enhance conditionals (#3694)

lib/compress.js

@@ -7194,23 +7194,24 @@ merge(Compressor.prototype, {
             expressions.push(self);
             return make_sequence(self, expressions);
         }
-        var cond = self.condition.is_truthy() || self.condition.tail_node().evaluate(compressor);
-        if (!cond) {
+        var condition = self.condition.is_truthy() || self.condition.evaluate(compressor);
+        if (!condition) {
             AST_Node.warn("Condition always false [{file}:{line},{col}]", self.start);
             return make_sequence(self, [ self.condition, self.alternative ]).optimize(compressor);
-        } else if (!(cond instanceof AST_Node)) {
+        } else if (!(condition instanceof AST_Node)) {
             AST_Node.warn("Condition always true [{file}:{line},{col}]", self.start);
             return make_sequence(self, [ self.condition, self.consequent ]).optimize(compressor);
         }
-        var negated = cond.negate(compressor, first_in_statement(compressor));
-        if (best_of(compressor, cond, negated) === negated) {
+        var negated = condition.negate(compressor, first_in_statement(compressor));
+        if (best_of(compressor, condition, negated) === negated) {
             self = make_node(AST_Conditional, self, {
                 condition: negated,
                 consequent: self.alternative,
                 alternative: self.consequent
             });
+            negated = condition;
+            condition = self.condition;
         }
-        var condition = self.condition;
         var consequent = self.consequent;
         var alternative = self.alternative;
         // x ? x : y => x || y
@@ -7298,6 +7299,19 @@ merge(Compressor.prototype, {
                 alternative: alternative
             });
         }
+        // x ? (y ? a : b) : a => !x || y ? a : b
+        if (consequent instanceof AST_Conditional
+            && consequent.consequent.equivalent_to(alternative)) {
+            return make_node(AST_Conditional, self, {
+                condition: make_node(AST_Binary, self, {
+                    left: negated,
+                    operator: "||",
+                    right: consequent.condition
+                }),
+                consequent: alternative,
+                alternative: consequent.alternative
+            });
+        }
         // x ? a : (y ? a : b) => x || y ? a : b
         if (alternative instanceof AST_Conditional
             && consequent.equivalent_to(alternative.consequent)) {
@@ -7311,7 +7325,20 @@ merge(Compressor.prototype, {
                 alternative: alternative.alternative
             });
         }
-        // x ? (y, w) : (z, w) => x ? y : z, w
+        // x ? b : (y ? a : b) => !x && y ? a : b
+        if (alternative instanceof AST_Conditional
+            && consequent.equivalent_to(alternative.alternative)) {
+            return make_node(AST_Conditional, self, {
+                condition: make_node(AST_Binary, self, {
+                    left: negated,
+                    operator: "&&",
+                    right: alternative.condition
+                }),
+                consequent: alternative.consequent,
+                alternative: consequent
+            });
+        }
+        // x ? (a, c) : (b, c) => x ? a : b, c
         if ((consequent instanceof AST_Sequence || alternative instanceof AST_Sequence)
             && consequent.tail_node().equivalent_to(alternative.tail_node())) {
             return make_sequence(self, [
@@ -7323,7 +7350,21 @@ merge(Compressor.prototype, {
                 consequent.tail_node()
             ]).optimize(compressor);
         }
-        // x ? y || z : z => x && y || z
+        // x ? y && a : a => (!x || y) && a
+        if (consequent instanceof AST_Binary
+            && consequent.operator == "&&"
+            && consequent.right.equivalent_to(alternative)) {
+            return make_node(AST_Binary, self, {
+                operator: "&&",
+                left: make_node(AST_Binary, self, {
+                    operator: "||",
+                    left: negated,
+                    right: consequent.left
+                }),
+                right: alternative
+            }).optimize(compressor);
+        }
+        // x ? y || a : a => x && y || a
         if (consequent instanceof AST_Binary
             && consequent.operator == "||"
             && consequent.right.equivalent_to(alternative)) {
@@ -7337,6 +7378,34 @@ merge(Compressor.prototype, {
                 right: alternative
             }).optimize(compressor);
         }
+        // x ? a : y && a => (x || y) && a
+        if (alternative instanceof AST_Binary
+            && alternative.operator == "&&"
+            && alternative.right.equivalent_to(consequent)) {
+            return make_node(AST_Binary, self, {
+                operator: "&&",
+                left: make_node(AST_Binary, self, {
+                    operator: "||",
+                    left: condition,
+                    right: alternative.left
+                }),
+                right: consequent
+            }).optimize(compressor);
+        }
+        // x ? a : y || a => !x && y || a
+        if (alternative instanceof AST_Binary
+            && alternative.operator == "||"
+            && alternative.right.equivalent_to(consequent)) {
+            return make_node(AST_Binary, self, {
+                operator: "||",
+                left: make_node(AST_Binary, self, {
+                    operator: "&&",
+                    left: negated,
+                    right: alternative.left
+                }),
+                right: consequent
+            }).optimize(compressor);
+        }
         var in_bool = compressor.option("booleans") && compressor.in_boolean_context();
         if (is_true(consequent)) {
             if (is_false(alternative)) {