[ARM] Transforming memcpy to Tail predicated Loop

[malharJ]

Summary

This patch converts llvm.memcpy intrinsic into Tail Predicated
Hardware loops for a target that supports the Arm M-profile
Vector Extension (MVE).

From an implementation point of view, the patch

• adds an ARM specific SDAG Node (to which the llvm.memcpy intrinsic is lowered to, during first phase of ISel)
• adds a corresponding TableGen entry to generate a pseudo instruction, with a custom inserter, on matching the above node.
• Adds a custom inserter function that expands the pseudo instruction into MIR suitable to be (by later passes) into a WLSTP loop.

[SjoerdMeijer]

I know you've worked on this for a while and investigated different strategies, but I think we also need to argue here why we would like to emit a memcpy loop instead of e.g. having optimised versions in the clib. In other words, is this the best we can do for all different alignments, sizes, etc.?

[malharJ]

Added some comments to better illustrate transform.
Also renamed some variables to maintain consistency.

[dmgreen]

llvm/lib/Target/ARM/ARMISelLowering.cpp

11078

Can you look into all these clang-tidy errors. LLVM usually uses CamelCase for variable names, and the MBB_ looks a little odd. They should start with a capital and I would drop the "t2", that's not adding much.

llvm/lib/Target/ARM/ARMInstrMVE.td

6873

Can you improve this formatting. If you clang-formatted it, it doesn't do well with .td files and manually making it look more like the others will do better.

llvm/test/CodeGen/Thumb2/LowOverheadLoops/memcall.ll

21

Why does this not use r3 directly?

llvm/test/CodeGen/Thumb2/mve_tp_loop.ll

36

What is this generating r3 for? I thought those should be removed.

56

Why is this using printf? It looks like an execution test, not a unit test. Is it testing anything specifically? If so it can probably use any call, not a variadic version of printf.

64

Remove hidden and local_unnamed_addr #0

[malharJ]

1. Addressed comments (review comments + clang-tidy and clang-format fixes)

2. Updated transform to not generate preHeader block due to issues with phi-node-elimination pass placing copy/movs in the generated preHeader.

Details provided in comment below.

[malharJ]

llvm/lib/Target/ARM/ARMInstrMVE.td

6873

Had clang formatted it but yeah doesnt look good.
Updated now.

llvm/test/CodeGen/Thumb2/LowOverheadLoops/memcall.ll

21

This seems to be an issue with generating a preHeader during the transform ..

The phi-node-elimination pass is lowering the phi instructions (in the TP loopBody) as COPY operations (into the PreHeader).
In this instance, the copy/mov can be seen below on line 32:

mov r7, r3

I've fixed this issue as of now by not generating an extra preHeader during the transform ..
so the mov ends up above the t2WhileLoopStartLR and overall it seems to work.

Please see my comment about the latest changes for more details on this.

llvm/test/CodeGen/Thumb2/mve_tp_loop.ll

36

Good spot,

I think this is because DCE was not happening for the instructions calculating iterationCount.

I had a quick look at ARMLowOverheadLoops::IterationCountDCE( ), and it seems
that the expectation from the generated MIR is:

//   $lr = big-itercount-expression
//   ..
//   $lr = t2DoLoopStart/t2WhileLoopStartLR renamable $lr
//   vector.body:

I've updated the final expression (in the generated MIR) calculating iteration count to now return
the result in LR (earlier it was returning in one of the rGPRs) and these are now getting removed.

56

So the intent of the test was just to check whether code surrounding memcpy call site is properly transformed. I simply used printf to prevent the code from getting optimized away (seems like a poor way now that I think about it).

I've removed this test now since the transformation involving nested loops (in memcall.ll) is already testing the mentioned intent.

[malharJ]

So I've updated transform to not generate a preHeader block as there seems to be an issue
when generating a preHeader during the transform:

The issue:

The phi-node-elimination pass introduces COPY operations (for each PHI instruction in the TP loopBody) into the preHeader.

While most of them get removed by simple-register-coalescing pass, one copy in particular is not
getting removed. This is the one involving memcpy transfer size/vector element count. Regarding
why the register coalescing is unable to get rid of this particular copy/mov, I had a look at the
llc --debug output and it seems that it cant remove the mov/copy because the liveness range of
element count register intersects with liveness range of the target of the copy/mov.

An example of the generated (incorrect) assembly is shown below:

Relevant MIR:

TP Entry
         ...
	lr = t2WhileLoopStartLR r4 (r4 may be holding something other than element count)

TP preHeader
	...
	mov r4, r2 (assume r2 holds element count)
	...
TP body
	...
	VCTP r4
	...

Existing logic:

So this value (r4 above) feeds into the loopBody PHI nodes and then the VCTP receives it (which is fine).
But when the ARMLowOverHeadsLoop pass tries to use element count operand of VCTP to feed back to t2WhileLoopStartLR,
it is providing r4 (which is incorrect because the mov is happening after the t2WhileLoopStartLR).

So I tried to see if I could fix this by looking into LowOverheadLoop::ValidateTailPredicate(),
as it defines the "TPNumElements" variable. There is some logic there that handles the case for
local redefinitions of the elementCount physical register, by moving it forward/backward using ReachingDefAnalysis.
But in this instance, we have a redefinition (the mov) in a different BasicBlock so that code doesn't seem to fix this.

---

I'm not entirely certain if it's acceptable to not generate the preHeader, but unless there is a reasonably
simple fix for the above issue, I can't see another way.

[malharJ]

Fixed some more clang-format errors.

[dmgreen]

I'm a little worried that WLSTP is going to cause problems, with it not used anywhere else. Lets at least add an option for disabling it needed.

llvm/lib/Target/ARM/ARMBaseInstrInfo.h

370 ↗

(On Diff #335222)

Please split this out into a separate review. I think it makes sense (I'm pretty sure I remember writing it, it must have been lost in a refactoring).

llvm/lib/Target/ARM/ARMISelLowering.cpp

11282

When will this happen?

11301

-> "for a more natural layout"?

I think there may be benefits from getting the order roughly correct at this stage, if we are relying on WLS branches. They can be fixed up later, but if we get them more correct at this point, that can only help.

llvm/lib/Target/ARM/ARMISelLowering.h

336

Don't format any of this - it's unrelated.

llvm/lib/Target/ARM/ARMSelectionDAGInfo.cpp

141

Can we add an option that turns this inline memcpy on/off. If the option is true, we always use the MEMCPYLOOP, if it's false we never do, and if it's unset we use this default logic.

Also consider pulling the if logic into a lambda for readability.

llvm/test/CodeGen/Thumb2/mve_tp_loop.ll

10

Can you make sure there are tests where the i32 is a different type, one that is not legal like an i64.

llvm/test/CodeGen/Thumb2/mve_tp_loop.mir

137

Some of this can be removed, to help keep the test smaller.

[malharJ]

addressed some of the review comments:

• added a cli option for generation of TP loop for memcpy
• simplified the mir test

[malharJ]

I'm a little worried that WLSTP is going to cause problems ...

Would it better to use DLSTP in that case ? or perhaps a command line option
for choosing between DLSTP/WLSTP implementations ?

llvm/lib/Target/ARM/ARMBaseInstrInfo.h

370 ↗

(On Diff #335222)

Do you mean just this single line update as a separate review ?

llvm/lib/Target/ARM/ARMISelLowering.cpp

11282

This happens if MVE_MEMCPYLOOPINST is the only instruction in the block.
splitAt() returns the same block if there is nothing after the instruction at which the split is done..

This happens when for loops are implicitly converted to memcpys, the memcpy call
ends up being the only instruction in the preheader.

There is already a test case for this as test2 in llvm/test/CodeGen/Thumb2/mve_tp_loop.mir

llvm/lib/Target/ARM/ARMISelLowering.h

336

I had to fix it because patch was failing on clang-format error.

llvm/test/CodeGen/Thumb2/mve_tp_loop.ll

10

Do you mean something like:

define void @test(i8* noalias %X, i8* noalias %Y, i64 %n){
    call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %X, i8* align 4 %Y, i64 %n, i1 false)
    ret void
}

I get an error when I try to generate the assembly. Since i64 is illegal,
what is the expectation here ?

As a side note, if I generate the IR from C code, the IR always truncates the memcpy size variable to a i32
before calling llvm.memcpy( )

[dmgreen]

llvm/lib/Target/ARM/ARMBaseInstrInfo.h

370 ↗

(On Diff #335222)

Yeah... it should preferably be a separate patch. Do you have a test case? Some reason why you changed it?

llvm/lib/Target/ARM/ARMISelLowering.cpp

11282

OK. I thought it was more eager about putting branches on the end of blocks, even if they are fallthroughs.

llvm/lib/Target/ARM/ARMISelLowering.h

336

That's fine. We can ignore the precommit bot where it's more noisy than helpful.

llvm/test/CodeGen/Thumb2/mve_tp_loop.ll

10

Yeah sure. I think they can still come up, from other places creating memcpy calls.

You can probably use DAG.getZExtOrTrunc(Size, MVT::i32), instead of using the size directly.

[malharJ]

Addressed remaining review comments:

• Separated a change into it's own patch and added as dependency
• minor formatting updates
• added a testcase with size of type other than i32

[malharJ]

llvm/lib/Target/ARM/ARMBaseInstrInfo.h

370 ↗

(On Diff #335222)

Ok, I've now created a separate patch for this: https://reviews.llvm.org/D100376

[dmgreen]

llvm/lib/Target/ARM/ARMISelLowering.cpp

11257

Great comment by the way. Is it possible to make the loop MBB look like a bit like a loop? To show there is a backedge too.

llvm/lib/Target/ARM/ARMSelectionDAGInfo.cpp

140

[=] ->[&] is more standard, even if it doesn't make a lot of difference here.

142

Probably better as:

if (DAG.getMachineFunction().getFunction().hasOptNone())
  return false;
if (!ConstantSize && (Alignment >= Align(4))
  return true;
if (...)
 ...

The EnableMemcpyTPLoop logic could be in here too, as it's just returning true/false at the right time.
What do we do for -Oz and -Os?

llvm/test/CodeGen/Thumb2/mve_tp_loop.ll

2

Shouldn't have -O1 or cpu, use the -mtriple from other similar tests. The test can be called llvm/test/CodeGen/Thumb2/mve-tp-loop.ll.

[malharJ]

Addressed review comments:

• renamed test files
• disabled inline memcpy for optimize size cases (-Os, -Oz) and added tests for the same
• also added tests for constant size inputs to ensure the threshold values are tested as well.
• minor formatting changes

llvm/lib/Target/ARM/ARMSelectionDAGInfo.cpp

142

Ok.

And I guess it would be best to disable in the case of -Os/-Oz in case
there are multiple memcpys in the source. I've made the update and added tests as well.

[dmgreen]

llvm/lib/Target/ARM/ARMSelectionDAGInfo.cpp

142

func -> Func. Or maybe just F, which is quite common in LLVM.

149

if (EnableMemcpyTPLoop == cl::BOU_FALSE)
  return false;

Is probably better, if it works as I expect. That keeps the indenting down, and the last if currently isn't in the block it looks like it should be.

Oh, and move EnableMemcpyTPLoop above the OptSIze/OptNone, in case we want to try and force it. (Even if OptNone doesn't work, using that combo is unlikely to be useful at any rate.)

154

Add a return false at the end?

[malharJ]

Addressed review comments:

• moved cli option (when set) to be of higher priority than optNone/optSize
• minor formatting updates.

llvm/lib/Target/ARM/ARMSelectionDAGInfo.cpp

149

Ok, my bad there with the braces.

I've moved the cases when the cli option is set to be of higher priority than the optNone/optSize cases ...
but the unset case is of Lower priority than (the optNone/optSize) since the user is no longer passing the cli option.
Hopefully that sounds sensible.

154

yep, had missed that out.

[malharJ]

Rebased patch and removed the dependency as it has been closed.

[tschuett]

For comparison:
https://github.com/llvm/llvm-project/blob/main/libc/src/string/memory_utils/memcpy_utils.h

[dmgreen]

In D99723#2697318, @tschuett wrote:

For comparison:
https://github.com/llvm/llvm-project/blob/main/libc/src/string/memory_utils/memcpy_utils.h

Yeah thanks, but this is for a different architecture. On M class we have access to MVE tail predicated loops that can be much more efficient for emitting inline memcpys. A-Class Arm with Neon will be very different.

This looks good to me now, with a couple of extra nits.

llvm/lib/Target/ARM/ARMISelLowering.cpp

1817

Remove newline.

llvm/lib/Target/ARM/ARMSelectionDAGInfo.h

19

Is this needed here? Can it be in the cpp file?

[malharJ]

Minor formatting updates.

[dmgreen]

Thanks. Can you rebase and make sure the patch is clang-formatted?

[malharJ]

Rebased patch + minor formatting updates.

[malharJ]

Fix for bug spotted by dmgreen (thank you):

Added an update to ensure that the block containing memcpy pseudo is always
split using splitAt().

An example case where this is important is when updating
phi instructions in successive blocks, which is taken care of by splitAt()
which calls transferSuccessorsAndUpdatePHIs() internally.
A test has been added for the same.

[malharJ]

llvm/test/CodeGen/Thumb2/mve-tp-loop.ll

241–250 ↗

(On Diff #342948)

Not entirely sure why this isn't a TP loop, might need to check ArmLOL pass as to why it's being reverted..

[dmgreen]

Thanks. It looks like the arm low overhead loop pass doesn't like that two loops have the same preheader. Which makes sense, I don't like that either.

What do you think about committing this with the flag off for the time being and flipping the switch when we have sorted out some of the problems this is running into? memset especially seems to come up in a lot of cases, and can run into problem with so many low overhead loops together.

[malharJ]

Changed cli option for conversion of memcpy to TP loop to be disabled by default.
The disable may be temporary, and will be removed after some more testing.

A custom enum replaces the cl::boolOrDefault to implement the required functionality.

[dmgreen]

Thanks. LGTM

llvm/lib/Target/ARM/ARMSelectionDAGInfo.cpp

143

Perhaps use == TPLoop::ForceDisable to make it clear.

[malharJ]

Thanks a lot for the review !

[malharJ]

Fix for MachineVerifier error during Buildbot failure
https://lab.llvm.org/buildbot/#/builders/16/builds/10462

The failure is happening during testing because the NoPHIs property is being
set to true by MIRParserImpl::computeFunctionProperties( ) as there are No phis (prior to transformation),
but during the transform phis are generated.
This results in an error during MachineVerifier, since the function is labelled
with NoPHIs=true while there are phi insructions in the code.

This fix resets the property to false during the transform.

[dmgreen]

Ah yes. Sorry I didn't suggest adding that to the tests - it can be useful.

Setting NoPHIs seems a bit odd. It's a side effect of the mir test having no PHI's as it's loaded but them being added here. I don't have a better suggestion for fixing it though, other than adding existing PHI's to the mir test which needlessly complicates it.

This sounds like a good fix to me.

llvm/lib/Target/ARM/ARMISelLowering.h

 class TargetLibraryInfo;
 class TargetMachine;
 class TargetRegisterInfo;
 class VectorType;
 
   namespace ARMISD {
 
     // ARM Specific DAG Nodes
     enum NodeType : unsigned {
       // Start the numbering where the builtin ops and target ops leave off.
       FIRST_NUMBER = ISD::BUILTIN_OP_END,
 
       Wrapper,      // Wrapper - A wrapper node for TargetConstantPool,
                     // TargetExternalSymbol, and TargetGlobalAddress.
       WrapperPIC,   // WrapperPIC - A wrapper node for TargetGlobalAddress in
                     // PIC mode.
       WrapperJT,    // WrapperJT - A wrapper node for TargetJumpTable
enum NodeType : unsigned {
 
       // Pseudo vector bitwise select
       VBSP,
 
       // Pseudo-instruction representing a memory copy using ldm/stm
       // instructions.
       MEMCPY,
 
+      // Pseudo-instruction representing a memory copy using a tail predicated
+      // loop
+      MEMCPYLOOP,
+
       // V8.1MMainline condition select
       CSINV, // Conditional select invert.
       CSNEG, // Conditional select negate.
       CSINC, // Conditional select increment.
 
       // Vector load N-element structure to all lanes:
       VLD1DUP = ISD::FIRST_TARGET_MEMORY_OPCODE,
       VLD2DUP,
enum NodeType : unsigned {
       VST4_UPD,
       VST2LN_UPD,
       VST3LN_UPD,
       VST4LN_UPD,
 
       // Load/Store of dual registers
       LDRD,
       STRD
     };
 
   } // end namespace ARMISD
 
   namespace ARM {
   /// Possible values of current rounding mode, which is specified in bits
   /// 23:22 of FPSCR.
   enum Rounding {
     RN = 0,    // Round to Nearest

llvm/lib/Target/ARM/ARMISelLowering.cpp

const char *ARMTargetLowering::getTargetNodeName(unsigned Opcode) const {
   case ARMISD::VST4LN_UPD:    return "ARMISD::VST4LN_UPD";
   case ARMISD::WLS:           return "ARMISD::WLS";
   case ARMISD::WLSSETUP:      return "ARMISD::WLSSETUP";
   case ARMISD::LE:            return "ARMISD::LE";
   case ARMISD::LOOP_DEC:      return "ARMISD::LOOP_DEC";
   case ARMISD::CSINV:         return "ARMISD::CSINV";
   case ARMISD::CSNEG:         return "ARMISD::CSNEG";
   case ARMISD::CSINC:         return "ARMISD::CSINC";
+  case ARMISD::MEMCPYLOOP:
+    return "ARMISD::MEMCPYLOOP";
   }
   return nullptr;
 }
 
 EVT ARMTargetLowering::getSetCCResultType(const DataLayout &DL, LLVMContext &,
                                           EVT VT) const {
   if (!VT.isVector())
     return getPointerTy(DL);
static bool checkAndUpdateCPSRKill(MachineBasicBlock::iterator SelectItr,
   }
 
   // We found a def, or hit the end of the basic block and CPSR wasn't live
   // out. SelectMI should have a kill flag on CPSR.
   SelectItr->addRegisterKilled(ARM::CPSR, TRI);
   return true;
 }
 
+/// Adds logic in loop entry MBB to calculate loop iteration count and adds
+/// t2WhileLoopSetup and t2WhileLoopStart to generate WLS loop
+static Register genTPEntry(MachineBasicBlock *TpEntry,
+                           MachineBasicBlock *TpLoopBody,
+                           MachineBasicBlock *TpExit, Register OpSizeReg,
+                           const TargetInstrInfo *TII, DebugLoc Dl,
+                           MachineRegisterInfo &MRI) {
+
+  // Calculates loop iteration count = ceil(n/16)/16 = ((n + 15)&(-16)) / 16.
+  Register AddDestReg = MRI.createVirtualRegister(&ARM::rGPRRegClass);
+  BuildMI(TpEntry, Dl, TII->get(ARM::t2ADDri), AddDestReg)
+      .addUse(OpSizeReg)
+      .addImm(15)
+      .add(predOps(ARMCC::AL))
+      .addReg(0);
+
+  Register BicDestReg = MRI.createVirtualRegister(&ARM::rGPRRegClass);
+  BuildMI(TpEntry, Dl, TII->get(ARM::t2BICri), BicDestReg)
+      .addUse(AddDestReg, RegState::Kill)
+      .addImm(16)
+      .add(predOps(ARMCC::AL))
+      .addReg(0);
+
+  Register LsrDestReg = MRI.createVirtualRegister(&ARM::GPRlrRegClass);
+  BuildMI(TpEntry, Dl, TII->get(ARM::t2LSRri), LsrDestReg)
+      .addUse(BicDestReg, RegState::Kill)
+      .addImm(4)
+      .add(predOps(ARMCC::AL))
+      .addReg(0);
+
+  Register TotalIterationsReg = MRI.createVirtualRegister(&ARM::GPRlrRegClass);
+  BuildMI(TpEntry, Dl, TII->get(ARM::t2WhileLoopSetup), TotalIterationsReg)
+      .addUse(LsrDestReg, RegState::Kill);
+
+  BuildMI(TpEntry, Dl, TII->get(ARM::t2WhileLoopStart))
+      .addUse(TotalIterationsReg)
+      .addMBB(TpExit);
+
+  return TotalIterationsReg;
+}
+
+/// Adds logic in the loopBody MBB to generate MVE_VCTP, t2DoLoopDec and
+/// t2DoLoopEnd. These are used by later passes to generate tail predicated
+/// loops.
+static void genTPLoopBody(MachineBasicBlock *TpLoopBody,
+                          MachineBasicBlock *TpEntry, MachineBasicBlock *TpExit,
+                          const TargetInstrInfo *TII, DebugLoc Dl,
+                          MachineRegisterInfo &MRI, Register OpSrcReg,
+                          Register OpDestReg, Register ElementCountReg,
+                          Register TotalIterationsReg) {
+
+  // First insert 4 PHI nodes for: Current pointer to Src, Dest array, loop
+  // iteration counter, predication counter Current position in the src array
+  Register SrcPhiReg = MRI.createVirtualRegister(&ARM::rGPRRegClass);
+  Register CurrSrcReg = MRI.createVirtualRegister(&ARM::rGPRRegClass);
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::PHI), SrcPhiReg)
+      .addUse(OpSrcReg)
+      .addMBB(TpEntry)
+      .addUse(CurrSrcReg)
+      .addMBB(TpLoopBody);
+
+  // Current position in the dest array
+  Register DestPhiReg = MRI.createVirtualRegister(&ARM::rGPRRegClass);
+  Register CurrDestReg = MRI.createVirtualRegister(&ARM::rGPRRegClass);
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::PHI), DestPhiReg)
+      .addUse(OpDestReg)
+      .addMBB(TpEntry)
+      .addUse(CurrDestReg)
+      .addMBB(TpLoopBody);
+
+  // Current loop counter
+  Register LoopCounterPhiReg = MRI.createVirtualRegister(&ARM::GPRlrRegClass);
+  Register RemainingLoopIterationsReg =
+      MRI.createVirtualRegister(&ARM::GPRlrRegClass);
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::PHI), LoopCounterPhiReg)
+      .addUse(TotalIterationsReg)
+      .addMBB(TpEntry)
+      .addUse(RemainingLoopIterationsReg)
+      .addMBB(TpLoopBody);
+
+  // Predication counter
+  Register PredCounterPhiReg = MRI.createVirtualRegister(&ARM::rGPRRegClass);
+  Register RemainingElementsReg = MRI.createVirtualRegister(&ARM::rGPRRegClass);
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::PHI), PredCounterPhiReg)
+      .addUse(ElementCountReg)
+      .addMBB(TpEntry)
+      .addUse(RemainingElementsReg)
+      .addMBB(TpLoopBody);
+
+  // Pass predication counter to VCTP
+  Register VccrReg = MRI.createVirtualRegister(&ARM::VCCRRegClass);
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::MVE_VCTP8), VccrReg)
+      .addUse(PredCounterPhiReg)
+      .addImm(ARMVCC::None)
+      .addReg(0);
+
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::t2SUBri), RemainingElementsReg)
+      .addUse(PredCounterPhiReg)
+      .addImm(16)
+      .add(predOps(ARMCC::AL))
+      .addReg(0);
+
+  // VLDRB and VSTRB instructions, predicated using VPR
+  Register LoadedValueReg = MRI.createVirtualRegister(&ARM::MQPRRegClass);
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::MVE_VLDRBU8_post))
+      .addDef(CurrSrcReg)
+      .addDef(LoadedValueReg)
+      .addReg(SrcPhiReg)
+      .addImm(16)
+      .addImm(ARMVCC::Then)
+      .addUse(VccrReg);
+
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::MVE_VSTRBU8_post))
+      .addDef(CurrDestReg)
+      .addUse(LoadedValueReg, RegState::Kill)
+      .addReg(DestPhiReg)
+      .addImm(16)
+      .addImm(ARMVCC::Then)
+      .addUse(VccrReg);
+
+  // Add the pseudoInstrs for decrementing the loop counter and marking the
+  // end:t2DoLoopDec and t2DoLoopEnd
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::t2LoopDec), RemainingLoopIterationsReg)
+      .addUse(LoopCounterPhiReg)
+      .addImm(1);
+
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::t2LoopEnd))
+      .addUse(RemainingLoopIterationsReg)
+      .addMBB(TpLoopBody);
+
+  BuildMI(TpLoopBody, Dl, TII->get(ARM::t2B))
+      .addMBB(TpExit)
+      .add(predOps(ARMCC::AL));
+}
+
 MachineBasicBlock *
 ARMTargetLowering::EmitInstrWithCustomInserter(MachineInstr &MI,
                                                MachineBasicBlock *BB) const {
   const TargetInstrInfo *TII = Subtarget->getInstrInfo();
   DebugLoc dl = MI.getDebugLoc();
   bool isThumb2 = Subtarget->isThumb2();
   switch (MI.getOpcode()) {
   default: {
BuildMI(*BB, MI, dl, TII->get(ARM::tLDMIA_UPD))
         .add(MI.getOperand(3))  // PredImm
         .add(MI.getOperand(4))  // PredReg
         .add(MI.getOperand(0))  // Rt
         .cloneMemRefs(MI);
     MI.eraseFromParent();
     return BB;
   }
 
+  case ARM::MVE_MEMCPYLOOPINST: {
+
+    // Transformation below expands MVE_MEMCPYLOOPINST Pseudo instruction
+    // into a Tail Predicated (TP) Loop. It adds the instructions to calculate
+    // the iteration count =ceil(size_in_bytes/16)) in the TP entry block and
+    // adds the relevant instructions in the TP loop Body for generation of a
+    // WLSTP loop.
+
+    // Below is relevant portion of the CFG after the transformation.
+    // The Machine Basic Blocks are shown along with branch conditions (in
+    // brackets). Note that TP entry/exit MBBs depict the entry/exit of this
+    // portion of the CFG and may not necessarily be the entry/exit of the
+    // function.
+
+    //             (Relevant) CFG after transformation:
+    //               TP entry MBB
+    //                   |
+    //          |-----------------|
+    //       (n <= 0)          (n > 0)
+    //          |                 |
+    //          |         TP loop Body MBB
+    //          \                |
+    //            \             /
+    //              TP exit MBB
+
+    MachineFunction *MF = BB->getParent();
+    MachineRegisterInfo &MRI = MF->getRegInfo();
+
+    Register OpDestReg = MI.getOperand(0).getReg();
+    Register OpSrcReg = MI.getOperand(1).getReg();
+    Register OpSizeReg = MI.getOperand(2).getReg();
+
+    // Allocate the required MBBs and add to parent function.
+    MachineBasicBlock *TpEntry = BB;
+    MachineBasicBlock *TpLoopBody = MF->CreateMachineBasicBlock();
+    MachineBasicBlock *TpExit;
+
+    MF->push_back(TpLoopBody);
+
+    // If any instructions are present in the current block after
+    // MVE_MEMCPYLOOPINST, move them into the exit block. This is required since
+    // a terminator(t2WhileLoopStart) will be placed at that site. If no
+    // instructions are present after MVE_MEMCPYLOOPINST, then fallthrough is
+    // the exit.
+    TpExit = BB->splitAt(MI, false);
+    if (TpExit == BB) {
+      assert(BB->canFallThrough() &&
+             "exit Block must be Fallthrough of the block containing memcpy");
+      TpExit = BB->getFallThrough();
+    }
+
+    // Add logic for iteration count
+    Register TotalIterationsReg =
+        genTPEntry(TpEntry, TpLoopBody, TpExit, OpSizeReg, TII, dl, MRI);
+
+    // Add the vectorized (and predicated) loads/store instructions
+    genTPLoopBody(TpLoopBody, TpEntry, TpExit, TII, dl, MRI, OpSrcReg,
+                  OpDestReg, OpSizeReg, TotalIterationsReg);
+
+    // Connect the blocks
+    TpEntry->addSuccessor(TpLoopBody);
+    TpLoopBody->addSuccessor(TpLoopBody);
+    TpLoopBody->addSuccessor(TpExit);
+
+    // Reorder for a more natural layout
+    TpLoopBody->moveAfter(TpEntry);
+    TpExit->moveAfter(TpLoopBody);
+
+    // Finally, remove the memcpy Psuedo Instruction
+    MI.eraseFromParent();
+
+    // Return the exit block as it may contain other instructions requiring a
+    // custom inserter
+    return TpExit;
+  }
+
   // The Thumb2 pre-indexed stores have the same MI operands, they just
   // define them differently in the .td files from the isel patterns, so
   // they need pseudos.
   case ARM::t2STR_preidx:
     MI.setDesc(TII->get(ARM::t2STR_PRE));
     return BB;
   case ARM::t2STRB_preidx:
     MI.setDesc(TII->get(ARM::t2STRB_PRE));

llvm/lib/Target/ARM/ARMInstrMVE.td

class MVE_WLSTP<string asm, bits<2> size>
   bits<11> label;
   let Inst{13} = 0b0;
   let Inst{11} = label{0};
   let Inst{10-1} = label{10-1};
   let isBranch = 1;
   let isTerminator = 1;
 }
 
+def SDT_MVEMEMCPYLOOPNODE
+    : SDTypeProfile<0, 3, [SDTCisPtrTy<0>, SDTCisPtrTy<1>, SDTCisVT<2, i32>]>;
+def MVE_MEMCPYLOOPNODE : SDNode<"ARMISD::MEMCPYLOOP", SDT_MVEMEMCPYLOOPNODE,
+                                [SDNPHasChain, SDNPMayStore, SDNPMayLoad]>;
+
+let usesCustomInserter = 1, hasNoSchedulingInfo = 1 in {
+  def MVE_MEMCPYLOOPINST : PseudoInst<(outs),
+        (ins rGPR:$dst, rGPR:$src, rGPR:$sz),
+        NoItinerary,
+        [(MVE_MEMCPYLOOPNODE rGPR:$dst, rGPR:$src, rGPR:$sz)]>;
+}
+
 def MVE_DLSTP_8  : MVE_DLSTP<"dlstp.8",  0b00>;
 def MVE_DLSTP_16 : MVE_DLSTP<"dlstp.16", 0b01>;
 def MVE_DLSTP_32 : MVE_DLSTP<"dlstp.32", 0b10>;
 def MVE_DLSTP_64 : MVE_DLSTP<"dlstp.64", 0b11>;
 
 def MVE_WLSTP_8  : MVE_WLSTP<"wlstp.8",  0b00>;
 def MVE_WLSTP_16 : MVE_WLSTP<"wlstp.16", 0b01>;
 def MVE_WLSTP_32 : MVE_WLSTP<"wlstp.32", 0b10>;

llvm/lib/Target/ARM/ARMSelectionDAGInfo.h

 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIB_TARGET_ARM_ARMSELECTIONDAGINFO_H
 #define LLVM_LIB_TARGET_ARM_ARMSELECTIONDAGINFO_H
 
 #include "MCTargetDesc/ARMAddressingModes.h"
 #include "llvm/CodeGen/RuntimeLibcalls.h"
 #include "llvm/CodeGen/SelectionDAGTargetInfo.h"
+#include "llvm/Support/CommandLine.h"
 
 namespace llvm {
 
 namespace ARM_AM {
   static inline ShiftOpc getShiftOpcForNode(unsigned Opcode) {
     switch (Opcode) {
     default:          return ARM_AM::no_shift;
     case ISD::SHL:    return ARM_AM::lsl;

llvm/lib/Target/ARM/ARMSelectionDAGInfo.cpp

 
 #include "ARMTargetMachine.h"
 #include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/IR/DerivedTypes.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "arm-selectiondag-info"
 
+static cl::opt<cl::boolOrDefault>
+    EnableMemcpyTPLoop("arm-memcpy-tploop", cl::Hidden,
+                       cl::desc("Enable/disable conversion of llvm.memcpy to "
+                                "Tail predicated loops (WLSTP)"));
+
 // Emit, if possible, a specialized version of the given Libcall. Typically this
 // means selecting the appropriately aligned version, but we also convert memset
 // of 0 into memclr.
 SDValue ARMSelectionDAGInfo::EmitSpecializedLibcall(
     SelectionDAG &DAG, const SDLoc &dl, SDValue Chain, SDValue Dst, SDValue Src,
     SDValue Size, unsigned Align, RTLIB::Libcall LC) const {
   const ARMSubtarget &Subtarget =
       DAG.getMachineFunction().getSubtarget<ARMSubtarget>();

 }
 
 SDValue ARMSelectionDAGInfo::EmitTargetCodeForMemcpy(
     SelectionDAG &DAG, const SDLoc &dl, SDValue Chain, SDValue Dst, SDValue Src,
     SDValue Size, Align Alignment, bool isVolatile, bool AlwaysInline,
     MachinePointerInfo DstPtrInfo, MachinePointerInfo SrcPtrInfo) const {
   const ARMSubtarget &Subtarget =
       DAG.getMachineFunction().getSubtarget<ARMSubtarget>();
+  ConstantSDNode *ConstantSize = dyn_cast<ConstantSDNode>(Size);
+
+  auto GenInlineTP = [=](const ARMSubtarget &Subtarget,
+                         const SelectionDAG &DAG) {
+    return !DAG.getMachineFunction().getFunction().hasOptNone() &&
+           ((!ConstantSize && (Alignment >= Align(4))) ||
+            (ConstantSize &&
+             ConstantSize->getZExtValue() >
+                 Subtarget.getMaxInlineSizeThreshold() &&
+             ConstantSize->getZExtValue() <
+                 Subtarget.getMaxTPLoopInlineSizeThreshold()));
+  };
+
+  if (Subtarget.hasMVEIntegerOps())
+    if ((EnableMemcpyTPLoop == cl::BOU_TRUE) ||
+        (EnableMemcpyTPLoop == cl::BOU_UNSET && GenInlineTP(Subtarget, DAG)))
+      return DAG.getNode(ARMISD::MEMCPYLOOP, dl, MVT::Other, Chain, Dst, Src,
+                         DAG.getZExtOrTrunc(Size, dl, MVT::i32));
+
   // Do repeated 4-byte loads and stores. To be improved.
   // This requires 4-byte alignment.
   if (Alignment < Align(4))
     return SDValue();
   // This requires the copy size to be a constant, preferably
   // within a subtarget-specific limit.
-  ConstantSDNode *ConstantSize = dyn_cast<ConstantSDNode>(Size);
   if (!ConstantSize)
     return EmitSpecializedLibcall(DAG, dl, Chain, Dst, Src, Size,
                                   Alignment.value(), RTLIB::MEMCPY);
   uint64_t SizeVal = ConstantSize->getZExtValue();
   if (!AlwaysInline && SizeVal > Subtarget.getMaxInlineSizeThreshold())
     return EmitSpecializedLibcall(DAG, dl, Chain, Dst, Src, Size,
                                   Alignment.value(), RTLIB::MEMCPY);
 

llvm/lib/Target/ARM/ARMSubtarget.h

ARMSubtarget(const Triple &TT, const std::string &CPU, const std::string &FS,
                bool MinSize = false);
 
   /// getMaxInlineSizeThreshold - Returns the maximum memset / memcpy size
   /// that still makes it profitable to inline the call.
   unsigned getMaxInlineSizeThreshold() const {
     return 64;
   }
 
+  /// getMaxTPLoopSizeThreshold - Returns the maximum memcpy size
+  /// that still makes it profitable to inline the call as a Tail
+  /// Predicated loop
+  unsigned getMaxTPLoopInlineSizeThreshold() const { return 128; }
+
   /// ParseSubtargetFeatures - Parses features string setting specified
   /// subtarget options.  Definition of function is auto generated by tblgen.
   void ParseSubtargetFeatures(StringRef CPU, StringRef TuneCPU, StringRef FS);
 
   /// initializeSubtargetDependencies - Initializes using a CPU and feature string
   /// so that we can use initializer lists for subtarget initialization.
   ARMSubtarget &initializeSubtargetDependencies(StringRef CPU, StringRef FS);
 

llvm/test/CodeGen/Thumb2/LowOverheadLoops/memcall.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc -mtriple=thumbv8.1m.main-none-none-eabi -mattr=+mve.fp -verify-machineinstrs -tail-predication=enabled -o - %s | FileCheck %s
 
 define void @test_memcpy(i32* nocapture %x, i32* nocapture readonly %y, i32 %n, i32 %m) {
 ; CHECK-LABEL: test_memcpy:
 ; CHECK:       @ %bb.0: @ %entry
-; CHECK-NEXT:    .save {r4, r5, r6, r7, r8, r9, lr}
-; CHECK-NEXT:    push.w {r4, r5, r6, r7, r8, r9, lr}
-; CHECK-NEXT:    .pad #4
-; CHECK-NEXT:    sub sp, #4
+; CHECK-NEXT:    .save {r4, r5, r6, r7, lr}
+; CHECK-NEXT:    push {r4, r5, r6, r7, lr}
 ; CHECK-NEXT:    cmp r2, #1
-; CHECK-NEXT:    blt .LBB0_3
+; CHECK-NEXT:    blt .LBB0_5
 ; CHECK-NEXT:  @ %bb.1: @ %for.body.preheader
-; CHECK-NEXT:    mov r8, r3
-; CHECK-NEXT:    mov r5, r2
-; CHECK-NEXT:    mov r9, r1
-; CHECK-NEXT:    mov r7, r0
-; CHECK-NEXT:    lsls r4, r3, #2
-; CHECK-NEXT:    movs r6, #0
+; CHECK-NEXT:    lsl.w r12, r3, #2
+; CHECK-NEXT:    movs r7, #0
+; CHECK-NEXT:    b .LBB0_2
 ; CHECK-NEXT:  .LBB0_2: @ %for.body
-; CHECK-NEXT:    @ =>This Inner Loop Header: Depth=1
-; CHECK-NEXT:    adds r0, r7, r6
-; CHECK-NEXT:    add.w r1, r9, r6
-; CHECK-NEXT:    mov r2, r8
-; CHECK-NEXT:    bl __aeabi_memcpy4
-; CHECK-NEXT:    add r6, r4
-; CHECK-NEXT:    subs r5, #1
-; CHECK-NEXT:    bne .LBB0_2
-; CHECK-NEXT:  .LBB0_3: @ %for.cond.cleanup
-; CHECK-NEXT:    add sp, #4
-; CHECK-NEXT:    pop.w {r4, r5, r6, r7, r8, r9, pc}
+; CHECK-NEXT:    @ =>This Loop Header: Depth=1
+; CHECK-NEXT:    @ Child Loop BB0_4 Depth 2
+; CHECK-NEXT:    adds r4, r1, r7
+; CHECK-NEXT:    adds r5, r0, r7
+; CHECK-NEXT:    mov r6, r3
+; CHECK-NEXT:    wlstp.8 lr, r6, .LBB0_3
+; CHECK-NEXT:    b .LBB0_4
+; CHECK-NEXT:  .LBB0_3: @ %for.body
+; CHECK-NEXT:    @ in Loop: Header=BB0_2 Depth=1
+; CHECK-NEXT:    add r7, r12
+; CHECK-NEXT:    subs r2, #1
+; CHECK-NEXT:    beq .LBB0_5
+; CHECK-NEXT:    b .LBB0_2
+; CHECK-NEXT:  .LBB0_4: @ Parent Loop BB0_2 Depth=1
+; CHECK-NEXT:    @ => This Inner Loop Header: Depth=2
+; CHECK-NEXT:    vldrb.u8 q0, [r4], #16
+; CHECK-NEXT:    vstrb.8 q0, [r5], #16
+; CHECK-NEXT:    letp lr, .LBB0_4
+; CHECK-NEXT:    b .LBB0_3
+; CHECK-NEXT:  .LBB0_5: @ %for.cond.cleanup
+; CHECK-NEXT:    pop {r4, r5, r6, r7, pc}
 entry:
   %cmp8 = icmp sgt i32 %n, 0
   br i1 %cmp8, label %for.body, label %for.cond.cleanup
 
 for.cond.cleanup:                                 ; preds = %for.body, %entry
   ret void
 
 for.body:                                         ; preds = %entry, %for.body

llvm/test/CodeGen/Thumb2/mve_tp_loop.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -O1 -mtriple=arm-arm-none-eabi -mcpu=cortex-m55 --verify-machineinstrs %s -o - | FileCheck %s
+
+; Check that WLSTP loop is not generated for alignment < 4
+; void test1(char* dest, char* src, int n){
+;    memcpy(dest, src, n);
+; }
+
+declare void @llvm.memcpy.p0i8.p0i8.i32(i8* noalias nocapture writeonly, i8* noalias nocapture readonly, i32, i1 immarg) #1
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* noalias nocapture writeonly, i8* noalias nocapture readonly, i64, i1 immarg) #1
+
+define void @test1(i8* noalias nocapture %X, i8* noalias nocapture readonly %Y, i32 %n){
+; CHECK-LABEL: test1:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    bl __aeabi_memcpy
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 1 %X, i8* align 1 %Y, i32 %n, i1 false)
+  ret void
+}
+
+
+; Check that WLSTP loop is generated for alignment >= 4
+; void test2(int* restrict X, int* restrict Y, int n){
+;     memcpy(X, Y, n);
+; }
+
+
+define void @test2(i32* noalias %X, i32* noalias readonly %Y, i32 %n){
+; CHECK-LABEL: test2:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    wlstp.8 lr, r2, .LBB1_2
+; CHECK-NEXT:  .LBB1_1: @ =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    vldrb.u8 q0, [r1], #16
+; CHECK-NEXT:    vstrb.8 q0, [r0], #16
+; CHECK-NEXT:    letp lr, .LBB1_1
+; CHECK-NEXT:  .LBB1_2: @ %entry
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %0 = bitcast i32* %X to i8*
+  %1 = bitcast i32* %Y to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 %0, i8* align 4 %1, i32 %n, i1 false)
+  ret void
+}
+
+
+; Checks that transform handles some arithmetic on the input arguments.
+; void test3(int* restrict X, int* restrict Y, int n)
+; {
+;     memcpy(X+2, Y+3, (n*2)+10);
+; }
+
+define void @test3(i32* noalias nocapture %X, i32* noalias nocapture readonly %Y, i32 %n) {
+; CHECK-LABEL: test3:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    movs r3, #10
+; CHECK-NEXT:    add.w r2, r3, r2, lsl #1
+; CHECK-NEXT:    adds r0, #8
+; CHECK-NEXT:    adds r1, #12
+; CHECK-NEXT:    wlstp.8 lr, r2, .LBB2_2
+; CHECK-NEXT:  .LBB2_1: @ =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    vldrb.u8 q0, [r1], #16
+; CHECK-NEXT:    vstrb.8 q0, [r0], #16
+; CHECK-NEXT:    letp lr, .LBB2_1
+; CHECK-NEXT:  .LBB2_2: @ %entry
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %add.ptr = getelementptr inbounds i32, i32* %X, i32 2
+  %0 = bitcast i32* %add.ptr to i8*
+  %add.ptr1 = getelementptr inbounds i32, i32* %Y, i32 3
+  %1 = bitcast i32* %add.ptr1 to i8*
+  %mul = shl nsw i32 %n, 1
+  %add = add nsw i32 %mul, 10
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* nonnull align 4 %0, i8* nonnull align 4 %1, i32 %add, i1 false)
+  ret void
+}
+
+
+; Checks that transform handles for loops that are implicitly converted to mempcy
+; void test4(int* restrict X, int* restrict Y, int n){
+;     for(int i = 0; i < n; ++i){
+;         X[i] = Y[i];
+;     }
+; }
+
+define void @test4(i32* noalias %X, i32* noalias readonly %Y, i32 %n) {
+; CHECK-LABEL: test4:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    cmp r2, #1
+; CHECK-NEXT:    it lt
+; CHECK-NEXT:    poplt {r7, pc}
+; CHECK-NEXT:  .LBB3_1: @ %for.body.preheader
+; CHECK-NEXT:    wlstp.8 lr, r2, .LBB3_3
+; CHECK-NEXT:  .LBB3_2: @ =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    vldrb.u8 q0, [r1], #16
+; CHECK-NEXT:    vstrb.8 q0, [r0], #16
+; CHECK-NEXT:    letp lr, .LBB3_2
+; CHECK-NEXT:  .LBB3_3: @ %for.cond.cleanup
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %cmp6 = icmp sgt i32 %n, 0
+  br i1 %cmp6, label %for.body.preheader, label %for.cond.cleanup
+
+for.body.preheader:                               ; preds = %entry
+  %X.bits = bitcast i32* %X to i8*
+  %Y.bits = bitcast i32* %Y to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 %X.bits, i8* align 4 %Y.bits, i32 %n, i1 false)
+  br label %for.cond.cleanup
+
+for.cond.cleanup:                                 ; preds = %for.body.preheader, %entry
+  ret void
+}
+
+; Checks that transform can handle > i32 size inputs
+define void @test5(i8* noalias %X, i8* noalias %Y, i64 %n){
+; CHECK-LABEL: test5:
+; CHECK:       @ %bb.0:
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    wlstp.8 lr, r2, .LBB4_2
+; CHECK-NEXT:  .LBB4_1: @ =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    vldrb.u8 q0, [r1], #16
+; CHECK-NEXT:    vstrb.8 q0, [r0], #16
+; CHECK-NEXT:    letp lr, .LBB4_1
+; CHECK-NEXT:  .LBB4_2:
+; CHECK-NEXT:    pop {r7, pc}
+    call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %X, i8* align 4 %Y, i64 %n, i1 false)
+    ret void
+}
+
+

llvm/test/CodeGen/Thumb2/mve_tp_loop.mir

+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -O1 -mtriple=arm-arm-none-eabi -mcpu=cortex-m55 -simplify-mir -run-pass=finalize-isel %s -o - | FileCheck %s
+--- |
+  ; ModuleID = 'llvm/test/CodeGen/Thumb2/mve_tp_loop.ll'
+  source_filename = "llvm/test/CodeGen/Thumb2/mve_tp_loop.ll"
+  target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+  target triple = "arm-arm-none-eabi"
+
+  ; Function Attrs: argmemonly nofree nosync nounwind willreturn
+  declare void @llvm.memcpy.p0i8.p0i8.i32(i8* noalias nocapture writeonly, i8* noalias nocapture readonly, i32, i1 immarg) #0
+
+  define void @test1(i32* noalias %X, i32* noalias readonly %Y, i32 %n) #1 {
+  entry:
+    %0 = bitcast i32* %X to i8*
+    %1 = bitcast i32* %Y to i8*
+    call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 %0, i8* align 4 %1, i32 %n, i1 false)
+    ret void
+  }
+
+  define void @test2(i32* noalias %X, i32* noalias readonly %Y, i32 %n) #1 {
+  entry:
+    %cmp6 = icmp sgt i32 %n, 0
+    br i1 %cmp6, label %for.body.preheader, label %for.cond.cleanup
+
+  for.body.preheader:                               ; preds = %entry
+    %X.bits = bitcast i32* %X to i8*
+    %Y.bits = bitcast i32* %Y to i8*
+    call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 %X.bits, i8* align 4 %Y.bits, i32 %n, i1 false)
+    br label %for.cond.cleanup
+
+  for.cond.cleanup:                                 ; preds = %for.body.preheader, %entry
+    ret void
+  }
+
+  attributes #0 = { argmemonly nofree nosync nounwind willreturn "target-cpu"="cortex-m55" }
+  attributes #1 = { "target-cpu"="cortex-m55" }
+
+...
+---
+name:            test1
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    liveins: $r0, $r1, $r2
+
+    ; CHECK-LABEL: name: test1
+    ; CHECK: liveins: $r0, $r1, $r2
+    ; CHECK: [[COPY:%[0-9]+]]:rgpr = COPY $r2
+    ; CHECK: [[COPY1:%[0-9]+]]:rgpr = COPY $r1
+    ; CHECK: [[COPY2:%[0-9]+]]:rgpr = COPY $r0
+    ; CHECK: [[t2ADDri:%[0-9]+]]:rgpr = t2ADDri [[COPY]], 15, 14 /* CC::al */, $noreg, $noreg
+    ; CHECK: [[t2BICri:%[0-9]+]]:rgpr = t2BICri killed [[t2ADDri]], 16, 14 /* CC::al */, $noreg, $noreg
+    ; CHECK: [[t2LSRri:%[0-9]+]]:gprlr = t2LSRri killed [[t2BICri]], 4, 14 /* CC::al */, $noreg, $noreg
+    ; CHECK: [[t2WhileLoopSetup:%[0-9]+]]:gprlr = t2WhileLoopSetup killed [[t2LSRri]]
+    ; CHECK: t2WhileLoopStart [[t2WhileLoopSetup]], %bb.2, implicit-def $cpsr
+    ; CHECK: .1:
+    ; CHECK: [[PHI:%[0-9]+]]:rgpr = PHI [[COPY1]], %bb.0, %8, %bb.1
+    ; CHECK: [[PHI1:%[0-9]+]]:rgpr = PHI [[COPY2]], %bb.0, %10, %bb.1
+    ; CHECK: [[PHI2:%[0-9]+]]:gprlr = PHI [[t2WhileLoopSetup]], %bb.0, %12, %bb.1
+    ; CHECK: [[PHI3:%[0-9]+]]:rgpr = PHI [[COPY]], %bb.0, %14, %bb.1
+    ; CHECK: [[MVE_VCTP8_:%[0-9]+]]:vccr = MVE_VCTP8 [[PHI3]], 0, $noreg
+    ; CHECK: [[t2SUBri:%[0-9]+]]:rgpr = t2SUBri [[PHI3]], 16, 14 /* CC::al */, $noreg, $noreg
+    ; CHECK: [[MVE_VLDRBU8_post:%[0-9]+]]:rgpr, [[MVE_VLDRBU8_post1:%[0-9]+]]:mqpr = MVE_VLDRBU8_post [[PHI]], 16, 1, [[MVE_VCTP8_]]
+    ; CHECK: [[MVE_VSTRBU8_post:%[0-9]+]]:rgpr = MVE_VSTRBU8_post killed [[MVE_VLDRBU8_post1]], [[PHI1]], 16, 1, [[MVE_VCTP8_]]
+    ; CHECK: [[t2LoopDec:%[0-9]+]]:gprlr = t2LoopDec [[PHI2]], 1
+    ; CHECK: t2LoopEnd [[t2LoopDec]], %bb.1, implicit-def $cpsr
+    ; CHECK: t2B %bb.2, 14 /* CC::al */, $noreg
+    ; CHECK: .2.entry:
+    ; CHECK: tBX_RET 14 /* CC::al */, $noreg
+    %2:rgpr = COPY $r2
+    %1:rgpr = COPY $r1
+    %0:rgpr = COPY $r0
+    MVE_MEMCPYLOOPINST %0, %1, %2
+    tBX_RET 14 /* CC::al */, $noreg
+
+...
+---
+name:            test2
+tracksRegLiveness: true
+body:             |
+  ; CHECK-LABEL: name: test2
+  ; CHECK: bb.0.entry:
+  ; CHECK:   successors: %bb.1(0x50000000), %bb.2(0x30000000)
+  ; CHECK:   liveins: $r0, $r1, $r2
+  ; CHECK:   [[COPY:%[0-9]+]]:rgpr = COPY $r2
+  ; CHECK:   [[COPY1:%[0-9]+]]:rgpr = COPY $r1
+  ; CHECK:   [[COPY2:%[0-9]+]]:rgpr = COPY $r0
+  ; CHECK:   t2CMPri [[COPY]], 1, 14 /* CC::al */, $noreg, implicit-def $cpsr
+  ; CHECK:   t2Bcc %bb.2, 11 /* CC::lt */, $cpsr
+  ; CHECK:   t2B %bb.1, 14 /* CC::al */, $noreg
+  ; CHECK: bb.1.for.body.preheader:
+  ; CHECK:   successors: %bb.2(0x80000000), %bb.3(0x00000000)
+  ; CHECK:   [[t2ADDri:%[0-9]+]]:rgpr = t2ADDri [[COPY]], 15, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[t2BICri:%[0-9]+]]:rgpr = t2BICri killed [[t2ADDri]], 16, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[t2LSRri:%[0-9]+]]:gprlr = t2LSRri killed [[t2BICri]], 4, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[t2WhileLoopSetup:%[0-9]+]]:gprlr = t2WhileLoopSetup killed [[t2LSRri]]
+  ; CHECK:   t2WhileLoopStart [[t2WhileLoopSetup]], %bb.2, implicit-def $cpsr
+  ; CHECK: bb.3:
+  ; CHECK:   [[PHI:%[0-9]+]]:rgpr = PHI [[COPY1]], %bb.1, %8, %bb.3
+  ; CHECK:   [[PHI1:%[0-9]+]]:rgpr = PHI [[COPY2]], %bb.1, %10, %bb.3
+  ; CHECK:   [[PHI2:%[0-9]+]]:gprlr = PHI [[t2WhileLoopSetup]], %bb.1, %12, %bb.3
+  ; CHECK:   [[PHI3:%[0-9]+]]:rgpr = PHI [[COPY]], %bb.1, %14, %bb.3
+  ; CHECK:   [[MVE_VCTP8_:%[0-9]+]]:vccr = MVE_VCTP8 [[PHI3]], 0, $noreg
+  ; CHECK:   [[t2SUBri:%[0-9]+]]:rgpr = t2SUBri [[PHI3]], 16, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[MVE_VLDRBU8_post:%[0-9]+]]:rgpr, [[MVE_VLDRBU8_post1:%[0-9]+]]:mqpr = MVE_VLDRBU8_post [[PHI]], 16, 1, [[MVE_VCTP8_]]
+  ; CHECK:   [[MVE_VSTRBU8_post:%[0-9]+]]:rgpr = MVE_VSTRBU8_post killed [[MVE_VLDRBU8_post1]], [[PHI1]], 16, 1, [[MVE_VCTP8_]]
+  ; CHECK:   [[t2LoopDec:%[0-9]+]]:gprlr = t2LoopDec [[PHI2]], 1
+  ; CHECK:   t2LoopEnd [[t2LoopDec]], %bb.3, implicit-def $cpsr
+  ; CHECK:   t2B %bb.2, 14 /* CC::al */, $noreg
+  ; CHECK: bb.2.for.cond.cleanup:
+  ; CHECK:   tBX_RET 14 /* CC::al */, $noreg
+  bb.0.entry:
+    successors: %bb.1(0x50000000), %bb.2(0x30000000)
+    liveins: $r0, $r1, $r2
+
+    %2:rgpr = COPY $r2
+    %1:rgpr = COPY $r1
+    %0:rgpr = COPY $r0
+    t2CMPri %2, 1, 14 /* CC::al */, $noreg, implicit-def $cpsr
+    t2Bcc %bb.2, 11 /* CC::lt */, $cpsr
+    t2B %bb.1, 14 /* CC::al */, $noreg
+
+  bb.1.for.body.preheader:
+    successors: %bb.2(0x80000000)
+
+    MVE_MEMCPYLOOPINST %0, %1, %2
+
+  bb.2.for.cond.cleanup:
+    tBX_RET 14 /* CC::al */, $noreg
+
+...