[ARM] Correct register for narrowing and widening MVE loads and stores.

[dmgreen]

Summary

The widening and narrowing MVE instructions like VLDRH.32 are only permitted to use low "thumb1" registers. This means that if they are used for a stack slots, where the register used is only decided during frame setup, we need to be able to correctly pick a thumb1 register over a normal GPR.

This attempts to add the required logic into eliminateFrameIndex and rewriteT2FrameIndex, only picking the FrameReg if it is a valid register for the operands register class, and picking a valid scratch register for the register class.

[ostannard]

llvm/lib/Target/ARM/Thumb2InstrInfo.cpp

659

Is it possible to get here with a virtual register of the wrong class? I think we'd need a call to constrainRegClass here in that case.

[dmgreen]

Thanks for taking a look

llvm/lib/Target/ARM/Thumb2InstrInfo.cpp

659

Hmm, I have not seen us hit this, but it's certainly better to be safe than sorry! I'll add a check.

[ostannard]

LGTM, thanks

[dmgreen]

Thanks!

This has survived a Thumb2 bootstrap without issue at least.

llvm/lib/Target/ARM/ARMBaseInstrInfo.h

 /// offset could not be handled directly in MI, and return the left-over
 /// portion by reference.
 bool rewriteARMFrameIndex(MachineInstr &MI, unsigned FrameRegIdx,
                           unsigned FrameReg, int &Offset,
                           const ARMBaseInstrInfo &TII);
 
 bool rewriteT2FrameIndex(MachineInstr &MI, unsigned FrameRegIdx,
                          unsigned FrameReg, int &Offset,
-                         const ARMBaseInstrInfo &TII);
+                         const ARMBaseInstrInfo &TII,
+                         const TargetRegisterInfo *TRI);
 
 /// Return true if Reg is defd between From and To
 bool registerDefinedBetween(unsigned Reg, MachineBasicBlock::iterator From,
                             MachineBasicBlock::iterator To,
                             const TargetRegisterInfo *TRI);
 
 /// Search backwards from a tBcc to find a tCMPi8 against 0, meaning
 /// we can convert them to a tCBZ or tCBNZ. Return nullptr if not found.

llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp

while (!MI.getOperand(i).isFI()) {
     ++i;
     assert(i < MI.getNumOperands() && "Instr doesn't have FrameIndex operand!");
   }
   bool Done = false;
   if (!AFI->isThumbFunction())
     Done = rewriteARMFrameIndex(MI, i, BaseReg, Off, TII);
   else {
     assert(AFI->isThumb2Function());
-    Done = rewriteT2FrameIndex(MI, i, BaseReg, Off, TII);
+    Done = rewriteT2FrameIndex(MI, i, BaseReg, Off, TII, this);
   }
   assert(Done && "Unable to resolve frame index!");
   (void)Done;
 }
 
 bool ARMBaseRegisterInfo::isFrameOffsetLegal(const MachineInstr *MI, unsigned BaseReg,
                                              int64_t Offset) const {
   const MCInstrDesc &Desc = MI->getDesc();
#endif // NDEBUG
   assert(!MI.isDebugValue() && "DBG_VALUEs should be handled in target-independent code");
 
   // Modify MI as necessary to handle as much of 'Offset' as possible
   bool Done = false;
   if (!AFI->isThumbFunction())
     Done = rewriteARMFrameIndex(MI, FIOperandNum, FrameReg, Offset, TII);
   else {
     assert(AFI->isThumb2Function());
-    Done = rewriteT2FrameIndex(MI, FIOperandNum, FrameReg, Offset, TII);
+    Done = rewriteT2FrameIndex(MI, FIOperandNum, FrameReg, Offset, TII, this);
   }
   if (Done)
     return;
 
   // If we get here, the immediate doesn't fit into the instruction.  We folded
   // as much as possible above, handle the rest, providing a register that is
   // SP+LargeImm.
-  assert((Offset ||
-          (MI.getDesc().TSFlags & ARMII::AddrModeMask) == ARMII::AddrMode4 ||
-          (MI.getDesc().TSFlags & ARMII::AddrModeMask) == ARMII::AddrMode6) &&
-         "This code isn't needed if offset already handled!");
+  assert(
+      (Offset ||
+       (MI.getDesc().TSFlags & ARMII::AddrModeMask) == ARMII::AddrMode6 ||
+       (MI.getDesc().TSFlags & ARMII::AddrModeMask) == ARMII::AddrModeT2_i7 ||
+       (MI.getDesc().TSFlags & ARMII::AddrModeMask) == ARMII::AddrModeT2_i7s2 ||
+       (MI.getDesc().TSFlags & ARMII::AddrModeMask) ==
+           ARMII::AddrModeT2_i7s4) &&
 
   unsigned ScratchReg = 0;
   int PIdx = MI.findFirstPredOperandIdx();
   ARMCC::CondCodes Pred = (PIdx == -1)
     ? ARMCC::AL : (ARMCC::CondCodes)MI.getOperand(PIdx).getImm();
   Register PredReg = (PIdx == -1) ? Register() : MI.getOperand(PIdx+1).getReg();
-  if (Offset == 0)
+
+  const MCInstrDesc &MCID = MI.getDesc();
+  const TargetRegisterClass *RegClass =
+      TII.getRegClass(MCID, FIOperandNum, this, *MI.getParent()->getParent());
+
+  if (Offset == 0 &&
+      (Register::isVirtualRegister(FrameReg) || RegClass->contains(FrameReg)))
     // Must be addrmode4/6.
     MI.getOperand(FIOperandNum).ChangeToRegister(FrameReg, false, false, false);
   else {
-    ScratchReg = MF.getRegInfo().createVirtualRegister(&ARM::GPRRegClass);
+    ScratchReg = MF.getRegInfo().createVirtualRegister(RegClass);
     if (!AFI->isThumbFunction())
       emitARMRegPlusImmediate(MBB, II, MI.getDebugLoc(), ScratchReg, FrameReg,
                               Offset, Pred, PredReg, TII);
     else {
       assert(AFI->isThumb2Function());
       emitT2RegPlusImmediate(MBB, II, MI.getDebugLoc(), ScratchReg, FrameReg,
                              Offset, Pred, PredReg, TII);
     }

llvm/lib/Target/ARM/Thumb2InstrInfo.cpp

default:
     break;
   }
 
   return 0;
 }
 
 bool llvm::rewriteT2FrameIndex(MachineInstr &MI, unsigned FrameRegIdx,
                                unsigned FrameReg, int &Offset,
-                               const ARMBaseInstrInfo &TII) {
+                               const ARMBaseInstrInfo &TII,
+                               const TargetRegisterInfo *TRI) {
   unsigned Opcode = MI.getOpcode();
   const MCInstrDesc &Desc = MI.getDesc();
   unsigned AddrMode = (Desc.TSFlags & ARMII::AddrModeMask);
   bool isSub = false;
 
+  MachineFunction &MF = *MI.getParent()->getParent();
+  const TargetRegisterClass *RegClass =
+      TII.getRegClass(Desc, FrameRegIdx, TRI, MF);
+
   // Memory operands in inline assembly always use AddrModeT2_i12.
   if (Opcode == ARM::INLINEASM || Opcode == ARM::INLINEASM_BR)
     AddrMode = ARMII::AddrModeT2_i12; // FIXME. mode for thumb2?
 
   if (Opcode == ARM::t2ADDri || Opcode == ARM::t2ADDri12) {
     Offset += MI.getOperand(FrameRegIdx+1).getImm();
 
     unsigned PredReg;
if (Opcode == ARM::t2ADDri || Opcode == ARM::t2ADDri12) {
     }
 
     if (NewOpc != Opcode)
       MI.setDesc(TII.get(NewOpc));
 
     MachineOperand &ImmOp = MI.getOperand(FrameRegIdx+1);
 
     // Attempt to fold address computation
-    // Common case: small offset, fits into instruction.
+    // Common case: small offset, fits into instruction. We need to make sure
+    // the register class is correct too, for instructions like the MVE
+    // VLDRH.32, which only accepts low tGPR registers.
     int ImmedOffset = Offset / Scale;
     unsigned Mask = (1 << NumBits) - 1;
-    if ((unsigned)Offset <= Mask * Scale) {
+    if ((unsigned)Offset <= Mask * Scale &&
+        (Register::isVirtualRegister(FrameReg) ||
+         RegClass->contains(FrameReg))) {
+      if (Register::isVirtualRegister(FrameReg)) {
+        // Make sure the register class for the virtual register is correct
+        MachineRegisterInfo *MRI = &MF.getRegInfo();
+        if (!MRI->constrainRegClass(FrameReg, RegClass))
+          llvm_unreachable("Unable to constrain virtual register class.");
+      }
+
       // Replace the FrameIndex with fp/sp
       MI.getOperand(FrameRegIdx).ChangeToRegister(FrameReg, false);
       if (isSub) {
         if (AddrMode == ARMII::AddrMode5 || AddrMode == ARMII::AddrMode5FP16)
           // FIXME: Not consistent.
           ImmedOffset |= 1 << NumBits;
         else
           ImmedOffset = -ImmedOffset;
if (isSub) {
           MI.setDesc(TII.get(positiveOffsetOpcode(NewOpc)));
       }
     }
     ImmOp.ChangeToImmediate(ImmedOffset);
     Offset &= ~(Mask*Scale);
   }
 
   Offset = (isSub) ? -Offset : Offset;
-  return Offset == 0;
+  return Offset == 0 && (Register::isVirtualRegister(FrameReg) ||
+                         RegClass->contains(FrameReg));
 }
 
 ARMCC::CondCodes llvm::getITInstrPredicate(const MachineInstr &MI,
                                            unsigned &PredReg) {
   unsigned Opc = MI.getOpcode();
   if (Opc == ARM::tBcc || Opc == ARM::t2Bcc)
     return ARMCC::AL;
   return getInstrPredicate(MI, PredReg);

llvm/test/CodeGen/Thumb2/mve-stack.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=thumbv8.1m.main-arm-none-eabi -mattr=+mve -verify-machineinstrs %s -o - | FileCheck %s
+
+define arm_aapcs_vfpcc void @vstrw32() {
+; CHECK-LABEL: vstrw32:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #16
+; CHECK-NEXT:    sub sp, #16
+; CHECK-NEXT:    vmov.i32 q0, #0x0
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    vstrw.32 q0, [sp, #8]
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    add sp, #16
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [4 x i32], align 2
+  %g = getelementptr inbounds [4 x i32], [4 x i32]* %d, i32 0, i32 2
+  %b = bitcast i32* %g to <4 x i32>*
+  store <4 x i32> zeroinitializer, <4 x i32>* %b, align 2
+  %arraydecay = getelementptr inbounds [4 x i32], [4 x i32]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i32*)*)(i32* %arraydecay)
+  ret void
+}
+
+define arm_aapcs_vfpcc void @vstrh16() {
+; CHECK-LABEL: vstrh16:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #16
+; CHECK-NEXT:    sub sp, #16
+; CHECK-NEXT:    vmov.i32 q0, #0x0
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    vstrh.16 q0, [sp, #4]
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    add sp, #16
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [8 x i16], align 2
+  %g = getelementptr inbounds [8 x i16], [8 x i16]* %d, i32 0, i32 2
+  %b = bitcast i16* %g to <8 x i16>*
+  store <8 x i16> zeroinitializer, <8 x i16>* %b, align 2
+  %arraydecay = getelementptr inbounds [8 x i16], [8 x i16]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i16*)*)(i16* %arraydecay)
+  ret void
+}
+
+define arm_aapcs_vfpcc void @vstrb8() {
+; CHECK-LABEL: vstrb8:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #16
+; CHECK-NEXT:    sub sp, #16
+; CHECK-NEXT:    vmov.i32 q0, #0x0
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    vstrh.16 q0, [sp, #2]
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    add sp, #16
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [16 x i8], align 2
+  %g = getelementptr inbounds [16 x i8], [16 x i8]* %d, i32 0, i32 2
+  %b = bitcast i8* %g to <16 x i8>*
+  store <16 x i8> zeroinitializer, <16 x i8>* %b, align 2
+  %arraydecay = getelementptr inbounds [16 x i8], [16 x i8]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i8*)*)(i8* %arraydecay)
+  ret void
+}
+
+define arm_aapcs_vfpcc void @vstrh32() {
+; CHECK-LABEL: vstrh32:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #8
+; CHECK-NEXT:    sub sp, #8
+; CHECK-NEXT:    vmov.i32 q0, #0x6
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    vstrh.32 q0, [r0, #4]
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    add sp, #8
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [4 x i16], align 2
+  %g = getelementptr inbounds [4 x i16], [4 x i16]* %d, i32 0, i32 2
+  %b = bitcast i16* %g to <4 x i16>*
+  store <4 x i16> <i16 6, i16 6, i16 6, i16 6>, <4 x i16>* %b, align 2
+  %arraydecay = getelementptr inbounds [4 x i16], [4 x i16]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i16*)*)(i16* %arraydecay)
+  ret void
+}
+
+define arm_aapcs_vfpcc void @vstrb32() {
+; CHECK-LABEL: vstrb32:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #8
+; CHECK-NEXT:    sub sp, #8
+; CHECK-NEXT:    vmov.i32 q0, #0x6
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    vstrb.32 q0, [r0, #6]
+; CHECK-NEXT:    add r0, sp, #4
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    add sp, #8
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [4 x i8], align 2
+  %g = getelementptr inbounds [4 x i8], [4 x i8]* %d, i32 0, i32 2
+  %b = bitcast i8* %g to <4 x i8>*
+  store <4 x i8> <i8 6, i8 6, i8 6, i8 6>, <4 x i8>* %b, align 2
+  %arraydecay = getelementptr inbounds [4 x i8], [4 x i8]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i8*)*)(i8* %arraydecay)
+  ret void
+}
+
+define arm_aapcs_vfpcc void @vstrb16() {
+; CHECK-LABEL: vstrb16:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #8
+; CHECK-NEXT:    sub sp, #8
+; CHECK-NEXT:    vmov.i32 q0, #0x0
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    vstrb.16 q0, [r0, #2]
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    add sp, #8
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [8 x i8], align 2
+  %g = getelementptr inbounds [8 x i8], [8 x i8]* %d, i32 0, i32 2
+  %b = bitcast i8* %g to <8 x i8>*
+  store <8 x i8> zeroinitializer, <8 x i8>* %b, align 2
+  %arraydecay = getelementptr inbounds [8 x i8], [8 x i8]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i8*)*)(i8* %arraydecay)
+  ret void
+}
+
+
+define arm_aapcs_vfpcc <4 x i32> @vldrw32() {
+; CHECK-LABEL: vldrw32:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #16
+; CHECK-NEXT:    sub sp, #16
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    vldrw.u32 q0, [sp, #8]
+; CHECK-NEXT:    add sp, #16
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [4 x i32], align 2
+  %arraydecay = getelementptr inbounds [4 x i32], [4 x i32]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i32*)*)(i32* %arraydecay)
+  %g = getelementptr inbounds [4 x i32], [4 x i32]* %d, i32 0, i32 2
+  %b = bitcast i32* %g to <4 x i32>*
+  %l = load <4 x i32>, <4 x i32>* %b, align 2
+  ret <4 x i32> %l
+}
+
+define arm_aapcs_vfpcc <8 x i16> @vldrh16() {
+; CHECK-LABEL: vldrh16:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #16
+; CHECK-NEXT:    sub sp, #16
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    vldrh.u16 q0, [sp, #4]
+; CHECK-NEXT:    add sp, #16
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [8 x i16], align 2
+  %arraydecay = getelementptr inbounds [8 x i16], [8 x i16]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i16*)*)(i16* %arraydecay)
+  %g = getelementptr inbounds [8 x i16], [8 x i16]* %d, i32 0, i32 2
+  %b = bitcast i16* %g to <8 x i16>*
+  %l = load <8 x i16>, <8 x i16>* %b, align 2
+  ret <8 x i16> %l
+}
+
+define arm_aapcs_vfpcc <16 x i8> @vldrb8() {
+; CHECK-LABEL: vldrb8:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #16
+; CHECK-NEXT:    sub sp, #16
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    vldrh.u16 q0, [sp, #2]
+; CHECK-NEXT:    add sp, #16
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [16 x i8], align 2
+  %arraydecay = getelementptr inbounds [16 x i8], [16 x i8]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i8*)*)(i8* %arraydecay)
+  %g = getelementptr inbounds [16 x i8], [16 x i8]* %d, i32 0, i32 2
+  %b = bitcast i8* %g to <16 x i8>*
+  %l = load <16 x i8>, <16 x i8>* %b, align 2
+  ret <16 x i8> %l
+}
+
+define arm_aapcs_vfpcc <4 x i16> @vldrh32() {
+; CHECK-LABEL: vldrh32:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #8
+; CHECK-NEXT:    sub sp, #8
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    vldrh.u32 q0, [r0, #4]
+; CHECK-NEXT:    add sp, #8
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [4 x i16], align 2
+  %arraydecay = getelementptr inbounds [4 x i16], [4 x i16]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i16*)*)(i16* %arraydecay)
+  %g = getelementptr inbounds [4 x i16], [4 x i16]* %d, i32 0, i32 2
+  %b = bitcast i16* %g to <4 x i16>*
+  %l = load <4 x i16>, <4 x i16>* %b, align 2
+  ret <4 x i16> %l
+}
+
+define arm_aapcs_vfpcc <4 x i8> @vldrb32() {
+; CHECK-LABEL: vldrb32:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #8
+; CHECK-NEXT:    sub sp, #8
+; CHECK-NEXT:    add r0, sp, #4
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    vldrb.u32 q0, [r0, #6]
+; CHECK-NEXT:    add sp, #8
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [4 x i8], align 2
+  %arraydecay = getelementptr inbounds [4 x i8], [4 x i8]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i8*)*)(i8* %arraydecay)
+  %g = getelementptr inbounds [4 x i8], [4 x i8]* %d, i32 0, i32 2
+  %b = bitcast i8* %g to <4 x i8>*
+  %l = load <4 x i8>, <4 x i8>* %b, align 2
+  ret <4 x i8> %l
+}
+
+define arm_aapcs_vfpcc <8 x i8> @vldrb16() {
+; CHECK-LABEL: vldrb16:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    .pad #8
+; CHECK-NEXT:    sub sp, #8
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    bl func
+; CHECK-NEXT:    mov r0, sp
+; CHECK-NEXT:    vldrb.u16 q0, [r0, #2]
+; CHECK-NEXT:    add sp, #8
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %d = alloca [8 x i8], align 2
+  %arraydecay = getelementptr inbounds [8 x i8], [8 x i8]* %d, i32 0, i32 0
+  call arm_aapcs_vfpcc void bitcast (void (...)* @func to void (i8*)*)(i8* %arraydecay)
+  %g = getelementptr inbounds [8 x i8], [8 x i8]* %d, i32 0, i32 2
+  %b = bitcast i8* %g to <8 x i8>*
+  %l = load <8 x i8>, <8 x i8>* %b, align 2
+  ret <8 x i8> %l
+}
+
+declare dso_local arm_aapcs_vfpcc void @func(...)