enhance reduce_vars (#5171)

test/compress/drop-unused.js

@@ -3062,7 +3062,7 @@ issue_4184: {
     expect_stdout: "42"
 }
 
-issue_4235: {
+issue_4235_1: {
     options = {
         inline: true,
         reduce_vars: true,
@@ -3081,13 +3081,37 @@ issue_4235: {
     }
     expect: {
         void function() {
-            var f;
-            console.log(f);
+            var f = console.log(f);
         }();
     }
     expect_stdout: "undefined"
 }
 
+issue_4235_2: {
+    options = {
+        inline: true,
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        unused: true,
+        varify: true,
+    }
+    input: {
+        (function() {
+            {
+                const f = 0;
+            }
+            (function f() {
+                var f = console.log(f);
+            })();
+        })();
+    }
+    expect: {
+        console.log(void 0);
+    }
+    expect_stdout: "undefined"
+}
+
 issue_4404: {
     options = {
         pure_getters: "strict",

test/compress/hoist_vars.js

@@ -135,7 +135,7 @@ issue_2295: {
     }
 }
 
-issue_4487: {
+issue_4487_1: {
     options = {
         functions: true,
         hoist_vars: true,
@@ -152,14 +152,37 @@ issue_4487: {
     }
     expect: {
         function a() {
-            var f;
-            console.log(typeof f);
+            var f = console.log(typeof f);
         }
         a();
     }
     expect_stdout: "undefined"
 }
 
+issue_4487_2: {
+    options = {
+        functions: true,
+        hoist_vars: true,
+        keep_fnames: true,
+        passes: 2,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = function f() {
+            var f = console.log(typeof f);
+        };
+        var b = a();
+    }
+    expect: {
+        (function a() {
+            console.log(typeof void 0);
+        })();
+    }
+    expect_stdout: "undefined"
+}
+
 issue_4489: {
     options = {
         collapse_vars: true,

test/compress/reduce_vars.js

@@ -7340,6 +7340,24 @@ local_assignment_modified: {
     expect_stdout: "42"
 }
 
+local_declaration: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        var a;
+        a || console.log(a = "PASS");
+    }
+    expect: {
+        var a;
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+}
+
 local_definition_modified: {
     options = {
         evaluate: true,