[DebugInfo] Avoid repeated hash lookups (NFC) (#127446)

Author: kazutakahirata

llvm/lib/DebugInfo/LogicalView/Readers/LVBinaryReader.cpp

@@ -65,20 +65,24 @@ LVSectionIndex LVSymbolTable::update(LVScope *Function) {
     Name = Function->getName();
   std::string SymbolName(Name);
 
-  if (SymbolName.empty() || (SymbolNames.find(SymbolName) == SymbolNames.end()))
+  if (SymbolName.empty())
+    return SectionIndex;
+
+  auto It = SymbolNames.find(SymbolName);
+  if (It == SymbolNames.end())
     return SectionIndex;
 
   // Update a recorded entry with its logical scope, only if the scope has
   // ranges. That is the case when in DWARF there are 2 DIEs connected via
   // the DW_AT_specification.
   if (Function->getHasRanges()) {
-    SymbolNames[SymbolName].Scope = Function;
-    SectionIndex = SymbolNames[SymbolName].SectionIndex;
+    It->second.Scope = Function;
+    SectionIndex = It->second.SectionIndex;
   } else {
     SectionIndex = UndefinedSectionIndex;
   }
 
-  if (SymbolNames[SymbolName].IsComdat)
+  if (It->second.IsComdat)
     Function->setIsComdat();
 
   LLVM_DEBUG({ print(dbgs()); });