[RISCV] Rename merge operand -> passthru. NFC (#100330)

We sometimes call the first tied dest operand in vector pseudos the
merge operand, and other times the passthru.

Passthru seems to be more common, and it's what the C intrinsics call
it[^1], so this renames all usages of merge to passthru to be
consistent. It also helps prevent confusion with vmerge.vvm in some of
the peephole optimisations.

[^1]:
https://github.com/riscv-non-isa/rvv-intrinsic-doc/blob/main/doc/rvv-intrinsic-spec.adoc#the-passthrough-vd-argument-in-the-intrinsics

Author: lukel97

llvm/lib/Target/RISCV/RISCVAsmPrinter.cpp

@@ -976,7 +976,7 @@ static bool lowerRISCVVMachineInstrToMCInst(const MachineInstr *MI,
     if (hasVLOutput && OpNo == 1)
       continue;
 
-    // Skip merge op. It should be the first operand after the defs.
+    // Skip passthru op. It should be the first operand after the defs.
     if (OpNo == MI->getNumExplicitDefs() && MO.isReg() && MO.isTied()) {
       assert(MCID.getOperandConstraint(OpNo, MCOI::TIED_TO) == 0 &&
              "Expected tied to first def.");

llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp

@@ -3633,7 +3633,7 @@ bool RISCVDAGToDAGISel::doPeepholeMaskedRVV(MachineSDNode *N) {
 #endif
 
   SmallVector<SDValue, 8> Ops;
-  // Skip the merge operand at index 0 if !UseTUPseudo.
+  // Skip the passthru operand at index 0 if !UseTUPseudo.
   for (unsigned I = !UseTUPseudo, E = N->getNumOperands(); I != E; I++) {
     // Skip the mask, and the Glue.
     SDValue Op = N->getOperand(I);
@@ -3696,9 +3696,9 @@ static unsigned GetVMSetForLMul(RISCVII::VLMUL LMUL) {
 // ->
 // %x = PseudoVADD_VV_MASK %false, ..., %mask
 //
-// We can only fold if vmerge's merge operand, vmerge's false operand and
-// %true's merge operand (if it has one) are the same. This is because we have
-// to consolidate them into one merge operand in the result.
+// We can only fold if vmerge's passthru operand, vmerge's false operand and
+// %true's passthru operand (if it has one) are the same. This is because we
+// have to consolidate them into one passthru operand in the result.
 //
 // If %true is masked, then we can use its mask instead of vmerge's if vmerge's
 // mask is all ones.
@@ -3709,20 +3709,20 @@ static unsigned GetVMSetForLMul(RISCVII::VLMUL LMUL) {
 // The resulting VL is the minimum of the two VLs.
 //
 // The resulting policy is the effective policy the vmerge would have had,
-// i.e. whether or not it's merge operand was implicit-def.
+// i.e. whether or not it's passthru operand was implicit-def.
 bool RISCVDAGToDAGISel::performCombineVMergeAndVOps(SDNode *N) {
-  SDValue Merge, False, True, VL, Mask, Glue;
+  SDValue Passthru, False, True, VL, Mask, Glue;
   // A vmv.v.v is equivalent to a vmerge with an all-ones mask.
   if (IsVMv(N)) {
-    Merge = N->getOperand(0);
+    Passthru = N->getOperand(0);
     False = N->getOperand(0);
     True = N->getOperand(1);
     VL = N->getOperand(2);
     // A vmv.v.v won't have a Mask or Glue, instead we'll construct an all-ones
     // mask later below.
   } else {
     assert(IsVMerge(N));
-    Merge = N->getOperand(0);
+    Passthru = N->getOperand(0);
     False = N->getOperand(1);
     True = N->getOperand(2);
     Mask = N->getOperand(3);
@@ -3733,9 +3733,9 @@ bool RISCVDAGToDAGISel::performCombineVMergeAndVOps(SDNode *N) {
   assert(!Mask || cast<RegisterSDNode>(Mask)->getReg() == RISCV::V0);
   assert(!Glue || Glue.getValueType() == MVT::Glue);
 
-  // We require that either merge and false are the same, or that merge
+  // We require that either passthru and false are the same, or that passthru
   // is undefined.
-  if (Merge != False && !isImplicitDef(Merge))
+  if (Passthru != False && !isImplicitDef(Passthru))
     return false;
 
   assert(True.getResNo() == 0 &&
@@ -3765,19 +3765,19 @@ bool RISCVDAGToDAGISel::performCombineVMergeAndVOps(SDNode *N) {
   if (!Info)
     return false;
 
-  // If True has a merge operand then it needs to be the same as vmerge's False,
-  // since False will be used for the result's merge operand.
+  // If True has a passthru operand then it needs to be the same as vmerge's
+  // False, since False will be used for the result's passthru operand.
   if (HasTiedDest && !isImplicitDef(True->getOperand(0))) {
-    SDValue MergeOpTrue = True->getOperand(0);
-    if (False != MergeOpTrue)
+    SDValue PassthruOpTrue = True->getOperand(0);
+    if (False != PassthruOpTrue)
       return false;
   }
 
   // If True is masked then the vmerge must have either the same mask or an all
   // 1s mask, since we're going to keep the mask from True.
   if (IsMasked && Mask) {
     // FIXME: Support mask agnostic True instruction which would have an
-    // undef merge operand.
+    // undef passthru operand.
     SDValue TrueMask =
         getMaskSetter(True->getOperand(Info->MaskOpIdx),
                       True->getOperand(True->getNumOperands() - 1));
@@ -3835,8 +3835,8 @@ bool RISCVDAGToDAGISel::performCombineVMergeAndVOps(SDNode *N) {
     return CLHS->getZExtValue() <= CRHS->getZExtValue() ? LHS : RHS;
   };
 
-  // Because N and True must have the same merge operand (or True's operand is
-  // implicit_def), the "effective" body is the minimum of their VLs.
+  // Because N and True must have the same passthru operand (or True's operand
+  // is implicit_def), the "effective" body is the minimum of their VLs.
   SDValue OrigVL = VL;
   VL = GetMinVL(TrueVL, VL);
   if (!VL)
@@ -3895,15 +3895,15 @@ bool RISCVDAGToDAGISel::performCombineVMergeAndVOps(SDNode *N) {
          "Expected instructions with mask have a tied dest.");
 #endif
 
-  // Use a tumu policy, relaxing it to tail agnostic provided that the merge
+  // Use a tumu policy, relaxing it to tail agnostic provided that the passthru
   // operand is undefined.
   //
   // However, if the VL became smaller than what the vmerge had originally, then
   // elements past VL that were previously in the vmerge's body will have moved
   // to the tail. In that case we always need to use tail undisturbed to
   // preserve them.
   bool MergeVLShrunk = VL != OrigVL;
-  uint64_t Policy = (isImplicitDef(Merge) && !MergeVLShrunk)
+  uint64_t Policy = (isImplicitDef(Passthru) && !MergeVLShrunk)
                         ? RISCVII::TAIL_AGNOSTIC
                         : /*TUMU*/ 0;
   SDValue PolicyOp =

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -3294,25 +3294,25 @@ static SDValue lowerVectorXRINT(SDValue Op, SelectionDAG &DAG,
 
 static SDValue
 getVSlidedown(SelectionDAG &DAG, const RISCVSubtarget &Subtarget,
-              const SDLoc &DL, EVT VT, SDValue Merge, SDValue Op,
+              const SDLoc &DL, EVT VT, SDValue Passthru, SDValue Op,
               SDValue Offset, SDValue Mask, SDValue VL,
               unsigned Policy = RISCVII::TAIL_UNDISTURBED_MASK_UNDISTURBED) {
-  if (Merge.isUndef())
+  if (Passthru.isUndef())
     Policy = RISCVII::TAIL_AGNOSTIC | RISCVII::MASK_AGNOSTIC;
   SDValue PolicyOp = DAG.getTargetConstant(Policy, DL, Subtarget.getXLenVT());
-  SDValue Ops[] = {Merge, Op, Offset, Mask, VL, PolicyOp};
+  SDValue Ops[] = {Passthru, Op, Offset, Mask, VL, PolicyOp};
   return DAG.getNode(RISCVISD::VSLIDEDOWN_VL, DL, VT, Ops);
 }
 
 static SDValue
 getVSlideup(SelectionDAG &DAG, const RISCVSubtarget &Subtarget, const SDLoc &DL,
-            EVT VT, SDValue Merge, SDValue Op, SDValue Offset, SDValue Mask,
+            EVT VT, SDValue Passthru, SDValue Op, SDValue Offset, SDValue Mask,
             SDValue VL,
             unsigned Policy = RISCVII::TAIL_UNDISTURBED_MASK_UNDISTURBED) {
-  if (Merge.isUndef())
+  if (Passthru.isUndef())
     Policy = RISCVII::TAIL_AGNOSTIC | RISCVII::MASK_AGNOSTIC;
   SDValue PolicyOp = DAG.getTargetConstant(Policy, DL, Subtarget.getXLenVT());
-  SDValue Ops[] = {Merge, Op, Offset, Mask, VL, PolicyOp};
+  SDValue Ops[] = {Passthru, Op, Offset, Mask, VL, PolicyOp};
   return DAG.getNode(RISCVISD::VSLIDEUP_VL, DL, VT, Ops);
 }
 
@@ -6086,8 +6086,8 @@ static unsigned getRISCVVLOp(SDValue Op) {
 #undef VP_CASE
 }
 
-/// Return true if a RISC-V target specified op has a merge operand.
-static bool hasMergeOp(unsigned Opcode) {
+/// Return true if a RISC-V target specified op has a passthru operand.
+static bool hasPassthruOp(unsigned Opcode) {
   assert(Opcode > RISCVISD::FIRST_NUMBER &&
          Opcode <= RISCVISD::LAST_RISCV_STRICTFP_OPCODE &&
          "not a RISC-V target specific op");
@@ -10953,7 +10953,7 @@ SDValue RISCVTargetLowering::lowerVectorStrictFSetcc(SDValue Op,
          True, VL});
     Mask =
         DAG.getNode(RISCVISD::VMAND_VL, DL, MaskVT, OrderMask1, OrderMask2, VL);
-    // Use Mask as the merge operand to let the result be 0 if either of the
+    // Use Mask as the passthru operand to let the result be 0 if either of the
     // inputs is unordered.
     Res = DAG.getNode(RISCVISD::STRICT_FSETCCS_VL, DL,
                       DAG.getVTList(MaskVT, MVT::Other),
@@ -11058,7 +11058,7 @@ SDValue RISCVTargetLowering::lowerFixedLengthVectorSelectToRVV(
 SDValue RISCVTargetLowering::lowerToScalableOp(SDValue Op,
                                                SelectionDAG &DAG) const {
   unsigned NewOpc = getRISCVVLOp(Op);
-  bool HasMergeOp = hasMergeOp(NewOpc);
+  bool HasPassthruOp = hasPassthruOp(NewOpc);
   bool HasMask = hasMaskOp(NewOpc);
 
   MVT VT = Op.getSimpleValueType();
@@ -11083,7 +11083,7 @@ SDValue RISCVTargetLowering::lowerToScalableOp(SDValue Op,
 
   SDLoc DL(Op);
   auto [Mask, VL] = getDefaultVLOps(VT, ContainerVT, DL, DAG, Subtarget);
-  if (HasMergeOp)
+  if (HasPassthruOp)
     Ops.push_back(DAG.getUNDEF(ContainerVT));
   if (HasMask)
     Ops.push_back(Mask);
@@ -11111,7 +11111,7 @@ SDValue RISCVTargetLowering::lowerToScalableOp(SDValue Op,
 //   types.
 SDValue RISCVTargetLowering::lowerVPOp(SDValue Op, SelectionDAG &DAG) const {
   unsigned RISCVISDOpc = getRISCVVLOp(Op);
-  bool HasMergeOp = hasMergeOp(RISCVISDOpc);
+  bool HasPassthruOp = hasPassthruOp(RISCVISDOpc);
 
   SDLoc DL(Op);
   MVT VT = Op.getSimpleValueType();
@@ -11124,9 +11124,9 @@ SDValue RISCVTargetLowering::lowerVPOp(SDValue Op, SelectionDAG &DAG) const {
   for (const auto &OpIdx : enumerate(Op->ops())) {
     SDValue V = OpIdx.value();
     assert(!isa<VTSDNode>(V) && "Unexpected VTSDNode node!");
-    // Add dummy merge value before the mask. Or if there isn't a mask, before
-    // EVL.
-    if (HasMergeOp) {
+    // Add dummy passthru value before the mask. Or if there isn't a mask,
+    // before EVL.
+    if (HasPassthruOp) {
       auto MaskIdx = ISD::getVPMaskIdx(Op.getOpcode());
       if (MaskIdx) {
         if (*MaskIdx == OpIdx.index())
@@ -14658,25 +14658,25 @@ struct CombineResult {
   /// The actual replacement is *not* done in that method.
   SDValue materialize(SelectionDAG &DAG,
                       const RISCVSubtarget &Subtarget) const {
-    SDValue Mask, VL, Merge;
+    SDValue Mask, VL, Passthru;
     std::tie(Mask, VL) =
         NodeExtensionHelper::getMaskAndVL(Root, DAG, Subtarget);
     switch (Root->getOpcode()) {
     default:
-      Merge = Root->getOperand(2);
+      Passthru = Root->getOperand(2);
       break;
     case ISD::ADD:
     case ISD::SUB:
     case ISD::MUL:
     case ISD::OR:
     case ISD::SHL:
-      Merge = DAG.getUNDEF(Root->getValueType(0));
+      Passthru = DAG.getUNDEF(Root->getValueType(0));
       break;
     }
     return DAG.getNode(TargetOpcode, SDLoc(Root), Root->getValueType(0),
                        LHS.getOrCreateExtendedOp(Root, DAG, Subtarget, LHSExt),
                        RHS.getOrCreateExtendedOp(Root, DAG, Subtarget, RHSExt),
-                       Merge, Mask, VL);
+                       Passthru, Mask, VL);
   }
 };
 
@@ -16159,8 +16159,8 @@ static SDValue combineToVWMACC(SDNode *N, SelectionDAG &DAG,
   SDValue MulOp = N->getOperand(1);
 
   if (N->getOpcode() == RISCVISD::ADD_VL) {
-    SDValue AddMergeOp = N->getOperand(2);
-    if (!AddMergeOp.isUndef())
+    SDValue AddPassthruOp = N->getOperand(2);
+    if (!AddPassthruOp.isUndef())
       return SDValue();
   }
 
@@ -16181,9 +16181,9 @@ static SDValue combineToVWMACC(SDNode *N, SelectionDAG &DAG,
   if (!IsVWMulOpc(MulOp.getOpcode()))
     return SDValue();
 
-  SDValue MulMergeOp = MulOp.getOperand(2);
+  SDValue MulPassthruOp = MulOp.getOperand(2);
 
-  if (!MulMergeOp.isUndef())
+  if (!MulPassthruOp.isUndef())
     return SDValue();
 
   auto [AddMask, AddVL] = [](SDNode *N, SelectionDAG &DAG,

llvm/lib/Target/RISCV/RISCVISelLowering.h

@@ -238,7 +238,7 @@ enum NodeType : unsigned {
   VECREDUCE_FMIN_VL,
   VECREDUCE_FMAX_VL,
 
-  // Vector binary ops with a merge as a third operand, a mask as a fourth
+  // Vector binary ops with a passthru as a third operand, a mask as a fourth
   // operand, and VL as a fifth operand.
   ADD_VL,
   AND_VL,
@@ -294,7 +294,7 @@ enum NodeType : unsigned {
   FABS_VL,
   FSQRT_VL,
   FCLASS_VL,
-  FCOPYSIGN_VL, // Has a merge operand
+  FCOPYSIGN_VL, // Has a passthru operand
   VFCVT_RTZ_X_F_VL,
   VFCVT_RTZ_XU_F_VL,
   VFCVT_X_F_VL,
@@ -322,7 +322,7 @@ enum NodeType : unsigned {
   VFWMSUB_VL,
   VFWNMSUB_VL,
 
-  // Widening instructions with a merge value a third operand, a mask as a
+  // Widening instructions with a passthru value a third operand, a mask as a
   // fourth operand, and VL as a fifth operand.
   VWMUL_VL,
   VWMULU_VL,

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp

@@ -182,7 +182,7 @@ static bool isMaskRegOp(const MachineInstr &MI) {
 /// Note that this is different from "agnostic" as defined by the vector
 /// specification.  Agnostic requires each lane to either be undisturbed, or
 /// take the value -1; no other value is allowed.
-static bool hasUndefinedMergeOp(const MachineInstr &MI) {
+static bool hasUndefinedPassthru(const MachineInstr &MI) {
 
   unsigned UseOpIdx;
   if (!MI.isRegTiedToUseOperand(0, &UseOpIdx))
@@ -443,13 +443,13 @@ DemandedFields getDemanded(const MachineInstr &MI, const RISCVSubtarget *ST) {
     Res.LMUL = DemandedFields::LMULNone;
     Res.SEWLMULRatio = false;
     Res.VLAny = false;
-    // For vmv.s.x and vfmv.s.f, if the merge operand is *undefined*, we don't
+    // For vmv.s.x and vfmv.s.f, if the passthru is *undefined*, we don't
     // need to preserve any other bits and are thus compatible with any larger,
     // etype and can disregard policy bits.  Warning: It's tempting to try doing
     // this for any tail agnostic operation, but we can't as TA requires
     // tail lanes to either be the original value or -1.  We are writing
     // unknown bits to the lanes here.
-    if (hasUndefinedMergeOp(MI)) {
+    if (hasUndefinedPassthru(MI)) {
       if (isFloatScalarMoveOrScalarSplatInstr(MI) && !ST->hasVInstructionsF64())
         Res.SEW = DemandedFields::SEWGreaterThanOrEqualAndLessThan64;
       else
@@ -469,7 +469,7 @@ DemandedFields getDemanded(const MachineInstr &MI, const RISCVSubtarget *ST) {
 
   if (RISCVII::hasVLOp(MI.getDesc().TSFlags)) {
     const MachineOperand &VLOp = MI.getOperand(getVLOpNum(MI));
-    // A slidedown/slideup with an *undefined* merge op can freely clobber
+    // A slidedown/slideup with an *undefined* passthru can freely clobber
     // elements not copied from the source vector (e.g. masked off, tail, or
     // slideup's prefix). Notes:
     // * We can't modify SEW here since the slide amount is in units of SEW.
@@ -478,7 +478,7 @@ DemandedFields getDemanded(const MachineInstr &MI, const RISCVSubtarget *ST) {
     // * The LMUL1 restriction is for machines whose latency may depend on VL.
     // * As above, this is only legal for tail "undefined" not "agnostic".
     if (isVSlideInstr(MI) && VLOp.isImm() && VLOp.getImm() == 1 &&
-        hasUndefinedMergeOp(MI)) {
+        hasUndefinedPassthru(MI)) {
       Res.VLAny = false;
       Res.VLZeroness = true;
       Res.LMUL = DemandedFields::LMULLessThanOrEqualToM1;
@@ -492,7 +492,7 @@ DemandedFields getDemanded(const MachineInstr &MI, const RISCVSubtarget *ST) {
     // careful to not increase the number of active vector registers (unlike for
     // vmv.s.x.)
     if (isScalarSplatInstr(MI) && VLOp.isImm() && VLOp.getImm() == 1 &&
-        hasUndefinedMergeOp(MI)) {
+        hasUndefinedPassthru(MI)) {
       Res.LMUL = DemandedFields::LMULLessThanOrEqualToM1;
       Res.SEWLMULRatio = false;
       Res.VLAny = false;
@@ -1000,7 +1000,7 @@ RISCVInsertVSETVLI::computeInfoForInstr(const MachineInstr &MI) const {
 
   bool TailAgnostic = true;
   bool MaskAgnostic = true;
-  if (!hasUndefinedMergeOp(MI)) {
+  if (!hasUndefinedPassthru(MI)) {
     // Start with undisturbed.
     TailAgnostic = false;
     MaskAgnostic = false;