[AsmParser] Avoid repeated map lookups (NFC) (#128629)

llvm/lib/AsmParser/LLParser.cpp

diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index 2e8487d..690e92a 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -1036,9 +1036,10 @@
 
     assert(NumberedMetadata[MetadataID] == Init && "Tracking VH didn't work");
   } else {
-    if (NumberedMetadata.count(MetadataID))
+    auto [It, Inserted] = NumberedMetadata.try_emplace(MetadataID);
+    if (!Inserted)
       return tokError("Metadata id is already used");
-    NumberedMetadata[MetadataID].reset(Init);
+    It->second.reset(Init);
   }
 
   return false;