[DAG] Remove DAGTypeLegalizer::GenWidenVectorTruncStores (PR42046)

[RKSimon]

Summary

Just scalarize trunc stores - GenWidenVectorTruncStores does the same thing but is flawed (PR42046) and unused.

[efriedma]

LGTM

This is by inspection - as was mentioned on the ticket, this code isn't active at all in the tests and I've not been able to get it to fire

In theory, you just need the right kind of node. That said, DAGCombiner specifically avoids bulding such a node, so not sure it ever happens in practice. I think I'm okay with this as-is.

[efriedma]

Err, actually, thinking about it a bit more, we should probably delete GenWidenVectorTruncStores in favor of using scalarizeVectorStore(), since they do basically the same thing.

[RKSimon]

Replace GenWidenVectorTruncStores with scalarizeVectorStore

[efriedma]

LGTM

llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h

SDValue GenWidenVectorExtLoads(SmallVectorImpl<SDValue> &LdChain,
                                  LoadSDNode *LD, ISD::LoadExtType ExtType);
 
   /// Helper function to generate a set of stores to store a widen vector into
   /// non-widen memory.
   ///   StChain: list of chains for the stores we have generated
   ///   ST:      store of a widen value
   void GenWidenVectorStores(SmallVectorImpl<SDValue> &StChain, StoreSDNode *ST);
 
-  /// Helper function to generate a set of stores to store a truncate widen
-  /// vector into non-widen memory.
-  ///   StChain: list of chains for the stores we have generated
-  ///   ST:      store of a widen value
-  void GenWidenVectorTruncStores(SmallVectorImpl<SDValue> &StChain,
-                                 StoreSDNode *ST);
-
   /// Modifies a vector input (widen or narrows) to a vector of NVT.  The
   /// input vector must have the same element type as NVT.
   /// When FillWithZeroes is "on" the vector will be widened with zeroes.
   /// By default, the vector will be widened with undefined values.
   SDValue ModifyToType(SDValue InOp, EVT NVT, bool FillWithZeroes = false);
 
   /// Return a mask of vector type MaskVT to replace InMask. Also adjust
   /// MaskVT to ToMaskVT if needed with vector extension or truncation.

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

 SDValue DAGTypeLegalizer::WidenVecOp_STORE(SDNode *N) {
   // We have to widen the value, but we want only to store the original
   // vector type.
   StoreSDNode *ST = cast<StoreSDNode>(N);
 
   if (!ST->getMemoryVT().getScalarType().isByteSized())
     return TLI.scalarizeVectorStore(ST, DAG);
 
-  SmallVector<SDValue, 16> StChain;
   if (ST->isTruncatingStore())
-    GenWidenVectorTruncStores(StChain, ST);
-  else
-    GenWidenVectorStores(StChain, ST);
+    return TLI.scalarizeVectorStore(ST, DAG);
+
+  SmallVector<SDValue, 16> StChain;
 
   if (StChain.size() == 1)
     return StChain[0];
   else
     return DAG.getNode(ISD::TokenFactor, SDLoc(ST), MVT::Other, StChain);
 }
 
 SDValue DAGTypeLegalizer::WidenVecOp_MSTORE(SDNode *N, unsigned OpNo) {
if (NewVT.isVector()) {
         IncrementPointer(cast<StoreSDNode>(PartStore), NewVT, MPI, BasePtr);
       } while (StWidth.isNonZero() && StWidth >= NewVTWidth);
       // Restore index back to be relative to the original widen element type.
       Idx = Idx * NewVTWidth.getFixedSize() / ValEltWidth;
     }
   }
 }
 
-void
-DAGTypeLegalizer::GenWidenVectorTruncStores(SmallVectorImpl<SDValue> &StChain,
-                                            StoreSDNode *ST) {
-  // For extension loads, it may not be more efficient to truncate the vector
-  // and then store it. Instead, we extract each element and then store it.
-  SDValue Chain = ST->getChain();
-  SDValue BasePtr = ST->getBasePtr();
-  MachineMemOperand::Flags MMOFlags = ST->getMemOperand()->getFlags();
-  AAMDNodes AAInfo = ST->getAAInfo();
-  SDValue ValOp = GetWidenedVector(ST->getValue());
-  SDLoc dl(ST);
-
-  EVT StVT = ST->getMemoryVT();
-  EVT ValVT = ValOp.getValueType();
-
-  // It must be true that the wide vector type is bigger than where we need to
-  // store.
-  assert(StVT.isVector() && ValOp.getValueType().isVector());
-  assert(StVT.isScalableVector() == ValOp.getValueType().isScalableVector());
-  assert(StVT.bitsLT(ValOp.getValueType()));
-
-  if (StVT.isScalableVector())
-    report_fatal_error("Generating widen scalable vector truncating stores not "
-                       "yet supported");
-
-  // For truncating stores, we can not play the tricks of chopping legal vector
-  // types and bitcast it to the right type. Instead, we unroll the store.
-  EVT StEltVT  = StVT.getVectorElementType();
-  EVT ValEltVT = ValVT.getVectorElementType();
-  unsigned Increment = ValEltVT.getSizeInBits() / 8;
-  unsigned NumElts = StVT.getVectorNumElements();
-  SDValue EOp = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl, ValEltVT, ValOp,
-                            DAG.getVectorIdxConstant(0, dl));
-  StChain.push_back(
-      DAG.getTruncStore(Chain, dl, EOp, BasePtr, ST->getPointerInfo(), StEltVT,
-                        ST->getOriginalAlign(), MMOFlags, AAInfo));
-  unsigned Offset = Increment;
-  for (unsigned i=1; i < NumElts; ++i, Offset += Increment) {
-    SDValue NewBasePtr =
-        DAG.getObjectPtrOffset(dl, BasePtr, TypeSize::Fixed(Offset));
-    SDValue EOp = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl, ValEltVT, ValOp,
-                              DAG.getVectorIdxConstant(0, dl));
-    StChain.push_back(DAG.getTruncStore(
-        Chain, dl, EOp, NewBasePtr, ST->getPointerInfo().getWithOffset(Offset),
-        StEltVT, ST->getOriginalAlign(), MMOFlags, AAInfo));
-  }
-}
-
 /// Modifies a vector input (widen or narrows) to a vector of NVT.  The
 /// input vector must have the same element type as NVT.
 /// FillWithZeroes specifies that the vector should be widened with zeroes.
 SDValue DAGTypeLegalizer::ModifyToType(SDValue InOp, EVT NVT,
                                        bool FillWithZeroes) {
   // Note that InOp might have been widened so it might already have
   // the right width or it might need be narrowed.
   EVT InVT = InOp.getValueType();