[DebugInfo] Support multiple location operands via DIArgList in DbgVariableIntrinsics

[StephenTozer]

Summary

Following from the previous patch in this series which adds the DIArgList metadata, allowing us to reference multiple Value pointers, this patch updates DbgVariableIntrinsics to make use of this functionality, resulting in a significant change to its interface.

This patch is not intended to update all IR passes to handle dbg.values with multiple location operands; that is being left to the next patch in the stack. This patch simply updates DbgVariableIntrinsic to handle DIArgLists, and updates code elsewhere to use the new interface. In some cases these changes are immediately valid, but in many they are not. All code outside of the intrinsics themselves assumes that an intrinsic will always have exactly one location operand; they will still support DIArgLists, but only if they contain exactly one Value.

Among other changes, the setOperand and setArgOperand functions in DbgVariableIntrinsic have been made private. This is to prevent code from setting the operands of these intrinsics directly, which could easily result in incorrect/invalid operands being set. Obviously this does not prevent these functions from being called on a debug intrinsic at all, as they can still be called on any CallInst pointer. My assumption however is that any code that is looking at a generic pointer without examining the type is going to be conservative about setting the operands to arbitrary values, and in any case where we could safely do so for any CallInst, we can safely do so for a DbgVariableIntrinsic. The intention for making these functions private is to prevent DIArgLists from being overwritten by code that's naively trying to replace one of the Values it points to, and also to fail fast if a DbgVariableIntrinsic is updated to use a DIArgList without a valid corresponding DIExpression.

[aprantl]

llvm/lib/IR/IntrinsicInst.cpp

46

Maybe this isn't such a big deal, but this function has a weird UI now — returning a SmallVector with nullptrs... I wonder if we should instead return a small iterator object? How is this used?

[StephenTozer]

llvm/lib/IR/IntrinsicInst.cpp

46

I agree that the UI to this function is weird. Frankly, I don't think this should ever have been returning nullptr in the first place - only a malformed debug intrinsic should have a first argument which isn't a valid MetadataAsValue (this is confirmed by the verifier). I've kept it here only because I was avoiding changing the behaviour of the existing code that uses the nullptr return value. If there must be an "error" response, it also shouldn't be the empty list, because we may want to use that for constants such as:

llvm.dbg.value(!DIArgList(), !"x", !DIExpression(DW_OP_uconst, 5, DW_OP_stack_value))

Putting the nullptr issue aside, it might still be better to return an iterator for this that casts individual arguments to Value* with each iteration. I returned a SmallVector here for simplicity's sake, but for general use it might be easier to define a custom iterator for this class. Do you think it'd be useful in that case?

[aprantl]

llvm/lib/IR/IntrinsicInst.cpp

46

I'm sorry for having brought this up — it's always the person who dares touching something who then gets tasked with fixing up our technical debt :-)

Putting the nullptr issue aside, it might still be better to return an iterator for this that casts individual arguments to Value* with each iteration. I returned a SmallVector here for simplicity's sake, but for general use it might be easier to define a custom iterator for this class. Do you think it'd be useful in that case?

The iterator is more elegant, but really the SmallVector affords the exact same UX, which is being able to write for (auto i : fn()). So I think I'll leave this up to you. The iterator will perform slightly better if we have early exists, so that good, but we can also decide to not fix this now and move on.

[StephenTozer]

Rebase onto recent master; no functional changes from rebase. Minor change to DbgVariableIntrinsic::setUndef to handle DIArglists in which the same value appears more than once.

[StephenTozer]

Rebased onto recent master, added smarter iterator for variable location operands.

[StephenTozer]

Landed in LLVM commit llvmorg-13-init-3801-ge5d958c45629.

llvm/include/llvm/IR/IntrinsicInst.h

 // hack working.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_IR_INTRINSICINST_H
 #define LLVM_IR_INTRINSICINST_H
 
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/FPEnv.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Value.h"

 };
 
 /// This is the common base class for debug info intrinsics for variables.
 class DbgVariableIntrinsic : public DbgInfoIntrinsic {
 public:
   /// Get the location corresponding to the variable referenced by the debug
   /// info intrinsic.  Depending on the intrinsic, this could be the
   /// variable's value or its address.
-  Value *getVariableLocation(bool AllowNullOp = true) const;
+  SmallVector<Value *, 4> getVariableLocationOps(bool AllowNullOp = true) const;
+  Value *getVariableLocationOp(unsigned OpIdx, bool AllowNullOp = true) const;
+
+  void replaceVariableLocationOp(Value *OldValue, Value *NewValue);
+
+  void setVariable(DILocalVariable *NewVar) {
+    setArgOperand(1, MetadataAsValue::get(NewVar->getContext(), NewVar));
+  }
+
+  void setExpression(DIExpression *NewExpr) {
+    setArgOperand(2, MetadataAsValue::get(NewExpr->getContext(), NewExpr));
+  }
+
+  unsigned getNumVariableLocationOps() const {
+    if (hasArgList())
+      return cast<DIArgList>(getRawLocation())->getArgs().size();
+  return 1;
+  }
+
+  bool hasArgList() const { return isa<DIArgList>(getRawLocation()); }
 
   /// Does this describe the address of a local variable. True for dbg.addr
   /// and dbg.declare, but not dbg.value, which describes its value.
   bool isAddressOfVariable() const {
     return getIntrinsicID() != Intrinsic::dbg_value;
   }
 
+  void setUndef() {
+    for (Value *OldValue : getVariableLocationOps()) {
+      Value *Undef = UndefValue::get(OldValue->getType());
+      replaceVariableLocationOp(OldValue, Undef);
+    }
+  }
+
+  bool isUndef() const {
+    return (getNumVariableLocationOps() == 0 &&
+            !getExpression()->isComplex()) ||
+           any_of(getVariableLocationOps(),
+                  [](Value *V) { return isa<UndefValue>(V); });
+  }
+
   DILocalVariable *getVariable() const {
     return cast<DILocalVariable>(getRawVariable());
   }
 
   DIExpression *getExpression() const {
     return cast<DIExpression>(getRawExpression());
   }
 
+  Metadata *getRawLocation() const {
+    return cast<MetadataAsValue>(getArgOperand(0))->getMetadata();
+  }
+
   Metadata *getRawVariable() const {
     return cast<MetadataAsValue>(getArgOperand(1))->getMetadata();
   }
 
   Metadata *getRawExpression() const {
     return cast<MetadataAsValue>(getArgOperand(2))->getMetadata();
   }
 
static bool classof(const IntrinsicInst *I) {
     default:
       return false;
     }
   }
   static bool classof(const Value *V) {
     return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
   }
   /// @}
+private:
+  void setArgOperand(unsigned i, Value *v) {
+    DbgInfoIntrinsic::setArgOperand(i, v);
+  }
+  void setOperand(unsigned i, Value *v) { DbgInfoIntrinsic::setOperand(i, v); }
 };
 
 /// This represents the llvm.dbg.declare instruction.
 class DbgDeclareInst : public DbgVariableIntrinsic {
 public:
-  Value *getAddress() const { return getVariableLocation(); }
+  Value *getAddress() const {
+    assert(getNumVariableLocationOps() == 1 &&
+           "dbg.declare must have exactly 1 location operand.");
+    return getVariableLocationOp(0);
+  }
 
   /// \name Casting methods
   /// @{
   static bool classof(const IntrinsicInst *I) {
     return I->getIntrinsicID() == Intrinsic::dbg_declare;
   }
   static bool classof(const Value *V) {
     return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
   }
   /// @}
 };
 
 /// This represents the llvm.dbg.addr instruction.
 class DbgAddrIntrinsic : public DbgVariableIntrinsic {
 public:
-  Value *getAddress() const { return getVariableLocation(); }
+  Value *getAddress() const {
+    assert(getNumVariableLocationOps() == 1 &&
+           "dbg.addr must have exactly 1 location operand.");
+    return getVariableLocationOp(0);
+  }
 
   /// \name Casting methods
   /// @{
   static bool classof(const IntrinsicInst *I) {
     return I->getIntrinsicID() == Intrinsic::dbg_addr;
   }
   static bool classof(const Value *V) {
     return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
   }
 };
 
 /// This represents the llvm.dbg.value instruction.
 class DbgValueInst : public DbgVariableIntrinsic {
 public:
-  Value *getValue() const {
-    return getVariableLocation(/* AllowNullOp = */ false);
+  // The default argument should only be used in ISel, and the default option
+  // should be removed once ISel support for multiple location ops is complete.
+  Value *getValue(unsigned OpIdx = 0) const {
+    return getVariableLocationOp(OpIdx, /* AllowNullOp = */ false);
+  }
+  SmallVector<Value *, 4> getValues() const {
+    return getVariableLocationOps(/* AllowNullOp = */ false);
   }
 
   /// \name Casting methods
   /// @{
   static bool classof(const IntrinsicInst *I) {
     return I->getIntrinsicID() == Intrinsic::dbg_value;
   }
   static bool classof(const Value *V) {

llvm/lib/Bitcode/Reader/MetadataLoader.cpp

for (auto &BB : F)
       for (auto &I : BB)
         if (auto *DDI = dyn_cast<DbgDeclareInst>(&I))
           if (auto *DIExpr = DDI->getExpression())
             if (DIExpr->startsWithDeref() &&
                 dyn_cast_or_null<Argument>(DDI->getAddress())) {
               SmallVector<uint64_t, 8> Ops;
               Ops.append(std::next(DIExpr->elements_begin()),
                          DIExpr->elements_end());
-              auto *E = DIExpression::get(Context, Ops);
-              DDI->setOperand(2, MetadataAsValue::get(Context, E));
+              DDI->setExpression(DIExpression::get(Context, Ops));
             }
   }
 
   /// Upgrade the expression from previous versions.
   Error upgradeDIExpression(uint64_t FromVersion,
                             MutableArrayRef<uint64_t> &Expr,
                             SmallVectorImpl<uint64_t> &Buffer) {
     auto N = Expr.size();

llvm/lib/CodeGen/CodeGenPrepare.cpp

void undo() override {
                         EndIt = OriginalUses.end();
            UseIt != EndIt; ++UseIt) {
         UseIt->Inst->setOperand(UseIt->Idx, Inst);
       }
       // RAUW has replaced all original uses with references to the new value,
       // including the debug uses. Since we are undoing the replacements,
       // the original debug uses must also be reinstated to maintain the
       // correctness and utility of debug value instructions.
-      for (auto *DVI: DbgValues) {
-        LLVMContext &Ctx = Inst->getType()->getContext();
-        auto *MV = MetadataAsValue::get(Ctx, ValueAsMetadata::get(Inst));
-        DVI->setOperand(0, MV);
-      }
+      for (auto *DVI: DbgValues)
+        DVI->replaceVariableLocationOp(DVI->getVariableLocationOp(0), Inst);
     }
   };
 
   /// Remove an instruction from the IR.
   class InstructionRemover : public TypePromotionAction {
     /// Original position of the instruction.
     InsertionHandler Inserter;
 

 
 // Some CGP optimizations may move or alter what's computed in a block. Check
 // whether a dbg.value intrinsic could be pointed at a more appropriate operand.
 bool CodeGenPrepare::fixupDbgValue(Instruction *I) {
   assert(isa<DbgValueInst>(I));
   DbgValueInst &DVI = *cast<DbgValueInst>(I);
 
   // Does this dbg.value refer to a sunk address calculation?
-  Value *Location = DVI.getVariableLocation();
+  Value *Location = DVI.getVariableLocationOp(0);
   WeakTrackingVH SunkAddrVH = SunkAddrs[Location];
   Value *SunkAddr = SunkAddrVH.pointsToAliveValue() ? SunkAddrVH : nullptr;
   if (SunkAddr) {
     // Point dbg.value at locally computed address, which should give the best
     // opportunity to be accurately lowered. This update may change the type of
     // pointer being referred to; however this makes no difference to debugging
     // information, and we can't generate bitcasts that may affect codegen.
-    DVI.setOperand(0, MetadataAsValue::get(DVI.getContext(),
-                                           ValueAsMetadata::get(SunkAddr)));
+    DVI.replaceVariableLocationOp(Location, SunkAddr);
     return true;
   }
   return false;
 }
 
 // A llvm.dbg.value may be using a value before its definition, due to
 // optimizations in this pass and others. Scan for such dbg.values, and rescue
 // them by moving the dbg.value to immediately after the value definition.

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

if (Val.getNode()) {
         SDV = getDbgValue(Val, Variable, Expr, dl,
                           std::max(DbgSDNodeOrder, ValSDNodeOrder));
         DAG.AddDbgValue(SDV, Val.getNode(), false);
       } else
         LLVM_DEBUG(dbgs() << "Resolved dangling debug info for " << *DI
                           << "in EmitFuncArgumentDbgValue\n");
     } else {
       LLVM_DEBUG(dbgs() << "Dropping debug info for " << *DI << "\n");
-      auto Undef =
-          UndefValue::get(DDI.getDI()->getVariableLocation()->getType());
+      auto Undef = UndefValue::get(DDI.getDI()->getValue()->getType());
       auto SDV =
           DAG.getConstantDbgValue(Variable, Expr, Undef, dl, DbgSDNodeOrder);
       DAG.AddDbgValue(SDV, nullptr, false);
     }
   }
   DDIV.clear();
 }
 
if (handleDebugValue(V, Var, Expr, DL, InstDL, SDOrder)) {
                         << DDI.getDI() << "\nBy stripping back to:\n  " << V);
       return;
     }
   }
 
   // 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.
-  auto Undef = UndefValue::get(DDI.getDI()->getVariableLocation()->getType());
+  auto Undef = UndefValue::get(DDI.getDI()->getValue()->getType());
   auto SDV = DAG.getConstantDbgValue(Var, Expr, Undef, DL, SDNodeOrder);
   DAG.AddDbgValue(SDV, nullptr, false);
 
   LLVM_DEBUG(dbgs() << "Dropping debug value info for:\n  " << DDI.getDI()
                     << "\n");
   LLVM_DEBUG(dbgs() << "  Last seen at:\n    " << *DDI.getDI()->getOperand(0)
                     << "\n");
 }
case Intrinsic::dbg_declare: {
     const auto &DI = cast<DbgVariableIntrinsic>(I);
     DILocalVariable *Variable = DI.getVariable();
     DIExpression *Expression = DI.getExpression();
     dropDanglingDebugInfo(Variable, Expression);
     assert(Variable && "Missing variable");
     LLVM_DEBUG(dbgs() << "SelectionDAG visiting debug intrinsic: " << DI
                       << "\n");
     // Check if address has undef value.
-    const Value *Address = DI.getVariableLocation();
+    const Value *Address = DI.getVariableLocationOp(0);
     if (!Address || isa<UndefValue>(Address) ||
         (Address->use_empty() && !isa<Argument>(Address))) {
       LLVM_DEBUG(dbgs() << "Dropping debug info for " << DI
                         << " (bad/undef/unused-arg address)\n");
       return;
     }
 
     bool isParameter = Variable->isParameter() || isa<Argument>(Address);

llvm/lib/IR/Constants.cpp

static bool removeDeadUsersOfConstant(const Constant *C) {
 
   while (!C->use_empty()) {
     const Constant *User = dyn_cast<Constant>(C->user_back());
     if (!User) return false; // Non-constant usage;
     if (!removeDeadUsersOfConstant(User))
       return false; // Constant wasn't dead
   }
 
+  // If C is only used by metadata, it should not be preserved but should have
+  // its uses replaced.
+  if (C->isUsedByMetadata()) {
+    const_cast<Constant *>(C)->replaceAllUsesWith(
+        UndefValue::get(C->getType()));
+  }
   const_cast<Constant*>(C)->destroyConstant();
   return true;
 }
 
 
 void Constant::removeDeadConstantUsers() const {
   Value::const_user_iterator I = user_begin(), E = user_end();
   Value::const_user_iterator LastNonDeadUser = E;

llvm/lib/IR/IntrinsicInst.cpp

 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 //===----------------------------------------------------------------------===//
 /// DbgVariableIntrinsic - This is the common base class for debug info
 /// intrinsics for variables.
 ///
 
-Value *DbgVariableIntrinsic::getVariableLocation(bool AllowNullOp) const {
+SmallVector<Value *, 4>
+DbgVariableIntrinsic::getVariableLocationOps(bool AllowNullOp) const {
+  SmallVector<Value *, 4> Result;
   Value *Op = getArgOperand(0);
-  if (AllowNullOp && !Op)
+  if (AllowNullOp && !Op) {
+    Result.push_back(nullptr);
+    return Result;
+  }
+
+  auto *MD = cast<MetadataAsValue>(Op)->getMetadata();
+  if (auto *V = dyn_cast<ValueAsMetadata>(MD)) {
+    Result.push_back(V->getValue());
+    return Result;
+  }
+  if (auto *AL = dyn_cast<DIArgList>(MD)) {
+    for (auto *V : AL->getArgs())
+      Result.push_back(V->getValue());
+    return Result;
+  }
+
+  // When the value goes to null, it gets replaced by an empty MDNode.
+  assert(!cast<MDNode>(MD)->getNumOperands() && "Expected an empty MDNode");
+  Result.push_back(nullptr);
+  return Result;
+}
+
+Value *DbgVariableIntrinsic::getVariableLocationOp(unsigned OpIdx,
+                                                   bool AllowNullOp) const {
+  Value *Op = getArgOperand(0);
+  if (AllowNullOp && !Op) {
     return nullptr;
+  }
 
   auto *MD = cast<MetadataAsValue>(Op)->getMetadata();
+  if (auto *AL = dyn_cast<DIArgList>(MD)) {
+    if (auto *VMD = AL->getArgs()[OpIdx])
+      return VMD->getValue();
+    return nullptr;
+  }
+  assert(OpIdx == 0 && "Operand Index must be 0 for a debug intrinsic with a "
+                       "single location operand.");
   if (auto *V = dyn_cast<ValueAsMetadata>(MD))
     return V->getValue();
 
   // When the value goes to null, it gets replaced by an empty MDNode.
   assert(!cast<MDNode>(MD)->getNumOperands() && "Expected an empty MDNode");
   return nullptr;
 }
 
+static ValueAsMetadata *getAsMetadata(Value *V) {
+  return isa<MetadataAsValue>(V) ? dyn_cast<ValueAsMetadata>(
+                                       cast<MetadataAsValue>(V)->getMetadata())
+                                 : ValueAsMetadata::get(V);
+}
+
+void DbgVariableIntrinsic::replaceVariableLocationOp(Value *OldValue,
+                                                     Value *NewValue) {
+  auto Locations = getVariableLocationOps();
+  auto OldIt = find(Locations, OldValue);
+  assert(OldIt != Locations.end() && "OldValue must be a current location");
+  if (!hasArgList()) {
+    Value *NewOperand = isa<MetadataAsValue>(NewValue)
+                            ? NewValue
+                            : MetadataAsValue::get(
+                                  getContext(), ValueAsMetadata::get(NewValue));
+    return setArgOperand(0, NewOperand);
+  }
+  SmallVector<ValueAsMetadata *, 4> MDs;
+  ValueAsMetadata *NewOperand = getAsMetadata(NewValue);
+  for (auto *VMD : Locations)
+    MDs.push_back(VMD == *OldIt ? NewOperand : getAsMetadata(VMD));
+  setArgOperand(
+      0, MetadataAsValue::get(getContext(), DIArgList::get(getContext(), MDs)));
+}
+
 Optional<uint64_t> DbgVariableIntrinsic::getFragmentSizeInBits() const {
   if (auto Fragment = getExpression()->getFragmentInfo())
     return Fragment->SizeInBits;
   return getVariable()->getSizeInBits();
 }
 
 int llvm::Intrinsic::lookupLLVMIntrinsicByName(ArrayRef<const char *> NameTable,
                                                StringRef Name) {

llvm/lib/IR/Verifier.cpp

Assert(FPI.getExceptionBehavior().hasValue(),
          "invalid exception behavior argument", &FPI);
   if (HasRoundingMD) {
     Assert(FPI.getRoundingMode().hasValue(),
            "invalid rounding mode argument", &FPI);
   }
 }
 
 void Verifier::visitDbgIntrinsic(StringRef Kind, DbgVariableIntrinsic &DII) {
-  auto *MD = cast<MetadataAsValue>(DII.getArgOperand(0))->getMetadata();
+  auto *MD = DII.getRawLocation();
   AssertDI(isa<ValueAsMetadata>(MD) || isa<DIArgList>(MD) ||
                (isa<MDNode>(MD) && !cast<MDNode>(MD)->getNumOperands()),
            "invalid llvm.dbg." + Kind + " intrinsic address/value", &DII, MD);
   AssertDI(isa<DILocalVariable>(DII.getRawVariable()),
          "invalid llvm.dbg." + Kind + " intrinsic variable", &DII,
          DII.getRawVariable());
   AssertDI(isa<DIExpression>(DII.getRawExpression()),
          "invalid llvm.dbg." + Kind + " intrinsic expression", &DII,

llvm/lib/Target/AArch64/AArch64StackTagging.cpp

Value *flatten(IRBuilder<> &IRB, Value *V) {
     return IRB.CreateBitOrPointerCast(
         V, IRB.getIntNTy(DL->getTypeStoreSize(V->getType()) * 8));
   }
 };
 
 class AArch64StackTagging : public FunctionPass {
   struct AllocaInfo {
     AllocaInst *AI;
+    TrackingVH<Instruction> OldAI; // Track through RAUW to replace debug uses.
     SmallVector<IntrinsicInst *, 2> LifetimeStart;
     SmallVector<IntrinsicInst *, 2> LifetimeEnd;
     SmallVector<DbgVariableIntrinsic *, 2> DbgVariableIntrinsics;
     int Tag; // -1 for non-tagged allocations
   };
 
   const bool MergeInit;
   const bool UseStackSafety;
bool AArch64StackTagging::runOnFunction(Function &Fn) {
   SmallVector<Instruction *, 8> RetVec;
   SmallVector<Instruction *, 4> UnrecognizedLifetimes;
 
   for (auto &BB : *F) {
     for (BasicBlock::iterator IT = BB.begin(); IT != BB.end(); ++IT) {
       Instruction *I = &*IT;
       if (auto *AI = dyn_cast<AllocaInst>(I)) {
         Allocas[AI].AI = AI;
+        Allocas[AI].OldAI = AI;
         continue;
       }
 
       if (auto *DVI = dyn_cast<DbgVariableIntrinsic>(I)) {
         if (auto *AI =
-                dyn_cast_or_null<AllocaInst>(DVI->getVariableLocation())) {
+                dyn_cast_or_null<AllocaInst>(DVI->getVariableLocationOp(0))) {
           Allocas[AI].DbgVariableIntrinsics.push_back(DVI);
         }
         continue;
       }
 
       auto *II = dyn_cast<IntrinsicInst>(I);
       if (II && (II->getIntrinsicID() == Intrinsic::lifetime_start ||
                  II->getIntrinsicID() == Intrinsic::lifetime_end)) {
if (UnrecognizedLifetimes.empty() && Info.LifetimeStart.size() == 1 &&
       for (auto &II : Info.LifetimeStart)
         II->eraseFromParent();
       for (auto &II : Info.LifetimeEnd)
         II->eraseFromParent();
     }
 
     // Fixup debug intrinsics to point to the new alloca.
     for (auto DVI : Info.DbgVariableIntrinsics)
-      DVI->setArgOperand(
-          0,
-          MetadataAsValue::get(F->getContext(), LocalAsMetadata::get(Info.AI)));
+      DVI->replaceVariableLocationOp(Info.OldAI, Info.AI);
   }
 
   // If we have instrumented at least one alloca, all unrecognized lifetime
   // instrinsics have to go.
   for (auto &I : UnrecognizedLifetimes)
     I->eraseFromParent();
 
   return true;
 }

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
 
   // Update the arguments of a dbg.declare instruction, so that it
   // does not point into a sunk instruction.
   auto updateDbgDeclare = [&I](DbgVariableIntrinsic *DII) {
     if (!isa<DbgDeclareInst>(DII))
       return false;
 
     if (isa<CastInst>(I))
-      DII->setOperand(
-          0, MetadataAsValue::get(I->getContext(),
-                                  ValueAsMetadata::get(I->getOperand(0))));
+      DII->replaceVariableLocationOp(DII->getVariableLocationOp(0),
+                                     I->getOperand(0));
     return true;
   };
 
   SmallVector<DbgVariableIntrinsic *, 2> DIIClones;
   for (auto User : DbgUsers) {
     // A dbg.declare instruction should not be cloned, since there can only be
     // one per variable fragment. It should be left in the original place
     // because the sunk instruction is not an alloca (otherwise we could not be

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

AI->replaceUsesWithIf(Replacement,
                           [AILong](Use &U) { return U.getUser() != AILong; });
 
     for (auto *DDI : AllocaDbgMap.lookup(AI)) {
       // Prepend "tag_offset, N" to the dwarf expression.
       // Tag offset logically applies to the alloca pointer, and it makes sense
       // to put it at the beginning of the expression.
       SmallVector<uint64_t, 8> NewOps = {dwarf::DW_OP_LLVM_tag_offset,
                                          RetagMask(N)};
-      DDI->setArgOperand(
-          2, MetadataAsValue::get(*C, DIExpression::prependOpcodes(
-                                          DDI->getExpression(), NewOps)));
+      auto Locations = DDI->getVariableLocationOps();
+      unsigned LocNo = std::distance(Locations.begin(), find(Locations, AI));
+      DDI->setExpression(
+          DIExpression::appendOpsToArg(DDI->getExpression(), NewOps, LocNo));
     }
 
     size_t Size = getAllocaSizeInBytes(*AI);
     tagAlloca(IRB, AI, Tag, Size);
 
     for (auto RI : RetVec) {
       IRB.SetInsertPoint(RI);
 
for (auto &Inst : BB) {
         }
 
       if (isa<ReturnInst>(Inst) || isa<ResumeInst>(Inst) ||
           isa<CleanupReturnInst>(Inst))
         RetVec.push_back(&Inst);
 
       if (auto *DDI = dyn_cast<DbgVariableIntrinsic>(&Inst))
         if (auto *Alloca =
-                dyn_cast_or_null<AllocaInst>(DDI->getVariableLocation()))
+                dyn_cast_or_null<AllocaInst>(DDI->getVariableLocationOp(0)))
           AllocaDbgMap[Alloca].push_back(DDI);
 
       if (InstrumentLandingPads && isa<LandingPadInst>(Inst))
         LandingPadVec.push_back(&Inst);
 
       getInterestingMemoryOperands(&Inst, OperandsToInstrument);
 
       if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(&Inst))
for (AllocaInst *AI : AllocasToInstrument) {
     }
   }
 
   if (!AllocaToPaddedAllocaMap.empty()) {
     for (auto &BB : F)
       for (auto &Inst : BB)
         if (auto *DVI = dyn_cast<DbgVariableIntrinsic>(&Inst))
           if (auto *AI =
-                  dyn_cast_or_null<AllocaInst>(DVI->getVariableLocation()))
+                  dyn_cast_or_null<AllocaInst>(DVI->getVariableLocationOp(0)))
             if (auto *NewAI = AllocaToPaddedAllocaMap.lookup(AI))
-              DVI->setArgOperand(
-                  0, MetadataAsValue::get(*C, LocalAsMetadata::get(NewAI)));
+              DVI->replaceVariableLocationOp(AI, NewAI);
     for (auto &P : AllocaToPaddedAllocaMap)
       P.first->eraseFromParent();
   }
 
   // If we split the entry block, move any allocas that were originally in the
   // entry block back into the entry block so that they aren't treated as
   // dynamic allocas.
   if (EntryIRB.GetInsertBlock() != &F.getEntryBlock()) {

llvm/lib/Transforms/Scalar/ADCE.cpp

for (Instruction &I : instructions(F)) {
       if (auto *DII = dyn_cast<DbgVariableIntrinsic>(&I)) {
         // Check if the scope of this variable location is alive.
         if (AliveScopes.count(DII->getDebugLoc()->getScope()))
           continue;
 
         // If intrinsic is pointing at a live SSA value, there may be an
         // earlier optimization bug: if we know the location of the variable,
         // why isn't the scope of the location alive?
-        if (Value *V = DII->getVariableLocation())
+        if (Value *V = DII->getVariableLocationOp(0))
           if (Instruction *II = dyn_cast<Instruction>(V))
             if (isLive(II))
               dbgs() << "Dropping debug info for " << *DII << "\n";
       }
     }
   });
 
   // The inverse of the live set is the dead set.  These are those instructions

llvm/lib/Transforms/Scalar/SpeculativeExecution.cpp

 
 bool SpeculativeExecutionPass::considerHoistingFromTo(
     BasicBlock &FromBlock, BasicBlock &ToBlock) {
   SmallPtrSet<const Instruction *, 8> NotHoisted;
   const auto AllPrecedingUsesFromBlockHoisted = [&NotHoisted](const User *U) {
     // Debug variable has special operand to check it's not hoisted.
     if (const auto *DVI = dyn_cast<DbgVariableIntrinsic>(U)) {
       if (const auto *I =
-              dyn_cast_or_null<Instruction>(DVI->getVariableLocation()))
+              dyn_cast_or_null<Instruction>(DVI->getVariableLocationOp(0)))
         if (NotHoisted.count(I) == 0)
           return true;
       return false;
     }
 
     // Usially debug label instrinsic corresponds to label in LLVM IR. In these
     // cases we should not move it here.
     // TODO: Possible special processing needed to detect it is related to a

llvm/lib/Transforms/Utils/CodeExtractor.cpp

if (auto *DLI = dyn_cast<DbgLabelInst>(&I)) {
                                 OldLabel->getFile(), OldLabel->getLine());
       DLI->setArgOperand(0, MetadataAsValue::get(Ctx, NewLabel));
       continue;
     }
 
     // If the location isn't a constant or an instruction, delete the
     // intrinsic.
     auto *DVI = cast<DbgVariableIntrinsic>(DII);
-    Value *Location = DVI->getVariableLocation();
+    Value *Location = DVI->getVariableLocationOp(0);
     if (!Location ||
         (!isa<Constant>(Location) && !isa<Instruction>(Location))) {
       DebugIntrinsicsToDelete.push_back(DVI);
       continue;
     }
 
     // If the variable location is an instruction but isn't in the new
     // function, delete the intrinsic.
     Instruction *LocationInst = dyn_cast<Instruction>(Location);
     if (LocationInst && LocationInst->getFunction() != &NewFunc) {
       DebugIntrinsicsToDelete.push_back(DVI);
       continue;
     }
 
     // Point the intrinsic to a fresh variable within the new function.
     DILocalVariable *OldVar = DVI->getVariable();
     DINode *&NewVar = RemappedMetadata[OldVar];
     if (!NewVar)
       NewVar = DIB.createAutoVariable(
           NewSP, OldVar->getName(), OldVar->getFile(), OldVar->getLine(),
           OldVar->getType(), /*AlwaysPreserve=*/false, DINode::FlagZero,
           OldVar->getAlignInBits());
-    DVI->setArgOperand(1, MetadataAsValue::get(Ctx, NewVar));
+    DVI->setVariable(cast<DILocalVariable>(NewVar));
   }
   for (auto *DII : DebugIntrinsicsToDelete)
     DII->eraseFromParent();
   DIB.finalizeSubprogram(NewSP);
 
   // Fix up the scope information attached to the line locations in the new
   // function.
   for (Instruction &I : instructions(NewFunc)) {

llvm/lib/Transforms/Utils/LCSSA.cpp

for (auto DVI : DbgValues) {
       if (InstBB == UserBB || L->contains(UserBB))
         continue;
       // We currently only handle debug values residing in blocks that were
       // traversed while rewriting the uses. If we inserted just a single PHI,
       // we will handle all relevant debug values.
       Value *V = AddedPHIs.size() == 1 ? AddedPHIs[0]
                                        : SSAUpdate.FindValueForBlock(UserBB);
       if (V)
-        DVI->setOperand(0, MetadataAsValue::get(Ctx, ValueAsMetadata::get(V)));
+        DVI->replaceVariableLocationOp(I, V);
     }
 
     // SSAUpdater might have inserted phi-nodes inside other loops. We'll need
     // to post-process them to keep LCSSA form.
     for (PHINode *InsertedPN : InsertedPHIs) {
       if (auto *OtherLoop = LI.getLoopFor(InsertedPN->getParent()))
         if (!L->contains(OtherLoop))
           PostProcessPHIs.push_back(InsertedPN);

llvm/lib/Transforms/Utils/Local.cpp

void llvm::RecursivelyDeleteTriviallyDeadInstructions(
   }
 }
 
 bool llvm::replaceDbgUsesWithUndef(Instruction *I) {
   SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
   findDbgUsers(DbgUsers, I);
   for (auto *DII : DbgUsers) {
     Value *Undef = UndefValue::get(I->getType());
-    DII->setOperand(0, MetadataAsValue::get(DII->getContext(),
-                                            ValueAsMetadata::get(Undef)));
+    DII->replaceVariableLocationOp(I, Undef);
   }
   return !DbgUsers.empty();
 }
 
 /// areAllUsesEqual - Check whether the uses of a value are all the same.
 /// This is similar to Instruction::hasOneUse() except this will also return
 /// true when there are no uses or multiple uses that all refer to the same
 /// value.
static bool valueCoversEntireFragment(Type *ValTy, DbgVariableIntrinsic *DII) {
   const DataLayout &DL = DII->getModule()->getDataLayout();
   uint64_t ValueSize = DL.getTypeAllocSizeInBits(ValTy);
   if (auto FragmentSize = DII->getFragmentSizeInBits())
     return ValueSize >= *FragmentSize;
   // We can't always calculate the size of the DI variable (e.g. if it is a
   // VLA). Try to use the size of the alloca that the dbg intrinsic describes
   // intead.
   if (DII->isAddressOfVariable())
-    if (auto *AI = dyn_cast_or_null<AllocaInst>(DII->getVariableLocation()))
+    if (auto *AI = dyn_cast_or_null<AllocaInst>(DII->getVariableLocationOp(0)))
       if (auto FragmentSize = AI->getAllocationSizeInBits(DL))
         return ValueSize >= *FragmentSize;
   // Could not determine size of variable. Conservatively return false.
   return false;
 }
 
 /// Produce a DebugLoc to use for each dbg.declare/inst pair that are promoted
 /// to a dbg.value. Because no machine insts can come from debug intrinsics,
void llvm::insertDebugValuesForPHIs(BasicBlock *BB,
   assert(BB && "No BasicBlock to clone dbg.value(s) from.");
   if (InsertedPHIs.size() == 0)
     return;
 
   // Map existing PHI nodes to their dbg.values.
   ValueToValueMapTy DbgValueMap;
   for (auto &I : *BB) {
     if (auto DbgII = dyn_cast<DbgVariableIntrinsic>(&I)) {
-      if (auto *Loc = dyn_cast_or_null<PHINode>(DbgII->getVariableLocation()))
+      if (auto *Loc =
+              dyn_cast_or_null<PHINode>(DbgII->getVariableLocationOp(0)))
         DbgValueMap.insert({Loc, DbgII});
     }
   }
   if (DbgValueMap.size() == 0)
     return;
 
   // Then iterate through the new PHIs and look to see if they use one of the
   // previously mapped PHIs. If so, insert a new dbg.value intrinsic that will
   // propagate the info through the new PHI.
-  LLVMContext &C = BB->getContext();
   for (auto PHI : InsertedPHIs) {
     BasicBlock *Parent = PHI->getParent();
     // Avoid inserting an intrinsic into an EH block.
     if (Parent->getFirstNonPHI()->isEHPad())
       continue;
-    auto PhiMAV = MetadataAsValue::get(C, ValueAsMetadata::get(PHI));
     for (auto VI : PHI->operand_values()) {
       auto V = DbgValueMap.find(VI);
       if (V != DbgValueMap.end()) {
         auto *DbgII = cast<DbgVariableIntrinsic>(V->second);
-        Instruction *NewDbgII = DbgII->clone();
-        NewDbgII->setOperand(0, PhiMAV);
+        DbgVariableIntrinsic *NewDbgII =
+            cast<DbgVariableIntrinsic>(DbgII->clone());
+        NewDbgII->replaceVariableLocationOp(VI, PHI);
         auto InsertionPt = Parent->getFirstInsertionPt();
         assert(InsertionPt != Parent->end() && "Ill-formed basic block");
         NewDbgII->insertBefore(&*InsertionPt);
       }
     }
   }
 }
 

 void llvm::salvageDebugInfo(Instruction &I) {
   SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
   findDbgUsers(DbgUsers, &I);
   salvageDebugInfoForDbgValues(I, DbgUsers);
 }
 
 void llvm::salvageDebugInfoForDbgValues(
     Instruction &I, ArrayRef<DbgVariableIntrinsic *> DbgUsers) {
-  auto &Ctx = I.getContext();
   bool Salvaged = false;
-  auto wrapMD = [&](Value *V) { return wrapValueInMetadata(Ctx, V); };
 
   for (auto *DII : DbgUsers) {
     // Do not add DW_OP_stack_value for DbgDeclare and DbgAddr, because they
     // are implicitly pointing out the value as a DWARF memory location
     // description.
     bool StackValue = isa<DbgValueInst>(DII);
 
     DIExpression *DIExpr =
         salvageDebugInfoImpl(I, DII->getExpression(), StackValue);
 
     // salvageDebugInfoImpl should fail on examining the first element of
     // DbgUsers, or none of them.
     if (!DIExpr)
       break;
 
-    DII->setOperand(0, wrapMD(I.getOperand(0)));
-    DII->setOperand(2, MetadataAsValue::get(Ctx, DIExpr));
+    DII->replaceVariableLocationOp(&I, I.getOperand(0));
+    DII->setExpression(DIExpr);
     LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
     Salvaged = true;
   }
 
   if (Salvaged)
     return;
 
   for (auto *DII : DbgUsers) {
     Value *Undef = UndefValue::get(I.getType());
-    DII->setOperand(0, MetadataAsValue::get(DII->getContext(),
-                                            ValueAsMetadata::get(Undef)));
+    DII->replaceVariableLocationOp(&I, Undef);
   }
 }
 
 DIExpression *llvm::salvageDebugInfoImpl(Instruction &I,
                                          DIExpression *SrcDIExpr,
                                          bool WithStackValue) {
   auto &M = *I.getModule();
   auto &DL = M.getDataLayout();
if (isa<Instruction>(&To)) {
     }
   }
 
   // Update debug users without use-before-def risk.
   for (auto *DII : Users) {
     if (UndefOrSalvage.count(DII))
       continue;
 
-    LLVMContext &Ctx = DII->getContext();
     DbgValReplacement DVR = RewriteExpr(*DII);
     if (!DVR)
       continue;
 
-    DII->setOperand(0, wrapValueInMetadata(Ctx, &To));
-    DII->setOperand(2, MetadataAsValue::get(Ctx, *DVR));
+    DII->replaceVariableLocationOp(&From, &To);
+    DII->setExpression(*DVR);
     LLVM_DEBUG(dbgs() << "REWRITE:  " << *DII << '\n');
     Changed = true;
   }
 
   if (!UndefOrSalvage.empty()) {
     // Try to salvage the remaining debug users.
     salvageDebugInfo(From);
     Changed = true;

llvm/lib/Transforms/Utils/LoopRotationUtils.cpp

for (auto &DbgValue : DbgValues) {
       // available in UserBB, if not substitute undef.
       Value *NewVal;
       if (UserBB == OrigPreheader)
         NewVal = OrigPreHeaderVal;
       else if (SSA.HasValueForBlock(UserBB))
         NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
       else
         NewVal = UndefValue::get(OrigHeaderVal->getType());
-      DbgValue->setOperand(0,
-                           MetadataAsValue::get(OrigHeaderVal->getContext(),
-                                                ValueAsMetadata::get(NewVal)));
+      DbgValue->replaceVariableLocationOp(OrigHeaderVal, NewVal);
     }
   }
 }
 
 // Assuming both header and latch are exiting, look for a phi which is only
 // used outside the loop (via a LCSSA phi) in the exit from the header.
 // This means that rotating the loop can remove the phi.
 static bool profitableToRotateLoopExitingLatch(Loop *L) {
do {
     // For the rest of the instructions, either hoist to the OrigPreheader if
     // possible or create a clone in the OldPreHeader if not.
     Instruction *LoopEntryBranch = OrigPreheader->getTerminator();
 
     // Record all debug intrinsics preceding LoopEntryBranch to avoid duplication.
     using DbgIntrinsicHash =
       std::pair<std::pair<Value *, DILocalVariable *>, DIExpression *>;
     auto makeHash = [](DbgVariableIntrinsic *D) -> DbgIntrinsicHash {
-      return {{D->getVariableLocation(), D->getVariable()}, D->getExpression()};
+      return {{D->getVariableLocationOp(0), D->getVariable()},
+              D->getExpression()};
     };
     SmallDenseSet<DbgIntrinsicHash, 8> DbgIntrinsics;
     for (auto I = std::next(OrigPreheader->rbegin()), E = OrigPreheader->rend();
          I != E; ++I) {
       if (auto *DII = dyn_cast<DbgVariableIntrinsic>(&*I))
         DbgIntrinsics.insert(makeHash(DII));
       else
         break;

llvm/unittests/Transforms/Utils/LocalTest.cpp

TEST(Local, ReplaceAllDbgUsesWith) {
   EXPECT_TRUE(any_of(DDbgVals, [](DbgVariableIntrinsic *DII) {
     return isa<DbgDeclareInst>(DII);
   }));
 
   // Introduce a use-before-def. Check that the dbg.value for %a is salvaged.
   EXPECT_TRUE(replaceAllDbgUsesWith(A, F_, F_, DT));
 
   auto *ADbgVal = cast<DbgValueInst>(A.getNextNode());
-  EXPECT_EQ(ConstantInt::get(A.getType(), 0), ADbgVal->getVariableLocation());
+  EXPECT_EQ(ConstantInt::get(A.getType(), 0),
+            ADbgVal->getVariableLocationOp(0));
 
   // Introduce a use-before-def. Check that the dbg.values for %f become undef.
   EXPECT_TRUE(replaceAllDbgUsesWith(F_, G, G, DT));
 
   auto *FDbgVal = cast<DbgValueInst>(F_.getNextNode());
-  EXPECT_TRUE(isa<UndefValue>(FDbgVal->getVariableLocation()));
+  EXPECT_TRUE(isa<UndefValue>(FDbgVal->getVariableLocationOp(0)));
 
   SmallVector<DbgValueInst *, 1> FDbgVals;
   findDbgValues(FDbgVals, &F_);
   EXPECT_EQ(0U, FDbgVals.size());
 
   // Simulate i32 -> i64 conversion to test sign-extension. Here are some
   // interesting cases to handle:
   //  1) debug user has empty DIExpression