[CodeGen] Simplify code with *Map::operator[] (NFC) (#112075)

Author: kazutakahirata

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -630,8 +630,7 @@ static void finishCallSiteParams(ValT Val, const DIExpression *Expr,
 static void addToFwdRegWorklist(FwdRegWorklist &Worklist, unsigned Reg,
                                 const DIExpression *Expr,
                                 ArrayRef<FwdRegParamInfo> ParamsToAdd) {
-  auto I = Worklist.insert({Reg, {}});
-  auto &ParamsForFwdReg = I.first->second;
+  auto &ParamsForFwdReg = Worklist[Reg];
   for (auto Param : ParamsToAdd) {
     assert(none_of(ParamsForFwdReg,
                    [Param](const FwdRegParamInfo &D) {

llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp

@@ -120,8 +120,7 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
     for (WinEHTryBlockMapEntry &TBME : EHInfo.TryBlockMap) {
       for (WinEHHandlerType &H : TBME.HandlerArray) {
         if (const AllocaInst *AI = H.CatchObj.Alloca)
-          CatchObjects.insert({AI, {}}).first->second.push_back(
-              &H.CatchObj.FrameIndex);
+          CatchObjects[AI].push_back(&H.CatchObj.FrameIndex);
         else
           H.CatchObj.FrameIndex = INT_MAX;
       }