Cache common constants before lowering.

src/IceTargetLowering.cpp

 //===- subzero/src/IceTargetLowering.cpp - Basic lowering implementation --===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 679 matching lines @@
     } else {
       NextStackOffset += Increment;
     }
     if (UsesFramePointer)
       Var->setStackOffset(-NextStackOffset);
     else
       Var->setStackOffset(SpillAreaSizeBytes - NextStackOffset);
   }
 }
 
-InstCall *TargetLowering::makeHelperCall(const IceString &Name, Variable *Dest,
+InstCall *TargetLowering::makeHelperCall(RuntimeHelper FuncID, Variable *Dest,
                                          SizeT MaxSrcs) {
   constexpr bool HasTailCall = false;
-  Constant *CallTarget = Ctx->getConstantExternSym(Name);
+  Constant *CallTarget = Ctx->getRuntimeHelperFunc(FuncID);
   InstCall *Call =
       InstCall::create(Func, MaxSrcs, Dest, CallTarget, HasTailCall);
   return Call;
 }
 
 bool TargetLowering::shouldOptimizeMemIntrins() {
   return Ctx->getFlags().getOptLevel() >= Opt_1 ||
          Ctx->getFlags().getForceMemIntrinOpt();
 }
 
@@ skipping 167 matching lines @@
   case TARGET_LOWERING_CLASS_FOR(X):                                           \
     return ::X::createTargetHeaderLowering(Ctx);
 #include "SZTargets.def"
 #undef SUBZERO_TARGET
   }
 }
 
 TargetHeaderLowering::~TargetHeaderLowering() = default;
 
 } // end of namespace Ice