[DAG] Add SDPatternMatch::m_BitCast matcher (#123327)

Simplifies a future patch

Author: RKSimon

llvm/include/llvm/CodeGen/SDPatternMatch.h

@@ -896,6 +896,10 @@ inline UnaryOpc_match<Opnd, true> m_ChainedUnaryOp(unsigned Opc,
   return UnaryOpc_match<Opnd, true>(Opc, Op);
 }
 
+template <typename Opnd> inline UnaryOpc_match<Opnd> m_BitCast(const Opnd &Op) {
+  return UnaryOpc_match<Opnd>(ISD::BITCAST, Op);
+}
+
 template <typename Opnd>
 inline UnaryOpc_match<Opnd> m_BSwap(const Opnd &Op) {
   return UnaryOpc_match<Opnd>(ISD::BSWAP, Op);

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -15770,7 +15770,7 @@ SDValue DAGCombiner::foldBitcastedFPLogic(SDNode *N, SelectionDAG &DAG,
   // FIXME: I don't think looking for bitcast intrinsically makes sense, but
   // removing this would require more changes.
   auto IsBitCastOrFree = [&TLI, FPOpcode](SDValue Op, EVT VT) {
-    if (Op.getOpcode() == ISD::BITCAST && Op.getOperand(0).getValueType() == VT)
+    if (sd_match(Op, m_BitCast(m_SpecificVT(VT))))
       return true;
 
     return FPOpcode == ISD::FABS ? TLI.isFAbsFree(VT) : TLI.isFNegFree(VT);

llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp

@@ -392,6 +392,7 @@ TEST_F(SelectionDAGPatternMatchTest, matchUnaryOp) {
   SDValue FPToSI = DAG->getNode(ISD::FP_TO_SINT, DL, FloatVT, Op2);
   SDValue FPToUI = DAG->getNode(ISD::FP_TO_UINT, DL, FloatVT, Op2);
 
+  SDValue Bcast = DAG->getNode(ISD::BITCAST, DL, FloatVT, Op0);
   SDValue Brev = DAG->getNode(ISD::BITREVERSE, DL, Int32VT, Op0);
   SDValue Bswap = DAG->getNode(ISD::BSWAP, DL, Int32VT, Op0);
 
@@ -423,8 +424,12 @@ TEST_F(SelectionDAGPatternMatchTest, matchUnaryOp) {
   EXPECT_FALSE(sd_match(FPToUI, m_FPToSI(m_Value())));
   EXPECT_FALSE(sd_match(FPToSI, m_FPToUI(m_Value())));
 
+  EXPECT_TRUE(sd_match(Bcast, m_BitCast(m_Value())));
+  EXPECT_TRUE(sd_match(Bcast, m_BitCast(m_SpecificVT(MVT::i32))));
   EXPECT_TRUE(sd_match(Brev, m_BitReverse(m_Value())));
   EXPECT_TRUE(sd_match(Bswap, m_BSwap(m_Value())));
+  EXPECT_FALSE(sd_match(Bcast, m_BitReverse(m_Value())));
+  EXPECT_FALSE(sd_match(Bcast, m_BitCast(m_SpecificVT(MVT::f32))));
   EXPECT_FALSE(sd_match(Brev, m_BSwap(m_Value())));
   EXPECT_FALSE(sd_match(Bswap, m_BitReverse(m_Value())));