fix corner cases in reduce_vars & unused (#3955)

fixes #3953
fixes #3956
fixes #3957

test/compress/drop-unused.js

@@ -2652,3 +2652,41 @@ issue_3951: {
         "0",
     ]
 }
+
+issue_3956: {
+    options = {
+        collapse_vars: true,
+        evaluate: true,
+        inline: true,
+        passes: 2,
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        (function(a) {
+            function f(b) {
+                console.log(b);
+                a = 1;
+            }
+            var c = f(c += 0);
+            (function(d) {
+                console.log(d);
+            })(console.log(a) ^ 1, c);
+        })();
+    }
+    expect: {
+        var c, d;
+        c += 0,
+        console.log(NaN),
+        d = 1 ^ console.log(1),
+        console.log(d);
+    }
+    expect_stdout: [
+        "NaN",
+        "1",
+        "1",
+    ]
+}

test/compress/evaluate.js

@@ -2715,3 +2715,23 @@ issue_3944: {
     }
     expect_stdout: "false"
 }
+
+issue_3953: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+    }
+    input: {
+        function f(a) {
+            (a += 0 * (a = 0)) && console.log("PASS");
+        }
+        f(1);
+    }
+    expect: {
+        function f(a) {
+            (a += 0 * (a = 0)) && console.log("PASS");
+        }
+        f(1);
+    }
+    expect_stdout: "PASS"
+}

test/compress/reduce_vars.js

@@ -7273,3 +7273,53 @@ local_assignment_loop: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3957_1: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+    }
+    input: {
+        function f(a) {
+            while (a += console.log(a = 0))
+                a = 0;
+        }
+        f("FAIL");
+    }
+    expect: {
+        function f(a) {
+            while (a += console.log(a = 0))
+                a = 0;
+        }
+        f("FAIL");
+    }
+    expect_stdout: [
+        "0",
+        "0",
+    ]
+}
+
+issue_3957_2: {
+    options = {
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        function f(a) {
+            while (a += console.log(a = 0))
+                a = 0;
+        }
+        f("FAIL");
+    }
+    expect: {
+        function f(a) {
+            while (a += console.log(a = 0))
+                a = 0;
+        }
+        f("FAIL");
+    }
+    expect_stdout: [
+        "0",
+        "0",
+    ]
+}