fix corner case in dead_code (#5031)

fixes #5030

lib/compress.js

@@ -9858,7 +9858,7 @@ merge(Compressor.prototype, {
     OPT(AST_Sequence, function(self, compressor) {
         var expressions = filter_for_side_effects();
         var end = expressions.length - 1;
-        merge_conditional_assignments();
+        merge_assignments();
         trim_right_for_undefined();
         if (end == 0) {
             self = maintain_this_binding(compressor, compressor.parent(), compressor.self(), expressions[0]);
@@ -9895,19 +9895,33 @@ merge(Compressor.prototype, {
             }
         }
 
-        function merge_conditional_assignments() {
-            if (!compressor.option("conditionals")) return;
+        function is_simple_assign(node) {
+            return node instanceof AST_Assign
+                && node.operator == "="
+                && node.left instanceof AST_SymbolRef
+                && node.left.definition();
+        }
+
+        function merge_assignments() {
             for (var i = 1; i < end; i++) {
-                var assign = expressions[i - 1];
-                if (!(assign instanceof AST_Assign)) continue;
-                if (assign.operator != "=") continue;
-                if (!(assign.left instanceof AST_SymbolRef)) continue;
-                var def = assign.left.definition();
-                var cond = to_conditional_assignment(compressor, def, assign.right, expressions[i]);
-                if (!cond) continue;
-                assign.right = cond;
-                expressions.splice(i, 1);
-                end--;
+                var prev = expressions[i - 1];
+                var def = is_simple_assign(prev);
+                if (!def) continue;
+                var expr = expressions[i];
+                if (compressor.option("conditionals")) {
+                    var cond = to_conditional_assignment(compressor, def, prev.right, expr);
+                    if (cond) {
+                        prev.right = cond;
+                        expressions.splice(i--, 1);
+                        end--;
+                        continue;
+                    }
+                }
+                if (compressor.option("dead_code")
+                    && is_simple_assign(expr) === def
+                    && expr.right.is_constant_expression(def.scope.resolve())) {
+                    expressions[--i] = prev.right;
+                }
             }
         }
     });
@@ -11143,7 +11157,7 @@ merge(Compressor.prototype, {
         var scan_scope = new TreeWalker(function(node) {
             if (reachable) return true;
             if (node instanceof AST_Lambda && node !== self) {
-                if (!(is_async(node) || is_generator(node))) {
+                if (!(node.name || is_async(node) || is_generator(node))) {
                     var parent = scan_scope.parent();
                     if (parent instanceof AST_Call && parent.expression === node) return;
                 }

test/compress/dead-code.js

@@ -1103,6 +1103,21 @@ last_assign_finally: {
     expect_stdout: "PASS"
 }
 
+consecutive_assignments: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        while (a = void 0, a = "PASS", console.log(a));
+        var a;
+    }
+    expect: {
+        while (void 0, a = "PASS", console.log(a));
+        var a;
+    }
+    expect_stdout: "PASS"
+}
+
 issue_3578: {
     options = {
         dead_code: true,
@@ -1584,3 +1599,37 @@ issue_4570: {
     }
     expect_stdout: "NaN"
 }
+
+issue_5030: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        (function(a, b) {
+            a = function f() {
+                if (a)
+                    if (b--)
+                        setImmediate(f);
+                    else
+                        console.log("FAIL");
+                else
+                    console.log("PASS");
+            }();
+        })(42, 1);
+    }
+    expect: {
+        (function(a, b) {
+            a = function f() {
+                if (a)
+                    if (b--)
+                        setImmediate(f);
+                    else
+                        console.log("FAIL");
+                else
+                    console.log("PASS");
+            }();
+        })(42, 1);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=0.12"
+}

test/compress/default-values.js

@@ -422,7 +422,9 @@ inline_loop_1: {
 inline_loop_2: {
     options = {
         inline: true,
+        sequences: true,
         toplevel: true,
+        unused: true,
     }
     input: {
         while (function(a = [ "PASS" ]) {
@@ -432,10 +434,11 @@ inline_loop_2: {
         }());
     }
     expect: {
-        while (a = [ "PASS" ], a = function f(b) {
-            console.log(a[b]);
-        }(0), void 0) ;
-        var a;
+        while (a = [ "PASS" ],
+            b = void 0,
+            b = 0,
+            void (a = void console.log(a[b])));
+        var a, b;
     }
     expect_stdout: "PASS"
     node_version: ">=6"