[SelectionDAG] Add STRICT_BF16_TO_FP and STRICT_FP_TO_BF16

This patch adds the support for `STRICT_BF16_TO_FP` and `STRICT_FP_TO_BF16`.

Fix #78540.

Author: shiltian

llvm/include/llvm/CodeGen/ISDOpcodes.h

@@ -921,6 +921,8 @@ enum NodeType {
   /// has native conversions.
   BF16_TO_FP,
   FP_TO_BF16,
+  STRICT_BF16_TO_FP,
+  STRICT_FP_TO_BF16,
 
   /// Perform various unary floating-point operations inspired by libm. For
   /// FPOWI, the result is undefined if the integer operand doesn't fit into

llvm/include/llvm/CodeGen/SelectionDAGNodes.h

@@ -698,6 +698,8 @@ END_TWO_BYTE_PACK()
         return false;
       case ISD::STRICT_FP16_TO_FP:
       case ISD::STRICT_FP_TO_FP16:
+      case ISD::STRICT_BF16_TO_FP:
+      case ISD::STRICT_FP_TO_BF16:
 #define DAG_INSTRUCTION(NAME, NARG, ROUND_MODE, INTRINSIC, DAGN)               \
       case ISD::STRICT_##DAGN:
 #include "llvm/IR/ConstrainedOps.def"

llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -1034,6 +1034,7 @@ void SelectionDAGLegalize::LegalizeOp(SDNode *Node) {
                                     Node->getOperand(0).getValueType());
     break;
   case ISD::STRICT_FP_TO_FP16:
+  case ISD::STRICT_FP_TO_BF16:
   case ISD::STRICT_SINT_TO_FP:
   case ISD::STRICT_UINT_TO_FP:
   case ISD::STRICT_LRINT:
@@ -3263,12 +3264,15 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
       Results.push_back(Tmp1);
     break;
   }
+  case ISD::STRICT_BF16_TO_FP:
+    // We don't support this expansion for now.
+    break;
   case ISD::BF16_TO_FP: {
     // Always expand bf16 to f32 casts, they lower to ext + shift.
     //
     // Note that the operand of this code can be bf16 or an integer type in case
     // bf16 is not supported on the target and was softened.
-    SDValue Op = Node->getOperand(0);
+    SDValue Op = Node->getOperand(Node->getOpcode() == ISD::BF16_TO_FP ? 0 : 1);
     if (Op.getValueType() == MVT::bf16) {
       Op = DAG.getNode(ISD::ANY_EXTEND, dl, MVT::i32,
                        DAG.getNode(ISD::BITCAST, dl, MVT::i16, Op));
@@ -3286,10 +3290,15 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     Results.push_back(Op);
     break;
   }
+  case ISD::STRICT_FP_TO_BF16:
+    // We don't support this expansion for now.
+    break;
   case ISD::FP_TO_BF16: {
-    SDValue Op = Node->getOperand(0);
+    bool IsStrictFP = Node->getOpcode() == ISD::STRICT_FP_TO_BF16;
+    SDValue Op = Node->getOperand(IsStrictFP ? 1 : 0);
     if (Op.getValueType() != MVT::f32)
-      Op = DAG.getNode(ISD::FP_ROUND, dl, MVT::f32, Op,
+      Op = DAG.getNode(IsStrictFP ? ISD::STRICT_FP_ROUND : ISD::FP_ROUND, dl,
+                       MVT::f32, Op,
                        DAG.getIntPtrConstant(0, dl, /*isTarget=*/true));
     Op = DAG.getNode(
         ISD::SRL, dl, MVT::i32, DAG.getNode(ISD::BITCAST, dl, MVT::i32, Op),
@@ -4788,12 +4797,17 @@ void SelectionDAGLegalize::ConvertNodeToLibcall(SDNode *Node) {
     break;
   }
   case ISD::STRICT_FP_EXTEND:
-  case ISD::STRICT_FP_TO_FP16: {
-    RTLIB::Libcall LC =
-        Node->getOpcode() == ISD::STRICT_FP_TO_FP16
-            ? RTLIB::getFPROUND(Node->getOperand(1).getValueType(), MVT::f16)
-            : RTLIB::getFPEXT(Node->getOperand(1).getValueType(),
-                              Node->getValueType(0));
+  case ISD::STRICT_FP_TO_FP16:
+  case ISD::STRICT_FP_TO_BF16: {
+    RTLIB::Libcall LC = RTLIB::UNKNOWN_LIBCALL;
+    if (Node->getOpcode() == ISD::STRICT_FP_TO_FP16)
+      LC = RTLIB::getFPROUND(Node->getOperand(1).getValueType(), MVT::f16);
+    else if (Node->getOpcode() == ISD::STRICT_FP_TO_BF16)
+      LC = RTLIB::getFPROUND(Node->getOperand(1).getValueType(), MVT::bf16);
+    else
+      LC = RTLIB::getFPEXT(Node->getOperand(1).getValueType(),
+                           Node->getValueType(0));
+
     assert(LC != RTLIB::UNKNOWN_LIBCALL && "Unable to legalize as libcall");
 
     TargetLowering::MakeLibCallOptions CallOptions;

llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp

@@ -918,6 +918,7 @@ bool DAGTypeLegalizer::SoftenFloatOperand(SDNode *N, unsigned OpNo) {
   case ISD::STRICT_FP_TO_FP16:
   case ISD::FP_TO_FP16:  // Same as FP_ROUND for softening purposes
   case ISD::FP_TO_BF16:
+  case ISD::STRICT_FP_TO_BF16:
   case ISD::STRICT_FP_ROUND:
   case ISD::FP_ROUND:    Res = SoftenFloatOp_FP_ROUND(N); break;
   case ISD::STRICT_FP_TO_SINT:
@@ -2193,13 +2194,11 @@ static ISD::NodeType GetPromotionOpcodeStrict(EVT OpVT, EVT RetVT) {
   if (RetVT == MVT::f16)
     return ISD::STRICT_FP_TO_FP16;
 
-  if (OpVT == MVT::bf16) {
-    // TODO: return ISD::STRICT_BF16_TO_FP;
-  }
+  if (OpVT == MVT::bf16)
+    return ISD::STRICT_BF16_TO_FP;
 
-  if (RetVT == MVT::bf16) {
-    // TODO: return ISD::STRICT_FP_TO_BF16;
-  }
+  if (RetVT == MVT::bf16)
+    return ISD::STRICT_FP_TO_BF16;
 
   report_fatal_error("Attempt at an invalid promotion-related conversion");
 }
@@ -2999,10 +2998,16 @@ SDValue DAGTypeLegalizer::SoftPromoteHalfRes_FP_ROUND(SDNode *N) {
   EVT SVT = N->getOperand(0).getValueType();
 
   if (N->isStrictFPOpcode()) {
-    assert(RVT == MVT::f16);
-    SDValue Res =
-        DAG.getNode(ISD::STRICT_FP_TO_FP16, SDLoc(N), {MVT::i16, MVT::Other},
-                    {N->getOperand(0), N->getOperand(1)});
+    // FIXME: assume we only have two f16 variants for now.
+    unsigned Opcode;
+    if (RVT == MVT::f16)
+      Opcode = ISD::STRICT_FP_TO_FP16;
+    else if (RVT == MVT::bf16)
+      Opcode = ISD::STRICT_FP_TO_BF16;
+    else
+      llvm_unreachable("unknown half type");
+    SDValue Res = DAG.getNode(Opcode, SDLoc(N), {MVT::i16, MVT::Other},
+                              {N->getOperand(0), N->getOperand(1)});
     ReplaceValueWith(SDValue(N, 1), Res.getValue(1));
     return Res;
   }

llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp

@@ -165,6 +165,7 @@ void DAGTypeLegalizer::PromoteIntegerResult(SDNode *N, unsigned ResNo) {
   case ISD::FP_TO_FP16:
     Res = PromoteIntRes_FP_TO_FP16_BF16(N);
     break;
+  case ISD::STRICT_FP_TO_BF16:
   case ISD::STRICT_FP_TO_FP16:
     Res = PromoteIntRes_STRICT_FP_TO_FP16_BF16(N);
     break;

llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp

@@ -379,7 +379,9 @@ std::string SDNode::getOperationName(const SelectionDAG *G) const {
   case ISD::FP_TO_FP16:                 return "fp_to_fp16";
   case ISD::STRICT_FP_TO_FP16:          return "strict_fp_to_fp16";
   case ISD::BF16_TO_FP:                 return "bf16_to_fp";
+  case ISD::STRICT_BF16_TO_FP:          return "strict_bf16_to_fp";
   case ISD::FP_TO_BF16:                 return "fp_to_bf16";
+  case ISD::STRICT_FP_TO_BF16:          return "strict_fp_to_bf16";
   case ISD::LROUND:                     return "lround";
   case ISD::STRICT_LROUND:              return "strict_lround";
   case ISD::LLROUND:                    return "llround";