enhance `booleans` (#5022)

closes #5021

1 files changed, 80 insertions, 27 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 52979c92..0d98e456 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -8223,35 +8223,86 @@ merge(Compressor.prototype, {
         }
     }
 
+    function fuzzy_eval(compressor, node, nullish) {
+        if (node.truthy) return true;
+        if (node.falsy && !nullish) return false;
+        if (node.is_truthy()) return true;
+        return node.evaluate(compressor, true);
+    }
+
+    function mark_duplicate_condition(compressor, node) {
+        for (var level = 0, child = compressor.self(), parent; ; child = parent) {
+            parent = compressor.parent(level++);
+            if (parent instanceof AST_Binary) {
+                var op = parent.operator;
+                if (!lazy_op[op]) return;
+                var left = parent.left;
+                if (left === child) continue;
+                if (node.equivalent_to(left)) node[op == "&&" ? "truthy" : "falsy"] = true;
+            } else if (parent instanceof AST_Conditional) {
+                var cond = parent.condition;
+                if (cond === child) continue;
+                if (node.equivalent_to(cond)) switch (child) {
+                  case parent.consequent:
+                    node.truthy = true;
+                    break;
+                  case parent.alternative:
+                    node.falsy = true;
+                    break;
+                }
+            } else if (parent instanceof AST_Exit) {
+                break;
+            } else if (parent instanceof AST_If) {
+                break;
+            } else if (parent instanceof AST_Sequence) {
+                if (parent.expressions[0] === child) continue;
+            } else if (parent instanceof AST_SimpleStatement) {
+                break;
+            }
+            return;
+        }
+        while (true) {
+            child = parent;
+            parent = compressor.parent(level++);
+            if (parent instanceof AST_BlockStatement) {
+                if (parent.body[0] === child) continue;
+            } else if (parent instanceof AST_If) {
+                var cond = parent.condition;
+                if (cond === child) continue;
+                if (node.equivalent_to(cond)) switch (child) {
+                  case parent.body:
+                    node.truthy = true;
+                    break;
+                  case parent.alternative:
+                    node.falsy = true;
+                    break;
+                }
+            }
+            return;
+        }
+    }
+
     OPT(AST_If, function(self, compressor) {
         if (is_empty(self.alternative)) self.alternative = null;
 
         if (!compressor.option("conditionals")) return self;
+        if (compressor.option("booleans")) mark_duplicate_condition(compressor, self.condition);
         // if condition can be statically determined, warn and drop
         // one of the blocks.  note, statically determined implies
         // “has no side effects”; also it doesn't work for cases like
         // `x && true`, though it probably should.
         if (compressor.option("dead_code")) {
-            var cond = self.condition.evaluate(compressor);
-            if (cond instanceof AST_Node) {
-                cond = self.condition.is_truthy() || self.condition.evaluate(compressor, true);
-            }
+            var cond = fuzzy_eval(compressor, self.condition);
             if (!cond) {
                 AST_Node.warn("Condition always false [{file}:{line},{col}]", self.condition.start);
-                var body = [
-                    make_node(AST_SimpleStatement, self.condition, {
-                        body: self.condition
-                    }),
-                ];
+                var body = [ make_node(AST_SimpleStatement, self.condition, { body: self.condition }) ];
                 extract_declarations_from_unreachable_code(compressor, self.body, body);
                 if (self.alternative) body.push(self.alternative);
                 return make_node(AST_BlockStatement, self, { body: body }).optimize(compressor);
             } else if (!(cond instanceof AST_Node)) {
                 AST_Node.warn("Condition always true [{file}:{line},{col}]", self.condition.start);
                 var body = [
-                    make_node(AST_SimpleStatement, self.condition, {
-                        body: self.condition
-                    }),
+                    make_node(AST_SimpleStatement, self.condition, { body: self.condition }),
                     self.body,
                 ];
                 if (self.alternative) extract_declarations_from_unreachable_code(compressor, self.alternative, body);
@@ -8275,9 +8326,7 @@ merge(Compressor.prototype, {
         var body_exprs = sequencesize(self.body, body, var_defs, refs);
         var alt_exprs = sequencesize(self.alternative, body, var_defs, refs);
         if (body_exprs && alt_exprs) {
-            if (var_defs.length > 0) body.push(make_node(AST_Var, self, {
-                definitions: var_defs
-            }));
+            if (var_defs.length > 0) body.push(make_node(AST_Var, self, { definitions: var_defs }));
             if (body_exprs.length == 0) {
                 body.push(make_node(AST_SimpleStatement, self.condition, {
                     body: alt_exprs.length > 0 ? make_node(AST_Binary, self, {
@@ -10221,7 +10270,18 @@ merge(Compressor.prototype, {
             }
             break;
         }
-        var in_bool = compressor.option("booleans") && compressor.in_boolean_context();
+        var in_bool = false;
+        var parent = compressor.parent();
+        if (compressor.option("booleans")) {
+            var lhs = self.left;
+            if (lazy_op[self.operator] && !lhs.has_side_effects(compressor)) {
+                if (lhs.equivalent_to(self.right)) {
+                    return maintain_this_binding(compressor, parent, compressor.self(), lhs).optimize(compressor);
+                }
+                mark_duplicate_condition(compressor, lhs);
+            }
+            in_bool = compressor.in_boolean_context();
+        }
         if (in_bool) switch (self.operator) {
           case "+":
             var ll = self.left.evaluate(compressor);
@@ -10255,7 +10315,6 @@ merge(Compressor.prototype, {
             }
             break;
         }
-        var parent = compressor.parent();
         if (compressor.option("comparisons") && self.is_boolean(compressor)) {
             if (!(parent instanceof AST_Binary) || parent instanceof AST_Assign) {
                 var negated = best_of(compressor, self, make_node(AST_UnaryPrefix, self, {
@@ -10313,7 +10372,7 @@ merge(Compressor.prototype, {
             var associative = true;
             switch (self.operator) {
               case "&&":
-                var ll = fuzzy_eval(self.left);
+                var ll = fuzzy_eval(compressor, self.left);
                 if (!ll) {
                     AST_Node.warn("Condition left of && always false [{file}:{line},{col}]", self.start);
                     return maintain_this_binding(compressor, parent, compressor.self(), self.left).optimize(compressor);
@@ -10349,7 +10408,7 @@ merge(Compressor.prototype, {
               case "??":
                 var nullish = true;
               case "||":
-                var ll = fuzzy_eval(self.left, nullish);
+                var ll = fuzzy_eval(compressor, self.left, nullish);
                 if (nullish ? ll == null : !ll) {
                     AST_Node.warn("Condition left of {operator} always {value} [{file}:{line},{col}]", {
                         operator: self.operator,
@@ -10732,13 +10791,6 @@ merge(Compressor.prototype, {
             });
         }
 
-        function fuzzy_eval(node, nullish) {
-            if (node.truthy) return true;
-            if (node.falsy && !nullish) return false;
-            if (node.is_truthy()) return true;
-            return node.evaluate(compressor, true);
-        }
-
         function is_indexFn(node) {
             return node.TYPE == "Call"
                 && node.expression instanceof AST_Dot
@@ -11286,7 +11338,8 @@ merge(Compressor.prototype, {
             return make_sequence(self, expressions);
         }
         if (!compressor.option("conditionals")) return self;
-        var condition = self.condition.is_truthy() || self.condition.evaluate(compressor, true);
+        if (compressor.option("booleans")) mark_duplicate_condition(compressor, self.condition);
+        var condition = fuzzy_eval(compressor, self.condition);
         if (!condition) {
             AST_Node.warn("Condition always false [{file}:{line},{col}]", self.start);
             return make_sequence(self, [ self.condition, self.alternative ]).optimize(compressor);