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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-regalloc

Author: Kazu Hirata (kazutakahirata)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/130388.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/RegisterBankInfo.cpp (+9-9) 


``````````diff
diff --git a/llvm/lib/CodeGen/RegisterBankInfo.cpp b/llvm/lib/CodeGen/RegisterBankInfo.cpp
index a0061ece8add6..eaef13969a7a1 100644
--- a/llvm/lib/CodeGen/RegisterBankInfo.cpp
+++ b/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;

``````````

</details>


https://github.com/llvm/llvm-project/pull/130388