Add support for (expressing) vscale.

[sdesmalen]

Summary

In LLVM IR, vscale can be represented with an intrinsic. For some targets,
this is equivalent to the constexpr:

getelementptr <vscale x 1 x i8>, <vscale x 1 x i8>* null, i32 1

This can be used to propagate the value in CodeGenPrepare.

In ISel we add a node that can be legalized to one or more
instructions to materialize the runtime vector length.

This patch also adds SVE CodeGen support for VSCALE, which maps this
node to RDVL instructions (for scaled multiples of 16bytes) or CNT[HSD]
instructions (scaled multiples of 2, 4, or 8 bytes, respectively).

[cameron.mcinally]

What happens if we see IR like:

%1 = mul i16 vscale, -2

Would that be promoted to i32 through PromoteIntRes_VSCALE(...)?

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

5141 ↗

(On Diff #222364)

This should probably have a test. Same for ISD::MUL.

[cameron.mcinally]

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

5141 ↗

(On Diff #222364)

Sorry, just SHL. MUL tests are there...

[sdesmalen]

Added LLVM IR support to this patch; as intrinsic and constexpr pattern (following suggestions in D71636)

[lattner]

I'm not a comptent reviewer on the details for this whole patch, but the general intrinsic approach LGTM!

[SjoerdMeijer]

llvm/docs/LangRef.rst

17751

nit: perhaps "throughout the program" -> "throughout the program execution"?

17753

nit: perhaps just omit "for convenience"?

17766

nit: unrelated change, don't need this newline?

llvm/include/llvm/CodeGen/ISDOpcodes.h

919

nit: extra whitespace before IMM

920

Just curious, what do you mean by "usually", i.e. if it is not getVectorNumElements(), what else can it be?

llvm/test/CodeGen/AArch64/sve-vscale.ll

21

I don't think I understand this and test case above (haven't looked at the other yet). Essentially I don't understand why we remove the mul with 16.... which we are optimsing away? Is this correct? Where does this constant 16 comes from and what is the meaning of it? It could be I don't understand the RDVL instruction, or the vscale intrinsic definition. Can you explain this?

[sdesmalen]

• Changed some mul into shl in the test file, to test fold into vscale isd node.
• Addressed comments.

[sdesmalen]

In D68203#1809517, @lattner wrote:

I'm not a comptent reviewer on the details for this whole patch, but the general intrinsic approach LGTM!

Awesome, thanks for having a look!

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

5141 ↗

(On Diff #222364)

Good spot, I've replaced some of the mul in the test with shl.

llvm/include/llvm/CodeGen/ISDOpcodes.h

920

In the context of auto-vectorization, it is often used to increment an iteration counter with the number of elements, e.g. i = i + vscale x #elts.

I'll remove the sentence as I agree it adds unnecessary confusion.

llvm/test/CodeGen/AArch64/sve-vscale.ll

21

Here RDVL stores the current vector register size in bytes into x0 (multiplied by the immediate, in this case 1).
Given that there are vscale x 16 bytes in an SVE vector, this instruction folds that mul 16 away into the instruction, in which it is implicit.

[SjoerdMeijer]

llvm/test/CodeGen/AArch64/sve-vscale.ll

21

Ah, yes, thanks for clarifying. I got confused about bits, bytes, and sizes of everything, but I got it now and see that this makes sense. I will continue looking at this patch a bit more.

[SjoerdMeijer]

llvm/include/llvm/IR/PatternMatch.h

2021

Nit: how about renaming S to Scaling or something along those lines?

llvm/lib/Target/AArch64/AArch64SVEInstrInfo.td

1108

last question: is there a test case for this, can this be triggered?

[efriedma]

Does it make sense to have a special case for vscale * 1 or vscale * -1? Not that it's likely to come up in most cases, but it would look pretty silly to generate a madd that multiplies by 1.

llvm/docs/LangRef.rst

17753

What happens if the multiply overflows?

llvm/lib/CodeGen/CodeGenPrepare.cpp

2019

This should do the right thing, as far as I know.

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

5139

This multiply can overflow.

5180

This shift can overflow.

[sdesmalen]

• Simplified the llvm.vscale intrinsic to no longer take the scaling argument. This means the scaling is left to an explicit mul which has explicit wrapping flags. This in turn simplifies the code in SelectionDAG for merging the multiplier into the VSCALE ISD node (this should only happen when it is known that no wrapping occurs).
• Also made llvm.vscale overloadable, so that it can return vscale in different types.
• Added special patterns for mul vscale, 1 and mul vscale, -1.

[sdesmalen]

llvm/docs/LangRef.rst

17753

Fixed by removing the scaling argument and leaving this to an explicit mul (with wrapping flags to express (lack of) overflow).

llvm/include/llvm/IR/PatternMatch.h

2021

Because the scaling argument has been removed from the intrinsic, I've also removed the matching of any scaling from this function.

llvm/lib/Target/AArch64/AArch64SVEInstrInfo.td

1108

Yes! rdvl_3 is the test addresses that case.

[efriedma]

The new IR intrinsic makes more sense.

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

5139

This multiply can still overflow. (If it's supposed to wrap, please use an unsigned multiply.)

[sdesmalen]

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

5139

Sorry, I'm not really sure I understand how the multiply above can overflow. The code checks the NSW flag on the MUL node, so if VSCALE(Imm) *N2C does not wrap, why would Imm * N2C wrap?

Perhaps int64_t is the wrong choice here though and we should instead be using APInt for the VScale operand (for the general case where VT > int64_t)

[sdesmalen]

Changed scale argument to VSCALE from int64_t to APInt.

[efriedma]

LGTM.

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

5139

APInt is fine.

In the version you had, the multiply "can't overflow" in the sense that the operation produces poison if it overflows; that's not a problem. The problem would be undefined behavior in the compiler itself.

[sdesmalen]

In D68203#1820191, @efriedma wrote:

LGTM.

I was about to commit this patch today when I realised the differential wasn't yet in accepted state. Any objections for me to land the patch?

[efriedma]

Just forgot to click the button.

llvm/docs/LangRef.rst

 The result of ``ptrmask(ptr, mask)`` is equivalent to
 ``getelementptr ptr, (ptrtoint(ptr) & mask) - ptrtoint(ptr)``. Both the returned
 pointer and the first argument are based on the same underlying object (for more
 information on the *based on* terminology see
 :ref:`the pointer aliasing rules <pointeraliasing>`). If the bitwidth of the
 mask argument does not match the pointer size of the target, the mask is
 zero-extended or truncated accordingly.
 
+.. _int_vscale:
+
+'``llvm.vscale``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare i32 llvm.vscale.i32()
+      declare i64 llvm.vscale.i64()
+
+Overview:
+"""""""""
+
+The ``llvm.vscale`` intrinsic returns the value for ``vscale`` in scalable
+vectors such as ``<vscale x 16 x i8>``.
+
+Semantics:
+""""""""""
+
+``vscale`` is a positive value that is constant throughout program
+execution, but is unknown at compile time.
+If the result value does not fit in the result type, then the result is
+a :ref:`poison value <poisonvalues>`.
+
+
 Stack Map Intrinsics
 --------------------
 
 LLVM provides experimental intrinsics to support runtime patching
 mechanisms commonly desired in dynamic language JITs. These intrinsics
 are described in :doc:`StackMaps`.
 
 Element Wise Atomic Memory Intrinsics
 -------------------------------------
 
 These intrinsics are similar to the standard library memory intrinsics except
 that they perform memory transfer as a sequence of atomic memory accesses.
 
 .. _int_memcpy_element_unordered_atomic:
 
 '``llvm.memcpy.element.unordered.atomic``' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Syntax:
 """""""
 
 This is an overloaded intrinsic. You can use ``llvm.memcpy.element.unordered.atomic`` on

llvm/include/llvm/CodeGen/ISDOpcodes.h

enum NodeType {
     GC_TRANSITION_END,
 
     /// GET_DYNAMIC_AREA_OFFSET - get offset from native SP to the address of
     /// the most recent dynamic alloca. For most targets that would be 0, but
     /// for some others (e.g. PowerPC, PowerPC64) that would be compile-time
     /// known nonzero constant. The only operand here is the chain.
     GET_DYNAMIC_AREA_OFFSET,
 
+    /// VSCALE(IMM) - Returns the runtime scaling factor used to calculate the
+    /// number of elements within a scalable vector. IMM is a constant integer
+    /// multiplier that is applied to the runtime value.
+    VSCALE,
+
     /// Generic reduction nodes. These nodes represent horizontal vector
     /// reduction operations, producing a scalar result.
     /// The STRICT variants perform reductions in sequential order. The first
     /// operand is an initial scalar accumulator value, and the second operand
     /// is the vector to reduce.
     VECREDUCE_STRICT_FADD, VECREDUCE_STRICT_FMUL,
     /// These reductions are non-strict, and have a single vector operand.
     VECREDUCE_FADD, VECREDUCE_FMUL,

llvm/include/llvm/CodeGen/SelectionDAG.h

#endif
   /// Return true if the result of this operation is always undefined.
   bool isUndef(unsigned Opcode, ArrayRef<SDValue> Ops);
 
   /// Return an UNDEF node. UNDEF does not have a useful SDLoc.
   SDValue getUNDEF(EVT VT) {
     return getNode(ISD::UNDEF, SDLoc(), VT);
   }
 
+  /// Return a node that represents the runtime scaling 'MulImm * RuntimeVL'.
+  SDValue getVScale(const SDLoc &DL, EVT VT, int64_t MulImm=1) {
+    return getNode(ISD::VSCALE, DL, VT, getConstant(MulImm, DL, VT));
+  }
+
   /// Return a GLOBAL_OFFSET_TABLE node. This does not have a useful SDLoc.
   SDValue getGLOBAL_OFFSET_TABLE(EVT VT) {
     return getNode(ISD::GLOBAL_OFFSET_TABLE, SDLoc(), VT);
   }
 
   /// Gets or creates the specified node.
   ///
   SDValue getNode(unsigned Opcode, const SDLoc &DL, EVT VT,

llvm/include/llvm/IR/Intrinsics.td

def int_preserve_union_access_index : Intrinsic<[llvm_anyptr_ty],
                                                 [llvm_anyptr_ty, llvm_i32_ty],
                                                 [IntrNoMem, ImmArg<1>]>;
 def int_preserve_struct_access_index : Intrinsic<[llvm_anyptr_ty],
                                                  [llvm_anyptr_ty, llvm_i32_ty,
                                                   llvm_i32_ty],
                                                  [IntrNoMem, ImmArg<1>,
                                                   ImmArg<2>]>;
 
+//===---------- Intrinsics to query properties of scalable vectors --------===//
+def int_vscale : Intrinsic<[llvm_anyint_ty], [], [IntrNoMem]>;
+
+//===----------------------------------------------------------------------===//
+
 //===----------------------------------------------------------------------===//
 // Target-specific intrinsics
 //===----------------------------------------------------------------------===//
 
 include "llvm/IR/IntrinsicsPowerPC.td"
 include "llvm/IR/IntrinsicsX86.td"
 include "llvm/IR/IntrinsicsARM.td"
 include "llvm/IR/IntrinsicsAArch64.td"

llvm/include/llvm/IR/PatternMatch.h

 
 #ifndef LLVM_IR_PATTERNMATCH_H
 #define LLVM_IR_PATTERNMATCH_H
 
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/IR/Value.h"
 #include "llvm/Support/Casting.h"

 
 /// Match a single index ExtractValue instruction.
 /// For example m_ExtractValue<1>(...)
 template <int Ind, typename Val_t>
 inline ExtractValue_match<Ind, Val_t> m_ExtractValue(const Val_t &V) {
   return ExtractValue_match<Ind, Val_t>(V);
 }
 
+/// Matches patterns for `vscale`. This can either be a call to `llvm.vscale` or
+/// the constant expression
+///  `ptrtoint(gep <vscale x 1 x i8>, <vscale x 1 x i8>* null, i32 1>`
+/// under the right conditions determined by DataLayout.
+struct VScaleVal_match {
+private:
+  template <typename Base, typename Offset>
+  inline BinaryOp_match<Base, Offset, Instruction::GetElementPtr>
+  m_OffsetGep(const Base &B, const Offset &O) {
+    return BinaryOp_match<Base, Offset, Instruction::GetElementPtr>(B, O);
+  }
+
+public:
+  const DataLayout &DL;
+  VScaleVal_match(const DataLayout &DL) : DL(DL) {}
+
+  template <typename ITy> bool match(ITy *V) {
+    if (m_Intrinsic<Intrinsic::vscale>().match(V))
+      return true;
+
+    if (m_PtrToInt(m_OffsetGep(m_Zero(), m_SpecificInt(1))).match(V)) {
+      Type *PtrTy = cast<Operator>(V)->getOperand(0)->getType();
+      Type *DerefTy = PtrTy->getPointerElementType();
+      if (DerefTy->isVectorTy() && DerefTy->getVectorIsScalable() &&
+          DL.getTypeAllocSizeInBits(DerefTy).getKnownMinSize() == 8)
+        return true;
+    }
+
+    return false;
+  }
+};
+
+inline VScaleVal_match m_VScale(const DataLayout &DL) {
+  return VScaleVal_match(DL);
+}
+
 } // end namespace PatternMatch
 } // end namespace llvm
 
 #endif // LLVM_IR_PATTERNMATCH_H

llvm/include/llvm/Target/TargetSelectionDAG.td

 
 def imm        : SDNode<"ISD::Constant"  , SDTIntLeaf , [], "ConstantSDNode">;
 def timm       : SDNode<"ISD::TargetConstant",SDTIntLeaf, [], "ConstantSDNode">;
 def fpimm      : SDNode<"ISD::ConstantFP", SDTFPLeaf  , [], "ConstantFPSDNode">;
 def vt         : SDNode<"ISD::VALUETYPE" , SDTOther   , [], "VTSDNode">;
 def bb         : SDNode<"ISD::BasicBlock", SDTOther   , [], "BasicBlockSDNode">;
 def cond       : SDNode<"ISD::CONDCODE"  , SDTOther   , [], "CondCodeSDNode">;
 def undef      : SDNode<"ISD::UNDEF"     , SDTUNDEF   , []>;
+def vscale     : SDNode<"ISD::VSCALE"    , SDTIntUnaryOp, []>;
 def globaladdr : SDNode<"ISD::GlobalAddress",         SDTPtrLeaf, [],
                         "GlobalAddressSDNode">;
 def tglobaladdr : SDNode<"ISD::TargetGlobalAddress",  SDTPtrLeaf, [],
                          "GlobalAddressSDNode">;
 def globaltlsaddr : SDNode<"ISD::GlobalTLSAddress",         SDTPtrLeaf, [],
                           "GlobalAddressSDNode">;
 def tglobaltlsaddr : SDNode<"ISD::TargetGlobalTLSAddress",  SDTPtrLeaf, [],
                            "GlobalAddressSDNode">;

llvm/lib/Analysis/ConstantFolding.cpp

Constant *SymbolicallyEvaluateGEP(const GEPOperator *GEP,
                                   const DataLayout &DL,
                                   const TargetLibraryInfo *TLI) {
   const GEPOperator *InnermostGEP = GEP;
   bool InBounds = GEP->isInBounds();
 
   Type *SrcElemTy = GEP->getSourceElementType();
   Type *ResElemTy = GEP->getResultElementType();
   Type *ResTy = GEP->getType();
-  if (!SrcElemTy->isSized())
+  if (!SrcElemTy->isSized() ||
+      (SrcElemTy->isVectorTy() && SrcElemTy->getVectorIsScalable()))
     return nullptr;
 
   if (Constant *C = CastGEPIndices(SrcElemTy, Ops, ResTy,
                                    GEP->getInRangeIndex(), DL, TLI))
     return C;
 
   Constant *Ptr = Ops[0];
   if (!Ptr->getType()->isPointerTy())

llvm/lib/CodeGen/CodeGenPrepare.cpp

case Intrinsic::strip_invariant_group: {
       return true;
     }
     case Intrinsic::cttz:
     case Intrinsic::ctlz:
       // If counting zeros is expensive, try to avoid it.
       return despeculateCountZeros(II, TLI, DL, ModifiedDT);
     case Intrinsic::dbg_value:
       return fixupDbgValue(II);
+    case Intrinsic::vscale: {
+      // If datalayout has no special restrictions on vector data layout,
+      // replace `llvm.vscale` by an equivalent constant expression
+      // to benefit from cheap constant propagation.
+      Type *ScalableVectorTy =
+          VectorType::get(Type::getInt8Ty(II->getContext()), 1, true);
+      if (DL->getTypeAllocSize(ScalableVectorTy).getKnownMinSize() == 8) {
+        auto Null = Constant::getNullValue(ScalableVectorTy->getPointerTo());
+        auto One = ConstantInt::getSigned(II->getType(), 1);
+        auto *CGep =
+            ConstantExpr::getGetElementPtr(ScalableVectorTy, Null, One);
+        II->replaceAllUsesWith(ConstantExpr::getPtrToInt(CGep, II->getType()));
+        II->eraseFromParent();
+        return true;
+      }
+    }
     }
 
     if (TLI) {
       SmallVector<Value*, 2> PtrOps;
       Type *AccessTy;
       if (TLI->getAddrModeArguments(II, PtrOps, AccessTy))
         while (!PtrOps.empty()) {
           Value *PtrVal = PtrOps.pop_back_val();

llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp

#endif
   case ISD::SHL:         Res = PromoteIntRes_SHL(N); break;
   case ISD::SIGN_EXTEND_INREG:
                          Res = PromoteIntRes_SIGN_EXTEND_INREG(N); break;
   case ISD::SRA:         Res = PromoteIntRes_SRA(N); break;
   case ISD::SRL:         Res = PromoteIntRes_SRL(N); break;
   case ISD::TRUNCATE:    Res = PromoteIntRes_TRUNCATE(N); break;
   case ISD::UNDEF:       Res = PromoteIntRes_UNDEF(N); break;
   case ISD::VAARG:       Res = PromoteIntRes_VAARG(N); break;
+  case ISD::VSCALE:      Res = PromoteIntRes_VSCALE(N); break;
 
   case ISD::EXTRACT_SUBVECTOR:
                          Res = PromoteIntRes_EXTRACT_SUBVECTOR(N); break;
   case ISD::VECTOR_SHUFFLE:
                          Res = PromoteIntRes_VECTOR_SHUFFLE(N); break;
   case ISD::INSERT_VECTOR_ELT:
                          Res = PromoteIntRes_INSERT_VECTOR_ELT(N); break;
   case ISD::BUILD_VECTOR:
SDValue DAGTypeLegalizer::PromoteIntRes_XMULO(SDNode *N, unsigned ResNo) {
   return Mul;
 }
 
 SDValue DAGTypeLegalizer::PromoteIntRes_UNDEF(SDNode *N) {
   return DAG.getUNDEF(TLI.getTypeToTransformTo(*DAG.getContext(),
                                                N->getValueType(0)));
 }
 
+SDValue DAGTypeLegalizer::PromoteIntRes_VSCALE(SDNode *N) {
+  EVT VT = TLI.getTypeToTransformTo(*DAG.getContext(), N->getValueType(0));
+
+  int64_t MulImm = cast<ConstantSDNode>(N->getOperand(0))->getSExtValue();
+  return DAG.getVScale(SDLoc(N), VT, MulImm);
+}
+
 SDValue DAGTypeLegalizer::PromoteIntRes_VAARG(SDNode *N) {
   SDValue Chain = N->getOperand(0); // Get the chain.
   SDValue Ptr = N->getOperand(1); // Get the pointer.
   EVT VT = N->getValueType(0);
   SDLoc dl(N);
 
   MVT RegVT = TLI.getRegisterType(*DAG.getContext(), VT);
   unsigned NumRegs = TLI.getNumRegisters(*DAG.getContext(), VT);

llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h

private:
   SDValue PromoteIntRes_SIGN_EXTEND_INREG(SDNode *N);
   SDValue PromoteIntRes_SRA(SDNode *N);
   SDValue PromoteIntRes_SRL(SDNode *N);
   SDValue PromoteIntRes_TRUNCATE(SDNode *N);
   SDValue PromoteIntRes_UADDSUBO(SDNode *N, unsigned ResNo);
   SDValue PromoteIntRes_ADDSUBCARRY(SDNode *N, unsigned ResNo);
   SDValue PromoteIntRes_UNDEF(SDNode *N);
   SDValue PromoteIntRes_VAARG(SDNode *N);
+  SDValue PromoteIntRes_VSCALE(SDNode *N);
   SDValue PromoteIntRes_XMULO(SDNode *N, unsigned ResNo);
   SDValue PromoteIntRes_ADDSUBSAT(SDNode *N);
   SDValue PromoteIntRes_MULFIX(SDNode *N);
   SDValue PromoteIntRes_FLT_ROUNDS(SDNode *N);
   SDValue PromoteIntRes_VECREDUCE(SDNode *N);
   SDValue PromoteIntRes_ABS(SDNode *N);
 
   // Integer Operand Promotion.

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

case ISD::SUB:
     assert(VT.isInteger() && "This operator does not apply to FP types!");
     assert(N1.getValueType() == N2.getValueType() &&
            N1.getValueType() == VT && "Binary operator types must match!");
     // (X ^|+- 0) -> X.  This commonly occurs when legalizing i64 values, so
     // it's worth handling here.
     if (N2C && N2C->isNullValue())
       return N1;
     break;
+  case ISD::MUL:
+    assert(VT.isInteger() && "This operator does not apply to FP types!");
+    assert(N1.getValueType() == N2.getValueType() &&
+           N1.getValueType() == VT && "Binary operator types must match!");
+    if (N2C && (N1.getOpcode() == ISD::VSCALE) && Flags.hasNoSignedWrap()) {
+      int64_t MulImm = cast<ConstantSDNode>(N1->getOperand(0))->getSExtValue();
+      return getVScale(DL, VT, MulImm * N2C->getSExtValue());
+    }
+    break;
   case ISD::UDIV:
   case ISD::UREM:
   case ISD::MULHU:
   case ISD::MULHS:
-  case ISD::MUL:
   case ISD::SDIV:
   case ISD::SREM:
   case ISD::SMIN:
   case ISD::SMAX:
   case ISD::UMIN:
   case ISD::UMAX:
   case ISD::SADDSAT:
   case ISD::SSUBSAT:
case ISD::FREM:
     break;
   case ISD::FCOPYSIGN:   // N1 and result must match.  N1/N2 need not match.
     assert(N1.getValueType() == VT &&
            N1.getValueType().isFloatingPoint() &&
            N2.getValueType().isFloatingPoint() &&
            "Invalid FCOPYSIGN!");
     break;
   case ISD::SHL:
+    if (N2C && (N1.getOpcode() == ISD::VSCALE) && Flags.hasNoSignedWrap()) {
+      int64_t MulImm = cast<ConstantSDNode>(N1->getOperand(0))->getSExtValue();
+      return getVScale(DL, VT, MulImm << N2C->getSExtValue());
+    }
+    LLVM_FALLTHROUGH;
   case ISD::SRA:
   case ISD::SRL:
     if (SDValue V = simplifyShift(N1, N2))
       return V;
     LLVM_FALLTHROUGH;
   case ISD::ROTL:
   case ISD::ROTR:
     assert(VT == N1.getValueType() &&

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

if (const GlobalValue *GV = dyn_cast<GlobalValue>(C))
       return DAG.getGlobalAddress(GV, getCurSDLoc(), VT);
 
     if (isa<ConstantPointerNull>(C)) {
       unsigned AS = V->getType()->getPointerAddressSpace();
       return DAG.getConstant(0, getCurSDLoc(),
                              TLI.getPointerTy(DAG.getDataLayout(), AS));
     }
 
+    if (match(C, m_VScale(DAG.getDataLayout())))
+      return DAG.getVScale(getCurSDLoc(), VT);
+
     if (const ConstantFP *CFP = dyn_cast<ConstantFP>(C))
       return DAG.getConstantFP(*CFP, getCurSDLoc(), VT);
 
     if (isa<UndefValue>(C) && !V->getType()->isAggregateType())
       return DAG.getUNDEF(VT);
 
     if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
       visit(CE->getOpcode(), *CE);
void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
   DebugLoc dl = getCurDebugLoc();
   SDValue Res;
 
   switch (Intrinsic) {
   default:
     // By default, turn this into a target intrinsic node.
     visitTargetIntrinsic(I, Intrinsic);
     return;
+  case Intrinsic::vscale: {
+    match(&I, m_VScale(DAG.getDataLayout()));
+    EVT VT = TLI.getValueType(DAG.getDataLayout(), I.getType());
+    setValue(&I, DAG.getVScale(getCurSDLoc(), VT));
+    return;
+  }
   case Intrinsic::vastart:  visitVAStart(I); return;
   case Intrinsic::vaend:    visitVAEnd(I); return;
   case Intrinsic::vacopy:   visitVACopy(I); return;
   case Intrinsic::returnaddress:
     setValue(&I, DAG.getNode(ISD::RETURNADDR, sdl,
                              TLI.getPointerTy(DAG.getDataLayout()),
                              getValue(I.getArgOperand(0))));
     return;

llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp

#endif
   case ISD::TargetConstantPool:         return "TargetConstantPool";
   case ISD::TargetExternalSymbol:       return "TargetExternalSymbol";
   case ISD::MCSymbol:                   return "MCSymbol";
   case ISD::TargetBlockAddress:         return "TargetBlockAddress";
 
   case ISD::CopyToReg:                  return "CopyToReg";
   case ISD::CopyFromReg:                return "CopyFromReg";
   case ISD::UNDEF:                      return "undef";
+  case ISD::VSCALE:                     return "vscale";
   case ISD::MERGE_VALUES:               return "merge_values";
   case ISD::INLINEASM:                  return "inlineasm";
   case ISD::INLINEASM_BR:               return "inlineasm_br";
   case ISD::EH_LABEL:                   return "eh_label";
   case ISD::ANNOTATION_LABEL:           return "annotation_label";
   case ISD::HANDLENODE:                 return "handlenode";
 
   // Unary operators

llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp

public:
   void Select(SDNode *Node) override;
 
   /// SelectInlineAsmMemoryOperand - Implement addressing mode selection for
   /// inline asm expressions.
   bool SelectInlineAsmMemoryOperand(const SDValue &Op,
                                     unsigned ConstraintID,
                                     std::vector<SDValue> &OutOps) override;
 
+  template <signed Low, signed High, signed Scale>
+  bool SelectRDVLImm(SDValue N, SDValue &Imm);
+
   bool tryMLAV64LaneV128(SDNode *N);
   bool tryMULLV64LaneV128(unsigned IntNo, SDNode *N);
   bool SelectArithExtendedRegister(SDValue N, SDValue &Reg, SDValue &Shift);
   bool SelectArithImmed(SDValue N, SDValue &Val, SDValue &Shift);
   bool SelectNegArithImmed(SDValue N, SDValue &Val, SDValue &Shift);
   bool SelectArithShiftedRegister(SDValue N, SDValue &Reg, SDValue &Shift) {
     return SelectShiftedRegister(N, false, Reg, Shift);
   }
static SDValue narrowIfNeeded(SelectionDAG *CurDAG, SDValue N) {
 
   SDLoc dl(N);
   SDValue SubReg = CurDAG->getTargetConstant(AArch64::sub_32, dl, MVT::i32);
   MachineSDNode *Node = CurDAG->getMachineNode(TargetOpcode::EXTRACT_SUBREG,
                                                dl, MVT::i32, N, SubReg);
   return SDValue(Node, 0);
 }
 
+// Returns a suitable CNT/INC/DEC/RDVL multiplier to calculate VSCALE*N.
+template<signed Low, signed High, signed Scale>
+bool AArch64DAGToDAGISel::SelectRDVLImm(SDValue N, SDValue &Imm) {
+  if (!isa<ConstantSDNode>(N))
+    return false;
+
+  int64_t MulImm = cast<ConstantSDNode>(N)->getSExtValue();
+  if ((MulImm % std::abs(Scale)) == 0) {
+    int64_t RDVLImm = MulImm / Scale;
+    if ((RDVLImm >= Low) && (RDVLImm <= High)) {
+      Imm = CurDAG->getTargetConstant(RDVLImm, SDLoc(N), MVT::i32);
+      return true;
+    }
+  }
+
+  return false;
+}
 
 /// SelectArithExtendedRegister - Select a "extended register" operand.  This
 /// operand folds in an extend followed by an optional left shift.
 bool AArch64DAGToDAGISel::SelectArithExtendedRegister(SDValue N, SDValue &Reg,
                                                       SDValue &Shift) {
   unsigned ShiftVal = 0;
   AArch64_AM::ShiftExtendType Ext;
 

llvm/lib/Target/AArch64/AArch64ISelLowering.h

private:
   SDValue LowerFP_EXTEND(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerFP_ROUND(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVectorFP_TO_INT(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerFP_TO_INT(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerINT_TO_FP(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVectorOR(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerCONCAT_VECTORS(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerFSINCOS(SDValue Op, SelectionDAG &DAG) const;
+  SDValue LowerVSCALE(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVECREDUCE(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerATOMIC_LOAD_SUB(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerATOMIC_LOAD_AND(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerDYNAMIC_STACKALLOC(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerWindowsDYNAMIC_STACKALLOC(SDValue Op, SDValue Chain,
                                          SDValue &Size,
                                          SelectionDAG &DAG) const;
 

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

if (Subtarget->hasFullFP16()) {
         setOperationAction(ISD::FNEARBYINT, Ty, Legal);
         setOperationAction(ISD::FCEIL, Ty, Legal);
         setOperationAction(ISD::FRINT, Ty, Legal);
         setOperationAction(ISD::FTRUNC, Ty, Legal);
         setOperationAction(ISD::FROUND, Ty, Legal);
       }
     }
 
+    if (Subtarget->hasSVE())
+      setOperationAction(ISD::VSCALE, MVT::i32, Custom);
+
     setTruncStoreAction(MVT::v4i16, MVT::v4i8, Custom);
   }
 
   if (Subtarget->hasSVE()) {
     // FIXME: Add custom lowering of MLOAD to handle different passthrus (not a
     // splat of 0 or undef) once vector selects supported in SVE codegen. See
     // D68877 for more details.
     for (MVT VT : MVT::integer_scalable_vector_valuetypes()) {
SDValue AArch64TargetLowering::LowerOperation(SDValue Op,
   case ISD::VECREDUCE_FMIN:
     return LowerVECREDUCE(Op, DAG);
   case ISD::ATOMIC_LOAD_SUB:
     return LowerATOMIC_LOAD_SUB(Op, DAG);
   case ISD::ATOMIC_LOAD_AND:
     return LowerATOMIC_LOAD_AND(Op, DAG);
   case ISD::DYNAMIC_STACKALLOC:
     return LowerDYNAMIC_STACKALLOC(Op, DAG);
+  case ISD::VSCALE:
+    return LowerVSCALE(Op, DAG);
   }
 }
 
 //===----------------------------------------------------------------------===//
 //                      Calling Convention Implementation
 //===----------------------------------------------------------------------===//
 
 /// Selects the correct CCAssignFn for a given CallingConvention value.
AArch64TargetLowering::LowerDYNAMIC_STACKALLOC(SDValue Op,
 
   Chain = DAG.getCALLSEQ_END(Chain, DAG.getIntPtrConstant(0, dl, true),
                              DAG.getIntPtrConstant(0, dl, true), SDValue(), dl);
 
   SDValue Ops[2] = {SP, Chain};
   return DAG.getMergeValues(Ops, dl);
 }
 
+SDValue AArch64TargetLowering::LowerVSCALE(SDValue Op,
+                                           SelectionDAG &DAG) const {
+  EVT VT = Op.getValueType();
+  assert(VT != MVT::i64 && "Expected illegal VSCALE node");
+
+  SDLoc DL(Op);
+  int64_t MulImm = cast<ConstantSDNode>(Op.getOperand(0))->getSExtValue();
+  return DAG.getZExtOrTrunc(DAG.getVScale(DL, MVT::i64, MulImm), DL, VT);
+}
+
 /// getTgtMemIntrinsic - Represent NEON load and store intrinsics as
 /// MemIntrinsicNodes.  The associated MachineMemOperands record the alignment
 /// specified in the intrinsic calls.
 bool AArch64TargetLowering::getTgtMemIntrinsic(IntrinsicInfo &Info,
                                                const CallInst &I,
                                                MachineFunction &MF,
                                                unsigned Intrinsic) const {
   auto &DL = I.getModule()->getDataLayout();

llvm/lib/Target/AArch64/AArch64SVEInstrInfo.td

 def AArch64ld1_gather                : SDNode<"AArch64ISD::GLD1",               SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1_gather_scaled         : SDNode<"AArch64ISD::GLD1_SCALED",        SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1_gather_uxtw           : SDNode<"AArch64ISD::GLD1_UXTW",          SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1_gather_sxtw           : SDNode<"AArch64ISD::GLD1_SXTW",          SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1_gather_uxtw_scaled    : SDNode<"AArch64ISD::GLD1_UXTW_SCALED",   SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1_gather_sxtw_scaled    : SDNode<"AArch64ISD::GLD1_SXTW_SCALED",   SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1_gather_imm            : SDNode<"AArch64ISD::GLD1_IMM",           SDT_AArch64_GLD1_IMM, [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 
+// SVE CNT/INC/RDVL
+def sve_rdvl_imm : ComplexPattern<i32, 1, "SelectRDVLImm<-32, 31, 16>">;
+def sve_cnth_imm : ComplexPattern<i32, 1, "SelectRDVLImm<1, 16, 8>">;
+def sve_cntw_imm : ComplexPattern<i32, 1, "SelectRDVLImm<1, 16, 4>">;
+def sve_cntd_imm : ComplexPattern<i32, 1, "SelectRDVLImm<1, 16, 2>">;
+
+// SVE DEC
+def sve_cnth_imm_neg : ComplexPattern<i32, 1, "SelectRDVLImm<1, 16, -8>">;
+def sve_cntw_imm_neg : ComplexPattern<i32, 1, "SelectRDVLImm<1, 16, -4>">;
+def sve_cntd_imm_neg : ComplexPattern<i32, 1, "SelectRDVLImm<1, 16, -2>">;
+
 def AArch64ld1s_gather               : SDNode<"AArch64ISD::GLD1S",              SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1s_gather_scaled        : SDNode<"AArch64ISD::GLD1S_SCALED",       SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1s_gather_uxtw          : SDNode<"AArch64ISD::GLD1S_UXTW",         SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1s_gather_sxtw          : SDNode<"AArch64ISD::GLD1S_SXTW",         SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1s_gather_uxtw_scaled   : SDNode<"AArch64ISD::GLD1S_UXTW_SCALED",  SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1s_gather_sxtw_scaled   : SDNode<"AArch64ISD::GLD1S_SXTW_SCALED",  SDT_AArch64_GLD1,     [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 def AArch64ld1s_gather_imm           : SDNode<"AArch64ISD::GLD1S_IMM",          SDT_AArch64_GLD1_IMM, [SDNPHasChain, SDNPMayLoad, SDNPOptInGlue]>;
 

 
   def : Pat<(sext_inreg (nxv2i64 ZPR:$Zs), nxv2i32), (SXTW_ZPmZ_D (IMPLICIT_DEF), (PTRUE_D 31), ZPR:$Zs)>;
   def : Pat<(sext_inreg (nxv2i64 ZPR:$Zs), nxv2i16), (SXTH_ZPmZ_D (IMPLICIT_DEF), (PTRUE_D 31), ZPR:$Zs)>;
   def : Pat<(sext_inreg (nxv2i64 ZPR:$Zs), nxv2i8),  (SXTB_ZPmZ_D (IMPLICIT_DEF), (PTRUE_D 31), ZPR:$Zs)>;
   def : Pat<(sext_inreg (nxv4i32 ZPR:$Zs), nxv4i16), (SXTH_ZPmZ_S (IMPLICIT_DEF), (PTRUE_S 31), ZPR:$Zs)>;
   def : Pat<(sext_inreg (nxv4i32 ZPR:$Zs), nxv4i8),  (SXTB_ZPmZ_S (IMPLICIT_DEF), (PTRUE_S 31), ZPR:$Zs)>;
   def : Pat<(sext_inreg (nxv8i16 ZPR:$Zs), nxv8i8),  (SXTB_ZPmZ_H (IMPLICIT_DEF), (PTRUE_H 31), ZPR:$Zs)>;
 
+  // General case that we ideally never want to match.
+  def : Pat<(vscale GPR64:$scale), (MADDXrrr (UBFMXri (RDVLI_XI 1), 4, 63), $scale, XZR)>;
+
+  let AddedComplexity = 5 in {
+    def : Pat<(vscale (i64 1)), (UBFMXri (RDVLI_XI 1), 4, 63)>;
+    def : Pat<(vscale (i64 -1)), (SBFMXri (RDVLI_XI -1), 4, 63)>;
+
+    def : Pat<(vscale (sve_rdvl_imm i32:$imm)), (RDVLI_XI $imm)>;
+    def : Pat<(vscale (sve_cnth_imm i32:$imm)), (CNTH_XPiI 31, $imm)>;
+    def : Pat<(vscale (sve_cntw_imm i32:$imm)), (CNTW_XPiI 31, $imm)>;
+    def : Pat<(vscale (sve_cntd_imm i32:$imm)), (CNTD_XPiI 31, $imm)>;
+
+    def : Pat<(vscale (sve_cnth_imm_neg i32:$imm)), (SUBXrs XZR, (CNTH_XPiI 31, $imm), 0)>;
+    def : Pat<(vscale (sve_cntw_imm_neg i32:$imm)), (SUBXrs XZR, (CNTW_XPiI 31, $imm), 0)>;
+    def : Pat<(vscale (sve_cntd_imm_neg i32:$imm)), (SUBXrs XZR, (CNTD_XPiI 31, $imm), 0)>;
+  }
+
   def : Pat<(nxv16i8 (bitconvert (nxv8i16 ZPR:$src))), (nxv16i8 ZPR:$src)>;
   def : Pat<(nxv16i8 (bitconvert (nxv4i32 ZPR:$src))), (nxv16i8 ZPR:$src)>;
   def : Pat<(nxv16i8 (bitconvert (nxv2i64 ZPR:$src))), (nxv16i8 ZPR:$src)>;
   def : Pat<(nxv16i8 (bitconvert (nxv8f16 ZPR:$src))), (nxv16i8 ZPR:$src)>;
   def : Pat<(nxv16i8 (bitconvert (nxv4f32 ZPR:$src))), (nxv16i8 ZPR:$src)>;
   def : Pat<(nxv16i8 (bitconvert (nxv2f64 ZPR:$src))), (nxv16i8 ZPR:$src)>;
 
   def : Pat<(nxv8i16 (bitconvert (nxv16i8 ZPR:$src))), (nxv8i16 ZPR:$src)>;

llvm/test/CodeGen/AArch64/sve-vscale.ll

+; RUN: llc -mtriple aarch64 -mattr=+sve -asm-verbose=0 < %s | FileCheck %s
+; RUN: opt -codegenprepare -S < %s | llc -mtriple aarch64 -mattr=+sve -asm-verbose=0 | FileCheck %s
+
+;
+; RDVL
+;
+
+; CHECK-LABEL: rdvl_i8:
+; CHECK:       rdvl x0, #1
+; CHECK-NEXT:  ret
+define i8 @rdvl_i8() nounwind {
+  %vscale = call i8 @llvm.vscale.i8()
+  %1 = mul nsw i8 %vscale, 16
+  ret i8 %1
+}
+
+; CHECK-LABEL: rdvl_i16:
+; CHECK:       rdvl x0, #1
+; CHECK-NEXT:  ret
+define i16 @rdvl_i16() nounwind {
+  %vscale = call i16 @llvm.vscale.i16()
+  %1 = mul nsw i16 %vscale, 16
+  ret i16 %1
+}
+
+; CHECK-LABEL: rdvl_i32:
+; CHECK:       rdvl x0, #1
+; CHECK-NEXT:  ret
+define i32 @rdvl_i32() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, 16
+  ret i32 %1
+}
+
+; CHECK-LABEL: rdvl_i64:
+; CHECK:       rdvl x0, #1
+; CHECK-NEXT:  ret
+define i64 @rdvl_i64() nounwind {
+  %vscale = call i64 @llvm.vscale.i64()
+  %1 = mul nsw i64 %vscale, 16
+  ret i64 %1
+}
+
+; CHECK-LABEL: rdvl_const:
+; CHECK:       rdvl x0, #1
+; CHECK-NEXT:  ret
+define i32 @rdvl_const() nounwind {
+  ret i32 mul nsw (i32 ptrtoint (<vscale x 1 x i8>* getelementptr (<vscale x 1 x i8>, <vscale x 1 x i8>* null, i64 1) to i32), i32 16)
+}
+
+define i32 @vscale_1() nounwind {
+; CHECK-LABEL: vscale_1:
+; CHECK:       rdvl [[TMP:x[0-9]+]], #1
+; CHECK-NEXT:  lsr  x0, [[TMP]], #4
+; CHECK-NEXT:  ret
+  %vscale = call i32 @llvm.vscale.i32()
+  ret i32 %vscale
+}
+
+define i32 @vscale_neg1() nounwind {
+; CHECK-LABEL: vscale_neg1:
+; CHECK:       rdvl [[TMP:x[0-9]+]], #-1
+; CHECK-NEXT:  asr  x0, [[TMP]], #4
+; CHECK-NEXT:  ret
+  %vscale = call i32 @llvm.vscale.i32()
+  %neg = mul nsw i32 -1, %vscale
+  ret i32 %neg
+}
+
+; CHECK-LABEL: rdvl_3:
+; CHECK:       rdvl [[VL_B:x[0-9]+]], #1
+; CHECK-NEXT:  lsr  [[VL_Q:x[0-9]+]], [[VL_B]], #4
+; CHECK-NEXT:  mov  w[[MUL:[0-9]+]], #3
+; CHECK-NEXT:  mul  x0, [[VL_Q]], x[[MUL]]
+; CHECK-NEXT:  ret
+define i32 @rdvl_3() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, 3
+  ret i32 %1
+}
+
+
+; CHECK-LABEL: rdvl_min:
+; CHECK:       rdvl x0, #-32
+; CHECK-NEXT:  ret
+define i32 @rdvl_min() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, -512
+  ret i32 %1
+}
+
+; CHECK-LABEL: rdvl_max:
+; CHECK:       rdvl x0, #31
+; CHECK-NEXT:  ret
+define i32 @rdvl_max() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, 496
+  ret i32 %1
+}
+
+;
+; CNTH
+;
+
+; CHECK-LABEL: cnth:
+; CHECK:       cnth x0{{$}}
+; CHECK-NEXT:  ret
+define i32 @cnth() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = shl nsw i32 %vscale, 3
+  ret i32 %1
+}
+
+; CHECK-LABEL: cnth_max:
+; CHECK:       cnth x0, all, mul #15
+; CHECK-NEXT:  ret
+define i32 @cnth_max() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, 120
+  ret i32 %1
+}
+
+; CHECK-LABEL: cnth_neg:
+; CHECK:       cnth [[CNT:x[0-9]+]]
+; CHECK:       neg x0, [[CNT]]
+; CHECK-NEXT:  ret
+define i32 @cnth_neg() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, -8
+  ret i32 %1
+}
+
+;
+; CNTW
+;
+
+; CHECK-LABEL: cntw:
+; CHECK:       cntw x0{{$}}
+; CHECK-NEXT:  ret
+define i32 @cntw() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = shl nsw i32 %vscale, 2
+  ret i32 %1
+}
+
+; CHECK-LABEL: cntw_max:
+; CHECK:       cntw x0, all, mul #15
+; CHECK-NEXT:  ret
+define i32 @cntw_max() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, 60
+  ret i32 %1
+}
+
+; CHECK-LABEL: cntw_neg:
+; CHECK:       cntw [[CNT:x[0-9]+]]
+; CHECK:       neg x0, [[CNT]]
+; CHECK-NEXT:  ret
+define i32 @cntw_neg() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, -4
+  ret i32 %1
+}
+
+;
+; CNTD
+;
+
+; CHECK-LABEL: cntd:
+; CHECK:       cntd x0{{$}}
+; CHECK-NEXT:  ret
+define i32 @cntd() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = shl nsw i32 %vscale, 1
+  ret i32 %1
+}
+
+; CHECK-LABEL: cntd_max:
+; CHECK:       cntd x0, all, mul #15
+; CHECK-NEXT:  ret
+define i32 @cntd_max() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, 30
+  ret i32 %1
+}
+
+; CHECK-LABEL: cntd_neg:
+; CHECK:       cntd [[CNT:x[0-9]+]]
+; CHECK:       neg x0, [[CNT]]
+; CHECK-NEXT:  ret
+define i32 @cntd_neg() nounwind {
+  %vscale = call i32 @llvm.vscale.i32()
+  %1 = mul nsw i32 %vscale, -2
+  ret i32 %1
+}
+
+declare i8 @llvm.vscale.i8()
+declare i16 @llvm.vscale.i16()
+declare i32 @llvm.vscale.i32()
+declare i64 @llvm.vscale.i64()