AMDGPU: Widen f16 minimum/maximum to v2f16 on gfx950 (llvm#128121)

Unfortunately we only have the vector versions of v2f16 minimum3
and maximum. Widen to v2f16 so we can lower as minimum333(x, y, y).

Author: arsenm

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -869,8 +869,13 @@ SITargetLowering::SITargetLowering(const TargetMachine &TM,
     if (Subtarget->hasMinimum3Maximum3F32())
       setOperationAction({ISD::FMAXIMUM, ISD::FMINIMUM}, MVT::f32, Legal);
 
-    if (Subtarget->hasMinimum3Maximum3PKF16())
+    if (Subtarget->hasMinimum3Maximum3PKF16()) {
       setOperationAction({ISD::FMAXIMUM, ISD::FMINIMUM}, MVT::v2f16, Legal);
+
+      // If only the vector form is available, we need to widen to a vector.
+      if (!Subtarget->hasMinimum3Maximum3F16())
+        setOperationAction({ISD::FMAXIMUM, ISD::FMINIMUM}, MVT::f16, Custom);
+    }
   }
 
   setOperationAction(ISD::INTRINSIC_WO_CHAIN,
@@ -5964,6 +5969,9 @@ SDValue SITargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::FMINNUM:
   case ISD::FMAXNUM:
     return lowerFMINNUM_FMAXNUM(Op, DAG);
+  case ISD::FMINIMUM:
+  case ISD::FMAXIMUM:
+    return lowerFMINIMUM_FMAXIMUM(Op, DAG);
   case ISD::FLDEXP:
   case ISD::STRICT_FLDEXP:
     return lowerFLDEXP(Op, DAG);
@@ -5985,8 +5993,6 @@ SDValue SITargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::FMUL:
   case ISD::FMINNUM_IEEE:
   case ISD::FMAXNUM_IEEE:
-  case ISD::FMINIMUM:
-  case ISD::FMAXIMUM:
   case ISD::FMINIMUMNUM:
   case ISD::FMAXIMUMNUM:
   case ISD::UADDSAT:
@@ -6841,6 +6847,34 @@ SDValue SITargetLowering::lowerFMINNUM_FMAXNUM(SDValue Op,
   return Op;
 }
 
+SDValue SITargetLowering::lowerFMINIMUM_FMAXIMUM(SDValue Op,
+                                                 SelectionDAG &DAG) const {
+  EVT VT = Op.getValueType();
+  if (VT.isVector())
+    return splitBinaryVectorOp(Op, DAG);
+
+  assert(!Subtarget->hasIEEEMinMax() && !Subtarget->hasMinimum3Maximum3F16() &&
+         Subtarget->hasMinimum3Maximum3PKF16() && VT == MVT::f16 &&
+         "should not need to widen f16 minimum/maximum to v2f16");
+
+  // Widen f16 operation to v2f16
+
+  // fminimum f16:x, f16:y ->
+  //   extract_vector_elt (fminimum (v2f16 (scalar_to_vector x))
+  //                                (v2f16 (scalar_to_vector y))), 0
+  SDLoc SL(Op);
+  SDValue WideSrc0 =
+      DAG.getNode(ISD::SCALAR_TO_VECTOR, SL, MVT::v2f16, Op.getOperand(0));
+  SDValue WideSrc1 =
+      DAG.getNode(ISD::SCALAR_TO_VECTOR, SL, MVT::v2f16, Op.getOperand(1));
+
+  SDValue Widened =
+      DAG.getNode(Op.getOpcode(), SL, MVT::v2f16, WideSrc0, WideSrc1);
+
+  return DAG.getNode(ISD::EXTRACT_VECTOR_ELT, SL, MVT::f16, Widened,
+                     DAG.getConstant(0, SL, MVT::i32));
+}
+
 SDValue SITargetLowering::lowerFLDEXP(SDValue Op, SelectionDAG &DAG) const {
   bool IsStrict = Op.getOpcode() == ISD::STRICT_FLDEXP;
   EVT VT = Op.getValueType();

llvm/lib/Target/AMDGPU/SIISelLowering.h

@@ -146,6 +146,7 @@ class SITargetLowering final : public AMDGPUTargetLowering {
   /// Custom lowering for ISD::FP_ROUND for MVT::f16.
   SDValue lowerFP_ROUND(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerFMINNUM_FMAXNUM(SDValue Op, SelectionDAG &DAG) const;
+  SDValue lowerFMINIMUM_FMAXIMUM(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerFLDEXP(SDValue Op, SelectionDAG &DAG) const;
   SDValue promoteUniformOpToI32(SDValue Op, DAGCombinerInfo &DCI) const;
   SDValue lowerMUL(SDValue Op, SelectionDAG &DAG) const;