[clang] [Serialization] Avoid repeated hash lookups (NFC) (PR #126429)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-modules

Author: Kazu Hirata (kazutakahirata)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/126429.diff


1 Files Affected:

- (modified) clang/lib/Serialization/ASTReader.cpp (+6-4) 


``````````diff
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index b74bd586e74d7a9..3c64b67503195c3 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -645,10 +645,11 @@ collectMacroDefinitions(const PreprocessorOptions &PPOpts,
 
     // For an #undef'd macro, we only care about the name.
     if (IsUndef) {
-      if (MacroNames && !Macros.count(MacroName))
+      auto [It, Inserted] = Macros.try_emplace(MacroName);
+      if (MacroNames && Inserted)
         MacroNames->push_back(MacroName);
 
-      Macros[MacroName] = std::make_pair("", true);
+      It->second = std::make_pair("", true);
       continue;
     }
 
@@ -661,9 +662,10 @@ collectMacroDefinitions(const PreprocessorOptions &PPOpts,
       MacroBody = MacroBody.substr(0, End);
     }
 
-    if (MacroNames && !Macros.count(MacroName))
+    auto [It, Inserted] = Macros.try_emplace(MacroName);
+    if (MacroNames && Inserted)
       MacroNames->push_back(MacroName);
-    Macros[MacroName] = std::make_pair(MacroBody, false);
+    It->second = std::make_pair(MacroBody, false);
   }
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/126429