Fix issue 16592: Do not attempt to merge operations that do not have uses, otherwise we add force u…

tests/language/arithmetic_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Dart test program to test arithmetic operations.
 // VMOptions=--optimization-counter-threshold=10 --no-use-osr
 
 library arithmetic_test;
 import "package:expect/expect.dart";
 import 'dart:math';
 
@@ skipping 431 matching lines @@
     var f = sin(1.234) * cos(1.234) + cos(1.234);
     
     for (var i = 0; i < 20; i++) {
       Expect.approxEquals(e, sinCosSub(1.234));
       Expect.approxEquals(f, sinCosAddCos(1.234));
     }
     Expect.approxEquals(1.0, sinCosSub(3.14159265));
     Expect.approxEquals(1.0, sinCosSub(3.14159265 / 2.0));
   }
 
+  // Test fix for issue 16592.
+  static void testSinCosNoUse() {
+    for (var i = 0; i < 20; i++) {
+      sin(i);
+      cos(i);
+    }
+  }
+    
   static mySqrt(var x) => sqrt(x);
 
   static testSqrtDeopt() {
     for (var i = 0; i < 10; i++) mySqrt(4.0);
     Expect.equals(2.0, mySqrt(4.0));
     Expect.throws(() => mySqrt("abc"));
   }
 
   static self_equality(x) {
     return x == x;
   }
 
   static testDoubleEquality() {
     Expect.isFalse(self_equality(double.NAN));
     for (int i = 0; i < 20; i++) {
       self_equality(3.0);
     }
     Expect.isFalse(self_equality(double.NAN));
   }
 
   static testMain() {
     for (int i = 0; i < 20; i++) {
       runOne();
       testSmiDivDeopt();
       testSmiDivModDeopt();
       testSqrtDeopt();
       testDoubleEquality();
       testSinCos();
+      testSinCosNoUse();
     }
   }
 }
 
 main() {
   ArithmeticTest.testMain();
 }