AMDGPU: Fix creating minimum3/maximum3 nodes pre-gfx12 (#93027)

These would fail to select.

Author: arsenm

llvm/lib/Target/AMDGPU/GCNSubtarget.h

@@ -1312,6 +1312,9 @@ class GCNSubtarget final : public AMDGPUGenSubtargetInfo,
   // \returns true if the target has IEEE fminimum/fmaximum instructions
   bool hasIEEEMinMax() const { return getGeneration() >= GFX12; }
 
+  // \returns true if the target has IEEE fminimum3/fmaximum3 instructions
+  bool hasIEEEMinMax3() const { return hasIEEEMinMax(); }
+
   // \returns true if the target has WG_RR_MODE kernel descriptor mode bit
   bool hasRrWGMode() const { return getGeneration() >= GFX12; }
 

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -13199,6 +13199,33 @@ SDValue SITargetLowering::performFPMed3ImmCombine(SelectionDAG &DAG,
   return SDValue();
 }
 
+/// \return true if the subtarget supports minimum3 and maximum3 with the given
+/// base min/max opcode \p Opc for type \p VT.
+static bool supportsMin3Max3(const GCNSubtarget &Subtarget, unsigned Opc,
+                             EVT VT) {
+  switch (Opc) {
+  case ISD::FMINNUM:
+  case ISD::FMAXNUM:
+  case ISD::FMINNUM_IEEE:
+  case ISD::FMAXNUM_IEEE:
+  case AMDGPUISD::FMIN_LEGACY:
+  case AMDGPUISD::FMAX_LEGACY:
+    return (VT == MVT::f32) || (VT == MVT::f16 && Subtarget.hasMin3Max3_16());
+  case ISD::FMINIMUM:
+  case ISD::FMAXIMUM:
+    return (VT == MVT::f32 || VT == MVT::f16) && Subtarget.hasIEEEMinMax3();
+  case ISD::SMAX:
+  case ISD::SMIN:
+  case ISD::UMAX:
+  case ISD::UMIN:
+    return (VT == MVT::i32) || (VT == MVT::i16 && Subtarget.hasMin3Max3_16());
+  default:
+    return false;
+  }
+
+  llvm_unreachable("not a min/max opcode");
+}
+
 SDValue SITargetLowering::performMinMaxCombine(SDNode *N,
                                                DAGCombinerInfo &DCI) const {
   SelectionDAG &DAG = DCI.DAG;
@@ -13211,10 +13238,7 @@ SDValue SITargetLowering::performMinMaxCombine(SDNode *N,
   // Only do this if the inner op has one use since this will just increases
   // register pressure for no benefit.
 
-  if (Opc != AMDGPUISD::FMIN_LEGACY && Opc != AMDGPUISD::FMAX_LEGACY &&
-      !VT.isVector() &&
-      (VT == MVT::i32 || VT == MVT::f32 ||
-       ((VT == MVT::f16 || VT == MVT::i16) && Subtarget->hasMin3Max3_16()))) {
+  if (supportsMin3Max3(*Subtarget, Opc, VT)) {
     // max(max(a, b), c) -> max3(a, b, c)
     // min(min(a, b), c) -> min3(a, b, c)
     if (Op0.getOpcode() == Opc && Op0.hasOneUse()) {