Revert "[RISCV] Generaize reduction tree matching to all integer reductions (#68014)"

This reverts commit 7a0b9da and
63bbc25.

I'm seeing issues (e.g. on the GCC torture suite) where
combineBinOpOfExtractToReduceTree is called when the V extensions aren't
enabled and triggers a crash due to RISCVSubtarget::getElen asserting.

I'll aim to follow up with a minimal reproducer. Although it's pretty
obvious how to avoid this crash with some extra gating, there are a few
options as to where that should be inserted so I think it's best to
revert and agree the appropriate fix separately.

Author: asb

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -11112,31 +11112,6 @@ void RISCVTargetLowering::ReplaceNodeResults(SDNode *N,
   }
 }
 
-/// Given an integer binary operator, return the generic ISD::VECREDUCE_OP
-/// which corresponds to it.
-static unsigned getVecReduceOpcode(unsigned Opc) {
-  switch (Opc) {
-  default:
-    llvm_unreachable("Unhandled binary to transfrom reduction");
-  case ISD::ADD:
-    return ISD::VECREDUCE_ADD;
-  case ISD::UMAX:
-    return ISD::VECREDUCE_UMAX;
-  case ISD::SMAX:
-    return ISD::VECREDUCE_SMAX;
-  case ISD::UMIN:
-    return ISD::VECREDUCE_UMIN;
-  case ISD::SMIN:
-    return ISD::VECREDUCE_SMIN;
-  case ISD::AND:
-    return ISD::VECREDUCE_AND;
-  case ISD::OR:
-    return ISD::VECREDUCE_OR;
-  case ISD::XOR:
-    return ISD::VECREDUCE_XOR;
-  }
-}
-
 /// Perform two related transforms whose purpose is to incrementally recognize
 /// an explode_vector followed by scalar reduction as a vector reduction node.
 /// This exists to recover from a deficiency in SLP which can't handle
@@ -11155,15 +11130,8 @@ combineBinOpOfExtractToReduceTree(SDNode *N, SelectionDAG &DAG,
 
   const SDLoc DL(N);
   const EVT VT = N->getValueType(0);
-
-  // TODO: Handle floating point here.
-  if (!VT.isInteger())
-    return SDValue();
-
-  const unsigned Opc = N->getOpcode();
-  const unsigned ReduceOpc = getVecReduceOpcode(Opc);
-  assert(Opc == ISD::getVecReduceBaseOpcode(ReduceOpc) &&
-         "Inconsistent mappings");
+  [[maybe_unused]] const unsigned Opc = N->getOpcode();
+  assert(Opc == ISD::ADD && "extend this to other reduction types");
   const SDValue LHS = N->getOperand(0);
   const SDValue RHS = N->getOperand(1);
 
@@ -11193,13 +11161,13 @@ combineBinOpOfExtractToReduceTree(SDNode *N, SelectionDAG &DAG,
     EVT ReduceVT = EVT::getVectorVT(*DAG.getContext(), VT, 2);
     SDValue Vec = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, ReduceVT, SrcVec,
                               DAG.getVectorIdxConstant(0, DL));
-    return DAG.getNode(ReduceOpc, DL, VT, Vec);
+    return DAG.getNode(ISD::VECREDUCE_ADD, DL, VT, Vec);
   }
 
   // Match (binop (reduce (extract_subvector V, 0),
   //                      (extract_vector_elt V, sizeof(SubVec))))
   // into a reduction of one more element from the original vector V.
-  if (LHS.getOpcode() != ReduceOpc)
+  if (LHS.getOpcode() != ISD::VECREDUCE_ADD)
     return SDValue();
 
   SDValue ReduceVec = LHS.getOperand(0);
@@ -11215,7 +11183,7 @@ combineBinOpOfExtractToReduceTree(SDNode *N, SelectionDAG &DAG,
       EVT ReduceVT = EVT::getVectorVT(*DAG.getContext(), VT, Idx + 1);
       SDValue Vec = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, ReduceVT, SrcVec,
                                 DAG.getVectorIdxConstant(0, DL));
-      return DAG.getNode(ReduceOpc, DL, VT, Vec);
+      return DAG.getNode(ISD::VECREDUCE_ADD, DL, VT, Vec);
     }
   }
 
@@ -11723,8 +11691,6 @@ static SDValue performANDCombine(SDNode *N,
 
   if (SDValue V = combineBinOpToReduce(N, DAG, Subtarget))
     return V;
-  if (SDValue V = combineBinOpOfExtractToReduceTree(N, DAG, Subtarget))
-    return V;
 
   if (DCI.isAfterLegalizeDAG())
     if (SDValue V = combineDeMorganOfBoolean(N, DAG))
@@ -11777,8 +11743,6 @@ static SDValue performORCombine(SDNode *N, TargetLowering::DAGCombinerInfo &DCI,
 
   if (SDValue V = combineBinOpToReduce(N, DAG, Subtarget))
     return V;
-  if (SDValue V = combineBinOpOfExtractToReduceTree(N, DAG, Subtarget))
-    return V;
 
   if (DCI.isAfterLegalizeDAG())
     if (SDValue V = combineDeMorganOfBoolean(N, DAG))
@@ -11830,9 +11794,6 @@ static SDValue performXORCombine(SDNode *N, SelectionDAG &DAG,
 
   if (SDValue V = combineBinOpToReduce(N, DAG, Subtarget))
     return V;
-  if (SDValue V = combineBinOpOfExtractToReduceTree(N, DAG, Subtarget))
-    return V;
-
   // fold (xor (select cond, 0, y), x) ->
   //      (select cond, x, (xor x, y))
   return combineSelectAndUseCommutative(N, DAG, /*AllOnes*/ false, Subtarget);
@@ -14038,13 +13999,8 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
   case ISD::SMAX:
   case ISD::SMIN:
   case ISD::FMAXNUM:
-  case ISD::FMINNUM: {
-    if (SDValue V = combineBinOpToReduce(N, DAG, Subtarget))
-      return V;
-    if (SDValue V = combineBinOpOfExtractToReduceTree(N, DAG, Subtarget))
-      return V;
-    return SDValue();
-  }
+  case ISD::FMINNUM:
+    return combineBinOpToReduce(N, DAG, Subtarget);
   case ISD::SETCC:
     return performSETCCCombine(N, DAG, Subtarget);
   case ISD::SIGN_EXTEND_INREG: