[CodeGen] Avoid repeated hash lookups (NFC) (#130388)

Author: kazutakahirata

llvm/lib/CodeGen/RegisterBankInfo.cpp

@@ -282,13 +282,13 @@ RegisterBankInfo::getPartialMapping(unsigned StartIdx, unsigned Length,
   ++NumPartialMappingsAccessed;
 
   hash_code Hash = hashPartialMapping(StartIdx, Length, &RegBank);
-  const auto &It = MapOfPartialMappings.find(Hash);
-  if (It != MapOfPartialMappings.end())
+  auto [It, Inserted] = MapOfPartialMappings.try_emplace(Hash);
+  if (!Inserted)
     return *It->second;
 
   ++NumPartialMappingsCreated;
 
-  auto &PartMapping = MapOfPartialMappings[Hash];
+  auto &PartMapping = It->second;
   PartMapping = std::make_unique<PartialMapping>(StartIdx, Length, RegBank);
   return *PartMapping;
 }
@@ -316,13 +316,13 @@ RegisterBankInfo::getValueMapping(const PartialMapping *BreakDown,
   ++NumValueMappingsAccessed;
 
   hash_code Hash = hashValueMapping(BreakDown, NumBreakDowns);
-  const auto &It = MapOfValueMappings.find(Hash);
-  if (It != MapOfValueMappings.end())
+  auto [It, Inserted] = MapOfValueMappings.try_emplace(Hash);
+  if (!Inserted)
     return *It->second;
 
   ++NumValueMappingsCreated;
 
-  auto &ValMapping = MapOfValueMappings[Hash];
+  auto &ValMapping = It->second;
   ValMapping = std::make_unique<ValueMapping>(BreakDown, NumBreakDowns);
   return *ValMapping;
 }
@@ -390,13 +390,13 @@ RegisterBankInfo::getInstructionMappingImpl(
 
   hash_code Hash =
       hashInstructionMapping(ID, Cost, OperandsMapping, NumOperands);
-  const auto &It = MapOfInstructionMappings.find(Hash);
-  if (It != MapOfInstructionMappings.end())
+  auto [It, Inserted] = MapOfInstructionMappings.try_emplace(Hash);
+  if (!Inserted)
     return *It->second;
 
   ++NumInstructionMappingsCreated;
 
-  auto &InstrMapping = MapOfInstructionMappings[Hash];
+  auto &InstrMapping = It->second;
   InstrMapping = std::make_unique<InstructionMapping>(
       ID, Cost, OperandsMapping, NumOperands);
   return *InstrMapping;