Subzero: Reduce copying of Liveness bitvectors.

src/IceInstX86BaseImpl.h

 //===- subzero/src/IceInstX86BaseImpl.h - Generic X86 instructions -*- C++ -*=//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 80 matching lines @@
 }
 
 template <typename TraitsType>
 InstImpl<TraitsType>::InstX86Label::InstX86Label(Cfg *Func,
                                                  TargetLowering *Target)
     : InstX86Base(Func, InstX86Base::Label, 0, nullptr),
       Number(Target->makeNextLabelNumber()) {}
 
 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);
 }
 
 template <typename TraitsType>
 InstImpl<TraitsType>::InstX86Br::InstX86Br(
     Cfg *Func, const CfgNode *TargetTrue, const CfgNode *TargetFalse,
     const InstImpl<TraitsType>::InstX86Label *Label, BrCond Condition,
     Mode Kind)
     : InstX86Base(Func, InstX86Base::Br, 0, nullptr), Condition(Condition),
       TargetTrue(TargetTrue), TargetFalse(TargetFalse), Label(Label),
@@ skipping 2777 matching lines @@
     return;
   Ostream &Str = Func->getContext()->getStrDump();
   Str << "IACA_END";
 }
 
 } // end of namespace X86NAMESPACE
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEINSTX86BASEIMPL_H