[clang] [clang-tools-extra] [Clang] Add builtins that deduplicate and sort types (PR #106730)

[Erich Keane via cfe-commits]

================
@@ -3331,6 +3343,65 @@ checkBuiltinTemplateIdType(Sema &SemaRef, BuiltinTemplateDecl *BTD,
     QualType HasNoTypeMember = Converted[2].getAsType();
     return HasNoTypeMember;
   }
+  case BTK__builtin_dedup_pack: {
+    assert(Converted.size() == 1 && "__builtin_dedup_pack should be given "
+                                    "a parameter pack");
+    TemplateArgument Ts = Converted[0];
+    // Delay the computation until we can compute the final result. We choose
+    // not to remove the duplicates upfront before substitution to keep the code
+    // simple.
+    if (Ts.isDependent())
+      return QualType();
+    assert(Ts.getKind() == clang::TemplateArgument::Pack);
+    llvm::SmallVector<TemplateArgument> OutArgs;
+    llvm::SmallDenseSet<QualType> Seen;
+    // Synthesize a new template argument list, removing duplicates.
+    for (auto T : Ts.getPackAsArray()) {
+      assert(T.getKind() == clang::TemplateArgument::Type);
+      if (!Seen.insert(T.getAsType().getCanonicalType()).second)
+        continue;
+      OutArgs.push_back(T);
+    }
+    return Context.getSubstBuiltinTemplatePack(
+        TemplateArgument::CreatePackCopy(Context, OutArgs));
+  }
+  case BTK__builtin_sort_pack: {
+    assert(Converted.size() == 1);
+    assert(Converted[0].getKind() == TemplateArgument::Pack);
+    // Delay if we have any dependencies, the mangled names may change after
+    // subsistution or may not be well-defined for dependent types.
----------------
erichkeane wrote:

```suggestion
    // substitution or may not be well-defined for dependent types.
```

https://github.com/llvm/llvm-project/pull/106730