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

[Kazu Hirata via cfe-commits]

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

None

>From 99becba2d947d6f18ef6f2cfbf583b28bcd21713 Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Fri, 14 Feb 2025 02:44:22 -0800
Subject: [PATCH] [Index] Avoid repeated hash lookups (NFC)

---
 clang/lib/Index/USRGeneration.cpp | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

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>()) {