enhance conditionals (#5703)

Author: alexlamsl

lib/compress.js

@@ -11806,8 +11806,18 @@ Compressor.prototype.compress = function(node) {
                 }
             }
             // x && (y && z) ---> x && y && z
-            // x || (y || z) ---> x || y || z
-            if (self.right instanceof AST_Binary && self.operator == self.right.operator) swap_chain(self, compressor);
+            // w || (x, y || z) ---> w || (x, y) || z
+            var rhs = self.right.tail_node();
+            if (rhs instanceof AST_Binary && self.operator == rhs.operator) {
+                if (rhs !== self.right) {
+                    var exprs = self.right.expressions.slice(0, -1);
+                    exprs.push(rhs.left);
+                    rhs = rhs.clone();
+                    rhs.left = make_sequence(self.right, exprs);
+                    self.right = rhs;
+                }
+                swap_chain(self, compressor);
+            }
         }
         if (compressor.option("strings") && self.operator == "+") {
             // "foo" + 42 + "" ---> "foo" + 42
@@ -13101,7 +13111,7 @@ Compressor.prototype.compress = function(node) {
                 operator: "||",
                 left: booleanize(condition),
                 right: alternative,
-            });
+            }).optimize(compressor);
         }
         if (is_false(consequent)) {
             // c ? false : true ---> !c
@@ -13111,20 +13121,20 @@ Compressor.prototype.compress = function(node) {
                 operator: "&&",
                 left: booleanize(condition.negate(compressor)),
                 right: alternative,
-            });
+            }).optimize(compressor);
         }
         // c ? x : true ---> !c || x
         if (is_true(alternative)) return make_node(AST_Binary, self, {
             operator: "||",
             left: booleanize(condition.negate(compressor)),
             right: consequent,
-        });
+        }).optimize(compressor);
         // c ? x : false ---> !!c && x
         if (is_false(alternative)) return make_node(AST_Binary, self, {
             operator: "&&",
             left: booleanize(condition),
             right: consequent,
-        });
+        }).optimize(compressor);
         if (compressor.option("typeofs")) mark_locally_defined(condition, consequent, alternative);
         return self;
 

test/compress/transform.js

@@ -127,7 +127,7 @@ if_return: {
                 if (w) {
                     if (y) return;
                 } else if (z) return;
-                return x != y && (x && w(), y && z()), !0;
+                return x != y && (x && w(), y) && z(), !0;
             }
         }
     }