[SDPatternMatch] Add Matcher m_Undef (#122521)

Add Matcher `m_Undef`

Fixes: #122439

Author: AmrDeveloper

llvm/include/llvm/CodeGen/SDPatternMatch.h

@@ -138,6 +138,8 @@ struct Opcode_match {
 
 inline Opcode_match m_Opc(unsigned Opcode) { return Opcode_match(Opcode); }
 
+inline Opcode_match m_Undef() { return Opcode_match(ISD::UNDEF); }
+
 template <unsigned NumUses, typename Pattern> struct NUses_match {
   Pattern P;
 

llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp

@@ -474,6 +474,11 @@ TEST_F(SelectionDAGPatternMatchTest, matchConstants) {
   EXPECT_EQ(CC, ISD::SETULT);
   EXPECT_TRUE(sd_match(SetCC, m_Node(ISD::SETCC, m_Value(), m_Value(),
                                      m_SpecificCondCode(ISD::SETULT))));
+
+  SDValue UndefInt32VT = DAG->getUNDEF(Int32VT);
+  SDValue UndefVInt32VT = DAG->getUNDEF(VInt32VT);
+  EXPECT_TRUE(sd_match(UndefInt32VT, m_Undef()));
+  EXPECT_TRUE(sd_match(UndefVInt32VT, m_Undef()));
 }
 
 TEST_F(SelectionDAGPatternMatchTest, patternCombinators) {