[clang] [Index] Avoid repeated hash lookups (NFC) (PR #127300)

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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/127300.diff


1 Files Affected:

- (modified) clang/lib/Index/USRGeneration.cpp (+4-8) 


``````````diff
diff --git a/clang/lib/Index/USRGeneration.cpp b/clang/lib/Index/USRGeneration.cpp
index 1e54b413dc59c..0a5a1bcc74865 100644
--- a/clang/lib/Index/USRGeneration.cpp
+++ b/clang/lib/Index/USRGeneration.cpp
@@ -859,16 +859,12 @@ void USRGenerator::VisitType(QualType T) {
     }
 
     // If we have already seen this (non-built-in) type, use a substitution
-    // encoding.
-    llvm::DenseMap<const Type *, unsigned>::iterator Substitution
-      = TypeSubstitutions.find(T.getTypePtr());
-    if (Substitution != TypeSubstitutions.end()) {
+    // encoding.  Otherwise, record this as a substitution.
+    auto [Substitution, Inserted] =
+        TypeSubstitutions.try_emplace(T.getTypePtr(), TypeSubstitutions.size());
+    if (!Inserted) {
       Out << 'S' << Substitution->second << '_';
       return;
-    } else {
-      // Record this as a substitution.
-      unsigned Number = TypeSubstitutions.size();
-      TypeSubstitutions[T.getTypePtr()] = Number;
     }
 
     if (const PointerType *PT = T->getAs<PointerType>()) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/127300