[AArch64][SME] Support agnostic ZA functions in the MachineSMEABIPass

MacDue · MacDue · commit 323b82187d61 · 2025-08-05T10:37:39.000Z
This extends the MachineSMEABIPass to handle agnostic ZA functions. This
case is currently handled like shared ZA functions, but we don't require
ZA state to be reloaded before agnostic ZA calls.

Note: This patch does not yet fully handle agnostic ZA functions that
can catch exceptions. E.g.:

```
__arm_agnostic("sme_za_state") void try_catch_agnostic_za_callee()
{
  try {
    agnostic_za_call();
  } catch(...) {
    noexcept_agnostic_za_call();
  }
}
```

As in this case, we won't commit a ZA save before the
`agnostic_za_call()`, which would be needed to restore ZA in the catch
block. This will be handled in a later patch.

Change-Id: I9cce7b42ec8b64d5442b35231b65dfaf9d149eed
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -8244,7 +8244,7 @@ SDValue AArch64TargetLowering::LowerFormalArguments(
   if (Subtarget->hasCustomCallingConv())
     Subtarget->getRegisterInfo()->UpdateCustomCalleeSavedRegs(MF);
 
-  if (Subtarget->useNewSMEABILowering() && !Attrs.hasAgnosticZAInterface()) {
+  if (Subtarget->useNewSMEABILowering()) {
     if (Subtarget->isTargetWindows() || hasInlineStackProbe(MF)) {
       SDValue Size;
       if (Attrs.hasZAState()) {
@@ -9060,9 +9060,13 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
   bool UseNewSMEABILowering = Subtarget->useNewSMEABILowering();
   bool IsAgnosticZAFunction = CallAttrs.caller().hasAgnosticZAInterface();
   auto ZAMarkerNode = [&]() -> std::optional<unsigned> {
-    // TODO: Handle agnostic ZA functions.
-    if (!UseNewSMEABILowering || IsAgnosticZAFunction)
+    if (!UseNewSMEABILowering)
+      return std::nullopt;
+    if (IsAgnosticZAFunction) {
+      if (CallAttrs.requiresPreservingAllZAState())
+        return AArch64ISD::REQUIRES_ZA_SAVE;
       return std::nullopt;
+    }
     if (!CallAttrs.caller().hasZAState() && !CallAttrs.caller().hasZT0State())
       return std::nullopt;
     return CallAttrs.requiresLazySave() ? AArch64ISD::REQUIRES_ZA_SAVE
@@ -9142,7 +9146,8 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
   };
 
   bool RequiresLazySave = !UseNewSMEABILowering && CallAttrs.requiresLazySave();
-  bool RequiresSaveAllZA = CallAttrs.requiresPreservingAllZAState();
+  bool RequiresSaveAllZA =
+      !UseNewSMEABILowering && CallAttrs.requiresPreservingAllZAState();
   if (RequiresLazySave) {
     const TPIDR2Object &TPIDR2 = FuncInfo->getTPIDR2Obj();
     MachinePointerInfo MPI =
diff --git a/llvm/lib/Target/AArch64/MachineSMEABIPass.cpp b/llvm/lib/Target/AArch64/MachineSMEABIPass.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 //
 // This pass implements the SME ABI requirements for ZA state. This includes
-// implementing the lazy ZA state save schemes around calls.
+// implementing the lazy (and agnostic) ZA state save schemes around calls.
 //
 //===----------------------------------------------------------------------===//
 
@@ -128,7 +128,7 @@ struct MachineSMEABI : public MachineFunctionPass {
 
   void collectNeededZAStates(MachineFunction &MF, SMEAttrs);
   void pickBundleZAStates(MachineFunction &MF);
-  void insertStateChanges(MachineFunction &MF);
+  void insertStateChanges(MachineFunction &MF, bool IsAgnosticZA);
 
   // Emission routines for private and shared ZA functions (using lazy saves).
   void emitNewZAPrologue(MachineBasicBlock &MBB,
@@ -143,11 +143,46 @@ struct MachineSMEABI : public MachineFunctionPass {
   void emitZAOff(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
                  bool ClearTPIDR2);
 
+  // Emission routines for agnostic ZA functions.
+  void emitSetupFullZASave(MachineBasicBlock &MBB,
+                           MachineBasicBlock::iterator MBBI,
+                           LiveRegs PhysLiveRegs);
+  void emitFullZASaveRestore(MachineBasicBlock &MBB,
+                             MachineBasicBlock::iterator MBBI,
+                             LiveRegs PhysLiveRegs, bool IsSave);
+  void emitAllocateFullZASaveBuffer(MachineBasicBlock &MBB,
+                                    MachineBasicBlock::iterator MBBI,
+                                    LiveRegs PhysLiveRegs);
+
   void emitStateChange(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
-                       ZAState From, ZAState To, LiveRegs PhysLiveRegs);
+                       ZAState From, ZAState To, LiveRegs PhysLiveRegs,
+                       bool IsAgnosticZA);
+
+  // Helpers for switching between lazy/full ZA save/restore routines.
+  void emitZASave(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
+                  LiveRegs PhysLiveRegs, bool IsAgnosticZA) {
+    if (IsAgnosticZA)
+      return emitFullZASaveRestore(MBB, MBBI, PhysLiveRegs, /*IsSave=*/true);
+    return emitSetupLazySave(MBB, MBBI);
+  }
+  void emitZARestore(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
+                     LiveRegs PhysLiveRegs, bool IsAgnosticZA) {
+    if (IsAgnosticZA)
+      return emitFullZASaveRestore(MBB, MBBI, PhysLiveRegs, /*IsSave=*/false);
+    return emitRestoreLazySave(MBB, MBBI, PhysLiveRegs);
+  }
+  void emitAllocateZASaveBuffer(MachineBasicBlock &MBB,
+                                MachineBasicBlock::iterator MBBI,
+                                LiveRegs PhysLiveRegs, bool IsAgnosticZA) {
+    if (IsAgnosticZA)
+      return emitAllocateFullZASaveBuffer(MBB, MBBI, PhysLiveRegs);
+    return emitAllocateLazySaveBuffer(MBB, MBBI);
+  }
 
   TPIDR2State getTPIDR2Block(MachineFunction &MF);
 
+  Register getAgnosticZABufferPtr(MachineFunction &MF);
+
 private:
   struct InstInfo {
     ZAState NeededState{ZAState::ANY};
@@ -158,6 +193,7 @@ struct MachineSMEABI : public MachineFunctionPass {
   struct BlockInfo {
     ZAState FixedEntryState{ZAState::ANY};
     SmallVector<InstInfo> Insts;
+    LiveRegs PhysLiveRegsAtEntry = LiveRegs::None;
     LiveRegs PhysLiveRegsAtExit = LiveRegs::None;
   };
 
@@ -167,6 +203,9 @@ struct MachineSMEABI : public MachineFunctionPass {
     SmallVector<ZAState> BundleStates;
     std::optional<TPIDR2State> TPIDR2Block;
     std::optional<MachineBasicBlock::iterator> AfterSMEProloguePt;
+    Register AgnosticZABufferPtr = AArch64::NoRegister;
+    LiveRegs PhysLiveRegsAfterSMEPrologue = LiveRegs::None;
+    bool HasFullZASaveRestore = false;
   } State;
 
   EdgeBundles *Bundles = nullptr;
@@ -175,7 +214,8 @@ struct MachineSMEABI : public MachineFunctionPass {
 void MachineSMEABI::collectNeededZAStates(MachineFunction &MF,
                                           SMEAttrs SMEFnAttrs) {
   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
-  assert((SMEFnAttrs.hasZT0State() || SMEFnAttrs.hasZAState()) &&
+  assert((SMEFnAttrs.hasAgnosticZAInterface() || SMEFnAttrs.hasZT0State() ||
+          SMEFnAttrs.hasZAState()) &&
          "Expected function to have ZA/ZT0 state!");
 
   State.Blocks.resize(MF.getNumBlockIDs());
@@ -209,6 +249,7 @@ void MachineSMEABI::collectNeededZAStates(MachineFunction &MF,
 
     Block.PhysLiveRegsAtExit = GetPhysLiveRegs();
     auto FirstTerminatorInsertPt = MBB.getFirstTerminator();
+    auto FirstNonPhiInsertPt = MBB.getFirstNonPHI();
     for (MachineInstr &MI : reverse(MBB)) {
       MachineBasicBlock::iterator MBBI(MI);
       LiveUnits.stepBackward(MI);
@@ -219,15 +260,20 @@ void MachineSMEABI::collectNeededZAStates(MachineFunction &MF,
       // block setup.
       if (MI.getOpcode() == AArch64::SMEStateAllocPseudo) {
         State.AfterSMEProloguePt = MBBI;
+        State.PhysLiveRegsAfterSMEPrologue = PhysLiveRegs;
       }
+      // Note: We treat Agnostic ZA as inout_za with an alternate save/restore.
       auto [NeededState, InsertPt] = getInstNeededZAState(
-          TRI, MI, /*ZALiveAtReturn=*/SMEFnAttrs.hasSharedZAInterface());
+          TRI, MI, /*ZALiveAtReturn=*/SMEFnAttrs.hasSharedZAInterface() ||
+                       SMEFnAttrs.hasAgnosticZAInterface());
       assert((InsertPt == MBBI ||
               InsertPt->getOpcode() == AArch64::ADJCALLSTACKDOWN) &&
              "Unexpected state change insertion point!");
       // TODO: Do something to avoid state changes where NZCV is live.
       if (MBBI == FirstTerminatorInsertPt)
         Block.PhysLiveRegsAtExit = PhysLiveRegs;
+      if (MBBI == FirstNonPhiInsertPt)
+        Block.PhysLiveRegsAtEntry = PhysLiveRegs;
       if (NeededState != ZAState::ANY)
         Block.Insts.push_back({NeededState, InsertPt, PhysLiveRegs});
     }
@@ -294,7 +340,7 @@ void MachineSMEABI::pickBundleZAStates(MachineFunction &MF) {
   }
 }
 
-void MachineSMEABI::insertStateChanges(MachineFunction &MF) {
+void MachineSMEABI::insertStateChanges(MachineFunction &MF, bool IsAgnosticZA) {
   for (MachineBasicBlock &MBB : MF) {
     BlockInfo &Block = State.Blocks[MBB.getNumber()];
     ZAState InState =
@@ -309,7 +355,7 @@ void MachineSMEABI::insertStateChanges(MachineFunction &MF) {
     for (auto &Inst : Block.Insts) {
       if (CurrentState != Inst.NeededState)
         emitStateChange(MBB, Inst.InsertPt, CurrentState, Inst.NeededState,
-                        Inst.PhysLiveRegs);
+                        Inst.PhysLiveRegs, IsAgnosticZA);
       CurrentState = Inst.NeededState;
     }
 
@@ -318,7 +364,7 @@ void MachineSMEABI::insertStateChanges(MachineFunction &MF) {
 
     if (CurrentState != OutState)
       emitStateChange(MBB, MBB.getFirstTerminator(), CurrentState, OutState,
-                      Block.PhysLiveRegsAtExit);
+                      Block.PhysLiveRegsAtExit, IsAgnosticZA);
   }
 }
 
@@ -573,10 +619,98 @@ void MachineSMEABI::emitNewZAPrologue(MachineBasicBlock &MBB,
     emitZeroZA(TII, DL, MBB, MBBI, /*Mask=*/0b11111111);
 }
 
+Register MachineSMEABI::getAgnosticZABufferPtr(MachineFunction &MF) {
+  if (State.AgnosticZABufferPtr != AArch64::NoRegister)
+    return State.AgnosticZABufferPtr;
+  if (auto BufferPtr =
+          MF.getInfo<AArch64FunctionInfo>()->getEarlyAllocSMESaveBuffer();
+      BufferPtr != AArch64::NoRegister)
+    State.AgnosticZABufferPtr = BufferPtr;
+  else
+    State.AgnosticZABufferPtr =
+        MF.getRegInfo().createVirtualRegister(&AArch64::GPR64RegClass);
+  return State.AgnosticZABufferPtr;
+}
+
+void MachineSMEABI::emitFullZASaveRestore(MachineBasicBlock &MBB,
+                                          MachineBasicBlock::iterator MBBI,
+                                          LiveRegs PhysLiveRegs, bool IsSave) {
+  MachineFunction &MF = *MBB.getParent();
+  auto &Subtarget = MF.getSubtarget<AArch64Subtarget>();
+  const AArch64RegisterInfo &TRI = *Subtarget.getRegisterInfo();
+  const TargetInstrInfo &TII = *Subtarget.getInstrInfo();
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+
+  State.HasFullZASaveRestore = true;
+  DebugLoc DL = getDebugLoc(MBB, MBBI);
+  Register BufferPtr = AArch64::X0;
+
+  ScopedPhysRegSave ScopedPhysRegSave(MRI, TII, DL, MBB, MBBI, PhysLiveRegs);
+
+  // Copy the buffer pointer into X0.
+  BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::COPY), BufferPtr)
+      .addReg(getAgnosticZABufferPtr(MF));
+
+  // Call __arm_sme_save/__arm_sme_restore.
+  BuildMI(MBB, MBBI, DL, TII.get(AArch64::BL))
+      .addReg(BufferPtr, RegState::Implicit)
+      .addExternalSymbol(IsSave ? "__arm_sme_save" : "__arm_sme_restore")
+      .addRegMask(TRI.getCallPreservedMask(
+          MF,
+          CallingConv::AArch64_SME_ABI_Support_Routines_PreserveMost_From_X1));
+}
+
+void MachineSMEABI::emitAllocateFullZASaveBuffer(
+    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
+    LiveRegs PhysLiveRegs) {
+  MachineFunction &MF = *MBB.getParent();
+  MachineFrameInfo &MFI = MF.getFrameInfo();
+  auto &Subtarget = MF.getSubtarget<AArch64Subtarget>();
+  const TargetInstrInfo &TII = *Subtarget.getInstrInfo();
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+  auto *AFI = MF.getInfo<AArch64FunctionInfo>();
+
+  // Buffer already allocated in SelectionDAG.
+  if (AFI->getEarlyAllocSMESaveBuffer())
+    return;
+
+  DebugLoc DL = getDebugLoc(MBB, MBBI);
+  Register BufferPtr = getAgnosticZABufferPtr(MF);
+  Register BufferSize = MRI.createVirtualRegister(&AArch64::GPR64RegClass);
+
+  ScopedPhysRegSave ScopedPhysRegSave(MRI, TII, DL, MBB, MBBI, PhysLiveRegs);
+
+  // Calculate the SME state size.
+  {
+    const AArch64RegisterInfo *TRI = Subtarget.getRegisterInfo();
+    BuildMI(MBB, MBBI, DL, 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(MBB, MBBI, DL, TII.get(TargetOpcode::COPY), BufferSize)
+        .addReg(AArch64::X0);
+  }
+
+  // Allocate a buffer object of the size given __arm_sme_state_size.
+  {
+    BuildMI(MBB, MBBI, DL, TII.get(AArch64::SUBXrx64), AArch64::SP)
+        .addReg(AArch64::SP)
+        .addReg(BufferSize)
+        .addImm(AArch64_AM::getArithExtendImm(AArch64_AM::UXTX, 0));
+    BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::COPY), BufferPtr)
+        .addReg(AArch64::SP);
+
+    // We have just allocated a variable sized object, tell this to PEI.
+    MFI.CreateVariableSizedObject(Align(16), nullptr);
+  }
+}
+
 void MachineSMEABI::emitStateChange(MachineBasicBlock &MBB,
                                     MachineBasicBlock::iterator InsertPt,
                                     ZAState From, ZAState To,
-                                    LiveRegs PhysLiveRegs) {
+                                    LiveRegs PhysLiveRegs, bool IsAgnosticZA) {
 
   // ZA not used.
   if (From == ZAState::ANY || To == ZAState::ANY)
@@ -603,10 +737,11 @@ void MachineSMEABI::emitStateChange(MachineBasicBlock &MBB,
   }
 
   if (From == ZAState::ACTIVE && To == ZAState::LOCAL_SAVED)
-    emitSetupLazySave(MBB, InsertPt);
+    emitZASave(MBB, InsertPt, PhysLiveRegs, IsAgnosticZA);
   else if (From == ZAState::LOCAL_SAVED && To == ZAState::ACTIVE)
-    emitRestoreLazySave(MBB, InsertPt, PhysLiveRegs);
+    emitZARestore(MBB, InsertPt, PhysLiveRegs, IsAgnosticZA);
   else if (To == ZAState::OFF) {
+    assert(!IsAgnosticZA && "Should not turn ZA off in agnostic ZA function");
     // If we're exiting from the CALLER_DORMANT state that means this new ZA
     // function did not touch ZA (so ZA was never turned on).
     if (From != ZAState::CALLER_DORMANT)
@@ -629,7 +764,8 @@ bool MachineSMEABI::runOnMachineFunction(MachineFunction &MF) {
 
   auto *AFI = MF.getInfo<AArch64FunctionInfo>();
   SMEAttrs SMEFnAttrs = AFI->getSMEFnAttrs();
-  if (!SMEFnAttrs.hasZAState() && !SMEFnAttrs.hasZT0State())
+  if (!SMEFnAttrs.hasZAState() && !SMEFnAttrs.hasZT0State() &&
+      !SMEFnAttrs.hasAgnosticZAInterface())
     return false;
 
   assert(MF.getRegInfo().isSSA() && "Expected to be run on SSA form!");
@@ -638,20 +774,27 @@ bool MachineSMEABI::runOnMachineFunction(MachineFunction &MF) {
   State = PassState{};
   Bundles = &getAnalysis<EdgeBundlesWrapperLegacy>().getEdgeBundles();
 
+  bool IsAgnosticZA = SMEFnAttrs.hasAgnosticZAInterface();
+
   collectNeededZAStates(MF, SMEFnAttrs);
   pickBundleZAStates(MF);
-  insertStateChanges(MF);
+  insertStateChanges(MF, /*IsAgnosticZA=*/IsAgnosticZA);
 
   // Allocate save buffer (if needed).
-  if (State.TPIDR2Block.has_value()) {
+  if (State.HasFullZASaveRestore || State.TPIDR2Block.has_value()) {
     if (State.AfterSMEProloguePt) {
       // Note: With inline stack probes the AfterSMEProloguePt may not be in the
       // entry block (due to the probing loop).
-      emitAllocateLazySaveBuffer(*(*State.AfterSMEProloguePt)->getParent(),
-                                 *State.AfterSMEProloguePt);
+      emitAllocateZASaveBuffer(*(*State.AfterSMEProloguePt)->getParent(),
+                               *State.AfterSMEProloguePt,
+                               State.PhysLiveRegsAfterSMEPrologue,
+                               /*IsAgnosticZA=*/IsAgnosticZA);
     } else {
       MachineBasicBlock &EntryBlock = MF.front();
-      emitAllocateLazySaveBuffer(EntryBlock, EntryBlock.getFirstNonPHI());
+      emitAllocateZASaveBuffer(
+          EntryBlock, EntryBlock.getFirstNonPHI(),
+          State.Blocks[EntryBlock.getNumber()].PhysLiveRegsAtEntry,
+          /*IsAgnosticZA=*/IsAgnosticZA);
     }
   }
 
diff --git a/llvm/test/CodeGen/AArch64/sme-agnostic-za.ll b/llvm/test/CodeGen/AArch64/sme-agnostic-za.ll
