[MTE] Handle MTE instructions in AArch64LoadStoreOptimizer.

[eugenis]

Summary

Generate pre- and post-indexed forms of ST*G and STGP when possible.

[ostannard]

llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp

211 ↗

(On Diff #220773)

STZG and STZ2G store zero to the memory contents, so don't belong in this list according to the comment above. After reading the rest of the patch, I think it's the comment that's wrong, these instructions are allowed to write regular memory, but not with contents which depend on the address part of the input register.

llvm/test/CodeGen/AArch64/ldst-opt-mte.mir

4 ↗

(On Diff #220773)

We should also test a mis-aligned offset (e.g. $x0 = ADDXri $x0, 8, 0) as well as the edges of the range.

[eugenis]

Added merging of STGP with the same source and address register.
Added more tests.
Fixed a comment.

[eugenis]

I've noticed that the spec does not say that STGP with the same source and address register is unpredictable, and instead defines it to update the writeback register after the source register is read. This lets us merge STGP forward, but not backward. Implemented with tests.

llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp

211 ↗

(On Diff #220773)

Good point! Reworded the comment.

llvm/test/CodeGen/AArch64/ldst-opt-mte.mir

4 ↗

(On Diff #220773)

Added a test for mis-aligned offset. What do you mean by the edges of the range? There are tests for extreme values of the offset in ADDXri, see test_STG_post2 .. test_STG_post5 below and the same for STGP.

[ostannard]

LGTM

llvm/test/CodeGen/AArch64/ldst-opt-mte.mir

4 ↗

(On Diff #220773)

I meant the extreme values which you already have tests for.

llvm/trunk/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp

static bool isNarrowStore(unsigned Opc) {
   case AArch64::STRBBui:
   case AArch64::STURBBi:
   case AArch64::STRHHui:
   case AArch64::STURHHi:
     return true;
   }
 }
 
+// These instruction set memory tag and either keep memory contents unchanged or
+// set it to zero, ignoring the address part of the source register.
+static bool isTagStore(const MachineInstr &MI) {
+  switch (MI.getOpcode()) {
+  default:
+    return false;
+  case AArch64::STGOffset:
+  case AArch64::STZGOffset:
+  case AArch64::ST2GOffset:
+  case AArch64::STZ2GOffset:
+    return true;
+  }
+}
+
 // Scaling factor for unscaled load or store.
-static int getMemScale(MachineInstr &MI) {
+static int getMemScale(const MachineInstr &MI) {
   switch (MI.getOpcode()) {
   default:
     llvm_unreachable("Opcode has unknown scale!");
   case AArch64::LDRBBui:
   case AArch64::LDURBBi:
   case AArch64::LDRSBWui:
   case AArch64::LDURSBWi:
   case AArch64::STRBBui:
static int getMemScale(const MachineInstr &MI) {
   case AArch64::STPXi:
     return 8;
   case AArch64::LDRQui:
   case AArch64::LDURQi:
   case AArch64::STRQui:
   case AArch64::STURQi:
   case AArch64::LDPQi:
   case AArch64::STPQi:
+  case AArch64::STGOffset:
+  case AArch64::STZGOffset:
+  case AArch64::ST2GOffset:
+  case AArch64::STZ2GOffset:
+  case AArch64::STGPi:
     return 16;
   }
 }
 
 static unsigned getMatchingNonSExtOpcode(unsigned Opc,
                                          bool *IsValidLdStrOpc = nullptr) {
   if (IsValidLdStrOpc)
     *IsValidLdStrOpc = true;
static unsigned getPreIndexedOpcode(unsigned Opc) {
   case AArch64::STPDi:
     return AArch64::STPDpre;
   case AArch64::STPQi:
     return AArch64::STPQpre;
   case AArch64::STPWi:
     return AArch64::STPWpre;
   case AArch64::STPXi:
     return AArch64::STPXpre;
+  case AArch64::STGOffset:
+    return AArch64::STGPreIndex;
+  case AArch64::STZGOffset:
+    return AArch64::STZGPreIndex;
+  case AArch64::ST2GOffset:
+    return AArch64::ST2GPreIndex;
+  case AArch64::STZ2GOffset:
+    return AArch64::STZ2GPreIndex;
+  case AArch64::STGPi:
+    return AArch64::STGPpre;
   }
 }
 
 static unsigned getPostIndexedOpcode(unsigned Opc) {
   switch (Opc) {
   default:
     llvm_unreachable("Opcode has no post-indexed wise equivalent!");
   case AArch64::STRSui:
static unsigned getPostIndexedOpcode(unsigned Opc) {
   case AArch64::STPDi:
     return AArch64::STPDpost;
   case AArch64::STPQi:
     return AArch64::STPQpost;
   case AArch64::STPWi:
     return AArch64::STPWpost;
   case AArch64::STPXi:
     return AArch64::STPXpost;
+  case AArch64::STGOffset:
+    return AArch64::STGPostIndex;
+  case AArch64::STZGOffset:
+    return AArch64::STZGPostIndex;
+  case AArch64::ST2GOffset:
+    return AArch64::ST2GPostIndex;
+  case AArch64::STZ2GOffset:
+    return AArch64::STZ2GPostIndex;
+  case AArch64::STGPi:
+    return AArch64::STGPpost;
   }
 }
 
 static bool isPairedLdSt(const MachineInstr &MI) {
   switch (MI.getOpcode()) {
   default:
     return false;
   case AArch64::LDPSi:
   case AArch64::LDPSWi:
   case AArch64::LDPDi:
   case AArch64::LDPQi:
   case AArch64::LDPWi:
   case AArch64::LDPXi:
   case AArch64::STPSi:
   case AArch64::STPDi:
   case AArch64::STPQi:
   case AArch64::STPWi:
   case AArch64::STPXi:
+  case AArch64::STGPi:
     return true;
   }
 }
 
+// Returns the scale and offset range of pre/post indexed variants of MI.
+static void getPrePostIndexedMemOpInfo(const MachineInstr &MI, int &Scale,
+                                       int &MinOffset, int &MaxOffset) {
+  bool IsPaired = isPairedLdSt(MI);
+  bool IsTagStore = isTagStore(MI);
+  // ST*G and all paired ldst have the same scale in pre/post-indexed variants
+  // as in the "unsigned offset" variant.
+  // All other pre/post indexed ldst instructions are unscaled.
+  Scale = (IsTagStore || IsPaired) ? getMemScale(MI) : 1;
+
+  if (IsPaired) {
+    MinOffset = -64;
+    MaxOffset = 63;
+  } else {
+    MinOffset = -256;
+    MaxOffset = 255;
+  }
+}
+
 static const MachineOperand &getLdStRegOp(const MachineInstr &MI,
                                           unsigned PairedRegOp = 0) {
   assert(PairedRegOp < 2 && "Unexpected register operand idx.");
   unsigned Idx = isPairedLdSt(MI) ? PairedRegOp : 0;
   return MI.getOperand(Idx);
 }
 
 static const MachineOperand &getLdStBaseOp(const MachineInstr &MI) {
static bool isMergeableLdStUpdate(MachineInstr &MI) {
   case AArch64::STRBBui:
   case AArch64::LDRSui:
   case AArch64::LDRDui:
   case AArch64::LDRQui:
   case AArch64::LDRXui:
   case AArch64::LDRWui:
   case AArch64::LDRHHui:
   case AArch64::LDRBBui:
+  case AArch64::STGOffset:
+  case AArch64::STZGOffset:
+  case AArch64::ST2GOffset:
+  case AArch64::STZ2GOffset:
+  case AArch64::STGPi:
   // Unscaled instructions.
   case AArch64::STURSi:
   case AArch64::STURDi:
   case AArch64::STURQi:
   case AArch64::STURWi:
   case AArch64::STURXi:
   case AArch64::LDURSi:
   case AArch64::LDURDi:
AArch64LoadStoreOpt::mergeUpdateInsn(MachineBasicBlock::iterator I,
   assert(AArch64_AM::getShiftValue(Update->getOperand(3).getImm()) == 0 &&
          "Can't merge 1 << 12 offset into pre-/post-indexed load / store");
   if (Update->getOpcode() == AArch64::SUBXri)
     Value = -Value;
 
   unsigned NewOpc = IsPreIdx ? getPreIndexedOpcode(I->getOpcode())
                              : getPostIndexedOpcode(I->getOpcode());
   MachineInstrBuilder MIB;
+  int Scale, MinOffset, MaxOffset;
+  getPrePostIndexedMemOpInfo(*I, Scale, MinOffset, MaxOffset);
   if (!isPairedLdSt(*I)) {
     // Non-paired instruction.
     MIB = BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
               .add(getLdStRegOp(*Update))
               .add(getLdStRegOp(*I))
               .add(getLdStBaseOp(*I))
-              .addImm(Value)
+              .addImm(Value / Scale)
               .setMemRefs(I->memoperands())
               .setMIFlags(I->mergeFlagsWith(*Update));
   } else {
     // Paired instruction.
-    int Scale = getMemScale(*I);
     MIB = BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
               .add(getLdStRegOp(*Update))
               .add(getLdStRegOp(*I, 0))
               .add(getLdStRegOp(*I, 1))
               .add(getLdStBaseOp(*I))
               .addImm(Value / Scale)
               .setMemRefs(I->memoperands())
               .setMIFlags(I->mergeFlagsWith(*Update));
if (AArch64_AM::getShiftValue(MI.getOperand(3).getImm()))
       break;
 
     // The update instruction source and destination register must be the
     // same as the load/store base register.
     if (MI.getOperand(0).getReg() != BaseReg ||
         MI.getOperand(1).getReg() != BaseReg)
       break;
 
-    bool IsPairedInsn = isPairedLdSt(MemMI);
     int UpdateOffset = MI.getOperand(2).getImm();
     if (MI.getOpcode() == AArch64::SUBXri)
       UpdateOffset = -UpdateOffset;
 
-    // For non-paired load/store instructions, the immediate must fit in a
-    // signed 9-bit integer.
-    if (!IsPairedInsn && (UpdateOffset > 255 || UpdateOffset < -256))
-      break;
-
-    // For paired load/store instructions, the immediate must be a multiple of
-    // the scaling factor.  The scaled offset must also fit into a signed 7-bit
-    // integer.
-    if (IsPairedInsn) {
-      int Scale = getMemScale(MemMI);
-      if (UpdateOffset % Scale != 0)
-        break;
+    // The immediate must be a multiple of the scaling factor of the pre/post
+    // indexed instruction.
+    int Scale, MinOffset, MaxOffset;
+    getPrePostIndexedMemOpInfo(MemMI, Scale, MinOffset, MaxOffset);
 
-      int ScaledOffset = UpdateOffset / Scale;
-      if (ScaledOffset > 63 || ScaledOffset < -64)
-        break;
-    }
+    // Scaled offset must fit in the instruction immediate.
+    if (ScaledOffset > MaxOffset || ScaledOffset < MinOffset)
 
     // If we have a non-zero Offset, we check that it matches the amount
     // we're adding to the register.
     if (!Offset || Offset == UpdateOffset)
       return true;
     break;
   }
   return false;
MachineBasicBlock::iterator AArch64LoadStoreOpt::findMatchingUpdateInsnForward(
   int MIUnscaledOffset = getLdStOffsetOp(MemMI).getImm() * getMemScale(MemMI);
 
   // Scan forward looking for post-index opportunities.  Updating instructions
   // can't be formed if the memory instruction doesn't have the offset we're
   // looking for.
   if (MIUnscaledOffset != UnscaledOffset)
     return E;
 
-  // If the base register overlaps a destination register, we can't
-  // merge the update.
+  // If the base register overlaps a source/destination register, we can't
+  // merge the update. This does not apply to tag store instructions which
+  // ignore the address part of the source register.
+  // This does not apply to STGPi as well, which does not have unpredictable
+  // behavior in this case unlike normal stores, and always performs writeback
+  // after reading the source register value.
+  if (!isTagStore(MemMI) && MemMI.getOpcode() != AArch64::STGPi) {
     bool IsPairedInsn = isPairedLdSt(MemMI);
     for (unsigned i = 0, e = IsPairedInsn ? 2 : 1; i != e; ++i) {
       Register DestReg = getLdStRegOp(MemMI, i).getReg();
       if (DestReg == BaseReg || TRI->isSubRegister(BaseReg, DestReg))
         return E;
     }
+  }
 
   // Track which register units have been modified and used between the first
   // insn (inclusive) and the second insn.
   ModifiedRegUnits.clear();
   UsedRegUnits.clear();
   ++MBBI;
   for (unsigned Count = 0; MBBI != E && Count < Limit; ++MBBI) {
     MachineInstr &MI = *MBBI;
MachineBasicBlock::iterator AArch64LoadStoreOpt::findMatchingUpdateInsnBackward(
   int Offset = getLdStOffsetOp(MemMI).getImm();
 
   // If the load/store is the first instruction in the block, there's obviously
   // not any matching update. Ditto if the memory offset isn't zero.
   if (MBBI == B || Offset != 0)
     return E;
   // If the base register overlaps a destination register, we can't
   // merge the update.
+  if (!isTagStore(MemMI)) {
     bool IsPairedInsn = isPairedLdSt(MemMI);
     for (unsigned i = 0, e = IsPairedInsn ? 2 : 1; i != e; ++i) {
       Register DestReg = getLdStRegOp(MemMI, i).getReg();
       if (DestReg == BaseReg || TRI->isSubRegister(BaseReg, DestReg))
         return E;
     }
+  }
 
   // Track which register units have been modified and used between the first
   // insn (inclusive) and the second insn.
   ModifiedRegUnits.clear();
   UsedRegUnits.clear();
   unsigned Count = 0;
   do {
     --MBBI;
if (Update != E) {
     return true;
   }
 
   // The immediate in the load/store is scaled by the size of the memory
   // operation. The immediate in the add we're looking for,
   // however, is not, so adjust here.
   int UnscaledOffset = getLdStOffsetOp(MI).getImm() * getMemScale(MI);
 
-  // Look forward to try to find a post-index instruction. For example,
+  // Look forward to try to find a pre-index instruction. For example,
   // ldr x1, [x0, #64]
   // add x0, x0, #64
   //   merged into:
   // ldr x1, [x0, #64]!
   Update = findMatchingUpdateInsnForward(MBBI, UnscaledOffset, UpdateLimit);
   if (Update != E) {
     // Merge the update into the ld/st.
     MBBI = mergeUpdateInsn(MBBI, Update, /*IsPreIdx=*/true);

llvm/trunk/test/CodeGen/AArch64/ldst-opt-mte.mir

+# RUN: llc -mtriple=aarch64-none-linux-gnu -run-pass aarch64-ldst-opt  -verify-machineinstrs  -o - %s | FileCheck %s
+---
+
+### STG and its offset limits
+
+# CHECK-LABEL: name: test_STG_post
+# CHECK: STGPostIndex $x0, $x0, 7
+name: test_STG_post
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STGOffset $x0, $x0, 0
+    $x0 = ADDXri $x0, 112, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STG_post_same_reg
+# CHECK: STGPostIndex $x1, $x0, 7
+name: test_STG_post_same_reg
+body: |
+  bb.0.entry:
+    liveins: $x0, $x1
+
+    STGOffset $x1, $x0, 0
+    $x0 = ADDXri $x0, 112, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STG_post_unaligned
+# CHECK:      STGOffset $x0, $x0, 0
+# CHECK-NEXT: ADDXri $x0, 8, 0
+name: test_STG_post_unaligned
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STGOffset $x0, $x0, 0
+    $x0 = ADDXri $x0, 8, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STG_post2
+# CHECK: STGPostIndex $x0, $x0, -256
+name: test_STG_post2
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STGOffset $x0, $x0, 0
+    $x0 = SUBXri $x0, 4096, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STG_post3
+# CHECK:      STGOffset $x0, $x0, 0
+# CHECK-NEXT: SUBXri $x0, 4112, 0
+name: test_STG_post3
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STGOffset $x0, $x0, 0
+    $x0 = SUBXri $x0, 4112, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STG_post4
+# CHECK: STGPostIndex $x0, $x0, 255
+name: test_STG_post4
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STGOffset $x0, $x0, 0
+    $x0 = ADDXri $x0, 4080, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STG_post5
+# CHECK:      STGOffset $x0, $x0, 0
+# CHECK-NEXT: ADDXri $x0, 4096, 0
+name: test_STG_post5
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STGOffset $x0, $x0, 0
+    $x0 = ADDXri $x0, 4096, 0
+    RET_ReallyLR implicit $x0
+...
+
+### The rest of ST*G variants.
+
+# CHECK-LABEL: name: test_STZG_post
+# CHECK: STZGPostIndex $x0, $x0, 7
+name: test_STZG_post
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STZGOffset $x0, $x0, 0
+    $x0 = ADDXri $x0, 112, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_ST2G_post
+# CHECK: ST2GPostIndex $x0, $x0, 7
+name: test_ST2G_post
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    ST2GOffset $x0, $x0, 0
+    $x0 = ADDXri $x0, 112, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STZ2G_post
+# CHECK: STZ2GPostIndex $x0, $x0, 7
+name: test_STZ2G_post
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STZ2GOffset $x0, $x0, 0
+    $x0 = ADDXri $x0, 112, 0
+    RET_ReallyLR implicit $x0
+...
+
+### STGP and its offset limits
+
+# CHECK-LABEL: name: test_STGP_post
+# CHECK: STGPpost $x1, $x2, $x0, 7
+name: test_STGP_post
+body: |
+  bb.0.entry:
+    liveins: $x0, $x1, $x2
+
+    STGPi $x1, $x2, $x0, 0
+    $x0 = ADDXri $x0, 112, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STGP_post2
+# CHECK: STGPpost $x1, $x2, $x0, -64
+name: test_STGP_post2
+body: |
+  bb.0.entry:
+    liveins: $x0, $x1, $x2
+
+    STGPi $x1, $x2, $x0, 0
+    $x0 = SUBXri $x0, 1024, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STGP_post3
+# CHECK:      STGPi $x1, $x2, $x0, 0
+# CHECK-NEXT: SUBXri $x0, 1040, 0
+name: test_STGP_post3
+body: |
+  bb.0.entry:
+    liveins: $x0, $x1, $x2
+
+    STGPi $x1, $x2, $x0, 0
+    $x0 = SUBXri $x0, 1040, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STGP_post4
+# CHECK: STGPpost $x1, $x2, $x0, 63
+name: test_STGP_post4
+body: |
+  bb.0.entry:
+    liveins: $x0, $x1, $x2
+
+    STGPi $x1, $x2, $x0, 0
+    $x0 = ADDXri $x0, 1008, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STGP_post5
+# CHECK:      STGPi $x1, $x2, $x0, 0
+# CHECK-NEXT: ADDXri $x0, 1024, 0
+name: test_STGP_post5
+body: |
+  bb.0.entry:
+    liveins: $x0, $x1, $x2
+
+    STGPi $x1, $x2, $x0, 0
+    $x0 = ADDXri $x0, 1024, 0
+    RET_ReallyLR implicit $x0
+...
+
+### Pre-indexed forms
+
+# CHECK-LABEL: name: test_STG_pre
+# CHECK: STGPreIndex $x0, $x0, 10
+name: test_STG_pre
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STGOffset $x0, $x0, 10
+    $x0 = ADDXri $x0, 160, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STGP_pre
+# CHECK: STGPpre $x1, $x2, $x0, 10
+name: test_STGP_pre
+body: |
+  bb.0.entry:
+    liveins: $x0, $x1, $x2
+
+    STGPi $x1, $x2, $x0, 10
+    $x0 = ADDXri $x0, 160, 0
+    RET_ReallyLR implicit $x0
+...
+
+### Pre-indexed forms with add/sub coming before the store.
+
+# CHECK-LABEL: name: test_STG_pre_back
+# CHECK: STGPreIndex $x0, $x0, 2
+name: test_STG_pre_back
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    $x0 = ADDXri $x0, 32, 0
+    STGOffset $x0, $x0, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STGP_pre_back
+# CHECK: STGPpre $x1, $x2, $x0, -3
+name: test_STGP_pre_back
+body: |
+  bb.0.entry:
+    liveins: $x0, $x1, $x2
+
+    $x0 = SUBXri $x0, 48, 0
+    STGPi $x1, $x2, $x0, 0
+    RET_ReallyLR implicit $x0
+...
+
+### STGP with source register == address register
+
+# CHECK-LABEL: name: test_STGP_post_same_reg
+# CHECK: STGPpost $x0, $x0, $x0, 7
+name: test_STGP_post_same_reg
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STGPi $x0, $x0, $x0, 0
+    $x0 = ADDXri $x0, 112, 0
+    RET_ReallyLR implicit $x0
+...
+
+# CHECK-LABEL: name: test_STGP_pre_same_reg
+# CHECK: STGPpre $x0, $x0, $x0, 7
+name: test_STGP_pre_same_reg
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    STGPi $x0, $x0, $x0, 7
+    $x0 = ADDXri $x0, 112, 0
+    RET_ReallyLR implicit $x0
+...
+
+# This case can not be merged because the source register is always read before writeback.
+# CHECK-LABEL: name: test_STGP_pre_back_same_reg
+# CHECK:      SUBXri $x0, 48, 0
+# CHECK-NEXT: STGPi $x0, $x0, $x0, 0
+name: test_STGP_pre_back_same_reg
+body: |
+  bb.0.entry:
+    liveins: $x0
+
+    $x0 = SUBXri $x0, 48, 0
+    STGPi $x0, $x0, $x0, 0
+    RET_ReallyLR implicit $x0
+...

llvm/trunk/test/CodeGen/AArch64/stgp.ll

; CHECK: ret
   %q = getelementptr i8, i8* %p, i32 -1040
   call void @llvm.aarch64.stgp(i8* %q, i64 %a, i64 %b)
   ret void
 }
 
 define void @stgp_alloca(i64 %a, i64 %b) {
 entry:
 ; CHECK-LABEL: stgp_alloca:
-; CHECK: stgp x0, x1, [sp]
+; CHECK: stgp x0, x1, [sp, #-32]!
 ; CHECK: stgp x1, x0, [sp, #16]
 ; CHECK: ret
   %x = alloca i8, i32 32, align 16
   call void @llvm.aarch64.stgp(i8* %x, i64 %a, i64 %b)
   %x1 = getelementptr i8, i8* %x, i32 16
   call void @llvm.aarch64.stgp(i8* %x1, i64 %b, i64 %a)
   ret void
 }
 
 declare void @llvm.aarch64.stgp(i8* %p, i64 %a, i64 %b)