[llvm] [VPlan] Add m_Deferred. NFC (PR #133736)

[Ramkumar Ramachandra via llvm-commits]

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@@ -66,6 +66,27 @@ struct specificval_ty {
 
 inline specificval_ty m_Specific(const VPValue *VPV) { return VPV; }
 
+/// Stores a reference to the VPValue *, not the VPValue * itself,
+/// thus can be used in commutative matchers.
+template <typename Class> struct deferredval_ty {
+  Class *const &Val;
+
+  deferredval_ty(Class *const &V) : Val(V) {}
+
+  template <typename ITy> bool match(ITy *const V) { return V == Val; }
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artagnon wrote:

Mark match function const?

https://github.com/llvm/llvm-project/pull/133736