[clang] [clang] Share normalized constraints between decls with same constraint expressions (PR #226620)

[Younan Zhang via cfe-commits]

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@@ -15186,6 +15186,11 @@ class Sema final : public SemaBase {
   /// here.
   llvm::DenseMap<ConstrainedDeclOrNestedRequirement, NormalizedConstraint *>
       NormalizationCache;
+  /// Caches the normal form of constraint expressions (and their pack
+  /// substitution index). These are shared by e.g. the members of all
+  /// specializations of a class template. Used to fill NormalizationCache.
+  llvm::DenseMap<std::pair<const Expr *, unsigned>, NormalizedConstraint *>
+      NormalizedConstraintExprCache;
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zyn0217 wrote:

(I think it would be much better if we could reuse anything since we have been maintaining a lot of cache KVs in concept checking)

https://github.com/llvm/llvm-project/pull/226620