enhance `conditionals` (#3643)

1 files changed, 48 insertions, 24 deletions

diff --git a/lib/compress.js b/lib/compress.js
index c5b67569..c00b9f07 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -7005,25 +7005,42 @@ merge(Compressor.prototype, {
                 });
             }
         }
-        // x ? y(a) : y(b) --> y(x ? a : b)
-        var arg_index;
+        // x ? y : y --> x, y
+        if (consequent.equivalent_to(alternative)) return make_sequence(self, [
+            condition,
+            consequent
+        ]).optimize(compressor);
         if (consequent instanceof AST_Call
             && alternative.TYPE === consequent.TYPE
-            && consequent.args.length > 0
-            && consequent.args.length == alternative.args.length
-            && consequent.expression.equivalent_to(alternative.expression)
-            && !condition.has_side_effects(compressor)
-            && !consequent.expression.has_side_effects(compressor)
-            && typeof (arg_index = single_arg_diff()) == "number") {
-            var node = consequent.clone();
-            node.args[arg_index] = make_node(AST_Conditional, self, {
-                condition: condition,
-                consequent: consequent.args[arg_index],
-                alternative: alternative.args[arg_index]
-            });
-            return node;
+            && consequent.args.length == alternative.args.length) {
+            var arg_index = arg_diff();
+            // x ? y(a) : z(a) --> (x ? y : z)(a)
+            if (arg_index == -1
+                && !(consequent.expression instanceof AST_PropAccess)
+                && !(alternative.expression instanceof AST_PropAccess)) {
+                var node = consequent.clone();
+                node.expression = make_node(AST_Conditional, self, {
+                    condition: condition,
+                    consequent: consequent.expression,
+                    alternative: alternative.expression
+                });
+                return node;
+            }
+            // x ? y(a) : y(b) --> y(x ? a : b)
+            if (arg_index >= 0
+                && consequent.expression.equivalent_to(alternative.expression)
+                && !condition.has_side_effects(compressor)
+                && !consequent.expression.has_side_effects(compressor)) {
+                var node = consequent.clone();
+                node.args[arg_index] = make_node(AST_Conditional, self, {
+                    condition: condition,
+                    consequent: consequent.args[arg_index],
+                    alternative: alternative.args[arg_index]
+                });
+                return node;
+            }
         }
-        // x?y?z:a:a --> x&&y?z:a
+        // x ? (y ? a : b) : b --> x && y ? a : b
         if (consequent instanceof AST_Conditional
             && consequent.alternative.equivalent_to(alternative)) {
             return make_node(AST_Conditional, self, {
@@ -7036,12 +7053,18 @@ merge(Compressor.prototype, {
                 alternative: alternative
             });
         }
-        // x ? y : y --> x, y
-        if (consequent.equivalent_to(alternative)) {
-            return make_sequence(self, [
-                condition,
-                consequent
-            ]).optimize(compressor);
+        // x ? a : (y ? a : b)--> x || y ? a : b
+        if (alternative instanceof AST_Conditional
+            && consequent.equivalent_to(alternative.consequent)) {
+            return make_node(AST_Conditional, self, {
+                condition: make_node(AST_Binary, self, {
+                    left: condition,
+                    operator: "||",
+                    right: alternative.condition
+                }),
+                consequent: consequent,
+                alternative: alternative.alternative
+            });
         }
         // x ? (y, w) : (z, w) --> x ? y : z, w
         if ((consequent instanceof AST_Sequence || alternative instanceof AST_Sequence)
@@ -7145,17 +7168,18 @@ merge(Compressor.prototype, {
                     && node.expression.getValue());
         }
 
-        function single_arg_diff() {
+        function arg_diff() {
             var a = consequent.args;
             var b = alternative.args;
             for (var i = 0, len = a.length; i < len; i++) {
                 if (!a[i].equivalent_to(b[i])) {
                     for (var j = i + 1; j < len; j++) {
-                        if (!a[j].equivalent_to(b[j])) return;
+                        if (!a[j].equivalent_to(b[j])) return -2;
                     }
                     return i;
                 }
             }
+            return -1;
         }
 
         function can_shift_lhs_of_tail(node) {