fix corner case in awaits (#4973)

fixes #4972

lib/compress.js

@@ -9898,7 +9898,16 @@ merge(Compressor.prototype, {
                 if (is_arrow(parent)) {
                     if (parent.value === node) return exp.optimize(compressor);
                 } else if (parent instanceof AST_Return) {
-                    return exp.optimize(compressor);
+                    var drop = true;
+                    do {
+                        node = parent;
+                        parent = compressor.parent(level++);
+                        if (parent instanceof AST_Try && parent.bfinally && parent.bfinally !== node) {
+                            drop = false;
+                            break;
+                        }
+                    } while (parent && !(parent instanceof AST_Scope));
+                    if (drop) return exp.optimize(compressor);
                 } else if (parent instanceof AST_Sequence) {
                     if (parent.tail_node() === node) continue;
                 }

test/compress/awaits.js

@@ -1574,3 +1574,111 @@ issue_4764_3: {
     expect_stdout: "PASS"
     node_version: ">=8"
 }
+
+issue_4972_1: {
+    options = {
+        awaits: true,
+        side_effects: true,
+    }
+    input: {
+        console.log("foo");
+        (async function() {
+            try {
+                return await "bar";
+            } finally {
+                console.log("baz");
+            }
+        })().then(console.log);
+        console.log("moo");
+    }
+    expect: {
+        console.log("foo");
+        (async function() {
+            try {
+                return await "bar";
+            } finally {
+                console.log("baz");
+            }
+        })().then(console.log);
+        console.log("moo");
+    }
+    expect_stdout: [
+        "foo",
+        "moo",
+        "baz",
+        "bar",
+    ]
+    node_version: ">=8"
+}
+
+issue_4972_2: {
+    options = {
+        awaits: true,
+        side_effects: true,
+    }
+    input: {
+        console.log("foo");
+        (async function() {
+            try {
+                console.log("bar");
+            } finally {
+                return await "baz";
+            }
+        })().then(console.log);
+        console.log("moo");
+    }
+    expect: {
+        console.log("foo");
+        (async function() {
+            try {
+                console.log("bar");
+            } finally {
+                return "baz";
+            }
+        })().then(console.log);
+        console.log("moo");
+    }
+    expect_stdout: [
+        "foo",
+        "bar",
+        "moo",
+        "baz",
+    ]
+    node_version: ">=8"
+}
+
+issue_4972_3: {
+    options = {
+        awaits: true,
+        side_effects: true,
+    }
+    input: {
+        console.log("foo");
+        try {
+            (async function() {
+                return await "bar";
+            })().then(console.log);
+        } finally {
+            console.log("baz");
+        }
+        console.log("moo");
+    }
+    expect: {
+        console.log("foo");
+        try {
+            (async function() {
+                return "bar";
+            })().then(console.log);
+        } finally {
+            console.log("baz");
+        }
+        console.log("moo");
+    }
+    expect_stdout: [
+        "foo",
+        "baz",
+        "moo",
+        "bar",
+    ]
+    node_version: ">=8"
+}