[clang] [clang] Optimize castToDeclContext for 2% improvement in build times (PR #76825)

[via cfe-commits]

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@@ -95,8 +103,31 @@ std::pair<ASTNode, ASTNode> ClangASTNodesEmitter::EmitNode(raw_ostream &OS,
   if (!Base.isAbstract())
     First = Last = Base;
 
+  class Comp {
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cor3ntin wrote:

Yes, this might as well be a lambda.
I also think some comment to explain what PriorizeIfSubclassOf is and why it is used would be useful;
We might very well forget why we put classes that are declcontext first in the future.

https://github.com/llvm/llvm-project/pull/76825