Subzero: Reduce copying of Liveness bitvectors.

src/IceInstX86BaseImpl.h

Index: src/IceInstX86BaseImpl.h
diff --git a/src/IceInstX86BaseImpl.h b/src/IceInstX86BaseImpl.h
index 64d235e6e57211e900396a7f999a50db10643e1f..a6ce132fc8f2e9ce056e4d621088ee52b4df1551 100644
--- a/src/IceInstX86BaseImpl.h
+++ b/src/IceInstX86BaseImpl.h
@@ -98,8 +98,11 @@ InstImpl<TraitsType>::InstX86Label::InstX86Label(Cfg *Func,
 
 template <typename TraitsType>
 IceString InstImpl<TraitsType>::InstX86Label::getName(const Cfg *Func) const {
+  // TODO(stichnot): Returning an empty string in a non-DUMP build can cause a
+  // huge degradation in ConstantRelocatable hashing.  Investigate and fix, but
+  // for now return something reasonably unique.
   if (!BuildDefs::dump())
-    return IceString();
+    return Func->getFunctionName() + std::to_string(Number);
   return ".L" + Func->getFunctionName() + "$local$__" + std::to_string(Number);
 }