fix corner cases in awaits (#4976)

fixes #4974
fixes #4975

lib/compress.js

@@ -7573,16 +7573,16 @@ merge(Compressor.prototype, {
                     }
                     return node;
                 });
-                var abort = arrow && exp.value && !is_primitive(compressor, exp.value);
+                var abort = !drop_body && exp.name || arrow && exp.value && !is_primitive(compressor, exp.value);
                 var tw = new TreeWalker(function(node) {
                     if (abort) return true;
+                    if (tw.parent() === exp && node.may_throw(compressor)) return abort = true;
                     if (node instanceof AST_Await) return abort = true;
                     if (node instanceof AST_Return) {
                         if (node.value && !is_primitive(compressor, node.value)) return abort = true;
                         return;
                     }
                     if (node instanceof AST_Scope && node !== exp) return true;
-                    if (tw.parent() === exp && node.may_throw(compressor)) return abort = true;
                 });
                 exp.walk(tw);
                 if (!abort) {

test/compress/awaits.js

@@ -1682,3 +1682,47 @@ issue_4972_3: {
     ]
     node_version: ">=8"
 }
+
+issue_4974: {
+    options = {
+        awaits: true,
+        side_effects: true,
+    }
+    input: {
+        (async function f() {
+            return 42 in f();
+        })();
+        console.log("PASS");
+    }
+    expect: {
+        (async function f() {
+            return 42 in f();
+        })();
+        console.log("PASS");
+    }
+    expect_stdout: true
+    node_version: ">=8"
+}
+
+issue_4975: {
+    options = {
+        awaits: true,
+        side_effects: true,
+    }
+    input: {
+        (async function f(a) {
+            try {
+                if (a) console.log(typeof f());
+            } catch (e) {}
+        })(42);
+    }
+    expect: {
+        (async function f(a) {
+            try {
+                if (a) console.log(typeof f());
+            } catch (e) {}
+        })(42);
+    }
+    expect_stdout: "object"
+    node_version: ">=8"
+}