[AArch64] SME implementation for agnostic-ZA functions (#120150)

This implements the lowering of calls from agnostic-ZA functions to
non-agnostic-ZA functions, using the ABI routines
`__arm_sme_state_size`, `__arm_sme_save` and `__arm_sme_restore`.

This implements the proposal described in the following PRs:
* ARM-software/acle#336
* ARM-software/abi-aa#264

Author: sdesmalen-arm

llvm/lib/IR/Verifier.cpp

@@ -2268,19 +2268,23 @@ void Verifier::verifyFunctionAttrs(FunctionType *FT, AttributeList Attrs,
   Check((Attrs.hasFnAttr("aarch64_new_za") + Attrs.hasFnAttr("aarch64_in_za") +
          Attrs.hasFnAttr("aarch64_inout_za") +
          Attrs.hasFnAttr("aarch64_out_za") +
-         Attrs.hasFnAttr("aarch64_preserves_za")) <= 1,
+         Attrs.hasFnAttr("aarch64_preserves_za") +
+         Attrs.hasFnAttr("aarch64_za_state_agnostic")) <= 1,
         "Attributes 'aarch64_new_za', 'aarch64_in_za', 'aarch64_out_za', "
-        "'aarch64_inout_za' and 'aarch64_preserves_za' are mutually exclusive",
+        "'aarch64_inout_za', 'aarch64_preserves_za' and "
+        "'aarch64_za_state_agnostic' are mutually exclusive",
         V);
 
-  Check(
-      (Attrs.hasFnAttr("aarch64_new_zt0") + Attrs.hasFnAttr("aarch64_in_zt0") +
-       Attrs.hasFnAttr("aarch64_inout_zt0") +
-       Attrs.hasFnAttr("aarch64_out_zt0") +
-       Attrs.hasFnAttr("aarch64_preserves_zt0")) <= 1,
-      "Attributes 'aarch64_new_zt0', 'aarch64_in_zt0', 'aarch64_out_zt0', "
-      "'aarch64_inout_zt0' and 'aarch64_preserves_zt0' are mutually exclusive",
-      V);
+  Check((Attrs.hasFnAttr("aarch64_new_zt0") +
+         Attrs.hasFnAttr("aarch64_in_zt0") +
+         Attrs.hasFnAttr("aarch64_inout_zt0") +
+         Attrs.hasFnAttr("aarch64_out_zt0") +
+         Attrs.hasFnAttr("aarch64_preserves_zt0") +
+         Attrs.hasFnAttr("aarch64_za_state_agnostic")) <= 1,
+        "Attributes 'aarch64_new_zt0', 'aarch64_in_zt0', 'aarch64_out_zt0', "
+        "'aarch64_inout_zt0', 'aarch64_preserves_zt0' and "
+        "'aarch64_za_state_agnostic' are mutually exclusive",
+        V);
 
   if (Attrs.hasFnAttr(Attribute::JumpTable)) {
     const GlobalValue *GV = cast<GlobalValue>(V);

llvm/lib/Target/AArch64/AArch64FastISel.cpp

@@ -5197,7 +5197,8 @@ FastISel *AArch64::createFastISel(FunctionLoweringInfo &FuncInfo,
   SMEAttrs CallerAttrs(*FuncInfo.Fn);
   if (CallerAttrs.hasZAState() || CallerAttrs.hasZT0State() ||
       CallerAttrs.hasStreamingInterfaceOrBody() ||
-      CallerAttrs.hasStreamingCompatibleInterface())
+      CallerAttrs.hasStreamingCompatibleInterface() ||
+      CallerAttrs.hasAgnosticZAInterface())
     return nullptr;
   return new AArch64FastISel(FuncInfo, LibInfo);
 }

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -2643,6 +2643,8 @@ const char *AArch64TargetLowering::getTargetNodeName(unsigned Opcode) const {
     break;
     MAKE_CASE(AArch64ISD::ALLOCATE_ZA_BUFFER)
     MAKE_CASE(AArch64ISD::INIT_TPIDR2OBJ)
+    MAKE_CASE(AArch64ISD::GET_SME_SAVE_SIZE)
+    MAKE_CASE(AArch64ISD::ALLOC_SME_SAVE_BUFFER)
     MAKE_CASE(AArch64ISD::COALESCER_BARRIER)
     MAKE_CASE(AArch64ISD::VG_SAVE)
     MAKE_CASE(AArch64ISD::VG_RESTORE)
@@ -3230,6 +3232,64 @@ AArch64TargetLowering::EmitAllocateZABuffer(MachineInstr &MI,
   return BB;
 }
 
+// TODO: Find a way to merge this with EmitAllocateZABuffer.
+MachineBasicBlock *
+AArch64TargetLowering::EmitAllocateSMESaveBuffer(MachineInstr &MI,
+                                                 MachineBasicBlock *BB) const {
+  MachineFunction *MF = BB->getParent();
+  MachineFrameInfo &MFI = MF->getFrameInfo();
+  AArch64FunctionInfo *FuncInfo = MF->getInfo<AArch64FunctionInfo>();
+  assert(!MF->getSubtarget<AArch64Subtarget>().isTargetWindows() &&
+         "Lazy ZA save is not yet supported on Windows");
+
+  const TargetInstrInfo *TII = Subtarget->getInstrInfo();
+  if (FuncInfo->isSMESaveBufferUsed()) {
+    // Allocate a buffer object of the size given by MI.getOperand(1).
+    auto Size = MI.getOperand(1).getReg();
+    auto Dest = MI.getOperand(0).getReg();
+    BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(AArch64::SUBXrx64), AArch64::SP)
+        .addReg(AArch64::SP)
+        .addReg(Size)
+        .addImm(AArch64_AM::getArithExtendImm(AArch64_AM::UXTX, 0));
+    BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(TargetOpcode::COPY), Dest)
+        .addReg(AArch64::SP);
+
+    // We have just allocated a variable sized object, tell this to PEI.
+    MFI.CreateVariableSizedObject(Align(16), nullptr);
+  } else
+    BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(TargetOpcode::IMPLICIT_DEF),
+            MI.getOperand(0).getReg());
+
+  BB->remove_instr(&MI);
+  return BB;
+}
+
+MachineBasicBlock *
+AArch64TargetLowering::EmitGetSMESaveSize(MachineInstr &MI,
+                                          MachineBasicBlock *BB) const {
+  // If the buffer is used, emit a call to __arm_sme_state_size()
+  MachineFunction *MF = BB->getParent();
+  AArch64FunctionInfo *FuncInfo = MF->getInfo<AArch64FunctionInfo>();
+  const TargetInstrInfo *TII = Subtarget->getInstrInfo();
+  if (FuncInfo->isSMESaveBufferUsed()) {
+    const AArch64RegisterInfo *TRI = Subtarget->getRegisterInfo();
+    BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(AArch64::BL))
+        .addExternalSymbol("__arm_sme_state_size")
+        .addReg(AArch64::X0, RegState::ImplicitDefine)
+        .addRegMask(TRI->getCallPreservedMask(
+            *MF, CallingConv::
+                     AArch64_SME_ABI_Support_Routines_PreserveMost_From_X1));
+    BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(TargetOpcode::COPY),
+            MI.getOperand(0).getReg())
+        .addReg(AArch64::X0);
+  } else
+    BuildMI(*BB, MI, MI.getDebugLoc(), TII->get(TargetOpcode::COPY),
+            MI.getOperand(0).getReg())
+        .addReg(AArch64::XZR);
+  BB->remove_instr(&MI);
+  return BB;
+}
+
 MachineBasicBlock *AArch64TargetLowering::EmitInstrWithCustomInserter(
     MachineInstr &MI, MachineBasicBlock *BB) const {
 
@@ -3264,6 +3324,10 @@ MachineBasicBlock *AArch64TargetLowering::EmitInstrWithCustomInserter(
     return EmitInitTPIDR2Object(MI, BB);
   case AArch64::AllocateZABuffer:
     return EmitAllocateZABuffer(MI, BB);
+  case AArch64::AllocateSMESaveBuffer:
+    return EmitAllocateSMESaveBuffer(MI, BB);
+  case AArch64::GetSMESaveSize:
+    return EmitGetSMESaveSize(MI, BB);
   case AArch64::F128CSEL:
     return EmitF128CSEL(MI, BB);
   case TargetOpcode::STATEPOINT:
@@ -7663,6 +7727,7 @@ CCAssignFn *AArch64TargetLowering::CCAssignFnForCall(CallingConv::ID CC,
   case CallingConv::AArch64_VectorCall:
   case CallingConv::AArch64_SVE_VectorCall:
   case CallingConv::AArch64_SME_ABI_Support_Routines_PreserveMost_From_X0:
+  case CallingConv::AArch64_SME_ABI_Support_Routines_PreserveMost_From_X1:
   case CallingConv::AArch64_SME_ABI_Support_Routines_PreserveMost_From_X2:
     return CC_AArch64_AAPCS;
   case CallingConv::ARM64EC_Thunk_X64:
@@ -8122,6 +8187,31 @@ SDValue AArch64TargetLowering::LowerFormalArguments(
     Chain = DAG.getNode(
         AArch64ISD::INIT_TPIDR2OBJ, DL, DAG.getVTList(MVT::Other),
         {/*Chain*/ Buffer.getValue(1), /*Buffer ptr*/ Buffer.getValue(0)});
+  } else if (SMEAttrs(MF.getFunction()).hasAgnosticZAInterface()) {
+    // Call __arm_sme_state_size().
+    SDValue BufferSize =
+        DAG.getNode(AArch64ISD::GET_SME_SAVE_SIZE, DL,
+                    DAG.getVTList(MVT::i64, MVT::Other), Chain);
+    Chain = BufferSize.getValue(1);
+
+    SDValue Buffer;
+    if (!Subtarget->isTargetWindows() && !hasInlineStackProbe(MF)) {
+      Buffer =
+          DAG.getNode(AArch64ISD::ALLOC_SME_SAVE_BUFFER, DL,
+                      DAG.getVTList(MVT::i64, MVT::Other), {Chain, BufferSize});
+    } else {
+      // Allocate space dynamically.
+      Buffer = DAG.getNode(
+          ISD::DYNAMIC_STACKALLOC, DL, DAG.getVTList(MVT::i64, MVT::Other),
+          {Chain, BufferSize, DAG.getConstant(1, DL, MVT::i64)});
+      MFI.CreateVariableSizedObject(Align(16), nullptr);
+    }
+
+    // Copy the value to a virtual register, and save that in FuncInfo.
+    Register BufferPtr =
+        MF.getRegInfo().createVirtualRegister(&AArch64::GPR64RegClass);
+    FuncInfo->setSMESaveBufferAddr(BufferPtr);
+    Chain = DAG.getCopyToReg(Chain, DL, BufferPtr, Buffer);
   }
 
   if (CallConv == CallingConv::PreserveNone) {
@@ -8410,6 +8500,7 @@ bool AArch64TargetLowering::isEligibleForTailCallOptimization(
   auto CalleeAttrs = CLI.CB ? SMEAttrs(*CLI.CB) : SMEAttrs(SMEAttrs::Normal);
   if (CallerAttrs.requiresSMChange(CalleeAttrs) ||
       CallerAttrs.requiresLazySave(CalleeAttrs) ||
+      CallerAttrs.requiresPreservingAllZAState(CalleeAttrs) ||
       CallerAttrs.hasStreamingBody())
     return false;
 
@@ -8734,6 +8825,33 @@ SDValue AArch64TargetLowering::changeStreamingMode(SelectionDAG &DAG, SDLoc DL,
   return DAG.getNode(Opcode, DL, DAG.getVTList(MVT::Other, MVT::Glue), Ops);
 }
 
+// Emit a call to __arm_sme_save or __arm_sme_restore.
+static SDValue emitSMEStateSaveRestore(const AArch64TargetLowering &TLI,
+                                       SelectionDAG &DAG,
+                                       AArch64FunctionInfo *Info, SDLoc DL,
+                                       SDValue Chain, bool IsSave) {
+  MachineFunction &MF = DAG.getMachineFunction();
+  AArch64FunctionInfo *FuncInfo = MF.getInfo<AArch64FunctionInfo>();
+  FuncInfo->setSMESaveBufferUsed();
+
+  TargetLowering::ArgListTy Args;
+  TargetLowering::ArgListEntry Entry;
+  Entry.Ty = PointerType::getUnqual(*DAG.getContext());
+  Entry.Node =
+      DAG.getCopyFromReg(Chain, DL, Info->getSMESaveBufferAddr(), MVT::i64);
+  Args.push_back(Entry);
+
+  SDValue Callee =
+      DAG.getExternalSymbol(IsSave ? "__arm_sme_save" : "__arm_sme_restore",
+                            TLI.getPointerTy(DAG.getDataLayout()));
+  auto *RetTy = Type::getVoidTy(*DAG.getContext());
+  TargetLowering::CallLoweringInfo CLI(DAG);
+  CLI.setDebugLoc(DL).setChain(Chain).setLibCallee(
+      CallingConv::AArch64_SME_ABI_Support_Routines_PreserveMost_From_X1, RetTy,
+      Callee, std::move(Args));
+  return TLI.LowerCallTo(CLI).second;
+}
+
 static unsigned getSMCondition(const SMEAttrs &CallerAttrs,
                                const SMEAttrs &CalleeAttrs) {
   if (!CallerAttrs.hasStreamingCompatibleInterface() ||
@@ -8894,6 +9012,8 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
   };
 
   bool RequiresLazySave = CallerAttrs.requiresLazySave(CalleeAttrs);
+  bool RequiresSaveAllZA =
+      CallerAttrs.requiresPreservingAllZAState(CalleeAttrs);
   if (RequiresLazySave) {
     const TPIDR2Object &TPIDR2 = FuncInfo->getTPIDR2Obj();
     MachinePointerInfo MPI =
@@ -8920,6 +9040,11 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
                                                    &MF.getFunction());
       return DescribeCallsite(R) << " sets up a lazy save for ZA";
     });
+  } else if (RequiresSaveAllZA) {
+    assert(!CalleeAttrs.hasSharedZAInterface() &&
+           "Cannot share state that may not exist");
+    Chain = emitSMEStateSaveRestore(*this, DAG, FuncInfo, DL, Chain,
+                                    /*IsSave=*/true);
   }
 
   SDValue PStateSM;
@@ -9467,9 +9592,13 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
         DAG.getConstant(Intrinsic::aarch64_sme_set_tpidr2, DL, MVT::i32),
         DAG.getConstant(0, DL, MVT::i64));
     TPIDR2.Uses++;
+  } else if (RequiresSaveAllZA) {
+    Result = emitSMEStateSaveRestore(*this, DAG, FuncInfo, DL, Chain,
+                                     /*IsSave=*/false);
   }
 
-  if (RequiresSMChange || RequiresLazySave || ShouldPreserveZT0) {
+  if (RequiresSMChange || RequiresLazySave || ShouldPreserveZT0 ||
+      RequiresSaveAllZA) {
     for (unsigned I = 0; I < InVals.size(); ++I) {
       // The smstart/smstop is chained as part of the call, but when the
       // resulting chain is discarded (which happens when the call is not part
@@ -28084,7 +28213,8 @@ bool AArch64TargetLowering::fallBackToDAGISel(const Instruction &Inst) const {
     auto CalleeAttrs = SMEAttrs(*Base);
     if (CallerAttrs.requiresSMChange(CalleeAttrs) ||
         CallerAttrs.requiresLazySave(CalleeAttrs) ||
-        CallerAttrs.requiresPreservingZT0(CalleeAttrs))
+        CallerAttrs.requiresPreservingZT0(CalleeAttrs) ||
+        CallerAttrs.requiresPreservingAllZAState(CalleeAttrs))
       return true;
   }
   return false;

llvm/lib/Target/AArch64/AArch64ISelLowering.h

@@ -466,6 +466,10 @@ enum NodeType : unsigned {
   ALLOCATE_ZA_BUFFER,
   INIT_TPIDR2OBJ,
 
+  // Needed for __arm_agnostic("sme_za_state")
+  GET_SME_SAVE_SIZE,
+  ALLOC_SME_SAVE_BUFFER,
+
   // Asserts that a function argument (i32) is zero-extended to i8 by
   // the caller
   ASSERT_ZEXT_BOOL,
@@ -667,6 +671,10 @@ class AArch64TargetLowering : public TargetLowering {
                                           MachineBasicBlock *BB) const;
   MachineBasicBlock *EmitAllocateZABuffer(MachineInstr &MI,
                                           MachineBasicBlock *BB) const;
+  MachineBasicBlock *EmitAllocateSMESaveBuffer(MachineInstr &MI,
+                                               MachineBasicBlock *BB) const;
+  MachineBasicBlock *EmitGetSMESaveSize(MachineInstr &MI,
+                                        MachineBasicBlock *BB) const;
 
   MachineBasicBlock *
   EmitInstrWithCustomInserter(MachineInstr &MI,

llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.h

@@ -229,6 +229,14 @@ class AArch64FunctionInfo final : public MachineFunctionInfo {
   // on function entry to record the initial pstate of a function.
   Register PStateSMReg = MCRegister::NoRegister;
 
+  // Holds a pointer to a buffer that is large enough to represent
+  // all SME ZA state and any additional state required by the
+  // __arm_sme_save/restore support routines.
+  Register SMESaveBufferAddr = MCRegister::NoRegister;
+
+  // true if SMESaveBufferAddr is used.
+  bool SMESaveBufferUsed = false;
+
   // Has the PNReg used to build PTRUE instruction.
   // The PTRUE is used for the LD/ST of ZReg pairs in save and restore.
   unsigned PredicateRegForFillSpill = 0;
@@ -252,6 +260,12 @@ class AArch64FunctionInfo final : public MachineFunctionInfo {
     return PredicateRegForFillSpill;
   }
 
+  Register getSMESaveBufferAddr() const { return SMESaveBufferAddr; };
+  void setSMESaveBufferAddr(Register Reg) { SMESaveBufferAddr = Reg; };
+
+  unsigned isSMESaveBufferUsed() const { return SMESaveBufferUsed; };
+  void setSMESaveBufferUsed(bool Used = true) { SMESaveBufferUsed = Used; };
+
   Register getPStateSMReg() const { return PStateSMReg; };
   void setPStateSMReg(Register Reg) { PStateSMReg = Reg; };
 

llvm/lib/Target/AArch64/AArch64SMEInstrInfo.td

@@ -52,6 +52,22 @@ let usesCustomInserter = 1 in {
   def InitTPIDR2Obj : Pseudo<(outs), (ins GPR64:$buffer), [(AArch64InitTPIDR2Obj GPR64:$buffer)]>, Sched<[WriteI]> {}
 }
 
+// Nodes to allocate a save buffer for SME.
+def AArch64SMESaveSize : SDNode<"AArch64ISD::GET_SME_SAVE_SIZE", SDTypeProfile<1, 0,
+                               [SDTCisInt<0>]>, [SDNPHasChain]>;
+let usesCustomInserter = 1, Defs = [X0] in {
+  def GetSMESaveSize : Pseudo<(outs GPR64:$dst), (ins), []>, Sched<[]> {}
+}
+def : Pat<(i64 AArch64SMESaveSize), (GetSMESaveSize)>;
+
+def AArch64AllocateSMESaveBuffer : SDNode<"AArch64ISD::ALLOC_SME_SAVE_BUFFER", SDTypeProfile<1, 1,
+                                          [SDTCisInt<0>, SDTCisInt<1>]>, [SDNPHasChain]>;
+let usesCustomInserter = 1, Defs = [SP] in {
+  def AllocateSMESaveBuffer : Pseudo<(outs GPR64sp:$dst), (ins GPR64:$size), []>, Sched<[WriteI]> {}
+}
+def : Pat<(i64 (AArch64AllocateSMESaveBuffer GPR64:$size)),
+          (AllocateSMESaveBuffer $size)>;
+
 //===----------------------------------------------------------------------===//
 // Instruction naming conventions.
 //===----------------------------------------------------------------------===//

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -261,7 +261,8 @@ bool AArch64TTIImpl::areInlineCompatible(const Function *Caller,
 
   if (CallerAttrs.requiresLazySave(CalleeAttrs) ||
       CallerAttrs.requiresSMChange(CalleeAttrs) ||
-      CallerAttrs.requiresPreservingZT0(CalleeAttrs)) {
+      CallerAttrs.requiresPreservingZT0(CalleeAttrs) ||
+      CallerAttrs.requiresPreservingAllZAState(CalleeAttrs)) {
     if (hasPossibleIncompatibleOps(Callee))
       return false;
   }

llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.cpp

@@ -38,6 +38,10 @@ void SMEAttrs::set(unsigned M, bool Enable) {
                         isPreservesZT0())) &&
       "Attributes 'aarch64_new_zt0', 'aarch64_in_zt0', 'aarch64_out_zt0', "
       "'aarch64_inout_zt0' and 'aarch64_preserves_zt0' are mutually exclusive");
+
+  assert(!(hasAgnosticZAInterface() && hasSharedZAInterface()) &&
+         "Function cannot have a shared-ZA interface and an agnostic-ZA "
+         "interface");
 }
 
 SMEAttrs::SMEAttrs(const CallBase &CB) {
@@ -56,6 +60,9 @@ SMEAttrs::SMEAttrs(StringRef FuncName) : Bitmask(0) {
   if (FuncName == "__arm_sc_memcpy" || FuncName == "__arm_sc_memset" ||
       FuncName == "__arm_sc_memmove" || FuncName == "__arm_sc_memchr")
     Bitmask |= SMEAttrs::SM_Compatible;
+  if (FuncName == "__arm_sme_save" || FuncName == "__arm_sme_restore" ||
+      FuncName == "__arm_sme_state_size")
+    Bitmask |= SMEAttrs::SM_Compatible | SMEAttrs::SME_ABI_Routine;
 }
 
 SMEAttrs::SMEAttrs(const AttributeList &Attrs) {
@@ -66,6 +73,8 @@ SMEAttrs::SMEAttrs(const AttributeList &Attrs) {
     Bitmask |= SM_Compatible;
   if (Attrs.hasFnAttr("aarch64_pstate_sm_body"))
     Bitmask |= SM_Body;
+  if (Attrs.hasFnAttr("aarch64_za_state_agnostic"))
+    Bitmask |= ZA_State_Agnostic;
   if (Attrs.hasFnAttr("aarch64_in_za"))
     Bitmask |= encodeZAState(StateValue::In);
   if (Attrs.hasFnAttr("aarch64_out_za"))