
 passes: {
@@ -2417,3 +2432,32 @@ issue_1850_4: {
     }
     expect_stdout: true
 }
+
+issue_1865: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        unsafe: true,
+    }
+    input: {
+        function f(a) {
+            a.b = false;
+        }
+        console.log(function() {
+            var some = { thing: true };
+            f(some);
+            return some.thing;
+        }());
+    }
+    expect: {
+        function f(a) {
+            a.b = false;
+        }
+        console.log(function() {
+            var some = { thing: true };
+            f(some);
+            return some.thing;
+        }());
+    }
+    expect_stdout: true
+}