[Turbofan]: Eliminate the check for -0 if it's not possible/observable.

test/mjsunit/compiler/math-mul.js

Index: test/mjsunit/compiler/math-mul.js
diff --git a/test/mjsunit/math-mul.js b/test/mjsunit/compiler/math-mul.js
similarity index 59%
rename from test/mjsunit/math-mul.js
rename to test/mjsunit/compiler/math-mul.js
index 027bb6024a26c5896c51507095a8e9c943fda3ab..7defb2904318e5d5eeb69d582ac3b982ed34d3f1 100644
--- a/test/mjsunit/math-mul.js
+++ b/test/mjsunit/compiler/math-mul.js
@@ -4,6 +4,20 @@
 
 // Flags: --allow-natives-syntax
 
+// For TurboFan, make sure we can eliminate the -0 return value check
+// by recognizing a constant value.
+function gotaconstant(y) { return 15 * y; }
+assertEquals(45, gotaconstant(3));
+gotaconstant(3);
+%OptimizeFunctionOnNextCall(gotaconstant);
+gotaconstant(3);
+
+function gotaconstant_truncated(x, y) { return x * y | 0; }
+assertEquals(45, gotaconstant_truncated(3, 15));
+gotaconstant_truncated(3, 15);
+%OptimizeFunctionOnNextCall(gotaconstant_truncated);
+gotaconstant_truncated(3, 15);
+
 function test(x, y) { return x * y; }
 
 assertEquals(12, test(3, 4));