ISel type legalization: add debug messages. NFC.

[SjoerdMeijer]

Summary

This adds some debug messages to the type legalizer and functions
like PromoteNode, ExpandNode, ExpandLibCall in an attempt to make
the debug messages a little bit more informative and useful.

[SjoerdMeijer]

Added some more.

[samparker]

Hi Sjoerd,

This is some good itch scratching! One comment from me, but no need to re-review. LGTM.

Thanks,
sam

lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

2392 ↗

(On Diff #117344)

I think this debug message and the one above would be more helpful contained in their corresponding if statement.

[SjoerdMeijer]

Hi Sam, many thanks for checking! Cheers, Sjoerd.

llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

if (Val.getValueType() == EltVT ||
 
       return DAG.getVectorShuffle(Vec.getValueType(), dl, Vec, ScVec, ShufOps);
     }
   }
   return PerformInsertVectorEltInMemory(Vec, Val, Idx, dl);
 }
 
 SDValue SelectionDAGLegalize::OptimizeFloatStore(StoreSDNode* ST) {
+  DEBUG(dbgs() << "Optimizing float store operations\n");
   // Turn 'store float 1.0, Ptr' -> 'store int 0x12345678, Ptr'
   // FIXME: We shouldn't do this for TargetConstantFP's.
   // FIXME: move this to the DAG Combiner!  Note that we can't regress due
   // to phase ordering between legalized code and the dag combiner.  This
   // probably means that we need to integrate dag combiner and legalizer
   // together.
   // We generally can't do this one for long doubles.
   SDValue Chain = ST->getChain();
if (CFP->getValueType(0) == MVT::f64) {
         return DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Lo, Hi);
       }
     }
   }
   return SDValue(nullptr, 0);
 }
 
 void SelectionDAGLegalize::LegalizeStoreOps(SDNode *Node) {
-    StoreSDNode *ST = cast<StoreSDNode>(Node);
-    SDValue Chain = ST->getChain();
-    SDValue Ptr = ST->getBasePtr();
-    SDLoc dl(Node);
 
-    unsigned Alignment = ST->getAlignment();
-    MachineMemOperand::Flags MMOFlags = ST->getMemOperand()->getFlags();
-    AAMDNodes AAInfo = ST->getAAInfo();
 
-    if (!ST->isTruncatingStore()) {
-      if (SDNode *OptStore = OptimizeFloatStore(ST).getNode()) {
-        ReplaceNode(ST, OptStore);
-        return;
-      }
+    DEBUG(dbgs() << "Legalizing store operation\n");
 
-      {
-        SDValue Value = ST->getValue();
-        MVT VT = Value.getSimpleValueType();
-        switch (TLI.getOperationAction(ISD::STORE, VT)) {
-        default: llvm_unreachable("This action is not supported yet!");
-        case TargetLowering::Legal: {
-          // If this is an unaligned store and the target doesn't support it,
-          // expand it.
-          EVT MemVT = ST->getMemoryVT();
-          unsigned AS = ST->getAddressSpace();
-          unsigned Align = ST->getAlignment();
-          const DataLayout &DL = DAG.getDataLayout();
-          if (!TLI.allowsMemoryAccess(*DAG.getContext(), DL, MemVT, AS, Align)) {
-            SDValue Result = TLI.expandUnalignedStore(ST, DAG);
-            ReplaceNode(SDValue(ST, 0), Result);
-          }
-          break;
-        }
-        case TargetLowering::Custom: {
-          SDValue Res = TLI.LowerOperation(SDValue(Node, 0), DAG);
-          if (Res && Res != SDValue(Node, 0))
-            ReplaceNode(SDValue(Node, 0), Res);
-          return;
-        }
-        case TargetLowering::Promote: {
-          MVT NVT = TLI.getTypeToPromoteTo(ISD::STORE, VT);
-          assert(NVT.getSizeInBits() == VT.getSizeInBits() &&
-                 "Can only promote stores to same size type");
-          Value = DAG.getNode(ISD::BITCAST, dl, NVT, Value);
-          SDValue Result =
-              DAG.getStore(Chain, dl, Value, Ptr, ST->getPointerInfo(),
-                           Alignment, MMOFlags, AAInfo);
-          ReplaceNode(SDValue(Node, 0), Result);
-          break;
-        }
-        }
-        return;
-      }
-    } else {
-      SDValue Value = ST->getValue();
+        DEBUG(dbgs() << "Expanding unsupported unaligned store\n");
+      } else
+        DEBUG(dbgs() << "Legal store\n");
+      DEBUG(dbgs() << "Trying custom lowering\n");
 
-      EVT StVT = ST->getMemoryVT();
-      unsigned StWidth = StVT.getSizeInBits();
-      auto &DL = DAG.getDataLayout();
+  DEBUG(dbgs() << "Legalizing truncating store operations\n");
+  SDValue Value = ST->getValue();
 
-      if (StWidth != StVT.getStoreSizeInBits()) {
-        // Promote to a byte-sized store with upper bits zero if not
-        // storing an integral number of bytes.  For example, promote
-        // TRUNCSTORE:i1 X -> TRUNCSTORE:i8 (and X, 1)
-        EVT NVT = EVT::getIntegerVT(*DAG.getContext(),
-                                    StVT.getStoreSizeInBits());
-        Value = DAG.getZeroExtendInReg(Value, dl, StVT);
-        SDValue Result =
-            DAG.getTruncStore(Chain, dl, Value, Ptr, ST->getPointerInfo(), NVT,
-                              Alignment, MMOFlags, AAInfo);
-        ReplaceNode(SDValue(Node, 0), Result);
-      } else if (StWidth & (StWidth - 1)) {
-        // If not storing a power-of-2 number of bits, expand as two stores.
-        assert(!StVT.isVector() && "Unsupported truncstore!");
-        unsigned RoundWidth = 1 << Log2_32(StWidth);
-        assert(RoundWidth < StWidth);
-        unsigned ExtraWidth = StWidth - RoundWidth;
-        assert(ExtraWidth < RoundWidth);
-        assert(!(RoundWidth % 8) && !(ExtraWidth % 8) &&
-               "Store size not an integral number of bytes!");
-        EVT RoundVT = EVT::getIntegerVT(*DAG.getContext(), RoundWidth);
-        EVT ExtraVT = EVT::getIntegerVT(*DAG.getContext(), ExtraWidth);
-        SDValue Lo, Hi;
-        unsigned IncrementSize;
 
-        if (DL.isLittleEndian()) {
-          // TRUNCSTORE:i24 X -> TRUNCSTORE:i16 X, TRUNCSTORE@+2:i8 (srl X, 16)
-          // Store the bottom RoundWidth bits.
-          Lo = DAG.getTruncStore(Chain, dl, Value, Ptr, ST->getPointerInfo(),
-                                 RoundVT, Alignment, MMOFlags, AAInfo);
 
-          // Store the remaining ExtraWidth bits.
-          IncrementSize = RoundWidth / 8;
-          Ptr = DAG.getNode(ISD::ADD, dl, Ptr.getValueType(), Ptr,
-                            DAG.getConstant(IncrementSize, dl,
-                                            Ptr.getValueType()));
-          Hi = DAG.getNode(
-              ISD::SRL, dl, Value.getValueType(), Value,
-              DAG.getConstant(RoundWidth, dl,
-                              TLI.getShiftAmountTy(Value.getValueType(), DL)));
-          Hi = DAG.getTruncStore(
-              Chain, dl, Hi, Ptr,
-              ST->getPointerInfo().getWithOffset(IncrementSize), ExtraVT,
-              MinAlign(Alignment, IncrementSize), MMOFlags, AAInfo);
-        } else {
-          // Big endian - avoid unaligned stores.
-          // TRUNCSTORE:i24 X -> TRUNCSTORE:i16 (srl X, 8), TRUNCSTORE@+2:i8 X
-          // Store the top RoundWidth bits.
-          Hi = DAG.getNode(
-              ISD::SRL, dl, Value.getValueType(), Value,
-              DAG.getConstant(ExtraWidth, dl,
-                              TLI.getShiftAmountTy(Value.getValueType(), DL)));
-          Hi = DAG.getTruncStore(Chain, dl, Hi, Ptr, ST->getPointerInfo(),
-                                 RoundVT, Alignment, MMOFlags, AAInfo);
 
-          // Store the remaining ExtraWidth bits.
-          IncrementSize = RoundWidth / 8;
-          Ptr = DAG.getNode(ISD::ADD, dl, Ptr.getValueType(), Ptr,
-                            DAG.getConstant(IncrementSize, dl,
-                                            Ptr.getValueType()));
-          Lo = DAG.getTruncStore(
-              Chain, dl, Value, Ptr,
-              ST->getPointerInfo().getWithOffset(IncrementSize), ExtraVT,
-              MinAlign(Alignment, IncrementSize), MMOFlags, AAInfo);
-        }
 
-        // The order of the stores doesn't matter.
-        SDValue Result = DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Lo, Hi);
-        ReplaceNode(SDValue(Node, 0), Result);
-      } else {
-        switch (TLI.getTruncStoreAction(ST->getValue().getValueType(), StVT)) {
-        default: llvm_unreachable("This action is not supported yet!");
-        case TargetLowering::Legal: {
-          EVT MemVT = ST->getMemoryVT();
-          unsigned AS = ST->getAddressSpace();
-          unsigned Align = ST->getAlignment();
-          // If this is an unaligned store and the target doesn't support it,
-          // expand it.
-          if (!TLI.allowsMemoryAccess(*DAG.getContext(), DL, MemVT, AS, Align)) {
-            SDValue Result = TLI.expandUnalignedStore(ST, DAG);
-            ReplaceNode(SDValue(ST, 0), Result);
-          }
-          break;
-        }
-        case TargetLowering::Custom: {
-          SDValue Res = TLI.LowerOperation(SDValue(Node, 0), DAG);
-          if (Res && Res != SDValue(Node, 0))
-            ReplaceNode(SDValue(Node, 0), Res);
-          return;
-        }
-        case TargetLowering::Expand:
-          assert(!StVT.isVector() &&
-                 "Vector Stores are handled in LegalizeVectorOps");
 
-          // TRUNCSTORE:i16 i32 -> STORE i16
-          assert(TLI.isTypeLegal(StVT) &&
-                 "Do not know how to expand this store!");
-          Value = DAG.getNode(ISD::TRUNCATE, dl, StVT, Value);
-          SDValue Result =
-              DAG.getStore(Chain, dl, Value, Ptr, ST->getPointerInfo(),
-                           Alignment, MMOFlags, AAInfo);
-          ReplaceNode(SDValue(Node, 0), Result);
-          break;
-        }
-      }
-    }
-}
 
 void SelectionDAGLegalize::LegalizeLoadOps(SDNode *Node) {
   LoadSDNode *LD = cast<LoadSDNode>(Node);
   SDValue Chain = LD->getChain();  // The chain.
   SDValue Ptr = LD->getBasePtr();  // The base pointer.
   SDValue Value;                   // The value returned by the load op.
   SDLoc dl(Node);
 
   ISD::LoadExtType ExtType = LD->getExtensionType();
   if (ExtType == ISD::NON_EXTLOAD) {
+    DEBUG(dbgs() << "Legalizing non-extending load operation\n");
     MVT VT = Node->getSimpleValueType(0);
     SDValue RVal = SDValue(Node, 0);
     SDValue RChain = SDValue(Node, 1);
 
     switch (TLI.getOperationAction(Node->getOpcode(), VT)) {
     default: llvm_unreachable("This action is not supported yet!");
     case TargetLowering::Legal: {
       EVT MemVT = LD->getMemoryVT();
if (RChain.getNode() != Node) {
         UpdatedNodes->insert(RVal.getNode());
         UpdatedNodes->insert(RChain.getNode());
       }
       ReplacedNode(Node);
     }
     return;
   }
 
+  DEBUG(dbgs() << "Legalizing extending load operation\n");
   EVT SrcVT = LD->getMemoryVT();
   unsigned SrcWidth = SrcVT.getSizeInBits();
   unsigned Alignment = LD->getAlignment();
   MachineMemOperand::Flags MMOFlags = LD->getMemOperand()->getFlags();
   AAMDNodes AAInfo = LD->getAAInfo();
 
   if (SrcWidth != SrcVT.getStoreSizeInBits() &&
       // Some targets pretend to have an i1 loading operation, and actually
if (SimpleFinishLegalizing) {
     }
 
     if (NewNode != Node) {
       ReplaceNode(Node, NewNode);
       Node = NewNode;
     }
     switch (Action) {
     case TargetLowering::Legal:
+      DEBUG(dbgs() << "Legal node: nothing to do\n");
       return;
     case TargetLowering::Custom:
+      DEBUG(dbgs() << "Trying custom legalization\n");
       // FIXME: The handling for custom lowering with multiple results is
       // a complete mess.
       if (SDValue Res = TLI.LowerOperation(SDValue(Node, 0), DAG)) {
         if (!(Res.getNode() != Node || Res.getResNo() != 0))
           return;
 
         if (Node->getNumValues() == 1) {
+          DEBUG(dbgs() << "Successfully custom legalized node\n");
           // We can just directly replace this node with the lowered value.
           ReplaceNode(SDValue(Node, 0), Res);
           return;
         }
 
         SmallVector<SDValue, 8> ResultVals;
         for (unsigned i = 0, e = Node->getNumValues(); i != e; ++i)
           ResultVals.push_back(Res.getValue(i));
+        DEBUG(dbgs() << "Successfully custom legalized node\n");
         ReplaceNode(Node, ResultVals.data());
         return;
       }
+      DEBUG(dbgs() << "Could not custom legalize node\n");
       LLVM_FALLTHROUGH;
     case TargetLowering::Expand:
       if (ExpandNode(Node))
         return;
       LLVM_FALLTHROUGH;
     case TargetLowering::LibCall:
       ConvertNodeToLibcall(Node);
       return;
CLI.setDebugLoc(SDLoc(Node))
                     std::move(Args))
       .setTailCall(isTailCall)
       .setSExtResult(isSigned)
       .setZExtResult(!isSigned)
       .setIsPostTypeLegalization(true);
 
   std::pair<SDValue, SDValue> CallInfo = TLI.LowerCallTo(CLI);
 
-  if (!CallInfo.second.getNode())
+  if (!CallInfo.second.getNode()) {
+    DEBUG(dbgs() << "Created tailcall: "; DAG.getRoot().dump());
     // It's a tailcall, return the chain (which is the DAG root).
     return DAG.getRoot();
+  }
 
+  DEBUG(dbgs() << "Created libcall: "; CallInfo.first.dump());
   return CallInfo.first;
 }
 
 /// Generate a libcall taking the given operands as arguments
 /// and returning a result of type RetVT.
 SDValue SelectionDAGLegalize::ExpandLibCall(RTLIB::Libcall LC, EVT RetVT,
                                             const SDValue *Ops, unsigned NumOps,
                                             bool isSigned, const SDLoc &dl) {

 /// This function is responsible for legalizing a
 /// INT_TO_FP operation of the specified operand when the target requests that
 /// we expand it.  At this point, we know that the result and operand types are
 /// legal for the target.
 SDValue SelectionDAGLegalize::ExpandLegalINT_TO_FP(bool isSigned, SDValue Op0,
                                                    EVT DestVT,
                                                    const SDLoc &dl) {
   // TODO: Should any fast-math-flags be set for the created nodes?
-
+  DEBUG(dbgs() << "Legalizing INT_TO_FP\n");
   if (Op0.getValueType() == MVT::i32 && TLI.isTypeLegal(MVT::f64)) {
-    // simple 32-bit [signed|unsigned] integer to float/double expansion
+    DEBUG(dbgs() << "32-bit [signed|unsigned] integer to float/double "
+                    "expansion\n");
 
     // Get the stack frame index of a 8 byte buffer.
     SDValue StackSlot = DAG.CreateStackTemporary(MVT::f64);
 
     // word offset constant for Hi/Lo address computation
     SDValue WordOff = DAG.getConstant(sizeof(int), dl,
                                       StackSlot.getValueType());
     // set up Hi and Lo (into buffer) address based on endian
SDValue SelectionDAGLegalize::ExpandLegalINT_TO_FP(bool isSigned, SDValue Op0,
   // Code below here assumes !isSigned without checking again.
 
   // Implementation of unsigned i64 to f64 following the algorithm in
   // __floatundidf in compiler_rt. This implementation has the advantage
   // of performing rounding correctly, both in the default rounding mode
   // and in all alternate rounding modes.
   // TODO: Generalize this for use with other types.
   if (Op0.getValueType() == MVT::i64 && DestVT == MVT::f64) {
+    DEBUG(dbgs() << "Converting unsigned i64 to f64\n");
     SDValue TwoP52 =
       DAG.getConstant(UINT64_C(0x4330000000000000), dl, MVT::i64);
     SDValue TwoP84PlusTwoP52 =
       DAG.getConstantFP(BitsToDouble(UINT64_C(0x4530000000100000)), dl,
                         MVT::f64);
     SDValue TwoP84 =
       DAG.getConstant(UINT64_C(0x4530000000000000), dl, MVT::i64);
 
     SDValue Lo = DAG.getZeroExtendInReg(Op0, dl, MVT::i32);
     SDValue Hi = DAG.getNode(ISD::SRL, dl, MVT::i64, Op0,
                              DAG.getConstant(32, dl, MVT::i64));
     SDValue LoOr = DAG.getNode(ISD::OR, dl, MVT::i64, Lo, TwoP52);
     SDValue HiOr = DAG.getNode(ISD::OR, dl, MVT::i64, Hi, TwoP84);
     SDValue LoFlt = DAG.getNode(ISD::BITCAST, dl, MVT::f64, LoOr);
     SDValue HiFlt = DAG.getNode(ISD::BITCAST, dl, MVT::f64, HiOr);
     SDValue HiSub = DAG.getNode(ISD::FSUB, dl, MVT::f64, HiFlt,
                                 TwoP84PlusTwoP52);
     return DAG.getNode(ISD::FADD, dl, MVT::f64, LoFlt, HiSub);
   }
 
-  // Implementation of unsigned i64 to f32.
   // TODO: Generalize this for use with other types.
   if (Op0.getValueType() == MVT::i64 && DestVT == MVT::f32) {
+    DEBUG(dbgs() << "Converting unsigned i64 to f32\n");
     // For unsigned conversions, convert them to signed conversions using the
     // algorithm from the x86_64 __floatundidf in compiler_rt.
     if (!isSigned) {
       SDValue Fast = DAG.getNode(ISD::SINT_TO_FP, dl, MVT::f32, Op0);
 
       SDValue ShiftConst = DAG.getConstant(
           1, dl, TLI.getShiftAmountTy(Op0.getValueType(), DAG.getDataLayout()));
       SDValue Shr = DAG.getNode(ISD::SRL, dl, MVT::i64, Op0, ShiftConst);
if (!TLI.isOperationLegalOrCustom(ISD::CTPOP, VT) &&
                          DAG.getConstant(VT.getSizeInBits(), dl, VT),
                          DAG.getNode(ISD::CTLZ, dl, VT, Tmp3));
     return DAG.getNode(ISD::CTPOP, dl, VT, Tmp3);
   }
   }
 }
 
 bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
+  DEBUG(dbgs() << "Trying to expand node\n");
   SmallVector<SDValue, 8> Results;
   SDLoc dl(Node);
   SDValue Tmp1, Tmp2, Tmp3, Tmp4;
   bool NeedInvert;
   switch (Node->getOpcode()) {
   case ISD::CTPOP:
   case ISD::CTLZ:
   case ISD::CTLZ_ZERO_UNDEF:
if (Node->getValueType(0) != MVT::f32) {
       // CodeGen the option of emitting that before resorting to a libcall.
       SDValue Res =
           DAG.getNode(ISD::FP16_TO_FP, dl, MVT::f32, Node->getOperand(0));
       Results.push_back(
           DAG.getNode(ISD::FP_EXTEND, dl, Node->getValueType(0), Res));
     }
     break;
   case ISD::FP_TO_FP16:
+    DEBUG(dbgs() << "Legalizing FP_TO_FP16\n");
     if (!TLI.useSoftFloat() && TM.Options.UnsafeFPMath) {
       SDValue Op = Node->getOperand(0);
       MVT SVT = Op.getSimpleValueType();
       if ((SVT == MVT::f64 || SVT == MVT::f80) &&
           TLI.isOperationLegalOrCustom(ISD::FP_TO_FP16, MVT::f32)) {
         // Under fastmath, we can expand this node into a fround followed by
         // a float-half conversion.
         SDValue FloatVal = DAG.getNode(ISD::FP_ROUND, dl, MVT::f32, Op,

   case ISD::INTRINSIC_W_CHAIN:
   case ISD::INTRINSIC_WO_CHAIN:
   case ISD::INTRINSIC_VOID:
     // FIXME: Custom lowering for these operations shouldn't return null!
     break;
   }
 
   // Replace the original node with the legalized result.
-  if (Results.empty())
+  if (Results.empty()) {
+    DEBUG(dbgs() << "Cannot expand node\n");
     return false;
+  }
 
+  DEBUG(dbgs() << "Succesfully expanded node\n");
   ReplaceNode(Node, Results.data());
   return true;
 }
 
 void SelectionDAGLegalize::ConvertNodeToLibcall(SDNode *Node) {
+  DEBUG(dbgs() << "Trying to convert node to libcall\n");
   SmallVector<SDValue, 8> Results;
   SDLoc dl(Node);
   SDValue Tmp1, Tmp2, Tmp3, Tmp4;
   unsigned Opc = Node->getOpcode();
   switch (Opc) {
   case ISD::ATOMIC_FENCE: {
     // If the target didn't lower this, lower it to '__sync_synchronize()' call
     // FIXME: handle "fence singlethread" more efficiently.
case ISD::MUL:
     Results.push_back(ExpandIntLibCall(Node, false,
                                        RTLIB::MUL_I8,
                                        RTLIB::MUL_I16, RTLIB::MUL_I32,
                                        RTLIB::MUL_I64, RTLIB::MUL_I128));
     break;
   }
 
   // Replace the original node with the legalized result.
-  if (!Results.empty())
+  if (!Results.empty()) {
+    DEBUG(dbgs() << "Successfully converted node to libcall\n");
     ReplaceNode(Node, Results.data());
+  } else
+    DEBUG(dbgs() << "Could not convert node to libcall\n");
 }
 
 // Determine the vector type to use in place of an original scalar element when
 // promoting equally sized vectors.
 static MVT getPromotedVectorElementType(const TargetLowering &TLI,
                                         MVT EltVT, MVT NewEltVT) {
   unsigned OldEltsPerNewElt = EltVT.getSizeInBits() / NewEltVT.getSizeInBits();
   MVT MidVT = MVT::getVectorVT(NewEltVT, OldEltsPerNewElt);
   assert(TLI.isTypeLegal(MidVT) && "unexpected");
   return MidVT;
 }
 
 void SelectionDAGLegalize::PromoteNode(SDNode *Node) {
+  DEBUG(dbgs() << "Trying to promote node\n");
   SmallVector<SDValue, 8> Results;
   MVT OVT = Node->getSimpleValueType(0);
   if (Node->getOpcode() == ISD::UINT_TO_FP ||
       Node->getOpcode() == ISD::SINT_TO_FP ||
       Node->getOpcode() == ISD::SETCC ||
       Node->getOpcode() == ISD::EXTRACT_VECTOR_ELT ||
       Node->getOpcode() == ISD::INSERT_VECTOR_ELT) {
     OVT = Node->getOperand(0).getSimpleValueType();
case ISD::SCALAR_TO_VECTOR: {
     SDValue Concat = DAG.getNode(ISD::CONCAT_VECTORS, SL, NVT, NewElts);
     SDValue CvtVec = DAG.getNode(ISD::BITCAST, SL, OVT, Concat);
     Results.push_back(CvtVec);
     break;
   }
   }
 
   // Replace the original node with the legalized result.
-  if (!Results.empty())
+  if (!Results.empty()) {
+    DEBUG(dbgs() << "Successfully promoted node\n");
     ReplaceNode(Node, Results.data());
+  } else
+    DEBUG(dbgs() << "Could not promote node\n");
 }
 
 /// This is the entry point for the file.
 void SelectionDAG::Legalize() {
   AssignTopologicalOrder();
 
   SmallPtrSet<SDNode *, 16> LegalizedNodes;
   // Use a delete listener to remove nodes which were deleted during

llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp

CLI.setDebugLoc(dl)
       .setTailCall(IsTC);
   std::pair<SDValue, SDValue> CI = TLI.LowerCallTo(CLI);
 
   // Return the chain (the DAG root) if it is a tail call
   return !CI.second.getNode() ? DAG.getRoot() : CI.first;
 }
 
 SDValue ARMTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
+  DEBUG(dbgs() << "Lowering node: "; Op.dump());
   switch (Op.getOpcode()) {
   default: llvm_unreachable("Don't know how to custom lower this!");
   case ISD::WRITE_REGISTER: return LowerWRITE_REGISTER(Op, DAG);
   case ISD::ConstantPool: return LowerConstantPool(Op, DAG);
   case ISD::BlockAddress:  return LowerBlockAddress(Op, DAG);
   case ISD::GlobalAddress: return LowerGlobalAddress(Op, DAG);
   case ISD::GlobalTLSAddress: return LowerGlobalTLSAddress(Op, DAG);
   case ISD::SELECT:        return LowerSELECT(Op, DAG);