[clang] [AST] Avoid repeated hash lookups (NFC) (PR #123285)

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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/123285.diff


1 Files Affected:

- (modified) clang/lib/AST/VTableBuilder.cpp (+2-2) 


``````````diff
diff --git a/clang/lib/AST/VTableBuilder.cpp b/clang/lib/AST/VTableBuilder.cpp
index e941c3bedb0a7e..fa3055dd1206f4 100644
--- a/clang/lib/AST/VTableBuilder.cpp
+++ b/clang/lib/AST/VTableBuilder.cpp
@@ -3831,8 +3831,8 @@ const VirtualBaseInfo &MicrosoftVTableContext::computeVBTableRelatedInformation(
   unsigned VBTableIndex = 1 + VBI->VBTableIndices.size();
   for (const auto &VB : RD->vbases()) {
     const CXXRecordDecl *CurVBase = VB.getType()->getAsCXXRecordDecl();
-    if (!VBI->VBTableIndices.count(CurVBase))
-      VBI->VBTableIndices[CurVBase] = VBTableIndex++;
+    if (VBI->VBTableIndices.try_emplace(CurVBase, VBTableIndex).second)
+      ++VBTableIndex;
   }
 
   return *VBI;

``````````

</details>


https://github.com/llvm/llvm-project/pull/123285