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

tests/language/arithmetic_test.dart

Index: tests/language/arithmetic_test.dart
===================================================================
--- tests/language/arithmetic_test.dart	(revision 32376)
+++ tests/language/arithmetic_test.dart	(working copy)
@@ -449,6 +449,14 @@
     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() {
@@ -477,6 +485,7 @@
       testSqrtDeopt();
       testDoubleEquality();
       testSinCos();
+      testSinCosNoUse();
     }
   }
 }