[llvm] [ADT] Move llvm::identity into IndexedMap (NFC) (PR #164568)

[Jakub Kuderski via llvm-commits]

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@@ -22,12 +22,22 @@
 
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/identity.h"
 #include <cassert>
 
 namespace llvm {
 
-template <typename T, typename ToIndexT = identity<unsigned>> class IndexedMap {
+namespace detail {
+template <class Ty> struct IdentityIndex {
+  using is_transparent = void;
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kuhar wrote:

Is this used anywhere? If not, maybe delete?

https://github.com/llvm/llvm-project/pull/164568