[llvm] DAG: Handle poison in m_Undef (PR #168288)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/168288

None

>From 460fdeda860a780d12da57003e7663eef3cd12d6 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Sun, 16 Nov 2025 12:34:45 -0800
Subject: [PATCH] DAG: Handle poison in m_Undef

---
 llvm/include/llvm/CodeGen/SDPatternMatch.h | 134 +++++++++++----------
 1 file changed, 68 insertions(+), 66 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/SDPatternMatch.h b/llvm/include/llvm/CodeGen/SDPatternMatch.h
index 511cb56f73dcb..3c8d46aea505c 100644
--- a/llvm/include/llvm/CodeGen/SDPatternMatch.h
+++ b/llvm/include/llvm/CodeGen/SDPatternMatch.h
@@ -155,9 +155,76 @@ struct Opcode_match {
   }
 };
 
+// === Patterns combinators ===
+template <typename... Preds> struct And {
+  template <typename MatchContext> bool match(const MatchContext &, SDValue N) {
+    return true;
+  }
+};
+
+template <typename Pred, typename... Preds>
+struct And<Pred, Preds...> : And<Preds...> {
+  Pred P;
+  And(const Pred &p, const Preds &...preds) : And<Preds...>(preds...), P(p) {}
+
+  template <typename MatchContext>
+  bool match(const MatchContext &Ctx, SDValue N) {
+    return P.match(Ctx, N) && And<Preds...>::match(Ctx, N);
+  }
+};
+
+template <typename... Preds> struct Or {
+  template <typename MatchContext> bool match(const MatchContext &, SDValue N) {
+    return false;
+  }
+};
+
+template <typename Pred, typename... Preds>
+struct Or<Pred, Preds...> : Or<Preds...> {
+  Pred P;
+  Or(const Pred &p, const Preds &...preds) : Or<Preds...>(preds...), P(p) {}
+
+  template <typename MatchContext>
+  bool match(const MatchContext &Ctx, SDValue N) {
+    return P.match(Ctx, N) || Or<Preds...>::match(Ctx, N);
+  }
+};
+
+template <typename Pred> struct Not {
+  Pred P;
+
+  explicit Not(const Pred &P) : P(P) {}
+
+  template <typename MatchContext>
+  bool match(const MatchContext &Ctx, SDValue N) {
+    return !P.match(Ctx, N);
+  }
+};
+// Explicit deduction guide.
+template <typename Pred> Not(const Pred &P) -> Not<Pred>;
+
+/// Match if the inner pattern does NOT match.
+template <typename Pred> inline Not<Pred> m_Unless(const Pred &P) {
+  return Not{P};
+}
+
+template <typename... Preds> And<Preds...> m_AllOf(const Preds &...preds) {
+  return And<Preds...>(preds...);
+}
+
+template <typename... Preds> Or<Preds...> m_AnyOf(const Preds &...preds) {
+  return Or<Preds...>(preds...);
+}
+
+template <typename... Preds> auto m_NoneOf(const Preds &...preds) {
+  return m_Unless(m_AnyOf(preds...));
+}
+
 inline Opcode_match m_Opc(unsigned Opcode) { return Opcode_match(Opcode); }
 
-inline Opcode_match m_Undef() { return Opcode_match(ISD::UNDEF); }
+template <typename... Preds> auto m_Undef() {
+  return m_AnyOf(Opcode_match(ISD::UNDEF), Opcode_match(ISD::POISON));
+}
 
 inline Opcode_match m_Poison() { return Opcode_match(ISD::POISON); }
 
@@ -373,71 +440,6 @@ template <typename Pattern> inline auto m_LegalType(const Pattern &P) {
                         P};
 }
 
-// === Patterns combinators ===
-template <typename... Preds> struct And {
-  template <typename MatchContext> bool match(const MatchContext &, SDValue N) {
-    return true;
-  }
-};
-
-template <typename Pred, typename... Preds>
-struct And<Pred, Preds...> : And<Preds...> {
-  Pred P;
-  And(const Pred &p, const Preds &...preds) : And<Preds...>(preds...), P(p) {}
-
-  template <typename MatchContext>
-  bool match(const MatchContext &Ctx, SDValue N) {
-    return P.match(Ctx, N) && And<Preds...>::match(Ctx, N);
-  }
-};
-
-template <typename... Preds> struct Or {
-  template <typename MatchContext> bool match(const MatchContext &, SDValue N) {
-    return false;
-  }
-};
-
-template <typename Pred, typename... Preds>
-struct Or<Pred, Preds...> : Or<Preds...> {
-  Pred P;
-  Or(const Pred &p, const Preds &...preds) : Or<Preds...>(preds...), P(p) {}
-
-  template <typename MatchContext>
-  bool match(const MatchContext &Ctx, SDValue N) {
-    return P.match(Ctx, N) || Or<Preds...>::match(Ctx, N);
-  }
-};
-
-template <typename Pred> struct Not {
-  Pred P;
-
-  explicit Not(const Pred &P) : P(P) {}
-
-  template <typename MatchContext>
-  bool match(const MatchContext &Ctx, SDValue N) {
-    return !P.match(Ctx, N);
-  }
-};
-// Explicit deduction guide.
-template <typename Pred> Not(const Pred &P) -> Not<Pred>;
-
-/// Match if the inner pattern does NOT match.
-template <typename Pred> inline Not<Pred> m_Unless(const Pred &P) {
-  return Not{P};
-}
-
-template <typename... Preds> And<Preds...> m_AllOf(const Preds &...preds) {
-  return And<Preds...>(preds...);
-}
-
-template <typename... Preds> Or<Preds...> m_AnyOf(const Preds &...preds) {
-  return Or<Preds...>(preds...);
-}
-
-template <typename... Preds> auto m_NoneOf(const Preds &...preds) {
-  return m_Unless(m_AnyOf(preds...));
-}
-
 // === Generic node matching ===
 template <unsigned OpIdx, typename... OpndPreds> struct Operands_match {
   template <typename MatchContext>