enhance assignments & unused

closes #3427
mishoo · May 28, 2019 · 4d42c5e · 4d42c5e
1 parent e4f5ba1
commit 4d42c5e
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Showing 4 changed files with 106 additions and 14 deletions.
diff --git a/lib/compress.js b/lib/compress.js
@@ -3618,7 +3618,7 @@ merge(Compressor.prototype, {
                     var value = null;
                     if (node instanceof AST_Assign) {
                         if (!in_use || node.left === sym && def.id in fixed_ids && fixed_ids[def.id] !== node) {
-                            value = node.right;
+                            value = get_rhs(node);
                         }
                     } else if (!in_use) {
                         value = make_node(AST_Number, node, {
@@ -3843,16 +3843,26 @@ merge(Compressor.prototype, {
             }
         }
 
+        function get_rhs(assign) {
+            var rhs = assign.right;
+            if (!assign.write_only) return rhs;
+            if (!(rhs instanceof AST_Binary && lazy_op[rhs.operator])) return rhs;
+            var sym = assign.left;
+            if (!(sym instanceof AST_SymbolRef) || sym.name != rhs.left.name) return rhs;
+            return rhs.right;
+        }
+
         function scan_ref_scoped(node, descend) {
             var node_def, props = [], sym = assign_as_unused(node, props);
             if (sym && self.variables.get(sym.name) === (node_def = sym.definition())) {
                 props.forEach(function(prop) {
                     prop.walk(tw);
                 });
                 if (node instanceof AST_Assign) {
-                    node.right.walk(tw);
+                    var right = get_rhs(node);
+                    right.walk(tw);
                     if (node.left === sym) {
-                        if (!node_def.chained && sym.fixed_value(true) === node.right) {
+                        if (!node_def.chained && sym.fixed_value(true) === right) {
                             fixed_ids[node_def.id] = node;
                         }
                         if (!node.write_only) {
@@ -5556,20 +5566,29 @@ merge(Compressor.prototype, {
                 self.right = tmp;
             }
         }
-        if (commutativeOperators[self.operator]) {
-            if (self.right.is_constant()
-                && !self.left.is_constant()) {
-                // if right is a constant, whatever side effects the
-                // left side might have could not influence the
-                // result.  hence, force switch.
-
-                if (!(self.left instanceof AST_Binary
-                      && PRECEDENCE[self.left.operator] >= PRECEDENCE[self.operator])) {
-                    reverse();
-                }
+        if (commutativeOperators[self.operator] && self.right.is_constant() && !self.left.is_constant()) {
+            // if right is a constant, whatever side effects the
+            // left side might have could not influence the
+            // result.  hence, force switch.
+            if (!(self.left instanceof AST_Binary
+                    && PRECEDENCE[self.left.operator] >= PRECEDENCE[self.operator])) {
+                reverse();
             }
         }
         self = self.lift_sequences(compressor);
+        if (compressor.option("assignments") && lazy_op[self.operator]) {
+            var assign = self.right;
+            // a || (a = x) => a = a || x
+            // a && (a = x) => a = a && x
+            if (self.left instanceof AST_SymbolRef
+                && assign instanceof AST_Assign
+                && assign.operator == "="
+                && self.left.equivalent_to(assign.left)) {
+                self.right = assign.right;
+                assign.right = self;
+                return assign;
+            }
+        }
         if (compressor.option("comparisons")) switch (self.operator) {
           case "===":
           case "!==":

diff --git a/test/compress/assignment.js b/test/compress/assignment.js
@@ -311,3 +311,19 @@ issue_3375: {
     }
     expect_stdout: "string"
 }
+
+issue_3427: {
+    options = {
+        assignments: true,
+        sequences: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        (function() {
+            var a;
+            a || (a = {});
+        })();
+    }
+    expect: {}
+}
diff --git a/test/compress/drop-unused.js b/test/compress/drop-unused.js
@@ -2028,3 +2028,37 @@ issue_3375: {
     }
     expect_stdout: "0 0"
 }
+
+issue_3427_1: {
+    options = {
+        sequences: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        (function() {
+            var a;
+            a = a || {};
+        })();
+    }
+    expect: {}
+}
+
+issue_3427_2: {
+    options = {
+        unused: true,
+    }
+    input: {
+        (function() {
+            var s = "PASS";
+            console.log(s = s || "FAIL");
+        })();
+    }
+    expect: {
+        (function() {
+            var s = "PASS";
+            console.log(s = s || "FAIL");
+        })();
+    }
+    expect_stdout: "PASS"
+}
diff --git a/test/compress/pure_getters.js b/test/compress/pure_getters.js
@@ -1187,3 +1187,26 @@ drop_arguments: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3427: {
+    options = {
+        assignments: true,
+        collapse_vars: true,
+        inline: true,
+        pure_getters: "strict",
+        sequences: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a;
+        (function(b) {
+            b.p = 42;
+        })(a || (a = {}));
+    }
+    expect: {
+        var a;
+        (a = a || {}).p = 42;
+    }
+}