Thumb2: Modify codegen for memcpy intrinsic to prefer LDM/STM.

We were previously codegen'ing these as regular load/store operations and
hoping that the register allocator would allocate registers in ascending order
so that we could apply an LDM/STM combine after register allocation. According
to the commit that first introduced this code (r37179), we planned to teach
the register allocator to allocate the registers in ascending order. This
never got implemented, and up to now we've been stuck with very poor codegen.

A much simpler approach for achiveing better codegen is to create LDM/STM
instructions with identical sets of virtual registers, let the register
allocator pick arbitrary registers and order register lists when printing an
MCInst. This approach also avoids the need to repeatedly calculate offsets
which ultimately ought to be eliminated pre-RA in order to decrease register
pressure.

This is implemented by lowering the memcpy intrinsic to a series of SD-only
MCOPY pseudo-instructions which performs a memory copy using a given number
of registers. During SD->MI lowering, we lower MCOPY to LDM/STM. This is a
little unusual, but it avoids the need to encode register lists in the SD,
and we can take advantage of SD use lists to decide whether to use the _UPD
variant of the instructions.

Fixes PR9199.

Differential Revision: http://reviews.llvm.org/D9508

llvm-svn: 238473

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -1122,6 +1122,7 @@ const char *ARMTargetLowering::getTargetNodeName(unsigned Opcode) const {
   case ARMISD::VORRIMM:       return "ARMISD::VORRIMM";
   case ARMISD::VBICIMM:       return "ARMISD::VBICIMM";
   case ARMISD::VBSL:          return "ARMISD::VBSL";
+  case ARMISD::MCOPY:         return "ARMISD::MCOPY";
   case ARMISD::VLD2DUP:       return "ARMISD::VLD2DUP";
   case ARMISD::VLD3DUP:       return "ARMISD::VLD3DUP";
   case ARMISD::VLD4DUP:       return "ARMISD::VLD4DUP";
@@ -7629,8 +7630,59 @@ ARMTargetLowering::EmitInstrWithCustomInserter(MachineInstr *MI,
   }
 }
 
+/// \brief Lowers MCOPY to either LDMIA/STMIA or LDMIA_UPD/STMID_UPD depending
+/// on whether the result is used. This is done as a post-isel lowering instead
+/// of as a custom inserter because we need the use list from the SDNode.
+static void LowerMCOPY(const ARMSubtarget *Subtarget, MachineInstr *MI,
+                       SDNode *Node) {
+  bool isThumb1 = Subtarget->isThumb1Only();
+  bool isThumb2 = Subtarget->isThumb2();
+  const ARMBaseInstrInfo *TII = Subtarget->getInstrInfo();
+
+  DebugLoc dl = MI->getDebugLoc();
+  MachineBasicBlock *BB = MI->getParent();
+  MachineFunction *MF = BB->getParent();
+  MachineRegisterInfo &MRI = MF->getRegInfo();
+
+  MachineInstrBuilder LD, ST;
+  if (isThumb1 || Node->hasAnyUseOfValue(1)) {
+    LD = BuildMI(*BB, MI, dl, TII->get(isThumb2 ? ARM::t2LDMIA_UPD
+                                                : isThumb1 ? ARM::tLDMIA_UPD
+                                                           : ARM::LDMIA_UPD))
+             .addOperand(MI->getOperand(1));
+  } else {
+    LD = BuildMI(*BB, MI, dl, TII->get(isThumb2 ? ARM::t2LDMIA : ARM::LDMIA));
+  }
+
+  if (isThumb1 || Node->hasAnyUseOfValue(0)) {
+    ST = BuildMI(*BB, MI, dl, TII->get(isThumb2 ? ARM::t2STMIA_UPD
+                                                : isThumb1 ? ARM::tSTMIA_UPD
+                                                           : ARM::STMIA_UPD))
+             .addOperand(MI->getOperand(0));
+  } else {
+    ST = BuildMI(*BB, MI, dl, TII->get(isThumb2 ? ARM::t2STMIA : ARM::STMIA));
+  }
+
+  LD.addOperand(MI->getOperand(3)).addImm(ARMCC::AL).addReg(0);
+  ST.addOperand(MI->getOperand(2)).addImm(ARMCC::AL).addReg(0);
+
+  for (unsigned I = 0; I != MI->getOperand(4).getImm(); ++I) {
+    unsigned TmpReg = MRI.createVirtualRegister(isThumb1 ? &ARM::tGPRRegClass
+                                                         : &ARM::GPRRegClass);
+    LD.addReg(TmpReg, RegState::Define);
+    ST.addReg(TmpReg, RegState::Kill);
+  }
+
+  MI->eraseFromParent();
+}
+
 void ARMTargetLowering::AdjustInstrPostInstrSelection(MachineInstr *MI,
                                                       SDNode *Node) const {
+  if (MI->getOpcode() == ARM::MCOPY) {
+    LowerMCOPY(Subtarget, MI, Node);
+    return;
+  }
+
   const MCInstrDesc *MCID = &MI->getDesc();
   // Adjust potentially 's' setting instructions after isel, i.e. ADC, SBC, RSB,
   // RSC. Coming out of isel, they have an implicit CPSR def, but the optional

llvm/lib/Target/ARM/ARMISelLowering.h

@@ -189,6 +189,10 @@ namespace llvm {
       // Vector bitwise select
       VBSL,
 
+      // Pseudo-instruction representing a memory copy using ldm/stm
+      // instructions.
+      MCOPY,
+
       // Vector load N-element structure to all lanes:
       VLD2DUP = ISD::FIRST_TARGET_MEMORY_OPCODE,
       VLD3DUP,

llvm/lib/Target/ARM/ARMInstrInfo.td

@@ -73,6 +73,10 @@ def SDT_ARMBFI : SDTypeProfile<1, 3, [SDTCisVT<0, i32>, SDTCisVT<1, i32>,
 def SDT_ARMVMAXNM : SDTypeProfile<1, 2, [SDTCisFP<0>, SDTCisFP<1>, SDTCisFP<2>]>;
 def SDT_ARMVMINNM : SDTypeProfile<1, 2, [SDTCisFP<0>, SDTCisFP<1>, SDTCisFP<2>]>;
 
+def SDT_ARMMCOPY  : SDTypeProfile<2, 3, [SDTCisVT<0, i32>, SDTCisVT<1, i32>,
+                                         SDTCisVT<2, i32>, SDTCisVT<3, i32>,
+                                         SDTCisVT<4, i32>]>;
+
 def SDTBinaryArithWithFlags : SDTypeProfile<2, 2,
                                             [SDTCisSameAs<0, 2>,
                                              SDTCisSameAs<0, 3>,
@@ -179,6 +183,10 @@ def ARMbfi           : SDNode<"ARMISD::BFI", SDT_ARMBFI>;
 def ARMvmaxnm        : SDNode<"ARMISD::VMAXNM", SDT_ARMVMAXNM, []>;
 def ARMvminnm        : SDNode<"ARMISD::VMINNM", SDT_ARMVMINNM, []>;
 
+def ARMmcopy : SDNode<"ARMISD::MCOPY", SDT_ARMMCOPY,
+                      [SDNPHasChain, SDNPInGlue, SDNPOutGlue,
+                       SDNPMayStore, SDNPMayLoad]>;
+
 //===----------------------------------------------------------------------===//
 // ARM Instruction Predicate Definitions.
 //
@@ -4552,6 +4560,13 @@ let usesCustomInserter = 1 in {
       [(ARMcopystructbyval GPR:$dst, GPR:$src, imm:$size, imm:$alignment)]>;
 }
 
+let hasPostISelHook = 1 in {
+    def MCOPY : PseudoInst<
+      (outs GPR:$newdst, GPR:$newsrc), (ins GPR:$dst, GPR:$src, i32imm:$nreg),
+      NoItinerary,
+      [(set GPR:$newdst, GPR:$newsrc, (ARMmcopy GPR:$dst, GPR:$src, imm:$nreg))]>;
+}
+
 def ldrex_1 : PatFrag<(ops node:$ptr), (int_arm_ldrex node:$ptr), [{
   return cast<MemIntrinsicSDNode>(N)->getMemoryVT() == MVT::i8;
 }]>;

llvm/lib/Target/ARM/ARMSelectionDAGInfo.cpp

@@ -164,41 +164,38 @@ ARMSelectionDAGInfo::EmitTargetCodeForMemcpy(SelectionDAG &DAG, SDLoc dl,
   unsigned VTSize = 4;
   unsigned i = 0;
   // Emit a maximum of 4 loads in Thumb1 since we have fewer registers
-  const unsigned MAX_LOADS_IN_LDM = Subtarget.isThumb1Only() ? 4 : 6;
+  const unsigned MaxLoadsInLDM = Subtarget.isThumb1Only() ? 4 : 6;
   SDValue TFOps[6];
   SDValue Loads[6];
   uint64_t SrcOff = 0, DstOff = 0;
 
-  // Emit up to MAX_LOADS_IN_LDM loads, then a TokenFactor barrier, then the
-  // same number of stores.  The loads and stores will get combined into
-  // ldm/stm later on.
-  while (EmittedNumMemOps < NumMemOps) {
-    for (i = 0;
-         i < MAX_LOADS_IN_LDM && EmittedNumMemOps + i < NumMemOps; ++i) {
-      Loads[i] = DAG.getLoad(VT, dl, Chain,
-                             DAG.getNode(ISD::ADD, dl, MVT::i32, Src,
-                                         DAG.getConstant(SrcOff, dl, MVT::i32)),
-                             SrcPtrInfo.getWithOffset(SrcOff), isVolatile,
-                             false, false, 0);
-      TFOps[i] = Loads[i].getValue(1);
-      SrcOff += VTSize;
-    }
-    Chain = DAG.getNode(ISD::TokenFactor, dl, MVT::Other,
-                        makeArrayRef(TFOps, i));
+  // FIXME: We should invent a VMCOPY pseudo-instruction that lowers to
+  // VLDM/VSTM and make this code emit it when appropriate. This would reduce
+  // pressure on the general purpose registers. However this seems harder to map
+  // onto the register allocator's view of the world.
 
-    for (i = 0;
-         i < MAX_LOADS_IN_LDM && EmittedNumMemOps + i < NumMemOps; ++i) {
-      TFOps[i] = DAG.getStore(Chain, dl, Loads[i],
-                              DAG.getNode(ISD::ADD, dl, MVT::i32, Dst,
-                                          DAG.getConstant(DstOff, dl, MVT::i32)),
-                              DstPtrInfo.getWithOffset(DstOff),
-                              isVolatile, false, 0);
-      DstOff += VTSize;
-    }
-    Chain = DAG.getNode(ISD::TokenFactor, dl, MVT::Other,
-                        makeArrayRef(TFOps, i));
+  // The number of MCOPY pseudo-instructions to emit. We use up to MaxLoadsInLDM
+  // registers per mcopy, which will get lowered into ldm/stm later on. This is
+  // a lower bound on the number of MCOPY operations we must emit.
+  unsigned NumMCOPYs = (NumMemOps + MaxLoadsInLDM - 1) / MaxLoadsInLDM;
+
+  SDVTList VTs = DAG.getVTList(MVT::i32, MVT::i32, MVT::Other, MVT::Glue);
+
+  for (unsigned I = 0; I != NumMCOPYs; ++I) {
+    // Evenly distribute registers among MCOPY operations to reduce register
+    // pressure.
+    unsigned NextEmittedNumMemOps = NumMemOps * (I + 1) / NumMCOPYs;
+    unsigned NumRegs = NextEmittedNumMemOps - EmittedNumMemOps;
+
+    Dst = DAG.getNode(ARMISD::MCOPY, dl, VTs, Chain, Dst, Src,
+                      DAG.getConstant(NumRegs, dl, MVT::i32));
+    Src = Dst.getValue(1);
+    Chain = Dst.getValue(2);
+
+    DstPtrInfo = DstPtrInfo.getWithOffset(NumRegs * VTSize);
+    SrcPtrInfo = SrcPtrInfo.getWithOffset(NumRegs * VTSize);
 
-    EmittedNumMemOps += i;
+    EmittedNumMemOps = NextEmittedNumMemOps;
   }
 
   if (BytesLeft == 0)

llvm/lib/Target/ARM/InstPrinter/ARMInstPrinter.cpp

@@ -744,10 +744,21 @@ void ARMInstPrinter::printRegisterList(const MCInst *MI, unsigned OpNum,
                                        const MCSubtargetInfo &STI,
                                        raw_ostream &O) {
   O << "{";
-  for (unsigned i = OpNum, e = MI->getNumOperands(); i != e; ++i) {
-    if (i != OpNum)
+
+  // The backend may have given us a register list in non-ascending order. Sort
+  // it now.
+  std::vector<MCOperand> RegOps(MI->size() - OpNum);
+  std::copy(MI->begin() + OpNum, MI->end(), RegOps.begin());
+  std::sort(RegOps.begin(), RegOps.end(),
+            [this](const MCOperand &O1, const MCOperand &O2) -> bool {
+              return MRI.getEncodingValue(O1.getReg()) <
+                     MRI.getEncodingValue(O2.getReg());
+            });
+
+  for (unsigned i = 0, e = RegOps.size(); i != e; ++i) {
+    if (i != 0)
       O << ", ";
-    printRegName(O, MI->getOperand(i).getReg());
+    printRegName(O, RegOps[i].getReg());
   }
   O << "}";
 }

llvm/lib/Target/ARM/Thumb2SizeReduction.cpp

@@ -125,7 +125,10 @@ namespace {
   { ARM::t2LDMIA, ARM::tLDMIA,  0,             0,   0,   1,   1,  1,1, 0,1,0 },
   { ARM::t2LDMIA_RET,0,         ARM::tPOP_RET, 0,   0,   1,   1,  1,1, 0,1,0 },
   { ARM::t2LDMIA_UPD,ARM::tLDMIA_UPD,ARM::tPOP,0,   0,   1,   1,  1,1, 0,1,0 },
-  // ARM::t2STM (with no basereg writeback) has no Thumb1 equivalent
+  // ARM::t2STMIA (with no basereg writeback) has no Thumb1 equivalent.
+  // tSTMIA_UPD is a change in semantics which can only be used if the base
+  // register is killed. This difference is correctly handled elsewhere.
+  { ARM::t2STMIA, ARM::tSTMIA_UPD, 0,          0,   0,   1,   1,  1,1, 0,1,0 },
   { ARM::t2STMIA_UPD,ARM::tSTMIA_UPD, 0,       0,   0,   1,   1,  1,1, 0,1,0 },
   { ARM::t2STMDB_UPD, 0,        ARM::tPUSH,    0,   0,   1,   1,  1,1, 0,1,0 }
   };
@@ -432,6 +435,14 @@ Thumb2SizeReduce::ReduceLoadStore(MachineBasicBlock &MBB, MachineInstr *MI,
     isLdStMul = true;
     break;
   }
+  case ARM::t2STMIA: {
+    // If the base register is killed, we don't care what its value is after the
+    // instruction, so we can use an updating STMIA.
+    if (!MI->getOperand(0).isKill())
+      return false;
+
+    break;
+  }
   case ARM::t2LDMIA_RET: {
     unsigned BaseReg = MI->getOperand(1).getReg();
     if (BaseReg != ARM::SP)
@@ -489,6 +500,12 @@ Thumb2SizeReduce::ReduceLoadStore(MachineBasicBlock &MBB, MachineInstr *MI,
   // Add the 16-bit load / store instruction.
   DebugLoc dl = MI->getDebugLoc();
   MachineInstrBuilder MIB = BuildMI(MBB, MI, dl, TII->get(Opc));
+
+  // tSTMIA_UPD takes a defining register operand. We've already checked that
+  // the register is killed, so mark it as dead here.
+  if (Entry.WideOpc == ARM::t2STMIA)
+    MIB.addReg(MI->getOperand(0).getReg(), RegState::Define | RegState::Dead);
+
   if (!isLdStMul) {
     MIB.addOperand(MI->getOperand(0));
     MIB.addOperand(MI->getOperand(1));

llvm/test/CodeGen/Thumb/ldm-stm-base-materialization.ll

@@ -6,15 +6,17 @@ target triple = "thumbv6m-none--eabi"
 @b = external global i32*
 
 ; Function Attrs: nounwind
-define void @foo() #0 {
+define void @foo24() #0 {
 entry:
-; CHECK-LABEL: foo:
-; CHECK: ldr r[[SB:[0-9]]], .LCPI
+; CHECK-LABEL: foo24:
 ; CHECK: ldr r[[LB:[0-9]]], .LCPI
 ; CHECK: adds r[[NLB:[0-9]]], r[[LB]], #4
-; CHECK-NEXT: ldm r[[NLB]],
+; CHECK: ldr r[[SB:[0-9]]], .LCPI
 ; CHECK: adds r[[NSB:[0-9]]], r[[SB]], #4
-; CHECK-NEXT: stm r[[NSB]]
+; CHECK-NEXT: ldm r[[NLB]]!, {r[[R1:[0-9]]], r[[R2:[0-9]]], r[[R3:[0-9]]]}
+; CHECK-NEXT: stm r[[NSB]]!, {r[[R1]], r[[R2]], r[[R3]]}
+; CHECK-NEXT: ldm r[[NLB]]!, {r[[R1:[0-9]]], r[[R2:[0-9]]], r[[R3:[0-9]]]}
+; CHECK-NEXT: stm r[[NSB]]!, {r[[R1]], r[[R2]], r[[R3]]}
   %0 = load i32*, i32** @a, align 4
   %arrayidx = getelementptr inbounds i32, i32* %0, i32 1
   %1 = bitcast i32* %arrayidx to i8*
@@ -25,5 +27,70 @@ entry:
   ret void
 }
 
+define void @foo28() #0 {
+entry:
+; CHECK-LABEL: foo28:
+; CHECK: ldr r[[LB:[0-9]]], .LCPI
+; CHECK: adds r[[NLB:[0-9]]], r[[LB]], #4
+; CHECK: ldr r[[SB:[0-9]]], .LCPI
+; CHECK: adds r[[NSB:[0-9]]], r[[SB]], #4
+; CHECK-NEXT: ldm r[[NLB]]!, {r[[R1:[0-9]]], r[[R2:[0-9]]], r[[R3:[0-9]]]}
+; CHECK-NEXT: stm r[[NSB]]!, {r[[R1]], r[[R2]], r[[R3]]}
+; CHECK-NEXT: ldm r[[NLB]]!, {r[[R1:[0-9]]], r[[R2:[0-9]]], r[[R3:[0-9]]], r[[R4:[0-9]]]}
+; CHECK-NEXT: stm r[[NSB]]!, {r[[R1]], r[[R2]], r[[R3]], r[[R4]]}
+  %0 = load i32*, i32** @a, align 4
+  %arrayidx = getelementptr inbounds i32, i32* %0, i32 1
+  %1 = bitcast i32* %arrayidx to i8*
+  %2 = load i32*, i32** @b, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %2, i32 1
+  %3 = bitcast i32* %arrayidx1 to i8*
+  tail call void @llvm.memcpy.p0i8.p0i8.i32(i8* %1, i8* %3, i32 28, i32 4, i1 false)
+  ret void
+}
+
+define void @foo32() #0 {
+entry:
+; CHECK-LABEL: foo32:
+; CHECK: ldr r[[LB:[0-9]]], .LCPI
+; CHECK: adds r[[NLB:[0-9]]], r[[LB]], #4
+; CHECK: ldr r[[SB:[0-9]]], .LCPI
+; CHECK: adds r[[NSB:[0-9]]], r[[SB]], #4
+; CHECK-NEXT: ldm r[[NLB]]!, {r[[R1:[0-9]]], r[[R2:[0-9]]], r[[R3:[0-9]]], r[[R4:[0-9]]]}
+; CHECK-NEXT: stm r[[NSB]]!, {r[[R1]], r[[R2]], r[[R3]], r[[R4]]}
+; CHECK-NEXT: ldm r[[NLB]]!, {r[[R1:[0-9]]], r[[R2:[0-9]]], r[[R3:[0-9]]], r[[R4:[0-9]]]}
+; CHECK-NEXT: stm r[[NSB]]!, {r[[R1]], r[[R2]], r[[R3]], r[[R4]]}
+  %0 = load i32*, i32** @a, align 4
+  %arrayidx = getelementptr inbounds i32, i32* %0, i32 1
+  %1 = bitcast i32* %arrayidx to i8*
+  %2 = load i32*, i32** @b, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %2, i32 1
+  %3 = bitcast i32* %arrayidx1 to i8*
+  tail call void @llvm.memcpy.p0i8.p0i8.i32(i8* %1, i8* %3, i32 32, i32 4, i1 false)
+  ret void
+}
+
+define void @foo36() #0 {
+entry:
+; CHECK-LABEL: foo36:
+; CHECK: ldr r[[LB:[0-9]]], .LCPI
+; CHECK: adds r[[NLB:[0-9]]], r[[LB]], #4
+; CHECK: ldr r[[SB:[0-9]]], .LCPI
+; CHECK: adds r[[NSB:[0-9]]], r[[SB]], #4
+; CHECK-NEXT: ldm r[[NLB]]!, {r[[R1:[0-9]]], r[[R2:[0-9]]], r[[R3:[0-9]]]}
+; CHECK-NEXT: stm r[[NSB]]!, {r[[R1]], r[[R2]], r[[R3]]}
+; CHECK-NEXT: ldm r[[NLB]]!, {r[[R1:[0-9]]], r[[R2:[0-9]]], r[[R3:[0-9]]]}
+; CHECK-NEXT: stm r[[NSB]]!, {r[[R1]], r[[R2]], r[[R3]]}
+; CHECK-NEXT: ldm r[[NLB]]!, {r[[R1:[0-9]]], r[[R2:[0-9]]], r[[R3:[0-9]]]}
+; CHECK-NEXT: stm r[[NSB]]!, {r[[R1]], r[[R2]], r[[R3]]}
+  %0 = load i32*, i32** @a, align 4
+  %arrayidx = getelementptr inbounds i32, i32* %0, i32 1
+  %1 = bitcast i32* %arrayidx to i8*
+  %2 = load i32*, i32** @b, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %2, i32 1
+  %3 = bitcast i32* %arrayidx1 to i8*
+  tail call void @llvm.memcpy.p0i8.p0i8.i32(i8* %1, i8* %3, i32 36, i32 4, i1 false)
+  ret void
+}
+
 ; Function Attrs: nounwind
 declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture readonly, i32, i32, i1) #1

llvm/test/CodeGen/Thumb/thumb-memcpy-ldm-stm.ll

@@ -7,8 +7,8 @@ define void @t1() #0 {
 entry:
 ; CHECK-LABEL: t1:
 ; CHECK: ldr r[[LB:[0-9]]],
-; CHECK-NEXT: ldm r[[LB]]!,
 ; CHECK-NEXT: ldr r[[SB:[0-9]]],
+; CHECK-NEXT: ldm r[[LB]]!,
 ; CHECK-NEXT: stm r[[SB]]!,
 ; CHECK-NEXT: ldrb {{.*}}, [r[[LB]]]
 ; CHECK-NEXT: strb {{.*}}, [r[[SB]]]
@@ -21,8 +21,8 @@ define void @t2() #0 {
 entry:
 ; CHECK-LABEL: t2:
 ; CHECK: ldr r[[LB:[0-9]]],
-; CHECK-NEXT: ldm r[[LB]]!,
 ; CHECK-NEXT: ldr r[[SB:[0-9]]],
+; CHECK-NEXT: ldm r[[LB]]!,
 ; CHECK-NEXT: stm r[[SB]]!,
 ; CHECK-NEXT: ldrh {{.*}}, [r[[LB]]]
 ; CHECK-NEXT: ldrb {{.*}}, [r[[LB]], #2]