Tweak HConstant::EmitAtUses() to eliminate useless constant generation

BUG=2881
R=danno@chromium.org

Review URL: https://codereview.chromium.org/23811011

Patch from Weiliang Lin <weiliang.lin2@gmail.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16731 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.cc

@@ -2526,9 +2526,11 @@ void HConstant::Initialize(Representation r) {
 
 bool HConstant::EmitAtUses() {
   ASSERT(IsLinked());
-  if (block()->graph()->has_osr()) {
-    return block()->graph()->IsStandardConstant(this);
+  if (block()->graph()->has_osr() &&
+      block()->graph()->IsStandardConstant(this)) {
+    return true;
   }
+  if (UseCount() == 0) return true;
   if (IsCell()) return false;
   if (representation().IsDouble()) return false;
   return true;