Change clamping 0..255 instruction sequence for pixel array code

src/x64/ic-x64.cc

Index: src/x64/ic-x64.cc
===================================================================
--- src/x64/ic-x64.cc	(revision 3022)
+++ src/x64/ic-x64.cc	(working copy)
@@ -491,11 +491,8 @@
     Label done, is_negative;
     __ testl(rax, Immediate(0xFFFFFF00));
     __ j(zero, &done);
-    __ j(negative, &is_negative);
-    __ movl(rax, Immediate(255));
-    __ jmp(&done);
-    __ bind(&is_negative);
-    __ xorl(rax, rax);  // Clear rax.
+    __ setcc(negative, rax);  // 1 if negative, 0 if positive.
+    __ decb(rax);  // 0 if negative, 255 if positive.
     __ bind(&done);
   }
   __ movq(rcx, FieldOperand(rcx, PixelArray::kExternalPointerOffset));