improve boolean compression (#2548)

fixes #2535

1 files changed, 50 insertions, 20 deletions

diff --git a/lib/compress.js b/lib/compress.js
index adfbb793..5301d48f 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -158,6 +158,7 @@ merge(Compressor.prototype, {
                 return true;
             }
             if (p instanceof AST_Binary && (p.operator == "&&" || p.operator == "||")
+                || p instanceof AST_Conditional
                 || p.tail_node() === self) {
                 self = p;
             } else {
@@ -4090,49 +4091,72 @@ merge(Compressor.prototype, {
         if (compressor.option("evaluate")) {
             switch (self.operator) {
               case "&&":
-                var ll = self.left.evaluate(compressor);
+                var ll = self.left.truthy ? true : self.left.falsy ? false : self.left.evaluate(compressor);
                 if (!ll) {
                     compressor.warn("Condition left of && always false [{file}:{line},{col}]", self.start);
                     return maintain_this_binding(compressor.parent(), compressor.self(), self.left).optimize(compressor);
-                } else if (ll !== self.left) {
+                } else if (!(ll instanceof AST_Node)) {
                     compressor.warn("Condition left of && always true [{file}:{line},{col}]", self.start);
-                    return maintain_this_binding(compressor.parent(), compressor.self(), self.right).optimize(compressor);
+                    return make_sequence(self, [ self.left, self.right ]).optimize(compressor);
                 }
-                if (compressor.in_boolean_context()) {
-                    var rr = self.right.evaluate(compressor);
-                    if (!rr) {
+                var rr = self.right.evaluate(compressor);
+                if (!rr) {
+                    if (compressor.in_boolean_context()) {
                         compressor.warn("Boolean && always false [{file}:{line},{col}]", self.start);
                         return make_sequence(self, [
                             self.left,
                             make_node(AST_False, self)
                         ]).optimize(compressor);
-                    } else if (rr !== self.right) {
-                        compressor.warn("Dropping side-effect-free && in boolean context [{file}:{line},{col}]", self.start);
+                    } else self.falsy = true;
+                } else if (!(rr instanceof AST_Node)) {
+                    var parent = compressor.parent();
+                    if (parent.operator == "&&" && parent.left === compressor.self() || compressor.in_boolean_context()) {
+                        compressor.warn("Dropping side-effect-free && [{file}:{line},{col}]", self.start);
                         return self.left.optimize(compressor);
                     }
                 }
+                // x || false && y ---> x ? y : false
+                if (self.left.operator == "||") {
+                    var lr = self.left.right.evaluate(compressor);
+                    if (!lr) return make_node(AST_Conditional, self, {
+                        condition: self.left.left,
+                        consequent: self.right,
+                        alternative: self.left.right
+                    }).optimize(compressor);
+                }
                 break;
               case "||":
-                var ll = self.left.evaluate(compressor);
+                var ll = self.left.truthy ? true : self.left.falsy ? false : self.left.evaluate(compressor);
                 if (!ll) {
                     compressor.warn("Condition left of || always false [{file}:{line},{col}]", self.start);
-                    return maintain_this_binding(compressor.parent(), compressor.self(), self.right).optimize(compressor);
-                } else if (ll !== self.left) {
+                    return make_sequence(self, [ self.left, self.right ]).optimize(compressor);
+                } else if (!(ll instanceof AST_Node)) {
                     compressor.warn("Condition left of || always true [{file}:{line},{col}]", self.start);
                     return maintain_this_binding(compressor.parent(), compressor.self(), self.left).optimize(compressor);
                 }
-                if (compressor.in_boolean_context()) {
-                    var rr = self.right.evaluate(compressor);
-                    if (!rr) {
-                        compressor.warn("Dropping side-effect-free || in boolean context [{file}:{line},{col}]", self.start);
+                var rr = self.right.evaluate(compressor);
+                if (!rr) {
+                    var parent = compressor.parent();
+                    if (parent.operator == "||" && parent.left === compressor.self() || compressor.in_boolean_context()) {
+                        compressor.warn("Dropping side-effect-free || [{file}:{line},{col}]", self.start);
                         return self.left.optimize(compressor);
-                    } else if (rr !== self.right) {
+                    }
+                } else if (!(rr instanceof AST_Node)) {
+                    if (compressor.in_boolean_context()) {
                         compressor.warn("Boolean || always true [{file}:{line},{col}]", self.start);
                         return make_sequence(self, [
                             self.left,
                             make_node(AST_True, self)
                         ]).optimize(compressor);
-                    }
+                    } else self.truthy = true;
+                }
+                if (self.left.operator == "&&") {
+                    var lr = self.left.right.evaluate(compressor);
+                    if (lr && !(lr instanceof AST_Node)) return make_node(AST_Conditional, self, {
+                        condition: self.left.left,
+                        consequent: self.left.right,
+                        alternative: self.right
+                    }).optimize(compressor);
                 }
                 break;
             }
@@ -4640,7 +4664,7 @@ merge(Compressor.prototype, {
                 consequent
             ]).optimize(compressor);
         }
-
+        var in_bool = compressor.in_boolean_context();
         if (is_true(self.consequent)) {
             if (is_false(self.alternative)) {
                 // c ? true : false ---> !!c
@@ -4696,18 +4720,24 @@ merge(Compressor.prototype, {
         // AST_True or !0
         function is_true(node) {
             return node instanceof AST_True
+                || in_bool
+                    && node instanceof AST_Constant
+                    && node.getValue()
                 || (node instanceof AST_UnaryPrefix
                     && node.operator == "!"
                     && node.expression instanceof AST_Constant
-                    && !node.expression.value);
+                    && !node.expression.getValue());
         }
         // AST_False or !1
         function is_false(node) {
             return node instanceof AST_False
+                || in_bool
+                    && node instanceof AST_Constant
+                    && !node.getValue()
                 || (node instanceof AST_UnaryPrefix
                     && node.operator == "!"
                     && node.expression instanceof AST_Constant
-                    && !!node.expression.value);
+                    && node.expression.getValue());
         }
     });