[Assignment Tracking Analysis][4/*] Plumb analysis results into SelectionDAG

[Orlando]

Summary

With assignment tracking enabled debug intrinsics are ignored by SelectionDAG and it instead reads location definitions generated by the analysis pass.

SelectionDAG itself has no fundamental need to refer to debug intrinsics directly so this change is fairly straightforward.

The analysis results are used in SelectionDAGBuilder::visit - fetching the batch of definitions that come just before each instruction that is about to be processed, and processing them as if they were debug intrinsics. They're also used in SelectionDAGISel::SelectAllBasicBlocks where dbg.declare intrinsic behaviour is mimicked for single memory location defs.

DanglingDebugInfo has been updated to point to a either a DbgValueInst or a VarLocRecord, and its API has been updated to fetch information from whichever it was initialised with.

---

With this, tests can be added - coming in the next patch.

[StephenTozer]

Mostly boilerplate, but the substance of this LGTM.

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

1337

Since processDbgDeclares is not the only function that will call this now-extracted code, probably best to just use the name of this function directly so as not to mislead.

[Orlando]

Thanks for the review.

+Update to address nit

[Orlando]

Squashed into 1d1de7467c32d52926ca56b9167a2c65c451ecfa

llvm/include/llvm/CodeGen/SelectionDAG.h

 class BlockAddress;
 class BlockFrequencyInfo;
 class Constant;
 class ConstantFP;
 class ConstantInt;
 class DataLayout;
 struct fltSemantics;
 class FunctionLoweringInfo;
+class FunctionVarLocs;
 class GlobalValue;
 struct KnownBits;
 class LegacyDivergenceAnalysis;
 class LLVMContext;
 class MachineBasicBlock;
 class MachineConstantPoolValue;
 class MCSymbol;
 class OptimizationRemarkEmitter;

 /// but is significantly more simple, powerful, and is a graph form instead of a
 /// linear form.
 ///
 class SelectionDAG {
   const TargetMachine &TM;
   const SelectionDAGTargetInfo *TSI = nullptr;
   const TargetLowering *TLI = nullptr;
   const TargetLibraryInfo *LibInfo = nullptr;
+  const FunctionVarLocs *FnVarLocs = nullptr;
   MachineFunction *MF;
   Pass *SDAGISelPass = nullptr;
   LLVMContext *Context;
   CodeGenOpt::Level OptLevel;
 
   LegacyDivergenceAnalysis * DA = nullptr;
   FunctionLoweringInfo * FLI = nullptr;
 
public:
   explicit SelectionDAG(const TargetMachine &TM, CodeGenOpt::Level);
   SelectionDAG(const SelectionDAG &) = delete;
   SelectionDAG &operator=(const SelectionDAG &) = delete;
   ~SelectionDAG();
 
   /// Prepare this SelectionDAG to process code in the given MachineFunction.
   void init(MachineFunction &NewMF, OptimizationRemarkEmitter &NewORE,
             Pass *PassPtr, const TargetLibraryInfo *LibraryInfo,
-            LegacyDivergenceAnalysis * Divergence,
-            ProfileSummaryInfo *PSIin, BlockFrequencyInfo *BFIin);
+            LegacyDivergenceAnalysis *Divergence, ProfileSummaryInfo *PSIin,
+            BlockFrequencyInfo *BFIin, FunctionVarLocs const *FnVarLocs);
 
   void setFunctionLoweringInfo(FunctionLoweringInfo * FuncInfo) {
     FLI = FuncInfo;
   }
 
   /// Clear state and free memory necessary to make this
   /// SelectionDAG ready to process a new block.
   void clear();
 
   MachineFunction &getMachineFunction() const { return *MF; }
   const Pass *getPass() const { return SDAGISelPass; }
 
   const DataLayout &getDataLayout() const { return MF->getDataLayout(); }
   const TargetMachine &getTarget() const { return TM; }
   const TargetSubtargetInfo &getSubtarget() const { return MF->getSubtarget(); }
   template <typename STC> const STC &getSubtarget() const {
     return MF->getSubtarget<STC>();
   }
   const TargetLowering &getTargetLoweringInfo() const { return *TLI; }
   const TargetLibraryInfo &getLibInfo() const { return *LibInfo; }
   const SelectionDAGTargetInfo &getSelectionDAGInfo() const { return *TSI; }
   const LegacyDivergenceAnalysis *getDivergenceAnalysis() const { return DA; }
+  /// Returns the result of the AssignmentTrackingAnalysis pass if it's
+  /// available, otherwise return nullptr.
+  const FunctionVarLocs *getFunctionVarLocs() const { return FnVarLocs; }
   LLVMContext *getContext() const { return Context; }
   OptimizationRemarkEmitter &getORE() const { return *ORE; }
   ProfileSummaryInfo *getPSI() const { return PSI; }
   BlockFrequencyInfo *getBFI() const { return BFI; }
 
   FlagInserter *getFlagInserter() { return Inserter; }
   void setFlagInserter(FlagInserter *FI) { Inserter = FI; }
 

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

SelectionDAG::SelectionDAG(const TargetMachine &tm, CodeGenOpt::Level OL)
     : TM(tm), OptLevel(OL),
       EntryNode(ISD::EntryToken, 0, DebugLoc(), getVTList(MVT::Other, MVT::Glue)),
       Root(getEntryNode()) {
   InsertNode(&EntryNode);
   DbgInfo = new SDDbgInfo();
 }
 
 void SelectionDAG::init(MachineFunction &NewMF,
-                        OptimizationRemarkEmitter &NewORE,
-                        Pass *PassPtr, const TargetLibraryInfo *LibraryInfo,
-                        LegacyDivergenceAnalysis * Divergence,
-                        ProfileSummaryInfo *PSIin,
-                        BlockFrequencyInfo *BFIin) {
+                        OptimizationRemarkEmitter &NewORE, Pass *PassPtr,
+                        const TargetLibraryInfo *LibraryInfo,
+                        LegacyDivergenceAnalysis *Divergence,
+                        ProfileSummaryInfo *PSIin, BlockFrequencyInfo *BFIin,
+                        FunctionVarLocs const *VarLocs) {
   MF = &NewMF;
   SDAGISelPass = PassPtr;
   ORE = &NewORE;
   TLI = getSubtarget().getTargetLowering();
   TSI = getSubtarget().getSelectionDAGInfo();
   LibInfo = LibraryInfo;
   Context = &MF->getFunction().getContext();
   DA = Divergence;
   PSI = PSIin;
   BFI = BFIin;
+  FnVarLocs = VarLocs;
 }
 
 SelectionDAG::~SelectionDAG() {
   assert(!UpdateListeners && "Dangling registered DAGUpdateListeners");
   allnodes_clear();
   OperandRecycler.clear(OperandAllocator);
   delete DbgInfo;
 }

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h

 #ifndef LLVM_LIB_CODEGEN_SELECTIONDAG_SELECTIONDAGBUILDER_H
 #define LLVM_LIB_CODEGEN_SELECTIONDAG_SELECTIONDAGBUILDER_H
 
 #include "StatepointLowering.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/CodeGen/AssignmentTrackingAnalysis.h"
 #include "llvm/CodeGen/CodeGenCommonISel.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
 #include "llvm/CodeGen/SelectionDAGNodes.h"
 #include "llvm/CodeGen/SwitchLoweringUtils.h"
 #include "llvm/CodeGen/TargetLowering.h"
 #include "llvm/CodeGen/ValueTypes.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Instruction.h"
class SelectionDAGBuilder {
   DenseMap<const Value*, SDValue> NodeMap;
 
   /// Maps argument value for unused arguments. This is used
   /// to preserve debug information for incoming arguments.
   DenseMap<const Value*, SDValue> UnusedArgNodeMap;
 
   /// Helper type for DanglingDebugInfoMap.
   class DanglingDebugInfo {
-    const DbgValueInst *DI = nullptr;
+    using DbgValTy = const DbgValueInst *;
+    using VarLocTy = const VarLocInfo *;
+    PointerUnion<DbgValTy, VarLocTy> Info;
     unsigned SDNodeOrder = 0;
 
   public:
     DanglingDebugInfo() = default;
     DanglingDebugInfo(const DbgValueInst *DI, unsigned SDNO)
-        : DI(DI), SDNodeOrder(SDNO) {
-      assert(!DI->hasArgList() &&
-             "Dangling variadic debug values not supported yet");
+        : Info(DI), SDNodeOrder(SDNO) {}
+    DanglingDebugInfo(const VarLocInfo *VarLoc, unsigned SDNO)
+        : Info(VarLoc), SDNodeOrder(SDNO) {}
+
+    DILocalVariable *getVariable(const FunctionVarLocs *Locs) const {
+      if (Info.is<VarLocTy>())
+        return Locs->getDILocalVariable(Info.get<VarLocTy>()->VariableID);
+      return Info.get<DbgValTy>()->getVariable();
+    }
+    DIExpression *getExpression() const {
+      if (Info.is<VarLocTy>())
+        return Info.get<VarLocTy>()->Expr;
+      return Info.get<DbgValTy>()->getExpression();
     }
-
-    DILocalVariable *getVariable() const { return DI->getVariable(); }
-    DIExpression *getExpression() const { return DI->getExpression(); }
     Value *getVariableLocationOp(unsigned Idx) const {
       assert(Idx == 0 && "Dangling variadic debug values not supported yet");
-      return DI->getVariableLocationOp(Idx);
+      if (Info.is<VarLocTy>())
+        return Info.get<VarLocTy>()->V;
+      return Info.get<DbgValTy>()->getVariableLocationOp(Idx);
+    }
+    DebugLoc getDebugLoc() const {
+      if (Info.is<VarLocTy>())
+        return Info.get<VarLocTy>()->DL;
+      return Info.get<DbgValTy>()->getDebugLoc();
     }
-    DebugLoc getDebugLoc() const { return DI->getDebugLoc(); }
     unsigned getSDNodeOrder() const { return SDNodeOrder; }
 
+    /// Helper for printing DanglingDebugInfo. This hoop-jumping is to
+    /// accommodate the fact that an argument is required for getVariable.
+    /// Call SelectionDAGBuilder::printDDI instead of using directly.
+    struct Print {
+      Print(const DanglingDebugInfo &DDI, const FunctionVarLocs *VarLocs)
+          : DDI(DDI), VarLocs(VarLocs) {}
+      const DanglingDebugInfo &DDI;
+      const FunctionVarLocs *VarLocs;
       friend raw_ostream &operator<<(raw_ostream &OS,
-                                   const DanglingDebugInfo &Info) {
-      OS << "DDI(var=" << *Info.getVariable()
-         << ", val= " << *Info.getVariableLocationOp(0)
-         << ", expr=" << *Info.getExpression()
-         << ", order=" << Info.getSDNodeOrder()
-         << ", loc=" << Info.getDebugLoc() << ")";
+                                     const DanglingDebugInfo::Print &P) {
+        OS << "DDI(var=" << *P.DDI.getVariable(P.VarLocs)
+           << ", val= " << *P.DDI.getVariableLocationOp(0)
+           << ", expr=" << *P.DDI.getExpression()
+           << ", order=" << P.DDI.getSDNodeOrder()
+           << ", loc=" << P.DDI.getDebugLoc() << ")";
         return OS;
       }
     };
+  };
+
+  /// Returns an object that defines `raw_ostream &operator<<` for printing.
+  /// Usage example:
+  ////    errs() << printDDI(MyDanglingInfo) << " is dangling\n";
+  DanglingDebugInfo::Print printDDI(const DanglingDebugInfo &DDI) {
+    return DanglingDebugInfo::Print(DDI, DAG.getFunctionVarLocs());
+  }
 
   /// Helper type for DanglingDebugInfoMap.
   typedef std::vector<DanglingDebugInfo> DanglingDebugInfoVector;
 
   /// Keeps track of dbg_values for which we have not yet seen the referent.
   /// We defer handling these until we do see it.
   MapVector<const Value*, DanglingDebugInfoVector> DanglingDebugInfoMap;
 
public:
   void visit(unsigned Opcode, const User &I);
 
   /// If there was virtual register allocated for the value V emit CopyFromReg
   /// of the specified type Ty. Return empty SDValue() otherwise.
   SDValue getCopyFromRegs(const Value *V, Type *Ty);
 
   /// Register a dbg_value which relies on a Value which we have not yet seen.
   void addDanglingDebugInfo(const DbgValueInst *DI, unsigned Order);
+  void addDanglingDebugInfo(const VarLocInfo *VarLoc, unsigned Order);
 
   /// If we have dangling debug info that describes \p Variable, or an
   /// overlapping part of variable considering the \p Expr, then this method
   /// will drop that debug info as it isn't valid any longer.
   void dropDanglingDebugInfo(const DILocalVariable *Variable,
                              const DIExpression *Expr);
 
   /// If we saw an earlier dbg_value referring to V, generate the debug data

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

 #include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/EHPersonalities.h"
 #include "llvm/Analysis/Loads.h"
 #include "llvm/Analysis/MemoryLocation.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/CodeGen/Analysis.h"
+#include "llvm/CodeGen/AssignmentTrackingAnalysis.h"
 #include "llvm/CodeGen/CodeGenCommonISel.h"
 #include "llvm/CodeGen/FunctionLoweringInfo.h"
 #include "llvm/CodeGen/GCMetadata.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineInstrBundleIterator.h"

 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/CallingConv.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GetElementPtrTypeIterator.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instructions.h"

 }
 
 void SelectionDAGBuilder::visit(const Instruction &I) {
   // Set up outgoing PHI node register values before emitting the terminator.
   if (I.isTerminator()) {
     HandlePHINodesInSuccessorBlocks(I.getParent());
   }
 
+  // Add SDDbgValue nodes for any var locs here. Do so before updating
+  // SDNodeOrder, as this mapping is {Inst -> Locs BEFORE Inst}.
+  if (FunctionVarLocs const *FnVarLocs = DAG.getFunctionVarLocs()) {
+    // Add SDDbgValue nodes for any var locs here. Do so before updating
+    // SDNodeOrder, as this mapping is {Inst -> Locs BEFORE Inst}.
+    for (auto It = FnVarLocs->locs_begin(&I), End = FnVarLocs->locs_end(&I);
+         It != End; ++It) {
+      auto *Var = FnVarLocs->getDILocalVariable(It->VariableID);
+      dropDanglingDebugInfo(Var, It->Expr);
+      if (!handleDebugValue(It->V, Var, It->Expr, It->DL, SDNodeOrder,
+                            /*IsVariadic=*/false))
+        addDanglingDebugInfo(It, SDNodeOrder);
+    }
+  }
+
   // Increase the SDNodeOrder if dealing with a non-debug instruction.
   if (!isa<DbgInfoIntrinsic>(I))
     ++SDNodeOrder;
 
   CurInst = &I;
 
   // Set inserted listener only if required.
   bool NodeInserted = false;
void SelectionDAGBuilder::visit(unsigned Opcode, const User &I) {
   default: llvm_unreachable("Unknown instruction type encountered!");
     // Build the switch statement using the Instruction.def file.
 #define HANDLE_INST(NUM, OPCODE, CLASS) \
     case Instruction::OPCODE: visit##OPCODE((const CLASS&)I); break;
 #include "llvm/IR/Instruction.def"
   }
 }
 
+void SelectionDAGBuilder::addDanglingDebugInfo(const VarLocInfo *VarLoc,
+                                               unsigned Order) {
+  DanglingDebugInfoMap[VarLoc->V].emplace_back(VarLoc, Order);
+}
+
 void SelectionDAGBuilder::addDanglingDebugInfo(const DbgValueInst *DI,
                                                unsigned Order) {
   // We treat variadic dbg_values differently at this stage.
   if (DI->hasArgList()) {
     // For variadic dbg_values we will now insert an undef.
     // FIXME: We can potentially recover these!
     SmallVector<SDDbgOperand, 2> Locs;
     for (const Value *V : DI->getValues()) {
assert(DI->getNumVariableLocationOps() == 1 &&
            "operand.");
     DanglingDebugInfoMap[DI->getValue(0)].emplace_back(DI, Order);
   }
 }
 
 void SelectionDAGBuilder::dropDanglingDebugInfo(const DILocalVariable *Variable,
                                                 const DIExpression *Expr) {
   auto isMatchingDbgValue = [&](DanglingDebugInfo &DDI) {
-    DIVariable *DanglingVariable = DDI.getVariable();
+    DIVariable *DanglingVariable = DDI.getVariable(DAG.getFunctionVarLocs());
     DIExpression *DanglingExpr = DDI.getExpression();
     if (DanglingVariable == Variable && Expr->fragmentsOverlap(DanglingExpr)) {
-      LLVM_DEBUG(dbgs() << "Dropping dangling debug info for " << DDI << "\n");
+      LLVM_DEBUG(dbgs() << "Dropping dangling debug info for " << printDDI(DDI)
+                        << "\n");
       return true;
     }
     return false;
   };
 
   for (auto &DDIMI : DanglingDebugInfoMap) {
     DanglingDebugInfoVector &DDIV = DDIMI.second;
 
void SelectionDAGBuilder::resolveDanglingDebugInfo(const Value *V,
   if (DanglingDbgInfoIt == DanglingDebugInfoMap.end())
     return;
 
   DanglingDebugInfoVector &DDIV = DanglingDbgInfoIt->second;
   for (auto &DDI : DDIV) {
     DebugLoc DL = DDI.getDebugLoc();
     unsigned ValSDNodeOrder = Val.getNode()->getIROrder();
     unsigned DbgSDNodeOrder = DDI.getSDNodeOrder();
-    DILocalVariable *Variable = DDI.getVariable();
+    DILocalVariable *Variable = DDI.getVariable(DAG.getFunctionVarLocs());
     DIExpression *Expr = DDI.getExpression();
     assert(Variable->isValidLocationForIntrinsic(DL) &&
            "Expected inlined-at fields to agree");
     SDDbgValue *SDV;
     if (Val.getNode()) {
       // FIXME: I doubt that it is correct to resolve a dangling DbgValue as a
       // FuncArgumentDbgValue (it would be hoisted to the function entry, and if
       // we couldn't resolve it directly when examining the DbgValue intrinsic
       // in the first place we should not be more successful here). Unless we
       // have some test case that prove this to be correct we should avoid
       // calling EmitFuncArgumentDbgValue here.
       if (!EmitFuncArgumentDbgValue(V, Variable, Expr, DL,
                                     FuncArgumentDbgValueKind::Value, Val)) {
-        LLVM_DEBUG(dbgs() << "Resolve dangling debug info for " << DDI << "\n");
+        LLVM_DEBUG(dbgs() << "Resolve dangling debug info for " << printDDI(DDI)
+                          << "\n");
         LLVM_DEBUG(dbgs() << "  By mapping to:\n    "; Val.dump());
         // Increase the SDNodeOrder for the DbgValue here to make sure it is
         // inserted after the definition of Val when emitting the instructions
         // after ISel. An alternative could be to teach
         // ScheduleDAGSDNodes::EmitSchedule to delay the insertion properly.
         LLVM_DEBUG(if (ValSDNodeOrder > DbgSDNodeOrder) dbgs()
                    << "changing SDNodeOrder from " << DbgSDNodeOrder << " to "
                    << ValSDNodeOrder << "\n");
         SDV = getDbgValue(Val, Variable, Expr, DL,
                           std::max(DbgSDNodeOrder, ValSDNodeOrder));
         DAG.AddDbgValue(SDV, false);
       } else
-        LLVM_DEBUG(dbgs() << "Resolved dangling debug info for " << DDI
-                          << "in EmitFuncArgumentDbgValue\n");
+        LLVM_DEBUG(dbgs() << "Resolved dangling debug info for "
+                          << printDDI(DDI) << " in EmitFuncArgumentDbgValue\n");
     } else {
-      LLVM_DEBUG(dbgs() << "Dropping debug info for " << DDI << "\n");
+      LLVM_DEBUG(dbgs() << "Dropping debug info for " << printDDI(DDI) << "\n");
       auto Undef = UndefValue::get(V->getType());
       auto SDV =
           DAG.getConstantDbgValue(Variable, Expr, Undef, DL, DbgSDNodeOrder);
       DAG.AddDbgValue(SDV, false);
     }
   }
   DDIV.clear();
 }
 
 void SelectionDAGBuilder::salvageUnresolvedDbgValue(DanglingDebugInfo &DDI) {
   // TODO: For the variadic implementation, instead of only checking the fail
   // state of `handleDebugValue`, we need know specifically which values were
   // invalid, so that we attempt to salvage only those values when processing
   // a DIArgList.
   Value *V = DDI.getVariableLocationOp(0);
   Value *OrigV = V;
-  DILocalVariable *Var = DDI.getVariable();
+  DILocalVariable *Var = DDI.getVariable(DAG.getFunctionVarLocs());
   DIExpression *Expr = DDI.getExpression();
   DebugLoc DL = DDI.getDebugLoc();
   unsigned SDOrder = DDI.getSDNodeOrder();
 
   // Currently we consider only dbg.value intrinsics -- we tell the salvager
   // that DW_OP_stack_value is desired.
   bool StackValue = true;
 
void SelectionDAGBuilder::salvageUnresolvedDbgValue(DanglingDebugInfo &DDI) {
 
   // This was the final opportunity to salvage this debug information, and it
   // couldn't be done. Place an undef DBG_VALUE at this location to terminate
   // any earlier variable location.
   assert(OrigV && "V shouldn't be null");
   auto *Undef = UndefValue::get(OrigV->getType());
   auto *SDV = DAG.getConstantDbgValue(Var, Expr, Undef, DL, SDNodeOrder);
   DAG.AddDbgValue(SDV, false);
-  LLVM_DEBUG(dbgs() << "Dropping debug value info for:\n  " << DDI << "\n");
+  LLVM_DEBUG(dbgs() << "Dropping debug value info for:\n  " << printDDI(DDI)
+                    << "\n");
 }
 
 bool SelectionDAGBuilder::handleDebugValue(ArrayRef<const Value *> Values,
                                            DILocalVariable *Var,
                                            DIExpression *Expr, DebugLoc DbgLoc,
                                            unsigned Order, bool IsVariadic) {
   if (Values.empty())
     return true;
SDValue Res = DAG.getNode(
         ISD::PREALLOCATED_ARG, sdl,
         DAG.getVTList(TLI.getPointerTy(DAG.getDataLayout()), MVT::Other), Ops);
     setValue(&I, Res);
     DAG.setRoot(Res.getValue(1));
     return;
   }
   case Intrinsic::dbg_addr:
   case Intrinsic::dbg_declare: {
+    // Debug intrinsics are handled seperately in assignment tracking mode.
+    if (getEnableAssignmentTracking())
+      return;
     // Assume dbg.addr and dbg.declare can not currently use DIArgList, i.e.
     // they are non-variadic.
     const auto &DI = cast<DbgVariableIntrinsic>(I);
     assert(!DI.hasArgList() && "Only dbg.value should currently use DIArgList");
     DILocalVariable *Variable = DI.getVariable();
     DIExpression *Expression = DI.getExpression();
     dropDanglingDebugInfo(Variable, Expression);
     assert(Variable && "Missing variable");
case Intrinsic::dbg_label: {
     DILabel *Label = DI.getLabel();
     assert(Label && "Missing label");
 
     SDDbgLabel *SDV;
     SDV = DAG.getDbgLabel(Label, dl, SDNodeOrder);
     DAG.AddDbgLabel(SDV);
     return;
   }
+  case Intrinsic::dbg_assign: {
+    // Debug intrinsics are handled seperately in assignment tracking mode.
+    assert(getEnableAssignmentTracking() &&
+           "expected assignment tracking to be enabled");
+    return;
+  }
   case Intrinsic::dbg_value: {
+    // Debug intrinsics are handled seperately in assignment tracking mode.
+    if (getEnableAssignmentTracking())
+      return;
     const DbgValueInst &DI = cast<DbgValueInst>(I);
     assert(DI.getVariable() && "Missing variable");
 
     DILocalVariable *Variable = DI.getVariable();
     DIExpression *Expression = DI.getExpression();
     dropDanglingDebugInfo(Variable, Expression);
     SmallVector<Value *, 4> Values(DI.getValues());
     if (Values.empty())

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

 #include "llvm/Analysis/CFG.h"
 #include "llvm/Analysis/EHPersonalities.h"
 #include "llvm/Analysis/LazyBlockFrequencyInfo.h"
 #include "llvm/Analysis/LegacyDivergenceAnalysis.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/ProfileSummaryInfo.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/CodeGen/AssignmentTrackingAnalysis.h"
 #include "llvm/CodeGen/CodeGenCommonISel.h"
 #include "llvm/CodeGen/FastISel.h"
 #include "llvm/CodeGen/FunctionLoweringInfo.h"
 #include "llvm/CodeGen/GCMetadata.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"

 #include "llvm/CodeGen/TargetInstrInfo.h"
 #include "llvm/CodeGen/TargetLowering.h"
 #include "llvm/CodeGen/TargetRegisterInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/CodeGen/ValueTypes.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
void SelectionDAGISel::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addRequired<StackProtector>();
   AU.addPreserved<GCModuleInfo>();
   AU.addRequired<TargetLibraryInfoWrapperPass>();
   AU.addRequired<TargetTransformInfoWrapperPass>();
   AU.addRequired<AssumptionCacheTracker>();
   if (UseMBPI && OptLevel != CodeGenOpt::None)
     AU.addRequired<BranchProbabilityInfoWrapperPass>();
   AU.addRequired<ProfileSummaryInfoWrapperPass>();
+  if (getEnableAssignmentTracking()) {
+    AU.addRequired<AssignmentTrackingAnalysis>();
+    AU.addPreserved<AssignmentTrackingAnalysis>();
+  }
   if (OptLevel != CodeGenOpt::None)
     LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU);
   MachineFunctionPass::getAnalysisUsage(AU);
 }
 
 static void computeUsesMSVCFloatingPoint(const Triple &TT, const Function &F,
                                          MachineModuleInfo &MMI) {
   // Only needed for MSVC
bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
   GFI = Fn.hasGC() ? &getAnalysis<GCModuleInfo>().getFunctionInfo(Fn) : nullptr;
   ORE = std::make_unique<OptimizationRemarkEmitter>(&Fn);
   AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(mf.getFunction());
   auto *PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
   BlockFrequencyInfo *BFI = nullptr;
   if (PSI && PSI->hasProfileSummary() && OptLevel != CodeGenOpt::None)
     BFI = &getAnalysis<LazyBlockFrequencyInfoPass>().getBFI();
 
+  FunctionVarLocs const *FnVarLocs = nullptr;
+  if (getEnableAssignmentTracking())
+    FnVarLocs = getAnalysis<AssignmentTrackingAnalysis>().getResults();
+
   LLVM_DEBUG(dbgs() << "\n\n\n=== " << Fn.getName() << "\n");
 
   CurDAG->init(*MF, *ORE, this, LibInfo,
-               getAnalysisIfAvailable<LegacyDivergenceAnalysis>(), PSI, BFI);
+               getAnalysisIfAvailable<LegacyDivergenceAnalysis>(), PSI, BFI,
+               FnVarLocs);
   FuncInfo->set(Fn, *MF, CurDAG);
   SwiftError->setFunction(*MF);
 
   // Now get the optional analyzes if we want to.
   // This is based on the possibly changed OptLevel (after optnone is taken
   // into account).  That's unfortunate but OK because it just means we won't
   // ask for passes that have been required anyway.
 
static bool isFoldedOrDeadInstruction(const Instruction *I,
                                       const FunctionLoweringInfo &FuncInfo) {
   return !I->mayWriteToMemory() && // Side-effecting instructions aren't folded.
          !I->isTerminator() &&     // Terminators aren't folded.
          !isa<DbgInfoIntrinsic>(I) && // Debug instructions aren't folded.
          !I->isEHPad() &&             // EH pad instructions aren't folded.
          !FuncInfo.isExportedInst(I); // Exported instrs must be computed.
 }
 
-/// Collect llvm.dbg.declare information. This is done after argument lowering
-/// in case the declarations refer to arguments.
-static void processDbgDeclares(FunctionLoweringInfo &FuncInfo) {
+static void processDbgDeclare(FunctionLoweringInfo &FuncInfo,
+                              const Value *Address, DIExpression *Expr,
+                              DILocalVariable *Var, DebugLoc DbgLoc) {
   MachineFunction *MF = FuncInfo.MF;
   const DataLayout &DL = MF->getDataLayout();
-  for (const BasicBlock &BB : *FuncInfo.Fn) {
-    for (const Instruction &I : BB) {
-      const DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(&I);
-      if (!DI)
-        continue;
 
-      assert(DI->getVariable() && "Missing variable");
-      assert(DI->getDebugLoc() && "Missing location");
-      const Value *Address = DI->getAddress();
-      if (!Address) {
-        LLVM_DEBUG(dbgs() << "processDbgDeclares skipping " << *DI
-                          << " (bad address)\n");
-        continue;
-      }
+  assert(Var && "Missing variable");
+  assert(DbgLoc && "Missing location");
 
-      // Look through casts and constant offset GEPs. These mostly come from
-      // inalloca.
-      APInt Offset(DL.getTypeSizeInBits(Address->getType()), 0);
-      Address = Address->stripAndAccumulateInBoundsConstantOffsets(DL, Offset);
 
-      // Check if the variable is a static alloca or a byval or inalloca
-      // argument passed in memory. If it is not, then we will ignore this
-      // intrinsic and handle this during isel like dbg.value.
-      int FI = std::numeric_limits<int>::max();
-      if (const auto *AI = dyn_cast<AllocaInst>(Address)) {
-        auto SI = FuncInfo.StaticAllocaMap.find(AI);
-        if (SI != FuncInfo.StaticAllocaMap.end())
-          FI = SI->second;
-      } else if (const auto *Arg = dyn_cast<Argument>(Address))
-        FI = FuncInfo.getArgumentFrameIndex(Arg);
 
-      if (FI == std::numeric_limits<int>::max())
-        continue;
+    return;
 
-      DIExpression *Expr = DI->getExpression();
-      if (Offset.getBoolValue())
-        Expr = DIExpression::prepend(Expr, DIExpression::ApplyOffset,
-                                     Offset.getZExtValue());
-      LLVM_DEBUG(dbgs() << "processDbgDeclares: setVariableDbgInfo FI=" << FI
-                        << ", " << *DI << "\n");
-      MF->setVariableDbgInfo(DI->getVariable(), Expr, FI, DI->getDebugLoc());
+
+  LLVM_DEBUG(dbgs() << "processDbgDeclare: setVariableDbgInfo Var=" << *Var
+                    << ", Expr=" << *Expr << ",  FI=" << FI
+                    << ", DbgLoc=" << DbgLoc << "\n");
+  MF->setVariableDbgInfo(Var, Expr, FI, DbgLoc);
+}
+
+/// Collect llvm.dbg.declare information. This is done after argument lowering
+/// in case the declarations refer to arguments.
+static void processDbgDeclares(FunctionLoweringInfo &FuncInfo) {
+  for (const BasicBlock &BB : *FuncInfo.Fn) {
+    for (const Instruction &I : BB) {
+      if (const DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(&I)) {
+        Value *Address = DI->getAddress();
+        if (!Address) {
+          LLVM_DEBUG(dbgs() << "processDbgDeclares skipping " << *DI
+                            << " (bad address)\n");
+          return;
+        }
+        processDbgDeclare(FuncInfo, Address, DI->getExpression(),
+                          DI->getVariable(), DI->getDebugLoc());
+      }
     }
   }
 }
 
+/// Collect single location variable information generated with assignment
+/// tracking. This is done after argument lowering in case the declarations
+/// refer to arguments.
+static void processSingleLocVars(FunctionLoweringInfo &FuncInfo,
+                                 FunctionVarLocs const *FnVarLocs) {
+  for (auto It = FnVarLocs->single_locs_begin(),
+            End = FnVarLocs->single_locs_end();
+       It != End; ++It)
+    processDbgDeclare(FuncInfo, It->V, It->Expr,
+                      FnVarLocs->getDILocalVariable(It->VariableID), It->DL);
+}
+
 void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
   FastISelFailed = false;
   // Initialize the Fast-ISel state, if needed.
   FastISel *FastIS = nullptr;
   if (TM.Options.EnableFastISel) {
     LLVM_DEBUG(dbgs() << "Enabling fast-isel\n");
     FastIS = TLI->createFastISel(*FuncInfo, LibInfo);
     if (FastIS)
else
       FastIS->setLastLocalValue(nullptr);
   }
 
   bool Inserted = SwiftError->createEntriesInEntryBlock(SDB->getCurDebugLoc());
 
   if (FastIS && Inserted)
     FastIS->setLastLocalValue(&*std::prev(FuncInfo->InsertPt));
 
+  if (getEnableAssignmentTracking()) {
+    assert(CurDAG->getFunctionVarLocs() &&
+           "expected AssignmentTrackingAnalysis pass results");
+    processSingleLocVars(*FuncInfo, CurDAG->getFunctionVarLocs());
+  } else {
     processDbgDeclares(*FuncInfo);
+  }
 
   // Iterate over all basic blocks in the function.
   StackProtector &SP = getAnalysis<StackProtector>();
   for (const BasicBlock *LLVMBB : RPOT) {
     if (OptLevel != CodeGenOpt::None) {
       bool AllPredsVisited = true;
       for (const BasicBlock *Pred : predecessors(LLVMBB)) {
         if (!FuncInfo->VisitedBBs.count(Pred)) {