[clang] [Clang] Avoid quadratic pack-indexing instantiation (store only the selected element) (PR #213790)

[Corentin Jabot via cfe-commits]

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@@ -17,8 +17,7 @@ V...[I] bar() {return {};}
 template <int I, typename... T>
 using First = T...[0];
 
-// CHECK-LABEL: define {{.*}} @_ZN8GH1120033bazILi0EJiEEEvDy_SUBSTPACK_Li0E
-// FIXME: handle indexing of partially substituted packs
+// CHECK-LABEL: define {{.*}} @_ZN8GH1120033bazILi0EJiEEEvi
 template <int I, typename...V>
 void baz(First<I, int, V...>){};
 
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cor3ntin wrote:

I do not think this is actually fixed. If I is dependent, we still have a partially substituted pack

https://github.com/llvm/llvm-project/pull/213790