[clang] [AST] Avoid repeated hash lookups (NFC) (PR #131064)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Kazu Hirata (kazutakahirata)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/131064.diff


1 Files Affected:

- (modified) clang/lib/AST/ASTImporter.cpp (+4-5) 


``````````diff
diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 82180486f3c7c..0d9b5afc4e4a6 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -10527,12 +10527,11 @@ void ASTImporter::CompleteDecl (Decl *D) {
 }
 
 Decl *ASTImporter::MapImported(Decl *From, Decl *To) {
-  llvm::DenseMap<Decl *, Decl *>::iterator Pos = ImportedDecls.find(From);
-  assert((Pos == ImportedDecls.end() || Pos->second == To) &&
-      "Try to import an already imported Decl");
-  if (Pos != ImportedDecls.end())
+  auto [Pos, Inserted] = ImportedDecls.try_emplace(From, To);
+  assert((Inserted || Pos->second == To) &&
+         "Try to import an already imported Decl");
+  if (!Inserted)
     return Pos->second;
-  ImportedDecls[From] = To;
   // This mapping should be maintained only in this function. Therefore do not
   // check for additional consistency.
   ImportedFromDecls[To] = From;

``````````

</details>


https://github.com/llvm/llvm-project/pull/131064