[clang-tools-extra] [clang-doc] Improve performance by adding a short circuit (PR #96809)

[Paul Kirth via cfe-commits]

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@@ -12,16 +12,25 @@
 #include "clang/AST/Comment.h"
 #include "clang/Index/USRGeneration.h"
 #include "llvm/ADT/StringExtras.h"
-#include "llvm/Support/Error.h"
+#include "llvm/Support/Mutex.h"
+#include <unordered_set>
 
 namespace clang {
 namespace doc {
 
+
+static std::unordered_set<std::string> USRVisited;
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ilovepi wrote:

Typically we prefer other set like containers over `unordered_set` (See https://llvm.org/docs/ProgrammersManual.html#other-set-like-container-options). https://llvm.org/docs/ProgrammersManual.html#set-like-containers-std-set-smallset-setvector-etc also lists some other alternatives, but likely you want `StringSet`.

https://github.com/llvm/llvm-project/pull/96809