fix corner cases in ie8 & side_effects (#4731)

fixes #4729
fixes #4730

lib/compress.js

@@ -7226,30 +7226,36 @@ merge(Compressor.prototype, {
             }
             var rhs = right.drop_side_effect_free(compressor, first_in_statement);
             if (!rhs) return left.drop_side_effect_free(compressor, first_in_statement);
-            if (lazy_op[op] && !(rhs instanceof AST_Function)) {
+            if (lazy_op[op] && rhs.has_side_effects(compressor)) {
                 var node = this;
                  if (op == "&&"
                     && rhs instanceof AST_PropAccess
                     && left.equivalent_to(rhs.expression)
                     && !left.has_side_effects(compressor)) {
-                    var prop = rhs instanceof AST_Sub && rhs.property.drop_side_effect_free(compressor);
+                    var prop = rhs instanceof AST_Sub
+                        && rhs.property.drop_side_effect_free(compressor, first_in_statement);
                     if (!prop) return left.drop_side_effect_free(compressor, first_in_statement);
                     node = node.clone();
                     node.right = prop;
-                } else if (rhs !== right) {
+                    return node.drop_side_effect_free(compressor, first_in_statement);
+                }
+                if (rhs !== right) {
                     node = node.clone();
                     node.right = rhs.drop_side_effect_free(compressor);
                 }
                 if (op == "??") return node;
-                return (first_in_statement ? best_of_statement : best_of_expression)(node, make_node(AST_Binary, this, {
+                var negated = make_node(AST_Binary, this, {
                     operator: op == "&&" ? "||" : "&&",
                     left: left.negate(compressor, first_in_statement),
                     right: node.right,
-                }));
+                });
+                return first_in_statement ? best_of_statement(node, negated) : best_of_expression(node, negated);
             } else {
                 var lhs = left.drop_side_effect_free(compressor, first_in_statement);
                 if (!lhs) return rhs;
-                return make_sequence(this, [ lhs, rhs.drop_side_effect_free(compressor) ]);
+                rhs = rhs.drop_side_effect_free(compressor);
+                if (!rhs) return lhs;
+                return make_sequence(this, [ lhs, rhs ]);
             }
         });
         def(AST_Call, function(compressor, first_in_statement) {

test/compress/ie8.js

@@ -2919,3 +2919,28 @@ issue_4568: {
     }
     expect_stdout: "undefined 1"
 }
+
+issue_4729: {
+    options = {
+        ie8: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        try {
+            f;
+        } catch(e) {
+            var a = a && a[function f() {}];
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            f;
+        } catch(e) {
+            (function f() {});
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}

test/compress/side_effects.js

@@ -558,3 +558,33 @@ drop_side_effect_free_call: {
     }
     expect_stdout: "PASS"
 }
+
+issue_4730_1: {
+    options = {
+        side_effects: true,
+    }
+    input: {
+        var a;
+        console.log("PASS") + (a && a[a.p]);
+    }
+    expect: {
+        var a;
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+}
+
+issue_4730_2: {
+    options = {
+        side_effects: true,
+    }
+    input: {
+        var a;
+        !console.log("PASS") || a && a[a.p];
+    }
+    expect: {
+        var a;
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+}