[llvm] [SDPatternMatch] Support conditionally binding the value matching a sub-pattern (PR #182091)

[Min-Yih Hsu via llvm-commits]

https://github.com/mshockwave updated https://github.com/llvm/llvm-project/pull/182091

>From 46af16ecfdf0b67d8581dbfd7da69e3c3bffc625 Mon Sep 17 00:00:00 2001
From: Min-Yih Hsu <min.hsu at sifive.com>
Date: Wed, 18 Feb 2026 10:08:15 -0800
Subject: [PATCH 1/2] [SDPatternMatch] Support conditionally binding the value
 matching a sub-pattern

---
 llvm/include/llvm/CodeGen/SDPatternMatch.h    | 20 ++++++++++++++----
 .../CodeGen/SelectionDAGPatternMatchTest.cpp  | 21 ++++++++++++++++++-
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/SDPatternMatch.h b/llvm/include/llvm/CodeGen/SDPatternMatch.h
index a30d2d7bde7c9..716df03f5b83f 100644
--- a/llvm/include/llvm/CodeGen/SDPatternMatch.h
+++ b/llvm/include/llvm/CodeGen/SDPatternMatch.h
@@ -259,18 +259,30 @@ template <unsigned N> inline NUses_match<N, Value_match> m_NUses() {
   return NUses_match<N, Value_match>(m_Value());
 }
 
-struct Value_bind {
+template <typename PredPattern> struct Value_bind {
   SDValue &BindVal;
+  PredPattern Pred;
 
-  explicit Value_bind(SDValue &N) : BindVal(N) {}
+  Value_bind(SDValue &N, const PredPattern &P) : BindVal(N), Pred(P) {}
+
+  template <typename MatchContext>
+  bool match(const MatchContext &Ctx, SDValue N) {
+    if (!Pred.match(Ctx, N))
+      return false;
 
-  template <typename MatchContext> bool match(const MatchContext &, SDValue N) {
     BindVal = N;
     return true;
   }
 };
 
-inline Value_bind m_Value(SDValue &N) { return Value_bind(N); }
+inline auto m_Value(SDValue &N) {
+  return Value_bind<Value_match>(N, m_Value());
+}
+/// Conditionally bind a SDValue based on the predicate.
+template <typename PredPattern>
+inline auto m_Value(SDValue &N, const PredPattern &P) {
+  return Value_bind<PredPattern>(N, P);
+}
 
 template <typename Pattern, typename PredFuncT> struct TLI_pred_match {
   Pattern P;
diff --git a/llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp b/llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp
index ad2cd9decd9f8..8f04aa67d729a 100644
--- a/llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp
+++ b/llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp
@@ -446,6 +446,7 @@ TEST_F(SelectionDAGPatternMatchTest, matchBinaryOp) {
   EXPECT_FALSE(sd_match(SMinDiffSign, DAG.get(),
                         m_UMinLike(m_Specific(Neg0), m_Specific(NonNeg1))));
 
+  SDValue BindVal;
   // By default, it matches any of the results.
   EXPECT_TRUE(
       sd_match(PartsDiff, m_Sub(m_Opc(ISD::SMUL_LOHI), m_Opc(ISD::SMUL_LOHI))));
@@ -455,11 +456,29 @@ TEST_F(SelectionDAGPatternMatchTest, matchBinaryOp) {
   EXPECT_FALSE(sd_match(PartsDiff, m_Sub(m_Opc(ISD::SMUL_LOHI),
                                          m_Result<0>(m_Opc(ISD::SMUL_LOHI)))));
 
-  SDValue BindVal;
+  // Conditionally bind the value from a certain sub-pattern.
+  EXPECT_TRUE(sd_match(PartsDiff, m_Sub(m_Value(BindVal, m_Opc(ISD::SMUL_LOHI)),
+                                        m_Opc(ISD::SMUL_LOHI))));
+  EXPECT_EQ(BindVal, SMulLoHi);
+  BindVal = SDValue();
+  EXPECT_FALSE(sd_match(PartsDiff, m_Sub(m_Value(BindVal, m_Opc(ISD::ADD)),
+                                         m_Opc(ISD::SMUL_LOHI))));
+  EXPECT_NE(BindVal, SMulLoHi);
+
+  BindVal = SDValue();
   EXPECT_TRUE(sd_match(SFAdd, m_ChainedBinOp(ISD::STRICT_FADD, m_Value(BindVal),
                                              m_Deferred(BindVal))));
   EXPECT_FALSE(sd_match(SFAdd, m_ChainedBinOp(ISD::STRICT_FADD, m_OtherVT(),
                                               m_SpecificVT(Float32VT))));
+  BindVal = SDValue();
+  EXPECT_TRUE(
+      sd_match(SFAdd, m_ChainedBinOp(ISD::STRICT_FADD,
+                                     m_Value(BindVal, m_SpecificVT(Float32VT)),
+                                     m_Deferred(BindVal))));
+  BindVal = SDValue();
+  EXPECT_FALSE(sd_match(SFAdd, m_ChainedBinOp(ISD::STRICT_FADD,
+                                              m_Value(BindVal, m_OtherVT()),
+                                              m_Deferred(BindVal))));
 
   EXPECT_TRUE(sd_match(SubVec, m_ExtractSubvector(m_Value(), m_Value())));
   EXPECT_TRUE(

>From 1106883654615a75508b4a148ebf09ca01e43d72 Mon Sep 17 00:00:00 2001
From: Min-Yih Hsu <min at myhsu.dev>
Date: Wed, 18 Feb 2026 12:48:36 -0800
Subject: [PATCH 2/2] Update llvm/include/llvm/CodeGen/SDPatternMatch.h

Co-authored-by: Stefan Weigl-Bosker <stefan at s00.xyz>
---
 llvm/include/llvm/CodeGen/SDPatternMatch.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/include/llvm/CodeGen/SDPatternMatch.h b/llvm/include/llvm/CodeGen/SDPatternMatch.h
index 716df03f5b83f..7a158dc87f9ae 100644
--- a/llvm/include/llvm/CodeGen/SDPatternMatch.h
+++ b/llvm/include/llvm/CodeGen/SDPatternMatch.h
@@ -278,7 +278,7 @@ template <typename PredPattern> struct Value_bind {
 inline auto m_Value(SDValue &N) {
   return Value_bind<Value_match>(N, m_Value());
 }
-/// Conditionally bind a SDValue based on the predicate.
+/// Conditionally bind an SDValue based on the predicate.
 template <typename PredPattern>
 inline auto m_Value(SDValue &N, const PredPattern &P) {
   return Value_bind<PredPattern>(N, P);