[Turbofan] Make the -0 deopt case more efficient in multiplication.

test/mjsunit/compiler/math-mul.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // 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));
@@ skipping 17 matching lines @@
 
 assertEquals(-0, test(-3, 0));
 assertEquals(-0, test(0, -0));
 
 
 const SMI_MAX = (1 << 29) - 1 + (1 << 29);  // Create without overflowing.
 const SMI_MIN = -SMI_MAX - 1;  // Create without overflowing.
 
 // multiply by 3 to avoid compiler optimizations that convert 2*x to x + x.
 assertEquals(SMI_MAX + SMI_MAX + SMI_MAX, test(SMI_MAX, 3));
+
+// Verify that strength reduction will reduce the -0 check quite a bit
+// if we have a negative integer constant.
+function negtest(y) { return -3 * y; }
+assertEquals(-12, negtest(4));
+assertEquals(-12, negtest(4));
+%OptimizeFunctionOnNextCall(negtest);
+negtest(4);
+