fix corner case in dead_code (#4373)

fixes #4372

lib/compress.js

@@ -9293,12 +9293,16 @@ merge(Compressor.prototype, {
                     node = parent;
                     parent = compressor.parent(level++);
                     if (parent instanceof AST_Assign) {
-                        if (parent.left instanceof AST_PropAccess) break;
+                        var found = false;
-                        if (!(parent.left instanceof AST_SymbolRef)) continue;
+                        if (parent.left.match_symbol(function(node) {
-                        if (parent.left.definition() !== def) continue;
+                            if (node instanceof AST_PropAccess) return true;
-                        if (in_try(level, parent)) break;
+                            if (!found && node instanceof AST_SymbolRef && node.definition() === def) {
-                        def.fixed = false;
+                                if (in_try(level, parent)) return true;
-                        return strip_assignment();
+                                def.fixed = false;
+                                found = true;
+                            }
+                        })) break;
+                        if (found) return strip_assignment();
                     } else if (parent instanceof AST_Exit) {
                         if (!local) break;
                         if (in_try(level, parent)) break;

test/compress/destructured.js

@@ -1806,3 +1806,41 @@ issue_4355: {
     expect_stdout: "2"
     node_version: ">=6"
 }
+
+issue_4372_1: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        var a = "FAIL";
+        a += {
+            [console.log(a)]: a,
+        } = a = "PASS";
+    }
+    expect: {
+        var a = "FAIL";
+        a += {
+            [console.log(a)]: a,
+        } = a = "PASS";
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_4372_2: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        var a;
+        [ a ] = a = [ "PASS", "FAIL" ];
+        console.log(a);
+    }
+    expect: {
+        var a;
+        [ a ] = [ "PASS", "FAIL" ];
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}