fix corner case in yields (#5750)

fixes #5749

lib/compress.js

@@ -8901,12 +8901,11 @@ Compressor.prototype.compress = function(node) {
                 exprs = trim(exprs, compressor, first_in_statement, array_spread);
                 return exprs && make_sequence(self, exprs.map(convert_spread));
             }
-            if (compressor.option("yields") && is_generator(exp)) {
+            if (compressor.option("yields") && is_generator(exp) && fn_name_unused(exp, compressor)) {
                 var call = self.clone();
                 call.expression = make_node(AST_Function, exp);
                 call.expression.body = [];
-                var opt = call.transform(compressor);
-                if (opt !== call) return opt.drop_side_effect_free(compressor, first_in_statement);
+                return call;
             }
             var dropped = drop_returns(compressor, exp);
             if (dropped) {

test/compress/yields.js

@@ -896,7 +896,7 @@ dont_inline_nested: {
     node_version: ">=4"
 }
 
-drop_body: {
+drop_body_1: {
     options = {
         side_effects: true,
         yields: true,
@@ -906,6 +906,27 @@ drop_body: {
             console.log("bar");
         })([ console.log("baz") ]);
     }
+    expect: {
+        void ([ [ , [][0] = console.log("foo") ] ] = [ [ console.log("baz") ] ]);
+    }
+    expect_stdout: [
+        "baz",
+        "foo",
+    ]
+    node_version: ">=6"
+}
+
+drop_body_2: {
+    options = {
+        passes: 2,
+        side_effects: true,
+        yields: true,
+    }
+    input: {
+        (function*([ , a = console.log("foo") ]) {
+            console.log("bar");
+        })([ console.log("baz") ]);
+    }
     expect: {
         [ [ , [][0] = console.log("foo") ] ] = [ [ console.log("baz") ] ];
     }
@@ -2019,7 +2040,7 @@ issue_5684: {
     node_version: ">=10"
 }
 
-issue_5707: {
+issue_5707_1: {
     options = {
         hoist_props: true,
         reduce_vars: true,
@@ -2033,6 +2054,28 @@ issue_5707: {
         function* f(c = (b = 42, console.log("PASS"))) {}
         b = f();
     }
+    expect: {
+        (function(c = console.log("PASS")) {})();
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5707_2: {
+    options = {
+        hoist_props: true,
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+        yields: true,
+    }
+    input: {
+        var a, b;
+        function* f(c = (b = 42, console.log("PASS"))) {}
+        b = f();
+    }
     expect: {
         console.log("PASS");
     }
@@ -2076,3 +2119,53 @@ issue_5710: {
     expect_stdout: "PASS"
     node_version: ">=10"
 }
+
+issue_5749_1: {
+    options = {
+        collapse_vars: true,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+        yields: true,
+    }
+    input: {
+        var a;
+        function* f() {}
+        a = f(new function() {
+            var b = a |= 0, c = a += console.log("PASS");
+        }());
+    }
+    expect: {
+        (function() {})(function() {
+            console.log("PASS");
+        }());
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}
+
+issue_5749_2: {
+    options = {
+        collapse_vars: true,
+        inline: true,
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+        yields: true,
+    }
+    input: {
+        var a;
+        function* f() {}
+        a = f(new function() {
+            var b = a |= 0, c = a += console.log("PASS");
+        }());
+    }
+    expect: {
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}