support safe reassignments in `reduce_vars` (#1823)

`var a=1;a=2;x(a)` => `x(2)`

fix pre-existing issues
- reference counting on assignment
- walking of anonymous functions
- chained assignment

2 files changed, 108 insertions, 16 deletions

diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 2264783d..c01572dd 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -1592,3 +1592,25 @@ var_side_effects_3: {
     }
     expect_stdout: true
 }
+
+reduce_vars_assign: {
+    options = {
+        collapse_vars: true,
+        reduce_vars: true,
+    }
+    input: {
+        !function() {
+            var a = 1;
+            a = [].length,
+            console.log(a);
+        }();
+    }
+    expect: {
+        !function() {
+            var a = 1;
+            a = [].length,
+            console.log(a);
+        }();
+    }
+    expect_stdout: "0"
+}
diff --git a/test/compress/reduce_vars.js b/test/compress/reduce_vars.js
index ad2c90bc..c5f26904 100644
--- a/test/compress/reduce_vars.js
+++ b/test/compress/reduce_vars.js
@@ -66,7 +66,7 @@ modified: {
         conditionals  : true,
         evaluate      : true,
         reduce_vars   : true,
-        unused        : true
+        unused        : true,
     }
     input: {
         function f0() {
@@ -136,12 +136,11 @@ modified: {
         }
 
         function f2() {
-            var b = 2;
-            b = 3;
-            console.log(1 + b);
-            console.log(b + 3);
+            3;
             console.log(4);
-            console.log(1 + b + 3);
+            console.log(6);
+            console.log(4);
+            console.log(7);
         }
 
         function f3() {
@@ -375,12 +374,11 @@ passes: {
     }
     expect: {
         function f() {
-            var b = 2;
-            b = 3;
-            console.log(1 + b);
-            console.log(b + 3);
+            3;
             console.log(4);
-            console.log(1 + b + 3);
+            console.log(6);
+            console.log(4);
+            console.log(7);
         }
     }
 }
@@ -573,7 +571,7 @@ inner_var_label: {
     }
 }
 
-inner_var_for: {
+inner_var_for_1: {
     options = {
         evaluate: true,
         reduce_vars: true,
@@ -602,6 +600,29 @@ inner_var_for: {
     }
 }
 
+inner_var_for_2: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        !function() {
+            var a = 1;
+            for (var b = 1; --b;) var a = 2;
+            console.log(a);
+        }();
+    }
+    expect: {
+        !function() {
+            a = 1;
+            for (var b = 1; --b;) var a = 2;
+            console.log(a);
+        }();
+    }
+    expect_stdout: "1"
+}
+
 inner_var_for_in_1: {
     options = {
         evaluate: true,
@@ -1828,10 +1849,7 @@ redefine_farg_3: {
         console.log(function(a) {
             var a;
             return typeof a;
-        }([]), "number", function(a) {
-            var a = void 0;
-            return typeof a;
-        }([]));
+        }([]), "number", "undefined");
     }
     expect_stdout: "object number undefined"
 }
@@ -2115,6 +2133,27 @@ var_assign_5: {
     expect_stdout: "2 undefined"
 }
 
+var_assign_6: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        !function() {
+            var a = function(){}(a = 1);
+            console.log(a);
+        }();
+    }
+    expect: {
+        !function() {
+            var a = function(){}(a = 1);
+            console.log(a);
+        }();
+    }
+    expect_stdout: "undefined"
+}
+
 immutable: {
     options = {
         evaluate: true,
@@ -2263,3 +2302,34 @@ cond_assign: {
     }
     expect_stdout: "undefined"
 }
+
+iife_assign: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        !function() {
+            var a = 1, b = 0;
+            !function() {
+                b++;
+                return;
+                a = 2;
+            }();
+            console.log(a);
+        }();
+    }
+    expect: {
+        !function() {
+            var a = 1, b = 0;
+            !function() {
+                b++;
+                return;
+                a = 2;
+            }();
+            console.log(a);
+        }();
+    }
+    expect_stdout: "1"
+}