PR32382: Emit complex DWARF expressions with the correct location description kind

[aprantl]

Summary

This fixes most of PR32382. It does not fix the DWARF 2 expressions yet; that part can be done as a separate, simpler follow-up commit.

The DWARF specification knows 3 kinds of non-empty simple location descriptions:

1. Register location descriptions
   • describe a variable in a register
   • consist of only a DW_OP_reg
2. Memory location descriptions
   • describe the address of a variable
3. Implicit location descriptions
   • describe the value of a variable
   • end with DW_OP_stack_value & friends

The existing DwarfExpression code is pretty much ignorant of these restrictions. This used to not matter because we only emitted very short expressions that we happened to get right by accident. This patch makes DwarfExpression aware of the rules defined by the DWARF standard and now chooses the right kind of location description for each expression being emitted.

There are two major changes in this patch:

• I had to fix the semantics of dbg.declare for describing function arguments. After this patch a dbg.declare always takes the *address* of a variable as the first argument, even if the argument is not an alloca.
• When lowering a DBG_VALUE, the decision of whether to emit a register location description or a memory location description depends on the MachineLocation — register machine locations may get promoted to memory locations based on their DIExpression. (Future) optimization passes that want to salvage implicit debug location for variables may do so by appending a DW_OP_stack_value. For example: DBG_VALUE, [RBP-8] --> DW_OP_fbreg -8 DBG_VALUE, RAX --> DW_OP_reg0 +0 DBG_VALUE, RAX, DIExpression(DW_OP_deref) --> DW_OP_reg0 +0

All testcases that were modified were regenerated from clang. I also added source-based testcases for each of these to the debuginfo-tests repository over the last week to make sure that no synchronized bugs slip in. The debuginfo-tests compile from source and run the debugger.

https://bugs.llvm.org/show_bug.cgi?id=32382
rdar://problem/31205000

[dblaikie]

There are a lot of small, careful changes in here - I might need a bit of a high level walkthrough of what the changes are and how they achieve the goal. More detail on how this changes behavior would be good. "makes LLVM aware of these DWARF restrictions" is a bit too high level.

lib/Bitcode/Reader/MetadataLoader.cpp

1559–1563

This seems a bit complicated - any way to simplify it/make it more obvious? (or at least add comments)

Some of it looks the same as the condition in the case 0 of this switch. Could it be factored into a common function wiht a name that might aid readability?

lib/Bitcode/Writer/BitcodeWriter.cpp

1760–1762

Where did the HasOpFragmentFlag go? Or it morphed into a version flag stored above the first bit?

lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

176

So is this another "not quite DWARF expression" contract it DIExpression? (like the LLVM_fragment?)

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

1522

Remove commented-out code.

[aprantl]

In D31439#713317, @dblaikie wrote:

There are a lot of small, careful changes in here - I might need a bit of a high level walkthrough of what the changes are and how they achieve the goal. More detail on how this changes behavior would be good. "makes LLVM aware of these DWARF restrictions" is a bit too high level.

This was unfortunately the smallest I could break the patch up into.
The observable behavior changes only for DIExpressions that have a DW_OP_deref operator *and* additional operators. The primary change is that the old code treated DW_OP_breg as if it where dereferencing the contents of the register. This happened to work if no other operations followed (because with no DW_OP_stack_value present, debuggers treat the expression as a memory location description, i.e.: deref the expression).

lib/Bitcode/Reader/MetadataLoader.cpp

1559–1563

It doesn't have enough in common to be factored out, but perhaps adding the comment

//[DW_OP_deref, ..., DW_OP_LLVM_fragment, x, y]
// -> [..., DW_OP_deref, DW_OP_LLVM_fragment, x, y]

makes it more obvious what is happening there.

lib/Bitcode/Writer/BitcodeWriter.cpp

1760–1762

It's rolled into the Version. I have a laundry list of future improvements to DIExpression, that will involve revving the version and are easier to handle as incremental upgrades rather than individual "features".

lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

176

Yes, this is a bit obtuse. We could also add an addAddress() call to DwarfExpression analogous to addMachineReg() that then sets the location description kind inside of DwarfExpression. We could effectively move all the code inside if (Global) into DwarfExpression::addAddress().

[aprantl]

Add DIEDwarfExpression::addAddress() and DIEDwarfExpression::addThreadLocalAddress().

[dblaikie]

Couple of minor things. Not sure I fully understand everything here, but seems plausible.

include/llvm/IR/DebugInfoMetadata.h

2252–2257

linear algorithm for testing the last element? that doesn't seem ideal (getElements().back() instead?) (conditional on !getElements().empty())

lib/Bitcode/Reader/MetadataLoader.cpp

1559–1563

Maybe it'd be easier if it were a std::copy?

if (deref) {
  auto End = Elts.end();
  if (Elts.size() >= 3 && std::prev(End, 3) == fragment)
    std::prev(End, 3);
  std::move(std::next(Elts.begin()), End, Elts.begin());
  *std::prev(End) = fragment;
}

Something like that?

lib/CodeGen/AsmPrinter/DwarfExpression.cpp

233–235

Should fixme be conditional on "when using DWARF N < M" (where M is whatever version that added stack_value). Would be good to mention that in the comment if that's the case.

[aprantl]

Thanks a lot for reviewing this, David! While I was preparing the next updated of the corresponding clang changes in https://reviews.llvm.org/D31440 I realized that there is one use-case that is not supported by this variant. To encode locations for by-ref captures clang wants to describe a location that is at an offset inside of a larger alloca. To support this use-case I need to remove the implicit DW_OP_deref that we are adding to dbg.declares everywhere and make it explicit instead.
This will be a good change:

• it will make a future patch that replaces all instances of dbg.declare with dbg.value very simple
• we won't need to rewrite DIExpressions when we lower dbg.declare -> dbg.value
• it will make the DW_OP_xderef use-case that I complain about in DwarfCompileUnit.cpp:570 appear less out-of-place.

I'll be back here with an updated (albeit somewhat longer) patch soon. Meanwhile I'm also extending the debuginfo-tests a bit to make sure I'm not breaking the integration between llvm and clang.

[aprantl]

Addressed David's review feedback for the DW_OP_deref bitcode upgrade.

[aprantl]

Added test coverage for SelectionDAG in sret.ll and ensured it matches the FastISel behavior.

[aprantl]

David, the review is still marked as accepted, but I did add a couple of changes since then, so I think I should be moving it back into "Request review".
Would you mind taking a second look?

As I mentioned in the description, all IR testcases that were modified were regenerated from clang. I also added source-based testcases for each of these to the debuginfo-tests repository over the last week to make sure that no synchronized bugs slip in. The debuginfo-tests compile from source and run the debugger and are exercised by the green dragon bots, so all these changes should be safe.
thanks!
adrian

[dblaikie]

Phab's not helping me see what the delta since the last time I accepted this are, but taking a very rough glance it seems ok - carry on :)

[aaboud]

This commit caused the following bug:
https://bugs.llvm.org/show_bug.cgi?id=33166

[aaboud]

In D31439#764342, @aaboud wrote:

This commit caused the following bug:
https://bugs.llvm.org/show_bug.cgi?id=33166

Seems like the issue was fixed in r301210. If that is true, then sorry for the noise.
Adrain, can you please confirm that?

Thanks

docs/LangRef.rst

 
 ``DIExpression`` nodes represent expressions that are inspired by the DWARF
 expression language. They are used in :ref:`debug intrinsics<dbg_intrinsics>`
 (such as ``llvm.dbg.declare`` and ``llvm.dbg.value``) to describe how the
 referenced LLVM variable relates to the source language variable.
 
 The current supported vocabulary is limited:
 
-- ``DW_OP_deref`` dereferences the working expression.
+- ``DW_OP_deref`` dereferences the top of the expression stack.
 - ``DW_OP_plus, 93`` adds ``93`` to the working expression.
 - ``DW_OP_LLVM_fragment, 16, 8`` specifies the offset and size (``16`` and ``8``
   here, respectively) of the variable fragment from the working expression. Note
   that contrary to DW_OP_bit_piece, the offset is describing the the location
   within the described source variable.
 - ``DW_OP_swap`` swaps top two stack entries.
 - ``DW_OP_xderef`` provides extended dereference mechanism. The entry at the top
   of the stack is treated as an address. The second stack entry is treated as an
   address space identifier.
 - ``DW_OP_stack_value`` marks a constant value.
 
 DIExpression nodes that contain a ``DW_OP_stack_value`` operator are standalone
 location descriptions that describe constant values. This form is used to
 describe global constants that have been optimized away. All other expressions
 are modifiers to another location: A debug intrinsic ties a location and a
-DIExpression together. Contrary to DWARF expressions, a DIExpression always
-describes the *value* of a source variable and never its *address*. In DWARF
-terminology, a DIExpression can always be considered an implicit location
-description regardless whether it contains a ``DW_OP_stack_value`` or not.
+DIExpression together.
 
-.. code-block:: text
+DWARF specifies three kinds of simple location descriptions: Register, memory,
+and implicit location descriptions. Register and memory location descriptions
+describe the *location* of a source variable (in the sense that a debugger might
+modify its value), whereas implicit locations describe merely the *value* of a
+source variable. DIExpressions also follow this model: A DIExpression that
+doesn't have a trailing ``DW_OP_stack_value`` will describe an *address* when
+combined with a concrete location.
+
+.. code-block:: llvm
 
     !0 = !DIExpression(DW_OP_deref)
     !1 = !DIExpression(DW_OP_plus, 3)
     !2 = !DIExpression(DW_OP_bit_piece, 3, 7)
     !3 = !DIExpression(DW_OP_deref, DW_OP_plus, 3, DW_OP_LLVM_fragment, 3, 7)
     !4 = !DIExpression(DW_OP_constu, 2, DW_OP_swap, DW_OP_xderef)
     !5 = !DIExpression(DW_OP_constu, 42, DW_OP_stack_value)
 

docs/SourceLevelDebugging.rst

 
 ``llvm.dbg.declare``
 ^^^^^^^^^^^^^^^^^^^^
 
 .. code-block:: llvm
 
   void @llvm.dbg.declare(metadata, metadata, metadata)
 
-This intrinsic provides information about a local element (e.g., variable).
-The first argument is metadata holding the alloca for the variable.  The second
+This intrinsic provides information about a local element (e.g., variable).  The
+first argument is metadata holding the alloca for the variable.  The second
 argument is a `local variable <LangRef.html#dilocalvariable>`_ containing a
 description of the variable.  The third argument is a `complex expression
-<LangRef.html#diexpression>`_.
+<LangRef.html#diexpression>`_.  An `llvm.dbg.declare` instrinsic describes the
+*location* of a source variable.
+
+.. code-block:: llvm
+
+    %i.addr = alloca i32, align 4
+    call void @llvm.dbg.declare(metadata i32* %i.addr, metadata !1, metadata !2), !dbg !3
+    !1 = !DILocalVariable(name: "i", ...) ; int i
+    !2 = !DIExpression()
+    !3 = !DILocation(...)
+    ...
+    %buffer = alloca [256 x i8], align 8
+    ; The address of i is buffer+64.
+    call void @llvm.dbg.declare(metadata [256 x i8]* %buffer, metadata !1, metadata !2)
+    !1 = !DILocalVariable(name: "i", ...) ; int i
+    !2 = !DIExpression(DW_OP_plus, 64)
+
 
 ``llvm.dbg.value``
 ^^^^^^^^^^^^^^^^^^
 
 .. code-block:: llvm
 
   void @llvm.dbg.value(metadata, i64, metadata, metadata)
 

include/llvm/CodeGen/MachineInstrBuilder.h

 /// for either a value in a register or a register-indirect+offset
 /// address and inserts it at position I.
 MachineInstrBuilder BuildMI(MachineBasicBlock &BB,
                             MachineBasicBlock::iterator I, const DebugLoc &DL,
                             const MCInstrDesc &MCID, bool IsIndirect,
                             unsigned Reg, unsigned Offset,
                             const MDNode *Variable, const MDNode *Expr);
 
+/// Clone a DBG_VALUE whose value has been spilled to FrameIndex.
+MachineInstr *buildDbgValueForSpill(MachineBasicBlock &BB,
+                                    MachineBasicBlock::iterator I,
+                                    const MachineInstr &Orig, int FrameIndex);
+
 inline unsigned getDefRegState(bool B) {
   return B ? RegState::Define : 0;
 }
 inline unsigned getImplRegState(bool B) {
   return B ? RegState::Implicit : 0;
 }
 inline unsigned getKillRegState(bool B) {
   return B ? RegState::Kill : 0;

include/llvm/IR/DebugInfoMetadata.h

public:
   /// \pre \a isValid() gives \c true.
   /// @{
   expr_op_iterator expr_op_begin() const {
     return expr_op_iterator(elements_begin());
   }
   expr_op_iterator expr_op_end() const {
     return expr_op_iterator(elements_end());
   }
+  iterator_range<expr_op_iterator> expr_ops() const {
+    return {expr_op_begin(), expr_op_end()};
+  }
   /// @}
 
   bool isValid() const;
 
   static bool classof(const Metadata *MD) {
     return MD->getMetadataID() == DIExpressionKind;
   }
 
-  /// Is the first element a DW_OP_deref?.
+  /// Return whether the first element a DW_OP_deref.
   bool startsWithDeref() const {
     return getNumElements() > 0 && getElement(0) == dwarf::DW_OP_deref;
   }
 
   /// Holds the characteristics of one fragment of a larger variable.
   struct FragmentInfo {
     uint64_t SizeInBits;
     uint64_t OffsetInBits;
   };
 
   /// Retrieve the details of this fragment expression.
   static Optional<FragmentInfo> getFragmentInfo(expr_op_iterator Start,
                                                 expr_op_iterator End);
 
   /// Retrieve the details of this fragment expression.
   Optional<FragmentInfo> getFragmentInfo() const {
     return getFragmentInfo(expr_op_begin(), expr_op_end());
   }
 

lib/Bitcode/Reader/BitcodeReader.cpp

Error BitcodeReader::globalCleanup() {
   // Patch the initializers for globals and aliases up.
   if (Error Err = resolveGlobalAndIndirectSymbolInits())
     return Err;
   if (!GlobalInits.empty() || !IndirectSymbolInits.empty())
     return error("Malformed global initializer set");
 
   // Look for intrinsic functions which need to be upgraded at some point
   for (Function &F : *TheModule) {
+    MDLoader->upgradeDebugIntrinsics(F);
     Function *NewFn;
     if (UpgradeIntrinsicFunction(&F, NewFn))
       UpgradedIntrinsics[&F] = NewFn;
     else if (auto Remangled = Intrinsic::remangleIntrinsicFunction(&F))
       // Some types could be renamed during loading if several modules are
       // loaded in the same LLVMContext (LTO scenario). In this case we should
       // remangle intrinsics names as well.
       RemangledIntrinsics[&F] = Remangled.getValue();

lib/Bitcode/Reader/MetadataLoader.h

public:
   Error parseMetadataAttachment(
       Function &F, const SmallVectorImpl<Instruction *> &InstructionList);
 
   /// Parse a `METADATA_KIND` block for the current module.
   Error parseMetadataKinds();
 
   unsigned size() const;
   void shrinkTo(unsigned N);
+
+  /// Perform bitcode upgrades on llvm.dbg.* calls.
+  void upgradeDebugIntrinsics(Function &F);
 };
 }
 
 #endif // LLVM_LIB_BITCODE_READER_METADATALOADER_H

lib/Bitcode/Reader/MetadataLoader.cpp

 #include "llvm/IR/GlobalObject.h"
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/ModuleSummaryIndex.h"
 #include "llvm/IR/OperandTraits.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/IR/TrackingMDRef.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/ValueHandle.h"
class MetadataLoader::MetadataLoaderImpl {
   SmallDenseMap<Function *, DISubprogram *, 16> FunctionsWithSPs;
 
   // Map the bitcode's custom MDKind ID to the Module's MDKind ID.
   DenseMap<unsigned, unsigned> MDKindMap;
 
   bool StripTBAA = false;
   bool HasSeenOldLoopTags = false;
   bool NeedUpgradeToDIGlobalVariableExpression = false;
+  bool NeedDeclareExpressionUpgrade = false;
 
   /// True if metadata is being parsed for a module being ThinLTO imported.
   bool IsImporting = false;
 
   Error parseOneMetadata(SmallVectorImpl<uint64_t> &Record, unsigned Code,
                          PlaceholderQueue &Placeholders, StringRef Blob,
                          unsigned &NextMetadataNo);
   Error parseMetadataStrings(ArrayRef<uint64_t> Record, StringRef Blob,
for (auto &GV : TheModule.globals()) {
           auto *DGVE =
               DIGlobalVariableExpression::getDistinct(Context, DGV, nullptr);
           GV.addMetadata(LLVMContext::MD_dbg, *DGVE);
         } else
           GV.addMetadata(LLVMContext::MD_dbg, *MD);
     }
   }
 
+  /// Remove a leading DW_OP_deref from DIExpressions in a dbg.declare that
+  /// describes a function argument.
+  void upgradeDeclareExpressions(Function &F) {
+    if (!NeedDeclareExpressionUpgrade)
+      return;
+
+    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));
+            }
+  }
+
   void upgradeDebugInfo() {
     upgradeCUSubprograms();
     upgradeCUVariables();
   }
 
 public:
   MetadataLoaderImpl(BitstreamCursor &Stream, Module &TheModule,
                      BitcodeReaderValueList &ValueList,
public:
 
   Error parseMetadataKinds();
 
   void setStripTBAA(bool Value) { StripTBAA = Value; }
   bool isStrippingTBAA() { return StripTBAA; }
 
   unsigned size() const { return MetadataList.size(); }
   void shrinkTo(unsigned N) { MetadataList.shrinkTo(N); }
+  void upgradeDebugIntrinsics(Function &F) { upgradeDeclareExpressions(F); }
 };
 
 static Error error(const Twine &Message) {
   return make_error<StringError>(
       Message, make_error_code(BitcodeError::CorruptedBitcode));
 }
 
 Expected<bool>
case bitc::METADATA_LOCAL_VAR: {
     NextMetadataNo++;
     break;
   }
   case bitc::METADATA_EXPRESSION: {
     if (Record.size() < 1)
       return error("Invalid record");
 
     IsDistinct = Record[0] & 1;
-    bool HasOpFragment = Record[0] & 2;
+    uint64_t Version = Record[0] >> 1;
     auto Elts = MutableArrayRef<uint64_t>(Record).slice(1);
-    if (!HasOpFragment)
-      if (unsigned N = Elts.size())
-        if (N >= 3 && Elts[N - 3] == dwarf::DW_OP_bit_piece)
-          Elts[N - 3] = dwarf::DW_OP_LLVM_fragment;
+    unsigned N = Elts.size();
+    // Perform various upgrades.
+    switch (Version) {
+    case 0:
+      LLVM_FALLTHROUGH;
+    case 1:
+      // Move DW_OP_deref to the end.
+      if (N && Elts[0] == dwarf::DW_OP_deref) {
+        auto End = Elts.end();
+        if (Elts.size() >= 3 && *std::prev(End, 3) == dwarf::DW_OP_LLVM_fragment)
+          End = std::prev(End, 3);
+        std::move(std::next(Elts.begin()), End, Elts.begin());
+        *std::prev(End) = dwarf::DW_OP_deref;
+      }
+      NeedDeclareExpressionUpgrade = true;
+      LLVM_FALLTHROUGH;
+    case 2:
+      // Up-to-date!
+      break;
+    default:
+      return error("Invalid record");
+    }
 
     MetadataList.assignValue(
         GET_OR_DISTINCT(DIExpression, (Context, makeArrayRef(Record).slice(1))),
         NextMetadataNo);
     NextMetadataNo++;
     break;
   }
   case bitc::METADATA_GLOBAL_VAR_EXPR: {

 void MetadataLoader::setStripTBAA(bool StripTBAA) {
   return Pimpl->setStripTBAA(StripTBAA);
 }
 
 bool MetadataLoader::isStrippingTBAA() { return Pimpl->isStrippingTBAA(); }
 
 unsigned MetadataLoader::size() const { return Pimpl->size(); }
 void MetadataLoader::shrinkTo(unsigned N) { return Pimpl->shrinkTo(N); }
+
+void MetadataLoader::upgradeDebugIntrinsics(Function &F) {
+  return Pimpl->upgradeDebugIntrinsics(F);
+}

lib/Bitcode/Writer/BitcodeWriter.cpp

void ModuleBitcodeWriter::writeDILocalVariable(
   Stream.EmitRecord(bitc::METADATA_LOCAL_VAR, Record, Abbrev);
   Record.clear();
 }
 
 void ModuleBitcodeWriter::writeDIExpression(const DIExpression *N,
                                             SmallVectorImpl<uint64_t> &Record,
                                             unsigned Abbrev) {
   Record.reserve(N->getElements().size() + 1);
-
-  const uint64_t HasOpFragmentFlag = 1 << 1;
-  Record.push_back((uint64_t)N->isDistinct() | HasOpFragmentFlag);
+  const uint64_t Version = 2 << 1;
+  Record.push_back((uint64_t)N->isDistinct() | Version);
   Record.append(N->elements_begin(), N->elements_end());
 
   Stream.EmitRecord(bitc::METADATA_EXPRESSION, Record, Abbrev);
   Record.clear();
 }
 
 void ModuleBitcodeWriter::writeDIGlobalVariableExpression(
     const DIGlobalVariableExpression *N, SmallVectorImpl<uint64_t> &Record,
     unsigned Abbrev) {

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

static bool emitDebugValueComment(const MachineInstr *MI, AsmPrinter &AP) {
   const DIExpression *Expr = MI->getDebugExpression();
   auto Fragment = Expr->getFragmentInfo();
   if (Fragment)
     OS << " [fragment offset=" << Fragment->OffsetInBits
        << " size=" << Fragment->SizeInBits << "]";
   OS << " <- ";
 
   // The second operand is only an offset if it's an immediate.
-  bool Deref = MI->getOperand(0).isReg() && MI->getOperand(1).isImm();
-  int64_t Offset = Deref ? MI->getOperand(1).getImm() : 0;
-
+  bool Deref = false;
+  bool MemLoc = MI->getOperand(0).isReg() && MI->getOperand(1).isImm();
+  int64_t Offset = MemLoc ? MI->getOperand(1).getImm() : 0;
   for (unsigned i = 0; i < Expr->getNumElements(); ++i) {
     uint64_t Op = Expr->getElement(i);
     if (Op == dwarf::DW_OP_LLVM_fragment) {
       // There can't be any operands after this in a valid expression
       break;
     } else if (Deref) {
       // We currently don't support extra Offsets or derefs after the first
-      // one. Bail out early instead of emitting an incorrect comment
+      // one. Bail out early instead of emitting an incorrect comment.
       OS << " [complex expression]";
       AP.OutStreamer->emitRawComment(OS.str());
       return true;
     } else if (Op == dwarf::DW_OP_deref) {
       Deref = true;
       continue;
     }
 
if (MI->getOperand(0).isFPImm()) {
     }
     if (Reg == 0) {
       // Suppress offset, it is not meaningful here.
       OS << "undef";
       // NOTE: Want this comment at start of line, don't emit with AddComment.
       AP.OutStreamer->emitRawComment(OS.str());
       return true;
     }
-    if (Deref)
+    if (MemLoc || Deref)
       OS << '[';
     OS << PrintReg(Reg, AP.MF->getSubtarget().getRegisterInfo());
   }
 
-  if (Deref)
+  if (MemLoc || Deref)
     OS << '+' << Offset << ']';
 
   // NOTE: Want this comment at start of line, don't emit with AddComment.
   AP.OutStreamer->emitRawComment(OS.str());
   return true;
 }
 
 AsmPrinter::CFIMoveType AsmPrinter::needsCFIMoves() {

lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

if (!Loc) {
       addToAccelTable = true;
       Loc = new (DIEValueAllocator) DIELoc;
       DwarfExpr = llvm::make_unique<DIEDwarfExpression>(*Asm, *this, *Loc);
     }
 
     if (Global) {
       const MCSymbol *Sym = Asm->getSymbol(Global);
       if (Global->isThreadLocal()) {
         if (Asm->TM.Options.EmulatedTLS) {
           // TODO: add debug info for emulated thread local mode.
         } else {
           // FIXME: Make this work with -gsplit-dwarf.
           unsigned PointerSize = Asm->getDataLayout().getPointerSize();
           assert((PointerSize == 4 || PointerSize == 8) &&
                  "Add support for other sizes if necessary");
           // Based on GCC's support for TLS:
           if (!DD->useSplitDwarf()) {
DIE *DwarfCompileUnit::constructVariableDIEImpl(const DbgVariable &DV,
   // .. else use frame index.
   if (!DV.hasFrameIndexExprs())
     return VariableDie;
 
   DIELoc *Loc = new (DIEValueAllocator) DIELoc;
   DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
   for (auto &Fragment : DV.getFrameIndexExprs()) {
     unsigned FrameReg = 0;
+    const DIExpression *Expr = Fragment.Expr;
     const TargetFrameLowering *TFI = Asm->MF->getSubtarget().getFrameLowering();
     int Offset = TFI->getFrameIndexReference(*Asm->MF, Fragment.FI, FrameReg);
-    DwarfExpr.addFragmentOffset(Fragment.Expr);
+    DwarfExpr.addFragmentOffset(Expr);
     SmallVector<uint64_t, 8> Ops;
     Ops.push_back(dwarf::DW_OP_plus);
     Ops.push_back(Offset);
-    Ops.push_back(dwarf::DW_OP_deref);
-    Ops.append(Fragment.Expr->elements_begin(), Fragment.Expr->elements_end());
-    DIExpressionCursor Expr(Ops);
-    DwarfExpr.addMachineRegExpression(
-        *Asm->MF->getSubtarget().getRegisterInfo(), Expr, FrameReg);
-    DwarfExpr.addExpression(std::move(Expr));
+    Ops.append(Expr->elements_begin(), Expr->elements_end());
+    DIExpressionCursor Cursor(Ops);
+    DwarfExpr.addMachineLocExpression(
+        *Asm->MF->getSubtarget().getRegisterInfo(), Cursor,
+        MachineLocation(FrameReg));
+    DwarfExpr.addExpression(std::move(Cursor));
   }
   addBlock(*VariableDie, dwarf::DW_AT_location, DwarfExpr.finalize());
 
   return VariableDie;
 }
 
 DIE *DwarfCompileUnit::constructVariableDIE(DbgVariable &DV,
                                             const LexicalScope &Scope,

 
 /// Add an address attribute to a die based on the location provided.
 void DwarfCompileUnit::addAddress(DIE &Die, dwarf::Attribute Attribute,
                                   const MachineLocation &Location) {
   DIELoc *Loc = new (DIEValueAllocator) DIELoc;
   DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
 
   SmallVector<uint64_t, 8> Ops;
-  if (Location.isIndirect()) {
+  if (Location.isIndirect() && Location.getOffset()) {
     Ops.push_back(dwarf::DW_OP_plus);
     Ops.push_back(Location.getOffset());
-    Ops.push_back(dwarf::DW_OP_deref);
   }
   DIExpressionCursor Cursor(Ops);
   const TargetRegisterInfo &TRI = *Asm->MF->getSubtarget().getRegisterInfo();
-  if (!DwarfExpr.addMachineRegExpression(TRI, Cursor, Location.getReg()))
+  if (!DwarfExpr.addMachineLocExpression(TRI, Cursor, Location))
     return;
   DwarfExpr.addExpression(std::move(Cursor));
 
   // Now attach the location information to the DIE.
   addBlock(Die, Attribute, DwarfExpr.finalize());
 }
 
 /// Start with the address based on the location provided, and generate the
 /// DWARF information necessary to find the actual variable given the extra
 /// address information encoded in the DbgVariable, starting from the starting
 /// location.  Add the DWARF information to the die.
 void DwarfCompileUnit::addComplexAddress(const DbgVariable &DV, DIE &Die,
                                          dwarf::Attribute Attribute,
                                          const MachineLocation &Location) {
   DIELoc *Loc = new (DIEValueAllocator) DIELoc;
   DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
   const DIExpression *DIExpr = DV.getSingleExpression();
   DwarfExpr.addFragmentOffset(DIExpr);
 
   SmallVector<uint64_t, 8> Ops;
-  if (Location.isIndirect()) {
+  if (Location.isIndirect() && Location.getOffset()) {
     Ops.push_back(dwarf::DW_OP_plus);
     Ops.push_back(Location.getOffset());
-    Ops.push_back(dwarf::DW_OP_deref);
   }
   Ops.append(DIExpr->elements_begin(), DIExpr->elements_end());
   DIExpressionCursor Cursor(Ops);
   const TargetRegisterInfo &TRI = *Asm->MF->getSubtarget().getRegisterInfo();
-  if (!DwarfExpr.addMachineRegExpression(TRI, Cursor, Location.getReg()))
+  if (!DwarfExpr.addMachineLocExpression(TRI, Cursor, Location))
     return;
   DwarfExpr.addExpression(std::move(Cursor));
 
   // Now attach the location information to the DIE.
   addBlock(Die, Attribute, DwarfExpr.finalize());
 }
 
 /// Add a Dwarf loclistptr attribute data and value.

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

static void emitDebugLocValue(const AsmPrinter &AP, const DIBasicType *BT,
   if (Value.isInt()) {
     if (BT && (BT->getEncoding() == dwarf::DW_ATE_signed ||
                BT->getEncoding() == dwarf::DW_ATE_signed_char))
       DwarfExpr.addSignedConstant(Value.getInt());
     else
       DwarfExpr.addUnsignedConstant(Value.getInt());
   } else if (Value.isLocation()) {
     MachineLocation Location = Value.getLoc();
-
     SmallVector<uint64_t, 8> Ops;
-    // FIXME: Should this condition be Location.isIndirect() instead?
-    if (Location.getOffset()) {
+    if (Location.isIndirect() && Location.getOffset()) {
       Ops.push_back(dwarf::DW_OP_plus);
       Ops.push_back(Location.getOffset());
-      Ops.push_back(dwarf::DW_OP_deref);
     }
     Ops.append(DIExpr->elements_begin(), DIExpr->elements_end());
     DIExpressionCursor Cursor(Ops);
     const TargetRegisterInfo &TRI = *AP.MF->getSubtarget().getRegisterInfo();
-    if (!DwarfExpr.addMachineRegExpression(TRI, Cursor, Location.getReg()))
+    if (!DwarfExpr.addMachineLocExpression(TRI, Cursor, Location))
       return;
     return DwarfExpr.addExpression(std::move(Cursor));
   } else if (Value.isConstantFP()) {
     APInt RawBytes = Value.getConstantFP()->getValueAPF().bitcastToAPInt();
     DwarfExpr.addUnsignedConstant(RawBytes);
   }
   DwarfExpr.addExpression(std::move(ExprCursor));
 }

lib/CodeGen/AsmPrinter/DwarfExpression.h

 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
 #define LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
 
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/Support/DataTypes.h"
+#include "llvm/MC/MachineLocation.h"
 
 namespace llvm {
 
 class AsmPrinter;
 class ByteStreamer;
 class TargetRegisterInfo;
 class DwarfUnit;
 class DIELoc;
protected:
   /// Current Fragment Offset in Bits.
   uint64_t OffsetInBits = 0;
   unsigned DwarfVersion;
 
   /// Sometimes we need to add a DW_OP_bit_piece to describe a subregister. 
   unsigned SubRegisterSizeInBits = 0;
   unsigned SubRegisterOffsetInBits = 0;
 
+  /// The kind of location description being produced.
+  enum { Unknown = 0, Register, Memory, Implicit } LocationKind = Unknown;
+
   /// Push a DW_OP_piece / DW_OP_bit_piece for emitting later, if one is needed
   /// to represent a subregister.
   void setSubRegisterPiece(unsigned SizeInBits, unsigned OffsetInBits) {
     SubRegisterSizeInBits = SizeInBits;
     SubRegisterOffsetInBits = OffsetInBits;
   }
 
+  void setMemoryLocationKind();
+
   /// Add masking operations to stencil out a subregister.
   void maskSubRegister();
 
   /// Output a dwarf operand and an optional assembler comment.
   virtual void emitOp(uint8_t Op, const char *Comment = nullptr) = 0;
   /// Emit a raw signed value.
   virtual void emitSigned(int64_t Value) = 0;
   /// Emit a raw unsigned value.
   virtual void emitUnsigned(uint64_t Value) = 0;
   /// Return whether the given machine register is the frame register in the
   /// current function.
   virtual bool isFrameRegister(const TargetRegisterInfo &TRI, unsigned MachineReg) = 0;
 
-  /// Emit a DW_OP_reg operation.
+  /// Emit a DW_OP_reg operation. Note that this is only legal inside a DWARF
+  /// register location description.
   void addReg(int DwarfReg, const char *Comment = nullptr);
   /// Emit a DW_OP_breg operation.
   void addBReg(int DwarfReg, int Offset);
   /// Emit DW_OP_fbreg <Offset>.
   void addFBReg(int Offset);
 
   /// Emit a partial DWARF register operation.
   ///
public:
   /// the prefix of a DwarfExpression if a more efficient representation for
   /// combining the register location and the first operation exists.
   ///
   /// \param FragmentOffsetInBits     If this is one fragment out of a fragmented
   ///                                 location, this is the offset of the
   ///                                 fragment inside the entire variable.
   /// \return                         false if no DWARF register exists
   ///                                 for MachineReg.
-  bool addMachineRegExpression(const TargetRegisterInfo &TRI,
-                               DIExpressionCursor &Expr, unsigned MachineReg,
+  bool addMachineLocExpression(const TargetRegisterInfo &TRI,
+                               DIExpressionCursor &Expr, MachineLocation Loc,
                                unsigned FragmentOffsetInBits = 0);
   /// Emit all remaining operations in the DIExpressionCursor.
   ///
   /// \param FragmentOffsetInBits     If this is one fragment out of multiple
   ///                                 locations, this is the offset of the
   ///                                 fragment inside the entire variable.
   void addExpression(DIExpressionCursor &&Expr,
                      unsigned FragmentOffsetInBits = 0);

lib/CodeGen/AsmPrinter/DwarfExpression.cpp

 #include "llvm/Support/Dwarf.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 
 using namespace llvm;
 
 void DwarfExpression::addReg(int DwarfReg, const char *Comment) {
-  assert(DwarfReg >= 0 && "invalid negative dwarf register number");
-  if (DwarfReg < 32) {
-    emitOp(dwarf::DW_OP_reg0 + DwarfReg, Comment);
+ assert((LocationKind == Unknown || LocationKind == Register) &&
+        "location description already locked down");
+ LocationKind = Register;
   } else {
     emitOp(dwarf::DW_OP_regx, Comment);
     emitUnsigned(DwarfReg);
   }
 }
 
 void DwarfExpression::addBReg(int DwarfReg, int Offset) {
   assert(DwarfReg >= 0 && "invalid negative dwarf register number");
+  assert(LocationKind != Register && "location description already locked down");
   if (DwarfReg < 32) {
     emitOp(dwarf::DW_OP_breg0 + DwarfReg);
   } else {
     emitOp(dwarf::DW_OP_bregx);
     emitUnsigned(DwarfReg);
   }
   emitSigned(Offset);
 }

 }
 
 void DwarfExpression::addStackValue() {
   if (DwarfVersion >= 4)
     emitOp(dwarf::DW_OP_stack_value);
 }
 
 void DwarfExpression::addSignedConstant(int64_t Value) {
+  assert(LocationKind == Implicit || LocationKind == Unknown);
+  LocationKind = Implicit;
   emitOp(dwarf::DW_OP_consts);
   emitSigned(Value);
-  addStackValue();
 }
 
 void DwarfExpression::addUnsignedConstant(uint64_t Value) {
+  assert(LocationKind == Implicit || LocationKind == Unknown);
+  LocationKind = Implicit;
   emitOp(dwarf::DW_OP_constu);
   emitUnsigned(Value);
-  addStackValue();
 }
 
 void DwarfExpression::addUnsignedConstant(const APInt &Value) {
+  assert(LocationKind == Implicit || LocationKind == Unknown);
+  LocationKind = Implicit;
+
   unsigned Size = Value.getBitWidth();
   const uint64_t *Data = Value.getRawData();
 
   // Chop it up into 64-bit pieces, because that's the maximum that
   // addUnsignedConstant takes.
   unsigned Offset = 0;
   while (Offset < Size) {
     addUnsignedConstant(*Data++);
     if (Offset == 0 && Size <= 64)
       break;
-    addOpPiece(std::min(Size-Offset, 64u), Offset);
+    addStackValue();
+    addOpPiece(std::min(Size - Offset, 64u), Offset);
     Offset += 64;
   }
 }
 
-bool DwarfExpression::addMachineRegExpression(const TargetRegisterInfo &TRI,
+bool DwarfExpression::addMachineLocExpression(const TargetRegisterInfo &TRI,
                                               DIExpressionCursor &ExprCursor,
-                                              unsigned MachineReg,
+                                              MachineLocation Loc,
                                               unsigned FragmentOffsetInBits) {
+  if (Loc.isIndirect())
+    LocationKind = Memory;
+
+  unsigned MachineReg = Loc.getReg();
   auto Fragment = ExprCursor.getFragmentInfo();
   if (!addMachineReg(TRI, MachineReg, Fragment ? Fragment->SizeInBits : ~1U))
     return false;
 
   bool HasComplexExpression = false;
   auto Op = ExprCursor.peek();
   if (Op && Op->getOp() != dwarf::DW_OP_LLVM_fragment)
     HasComplexExpression = true;
 
   // If the register can only be described by a complex expression (i.e.,
   // multiple subregisters) it doesn't safely compose with another complex
   // expression. For example, it is not possible to apply a DW_OP_deref
   // operation to multiple DW_OP_pieces.
   if (HasComplexExpression && DwarfRegs.size() > 1) {
     DwarfRegs.clear();
     return false;
   }
 
   // Handle simple register locations.
-  if (!HasComplexExpression) {
+  if (LocationKind != Memory && !HasComplexExpression) {
     for (auto &Reg : DwarfRegs) {
       if (Reg.DwarfRegNo >= 0)
         addReg(Reg.DwarfRegNo, Reg.Comment);
       addOpPiece(Reg.Size);
     }
     DwarfRegs.clear();
     return true;
   }
 
+  // FIXME:
+  // Don't emit locations that cannot be expressed without DW_OP_stack_value.
+
   assert(DwarfRegs.size() == 1);
   auto Reg = DwarfRegs[0];
-  bool FBReg = isFrameRegister(TRI, MachineReg); 
+  bool FBReg = isFrameRegister(TRI, MachineReg);
+  int SignedOffset = 0;
   assert(Reg.Size == 0 && "subregister has same size as superregister");
 
   // Pattern-match combinations for which more efficient representations exist.
-  switch (Op->getOp()) {
-  default: {
-    if (FBReg)
-      addFBReg(0);
-    else
-      addReg(Reg.DwarfRegNo, 0);
-    break;
-  }
-  case dwarf::DW_OP_plus:
-  case dwarf::DW_OP_minus: {
-    // [DW_OP_reg,Offset,DW_OP_plus, DW_OP_deref] --> [DW_OP_breg, Offset].
-    // [DW_OP_reg,Offset,DW_OP_minus,DW_OP_deref] --> [DW_OP_breg,-Offset].
-    auto N = ExprCursor.peekNext();
-    if (N && N->getOp() == dwarf::DW_OP_deref) {
-      int Offset = Op->getArg(0);
-      int SignedOffset = (Op->getOp() == dwarf::DW_OP_plus) ? Offset : -Offset;
-      if (FBReg)
-        addFBReg(SignedOffset);
-      else
-        addBReg(Reg.DwarfRegNo, SignedOffset);
-
-      ExprCursor.consume(2);
-      break;
-    }
-    addReg(Reg.DwarfRegNo, 0);
-    break;
-  }
+  // [Reg, Offset, DW_OP_plus] --> [DW_OP_breg, Offset].
+  // [Reg, Offset, DW_OP_minus] --> [DW_OP_breg, -Offset].
+  // If Reg is a subregister we need to mask it out before subtracting.
+  if (Op && ((Op->getOp() == dwarf::DW_OP_plus) ||
+             (Op->getOp() == dwarf::DW_OP_minus && !SubRegisterSizeInBits))) {
+    SignedOffset = (Op->getOp() == dwarf::DW_OP_plus) ? Offset : -Offset;
+    ExprCursor.take();
+  }
+  DwarfRegs.clear();
+  return true;
+
+/// Assuming a well-formed expression, match "DW_OP_deref* DW_OP_LLVM_fragment?".
+static bool isMemoryLocation(DIExpressionCursor ExprCursor) {
+  while (ExprCursor) {
+    auto Op = ExprCursor.take();
+    switch (Op->getOp()) {
     case dwarf::DW_OP_deref:
-    // [DW_OP_reg,DW_OP_deref] --> [DW_OP_breg].
-    if (FBReg)
-      addFBReg(0);
-    else
-      addBReg(Reg.DwarfRegNo, 0);
-    ExprCursor.take();
+    case dwarf::DW_OP_LLVM_fragment:
       break;
+    default:
+      return false;
+    }
   }
-  DwarfRegs.clear();
   return true;
 }
 
 void DwarfExpression::addExpression(DIExpressionCursor &&ExprCursor,
                                     unsigned FragmentOffsetInBits) {
-  while (ExprCursor) {
-    auto Op = ExprCursor.take();
-
-    // If we need to mask out a subregister, do it now, unless the next
-    // operation would emit an OpPiece anyway.
-    if (SubRegisterSizeInBits && Op->getOp() != dwarf::DW_OP_LLVM_fragment)
-      maskSubRegister();
+  auto N = ExprCursor.peek();
+  if (SubRegisterSizeInBits && N && (N->getOp() != dwarf::DW_OP_LLVM_fragment))
 
+  while (ExprCursor) {
+    auto Op = ExprCursor.take();
     switch (Op->getOp()) {
     case dwarf::DW_OP_LLVM_fragment: {
       unsigned SizeInBits = Op->getArg(1);
       unsigned FragmentOffset = Op->getArg(0);
       // The fragment offset must have already been adjusted by emitting an
       // empty DW_OP_piece / DW_OP_bit_piece before we emitted the base
       // location.
       assert(OffsetInBits >= FragmentOffset && "fragment offset not added?");
 
-      // If \a addMachineReg already emitted DW_OP_piece operations to represent
+      // If addMachineReg already emitted DW_OP_piece operations to represent
       // a super-register by splicing together sub-registers, subtract the size
       // of the pieces that was already emitted.
       SizeInBits -= OffsetInBits - FragmentOffset;
 
-      // If \a addMachineReg requested a DW_OP_bit_piece to stencil out a
+      // If addMachineReg requested a DW_OP_bit_piece to stencil out a
       // sub-register that is smaller than the current fragment's size, use it.
       if (SubRegisterSizeInBits)
         SizeInBits = std::min<unsigned>(SizeInBits, SubRegisterSizeInBits);
       
+      // Emit the DW_OP_piece.
       addOpPiece(SizeInBits, SubRegisterOffsetInBits);
       setSubRegisterPiece(0, 0);
-      break;
+      // Reset the location description kind.
+      LocationKind = Unknown;
+      return;
     }
     case dwarf::DW_OP_plus:
+      assert(LocationKind != Register);
       emitOp(dwarf::DW_OP_plus_uconst);
       emitUnsigned(Op->getArg(0));
       break;
     case dwarf::DW_OP_minus:
-      // There is no OP_minus_uconst.
+      assert(LocationKind != Register);
+      // There is no DW_OP_minus_uconst.
       emitOp(dwarf::DW_OP_constu);
       emitUnsigned(Op->getArg(0));
       emitOp(dwarf::DW_OP_minus);
       break;
-    case dwarf::DW_OP_deref:
+    case dwarf::DW_OP_deref: {
+      assert(LocationKind != Register);
+      if (LocationKind != Memory && isMemoryLocation(ExprCursor))
+        // Turning this into a memory location description makes the deref
+        // implicit.
+        LocationKind = Memory;
+      else
         emitOp(dwarf::DW_OP_deref);
       break;
+    }
     case dwarf::DW_OP_constu:
+      assert(LocationKind != Register);
       emitOp(dwarf::DW_OP_constu);
       emitUnsigned(Op->getArg(0));
       break;
     case dwarf::DW_OP_stack_value:
+      assert(LocationKind == Unknown || LocationKind == Implicit);
+      LocationKind = Implicit;
+      if (LocationKind == Implicit)
+        // Turn this into an implicit location description.
         addStackValue();
+
       break;
     case dwarf::DW_OP_swap:
+      assert(LocationKind != Register);
       emitOp(dwarf::DW_OP_swap);
       break;
     case dwarf::DW_OP_xderef:
+      assert(LocationKind != Register);
       emitOp(dwarf::DW_OP_xderef);
       break;
     default:
       llvm_unreachable("unhandled opcode found in expression");
     }
   }
+
+  if (LocationKind != Implicit)
+    return;
+  // Turn this into an implicit location description.
+  addStackValue();
 }
 
 /// add masking operations to stencil out a subregister.
 void DwarfExpression::maskSubRegister() {
   assert(SubRegisterSizeInBits && "no subregister was registered");
   if (SubRegisterOffsetInBits > 0)
     addShr(SubRegisterOffsetInBits);
   uint64_t Mask = (1ULL << (uint64_t)SubRegisterSizeInBits) - 1ULL;

lib/CodeGen/AsmPrinter/DwarfUnit.cpp

void DwarfUnit::addBlockByrefAddress(const DbgVariable &DV, DIE &Die,
   unsigned varFieldOffset = varField->getOffsetInBits() >> 2;
 
   // Decode the original location, and use that as the start of the byref
   // variable's location.
   DIELoc *Loc = new (DIEValueAllocator) DIELoc;
   DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
 
   SmallVector<uint64_t, 9> Ops;
-  if (Location.isIndirect()) {
+  if (Location.isIndirect() && Location.getOffset()) {
     Ops.push_back(dwarf::DW_OP_plus);
     Ops.push_back(Location.getOffset());
-    Ops.push_back(dwarf::DW_OP_deref);
   }
   // If we started with a pointer to the __Block_byref... struct, then
   // the first thing we need to do is dereference the pointer (DW_OP_deref).
   if (isPointer)
     Ops.push_back(dwarf::DW_OP_deref);
 
   // Next add the offset for the '__forwarding' field:
   // DW_OP_plus_uconst ForwardingFieldOffset.  Note there's no point in
void DwarfUnit::addBlockByrefAddress(const DbgVariable &DV, DIE &Die,
   // DW_OP_plus_uconst varFieldOffset.  Again, don't add if it's 0.
   if (varFieldOffset > 0) {
     Ops.push_back(dwarf::DW_OP_plus);
     Ops.push_back(varFieldOffset);
   }
 
   DIExpressionCursor Cursor(Ops);
   const TargetRegisterInfo &TRI = *Asm->MF->getSubtarget().getRegisterInfo();
-  if (!DwarfExpr.addMachineRegExpression(TRI, Cursor, Location.getReg()))
+  if (!DwarfExpr.addMachineLocExpression(TRI, Cursor, Location))
     return;
   DwarfExpr.addExpression(std::move(Cursor));
 
   // Now attach the location information to the DIE.
   addBlock(Die, Attribute, DwarfExpr.finalize());
 }
 
 /// Return true if type encoding is unsigned.

lib/CodeGen/InlineSpiller.cpp

void InlineSpiller::spillAroundUses(unsigned Reg) {
   for (MachineRegisterInfo::reg_bundle_iterator
        RegI = MRI.reg_bundle_begin(Reg), E = MRI.reg_bundle_end();
        RegI != E; ) {
     MachineInstr *MI = &*(RegI++);
 
     // Debug values are not allowed to affect codegen.
     if (MI->isDebugValue()) {
       // Modify DBG_VALUE now that the value is in a spill slot.
-      bool IsIndirect = MI->isIndirectDebugValue();
-      uint64_t Offset = IsIndirect ? MI->getOperand(1).getImm() : 0;
-      const MDNode *Var = MI->getDebugVariable();
-      const MDNode *Expr = MI->getDebugExpression();
-      DebugLoc DL = MI->getDebugLoc();
-      DEBUG(dbgs() << "Modifying debug info due to spill:" << "\t" << *MI);
       MachineBasicBlock *MBB = MI->getParent();
-      assert(cast<DILocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
-             "Expected inlined-at fields to agree");
-      BuildMI(*MBB, MBB->erase(MI), DL, TII.get(TargetOpcode::DBG_VALUE))
-          .addFrameIndex(StackSlot)
-          .addImm(Offset)
-          .addMetadata(Var)
-          .addMetadata(Expr);
+      DEBUG(dbgs() << "Modifying debug info due to spill:\t" << *MI);
+      buildDbgValueForSpill(*MBB, MI, *MI, StackSlot);
+      MBB->erase(MI);
       continue;
     }
 
     // Ignore copies to/from snippets. We'll delete them.
     if (SnippetCopies.count(MI))
       continue;
 
     // Stack slot accesses may coalesce away.

lib/CodeGen/MachineInstr.cpp

MachineInstrBuilder llvm::BuildMI(MachineBasicBlock &BB,
   assert(isa<DILocalVariable>(Variable) && "not a variable");
   assert(cast<DIExpression>(Expr)->isValid() && "not an expression");
   MachineFunction &MF = *BB.getParent();
   MachineInstr *MI =
       BuildMI(MF, DL, MCID, IsIndirect, Reg, Offset, Variable, Expr);
   BB.insert(I, MI);
   return MachineInstrBuilder(MF, MI);
 }
+
+MachineInstr *llvm::buildDbgValueForSpill(MachineBasicBlock &BB,
+                                          MachineBasicBlock::iterator I,
+                                          const MachineInstr &Orig,
+                                          int FrameIndex) {
+  const MDNode *Var = Orig.getDebugVariable();
+  auto *Expr = cast_or_null<DIExpression>(Orig.getDebugExpression());
+  bool IsIndirect = Orig.isIndirectDebugValue();
+  uint64_t Offset = IsIndirect ? Orig.getOperand(1).getImm() : 0;
+  DebugLoc DL = Orig.getDebugLoc();
+  assert(cast<DILocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
+         "Expected inlined-at fields to agree");
+  // If the DBG_VALUE already was a memory location, add an extra
+  // DW_OP_deref. Otherwise just turning this from a register into a
+  // memory/indirect location is sufficient.
+  if (IsIndirect) {
+    SmallVector<uint64_t, 8> Ops;
+    Ops.push_back(dwarf::DW_OP_deref);
+    if (Expr)
+      Ops.append(Expr->elements_begin(), Expr->elements_end());
+    Expr = DIExpression::get(Expr->getContext(), Ops);
+  }
+  return BuildMI(BB, I, DL, Orig.getDesc())
+      .addFrameIndex(FrameIndex)
+      .addImm(Offset)
+      .addMetadata(Var)
+      .addMetadata(Expr);
+}

lib/CodeGen/RegAllocFast.cpp

if (LR.Dirty) {
 
     // If this register is used by DBG_VALUE then insert new DBG_VALUE to
     // identify spilled location as the place to find corresponding variable's
     // value.
     SmallVectorImpl<MachineInstr *> &LRIDbgValues =
       LiveDbgValueMap[LRI->VirtReg];
     for (unsigned li = 0, le = LRIDbgValues.size(); li != le; ++li) {
       MachineInstr *DBG = LRIDbgValues[li];
-      const MDNode *Var = DBG->getDebugVariable();
-      const MDNode *Expr = DBG->getDebugExpression();
-      bool IsIndirect = DBG->isIndirectDebugValue();
-      uint64_t Offset = IsIndirect ? DBG->getOperand(1).getImm() : 0;
-      DebugLoc DL = DBG->getDebugLoc();
-      assert(cast<DILocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
-             "Expected inlined-at fields to agree");
-      MachineInstr *NewDV =
-          BuildMI(*MBB, MI, DL, TII->get(TargetOpcode::DBG_VALUE))
-              .addFrameIndex(FI)
-              .addImm(Offset)
-              .addMetadata(Var)
-              .addMetadata(Expr);
+      MachineInstr *NewDV = buildDbgValueForSpill(*MBB, MI, *DBG, FI);
       assert(NewDV->getParent() == MBB && "dangling parent pointer");
       (void)NewDV;
       DEBUG(dbgs() << "Inserting debug info due to spill:" << "\n" << *NewDV);
     }
     // Now this register is spilled there is should not be any DBG_VALUE
     // pointing to this register because they are all pointing to spilled value
     // now.
     LRIDbgValues.clear();

lib/CodeGen/SafeStack.cpp

for (Argument *Arg : ByValArguments) {
 
     Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
                                ConstantInt::get(Int32Ty, -Offset));
     Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
                                      Arg->getName() + ".unsafe-byval");
 
     // Replace alloc with the new location.
     replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
-                      /*Deref=*/true, -Offset);
+                      /*Deref=*/false, -Offset);
     Arg->replaceAllUsesWith(NewArg);
     IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
     IRB.CreateMemCpy(Off, Arg, Size, Arg->getParamAlignment());
   }
 
   // Allocate space for every unsafe static AllocaInst on the unsafe stack.
   for (AllocaInst *AI : StaticAllocas) {
     IRB.SetInsertPoint(AI);
     unsigned Offset = SSL.getObjectOffset(AI);
 
     uint64_t Size = getStaticAllocaAllocationSize(AI);
     if (Size == 0)
       Size = 1; // Don't create zero-sized stack objects.
 
-    replaceDbgDeclareForAlloca(AI, BasePointer, DIB, /*Deref=*/true, -Offset);
+    replaceDbgDeclareForAlloca(AI, BasePointer, DIB, /*Deref=*/false, -Offset);
     replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
 
     // Replace uses of the alloca with the new location.
     // Insert address calculation close to each use to work around PR27844.
     std::string Name = std::string(AI->getName()) + ".unsafe";
     while (!AI->use_empty()) {
       Use &U = *AI->use_begin();
       Instruction *User = cast<Instruction>(U.getUser());
for (AllocaInst *AI : DynamicAllocas) {
     IRB.CreateStore(NewTop, UnsafeStackPtr);
     if (DynamicTop)
       IRB.CreateStore(NewTop, DynamicTop);
 
     Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
     if (AI->hasName() && isa<Instruction>(NewAI))
       NewAI->takeName(AI);
 
-    replaceDbgDeclareForAlloca(AI, NewAI, DIB, /*Deref=*/true);
+    replaceDbgDeclareForAlloca(AI, NewAI, DIB, /*Deref=*/false);
     AI->replaceAllUsesWith(NewAI);
     AI->eraseFromParent();
   }
 
   if (!DynamicAllocas.empty()) {
     // Now go through the instructions again, replacing stacksave/stackrestore.
     for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
       Instruction *I = &*(It++);

lib/CodeGen/SelectionDAG/FastISel.cpp

if (!Op && !Address->use_empty() && isa<Instruction>(Address) &&
                                      false);
 
     if (Op) {
       assert(DI->getVariable()->isValidLocationForIntrinsic(DbgLoc) &&
              "Expected inlined-at fields to agree");
       if (Op->isReg()) {
         Op->setIsDebug(true);
         BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc,
-                TII.get(TargetOpcode::DBG_VALUE), false, Op->getReg(), 0,
+                TII.get(TargetOpcode::DBG_VALUE), true, Op->getReg(), 0,
                 DI->getVariable(), DI->getExpression());
       } else
         BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc,
                 TII.get(TargetOpcode::DBG_VALUE))
             .add(*Op)
             .addImm(0)
             .addMetadata(DI->getVariable())
             .addMetadata(DI->getExpression());

lib/Transforms/Instrumentation/AddressSanitizer.cpp

void FunctionStackPoisoner::processStaticAllocas() {
   }
 
   // Replace Alloca instructions with base+offset.
   for (const auto &Desc : SVD) {
     AllocaInst *AI = Desc.AI;
     Value *NewAllocaPtr = IRB.CreateIntToPtr(
         IRB.CreateAdd(LocalStackBase, ConstantInt::get(IntptrTy, Desc.Offset)),
         AI->getType());
-    replaceDbgDeclareForAlloca(AI, NewAllocaPtr, DIB, /*Deref=*/true);
+    replaceDbgDeclareForAlloca(AI, NewAllocaPtr, DIB, /*Deref=*/false);
     AI->replaceAllUsesWith(NewAllocaPtr);
   }
 
   // The left-most redzone has enough space for at least 4 pointers.
   // Write the Magic value to redzone[0].
   Value *BasePlus0 = IRB.CreateIntToPtr(LocalStackBase, IntptrPtrTy);
   IRB.CreateStore(ConstantInt::get(IntptrTy, kCurrentStackFrameMagic),
                   BasePlus0);

lib/Transforms/Utils/Local.cpp

if (AI && !isArray(AI)) {
           if (AIUse.getOperandNo() == 1)
             ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
         } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
           ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
         } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
           // This is a call by-value or some other instruction that
           // takes a pointer to the variable. Insert a *value*
           // intrinsic that describes the alloca.
-          SmallVector<uint64_t, 1> NewDIExpr;
-          auto *DIExpr = DDI->getExpression();
-          NewDIExpr.push_back(dwarf::DW_OP_deref);
-          NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end());
           DIB.insertDbgValueIntrinsic(AI, 0, DDI->getVariable(),
-                                      DIB.createExpression(NewDIExpr),
-                                      DDI->getDebugLoc(), CI);
+                                      DDI->getExpression(), DDI->getDebugLoc(),
+                                      CI);
         }
       }
       DDI->eraseFromParent();
     }
   }
   return true;
 }
 

test/Bitcode/DIExpression-aggresult.ll

+; RUN: llvm-dis -o - %s.bc | FileCheck %s
+%class.A = type { i32, i32, i32, i32 }
+
+define void @_Z3fooi(%class.A* sret %agg.result) #0 !dbg !3 {
+  ; CHECK: call void @llvm.dbg.declare({{.*}}, metadata ![[EXPR:[0-9]+]]), !dbg
+  ; CHECK: ![[EXPR]] = !DIExpression()
+  call void @llvm.dbg.declare(metadata %class.A* %agg.result, metadata !13, metadata !16), !dbg !17
+  ret void, !dbg !17
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+attributes #0 = { ssp }
+attributes #1 = { nounwind readnone }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "a.cc", directory: "/tmp")
+!2 = !{i32 1, !"Debug Info Version", i32 3}
+!3 = distinct !DISubprogram(name: "foo", linkageName: "_Z3fooi", scope: !1, file: !1, line: 4, type: !4, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: false, unit: !0)
+!4 = !DISubroutineType(types: !5)
+!5 = !{!6}
+!6 = !DICompositeType(tag: DW_TAG_class_type, name: "A", scope: !0, file: !1, line: 2, size: 128, align: 32, elements: !7)
+!7 = !{!8, !10, !11, !12}
+!8 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !1, file: !1, line: 2, baseType: !9, size: 32, align: 32)
+!9 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!10 = !DIDerivedType(tag: DW_TAG_member, name: "y", scope: !1, file: !1, line: 2, baseType: !9, size: 32, align: 32, offset: 32)
+!11 = !DIDerivedType(tag: DW_TAG_member, name: "z", scope: !1, file: !1, line: 2, baseType: !9, size: 32, align: 32, offset: 64)
+!12 = !DIDerivedType(tag: DW_TAG_member, name: "o", scope: !1, file: !1, line: 2, baseType: !9, size: 32, align: 32, offset: 96)
+!13 = !DILocalVariable(name: "my_a", scope: !14, file: !1, line: 9, type: !15)
+!14 = distinct !DILexicalBlock(scope: !3, file: !1, line: 4, column: 14)
+!15 = !DIDerivedType(tag: DW_TAG_reference_type, file: !1, baseType: !6)
+!16 = !DIExpression(DW_OP_deref)
+!17 = !DILocation(line: 9, column: 5, scope: !3)

test/Bitcode/DIExpression-deref.ll

+; RUN: llvm-dis -o - %s.bc | FileCheck %s
+
+!llvm.dbg.cu = !{!1}
+!llvm.module.flags = !{!20, !21}
+
+!0 = distinct !DIGlobalVariable(name: "g", scope: !1, file: !2, line: 1, type: !5, isLocal: false, isDefinition: true)
+!1 = distinct !DICompileUnit(language: DW_LANG_C99, file: !2, producer: "clang (llvm/trunk 288154)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !3, globals: !4)
+!2 = !DIFile(filename: "a.c", directory: "/")
+!3 = !{}
+!4 = !{!10, !11, !12, !13}
+!5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+; DW_OP_deref should be moved to the back of the expression.
+;
+; CHECK: !DIExpression(DW_OP_plus, 0, DW_OP_deref, DW_OP_LLVM_fragment, 8, 32)
+!6 = !DIExpression(DW_OP_deref, DW_OP_plus, 0, DW_OP_LLVM_fragment, 8, 32)
+; CHECK: !DIExpression(DW_OP_plus, 0, DW_OP_deref)
+!7 = !DIExpression(DW_OP_deref, DW_OP_plus, 0)
+; CHECK: !DIExpression(DW_OP_plus, 1, DW_OP_deref)
+!8 = !DIExpression(DW_OP_plus, 1, DW_OP_deref)
+; CHECK: !DIExpression(DW_OP_deref)
+!9 = !DIExpression(DW_OP_deref)
+!10 = !DIGlobalVariableExpression(var: !0, expr: !6)
+!11 = !DIGlobalVariableExpression(var: !0, expr: !7)
+!12 = !DIGlobalVariableExpression(var: !0, expr: !8)
+!13 = !DIGlobalVariableExpression(var: !0, expr: !9)
+!20 = !{i32 2, !"Dwarf Version", i32 4}
+!21 = !{i32 2, !"Debug Info Version", i32 3}

test/DebugInfo/ARM/selectiondag-deadcode.ll

 ; RUN: llc -filetype=asm < %s | FileCheck %s
 target triple = "thumbv7-apple-ios7.0.0"
 %class.Matrix3.0.6.10 = type { [9 x float] }
 define arm_aapcscc void @_Z9GetMatrixv(%class.Matrix3.0.6.10* noalias nocapture sret %agg.result) #0 !dbg !39 {
   br i1 fcmp oeq (float fadd (float fadd (float fmul (float undef, float undef), float fmul (float undef, float undef)), float fmul (float undef, float undef)), float 0.000000e+00), label %_ZN7Vector39NormalizeEv.exit, label %1
   tail call arm_aapcscc void @_ZL4Sqrtd() #3
   br label %_ZN7Vector39NormalizeEv.exit
 _ZN7Vector39NormalizeEv.exit:                     ; preds = %1, %0
   ; rdar://problem/15094721.
   ;
   ; When this (partially) dead use gets eliminated (and thus the def
   ; of the vreg holding %agg.result) the dbg_value becomes dangling
   ; and SelectionDAGISel crashes.  It should definitely not
   ; crash. Drop the dbg_value instead.
   ; CHECK-NOT: "matrix"
-  tail call void @llvm.dbg.declare(metadata %class.Matrix3.0.6.10* %agg.result, metadata !45, metadata !DIExpression(DW_OP_deref))
+  tail call void @llvm.dbg.declare(metadata %class.Matrix3.0.6.10* %agg.result, metadata !45, metadata !DIExpression())
   %2 = getelementptr inbounds %class.Matrix3.0.6.10, %class.Matrix3.0.6.10* %agg.result, i32 0, i32 0, i32 8
   ret void
 }
 declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
 declare arm_aapcscc void @_ZL4Sqrtd() #2
 !4 = !DICompositeType(tag: DW_TAG_class_type, name: "Matrix3", line: 20, size: 288, align: 32, file: !5, identifier: "_ZTS7Matrix3")
 !5 = !DIFile(filename: "test.ii", directory: "/Volumes/Data/radar/15094721")
 !39 = distinct !DISubprogram(name: "GetMatrix", linkageName: "_Z9GetMatrixv", line: 32, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, scopeLine: 32, file: !5, scope: !40, type: !41)
 !40 = !DIFile(filename: "test.ii", directory: "/Volumes/Data/radar/15094721")
 !41 = !DISubroutineType(types: null)
 !45 = !DILocalVariable(name: "matrix", line: 35, scope: !39, file: !40, type: !4)

test/DebugInfo/Generic/block-asan.ll

 ; RUN: opt -S -asan %s | FileCheck %s
 
 ; The IR of this testcase is generated from the following C code:
 ; void bar (int);
 ;
 ; void foo() {
 ;   __block int x;
 ;   bar(x);
 ; }
 ; by compiling it with 'clang -emit-llvm -g -S' and then by manually
 ; adding the sanitize_address attribute to the @foo() function (so
 ; that ASAN accepts to instrument the function in the above opt run).
 
 ; Check that the location of the ASAN instrumented __block variable is
 ; correct.
-; CHECK: !DIExpression(DW_OP_deref, DW_OP_plus, 8, DW_OP_deref, DW_OP_plus, 24)
+; CHECK: !DIExpression(DW_OP_plus, 8, DW_OP_deref, DW_OP_plus, 24)
 
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 
 %struct.__block_byref_x = type { i8*, %struct.__block_byref_x*, i32, i32, i32 }
 
 ; Function Attrs: nounwind ssp uwtable
 define void @foo() #0 !dbg !4 {
 entry:

test/DebugInfo/X86/dbg_value_direct.ll

 
 ; <label>:27                                      ; preds = %22
   call void @__asan_report_store4(i64 %16)
   call void asm sideeffect "", ""()
   unreachable
 
 ; <label>:28                                      ; preds = %22, %entry
   store i32 %0, i32* %3, align 4
-  call void @llvm.dbg.declare(metadata %struct.A* %agg.result, metadata !24, metadata !DIExpression(DW_OP_deref)), !dbg !25
+  call void @llvm.dbg.declare(metadata %struct.A* %agg.result, metadata !24, metadata !DIExpression()), !dbg !25
   call void @_ZN1AC1Ev(%struct.A* %agg.result), !dbg !25
   store i64 1172321806, i64* %4, !dbg !26
   %29 = inttoptr i64 %10 to i32*, !dbg !26
   store i32 0, i32* %29, !dbg !26
   %30 = add i64 %10, 4, !dbg !26
   %31 = inttoptr i64 %30 to i32*, !dbg !26
   store i32 0, i32* %31, !dbg !26
   %32 = add i64 %10, 8, !dbg !26

test/DebugInfo/X86/debug-info-block-captured-self.ll

 !84 = !DILocation(line: 33, scope: !38)
 !86 = !DILocalVariable(name: "self", line: 41, scope: !38, file: !1, type: !34)
 !87 = !DILocation(line: 41, scope: !38)
 !103 = !DILocation(line: 35, scope: !42)
 !105 = !DILocalVariable(name: "self", line: 40, scope: !42, file: !1, type: !34)
 !106 = !DILocation(line: 40, scope: !42)
 !107 = !DIFile(filename: "llvm/tools/clang/test/CodeGenObjC/debug-info-block-captured-self.m", directory: "")
 !108 = !{i32 1, !"Debug Info Version", i32 3}
-!109 = !DIExpression(DW_OP_deref, DW_OP_plus, 32)
-!110 = !DIExpression(DW_OP_deref, DW_OP_plus, 32)
+!109 = !DIExpression(DW_OP_plus, 32, DW_OP_deref)
+!110 = !DIExpression(DW_OP_plus, 32, DW_OP_deref)

test/DebugInfo/X86/dw_op_minus.ll

 ; Test dwarf codegen of DW_OP_minus.
 ; RUN: llc -O0 -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
 
 ; This was built by compiling the following source with SafeStack and
 ; simplifying the result a little.
 ; extern "C" {
 ; void Capture(int *);
 ; void f() {
 ;   int buf[100];
 ;   Capture(buf);
 ; }
 ; }
-; The interesting part is !DIExpression(DW_OP_deref, DW_OP_minus, 400)
+; The interesting part is !DIExpression(DW_OP_minus, 400)
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 @__safestack_unsafe_stack_ptr = external thread_local(initialexec) global i8*
 
 define void @f() !dbg !4 {
 entry:

 !9 = !DICompositeType(tag: DW_TAG_array_type, baseType: !10, size: 3200, align: 32, elements: !11)
 !10 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
 !11 = !{!12}
 !12 = !DISubrange(count: 100)
 !13 = !{i32 2, !"Dwarf Version", i32 4}
 !14 = !{i32 2, !"Debug Info Version", i32 3}
 !15 = !{!"clang version 3.8.0 (trunk 248518) (llvm/trunk 248512)"}
 !16 = !DILocation(line: 5, column: 3, scope: !4)
-!17 = !DIExpression(DW_OP_deref, DW_OP_minus, 400)
+!17 = !DIExpression(DW_OP_minus, 400)
 !18 = !DILocation(line: 5, column: 7, scope: !4)
 !19 = !DILocation(line: 6, column: 11, scope: !4)
 !20 = !DILocation(line: 6, column: 3, scope: !4)
 !21 = !DILocation(line: 7, column: 1, scope: !4)
 
 ; RCX - 400
-; CHECK:      .short  6                       # Loc expr size
+; CHECK:      .short  3                       # Loc expr size
 ; CHECK-NEXT: .byte 114                     # DW_OP_breg2
-; CHECK-NEXT: .byte 0                       # 0
-; CHECK-NEXT: .byte 16                      # DW_OP_constu
-; CHECK-NEXT: .byte 144                     # 400
-; CHECK-NEXT: .byte 3                       # DW_OP_minus
-; CHECK-NEXT: .byte 28
+; CHECK-NEXT: .byte 240                     # -400
+; CHECK-NEXT: .byte 124
 
 ; RCX is clobbered in call @Capture, but there is a spilled copy.
 ; *(RSP + 8) - 400
 ; CHECK:      .short  7                       # Loc expr size
 ; CHECK-NEXT: .byte 119                     # DW_OP_breg7
 ; CHECK-NEXT: .byte 8                       # 8
 ; CHECK-NEXT: .byte 6                       # DW_OP_deref
 ; CHECK-NEXT: .byte 16                      # DW_OP_constu
 ; CHECK-NEXT: .byte 144                     # 400
 ; CHECK-NEXT: .byte 3                       # DW_OP_minus
 ; CHECK-NEXT: .byte 28

test/DebugInfo/X86/dw_op_minus_direct.ll

 ; Test dwarf codegen of DW_OP_minus.
 ; RUN: llc -filetype=obj < %s | llvm-dwarfdump - | FileCheck %s
 
 ; This was derived manually from:
 ; int inc(int i) {
 ;  return i+1;
 ; }
 
 ; CHECK: Beginning address offset: 0x0000000000000000
 ; CHECK:    Ending address offset: 0x0000000000000004
-; CHECK:     Location description: 50 10 ff ff ff ff 0f 1a 10 01 1c
-;                                  rax, constu 0xffffffff, and, constu 0x00000001, minus
+; CHECK:     Location description: 70 00 10 ff ff ff ff 0f 1a 10 01 1c 9f
+;        rax+0, constu 0xffffffff, and, constu 0x00000001, minus, stack-value
 source_filename = "minus.c"
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx10.12.0"
 
 define i32 @inc(i32 %i) local_unnamed_addr #1 !dbg !7 {
 entry:
   %add = add nsw i32 %i, 1, !dbg !15
   tail call void @llvm.dbg.value(metadata i32 %add, i64 0, metadata !12, metadata !13), !dbg !14

 !5 = !{i32 1, !"PIC Level", i32 2}
 !6 = !{!"clang version 4.0.0 (trunk 286322) (llvm/trunk 286305)"}
 !7 = distinct !DISubprogram(name: "inc", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !11)
 !8 = !DISubroutineType(types: !9)
 !9 = !{!10, !10}
 !10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
 !11 = !{!12}
 !12 = !DILocalVariable(name: "i", arg: 1, scope: !7, file: !1, line: 1, type: !10)
-!13 = !DIExpression(DW_OP_minus, 1)
+!13 = !DIExpression(DW_OP_minus, 1, DW_OP_stack_value)
 !14 = !DILocation(line: 1, column: 13, scope: !7)
 !15 = !DILocation(line: 2, column: 11, scope: !7)
 !16 = !DILocation(line: 2, column: 3, scope: !7)

test/DebugInfo/X86/sret.ll

 entry:
   %this.addr = alloca %class.B*, align 8
   %nrvo = alloca i1
   %cleanup.dest.slot = alloca i32
   store %class.B* %this, %class.B** %this.addr, align 8
   call void @llvm.dbg.declare(metadata %class.B** %this.addr, metadata !89, metadata !DIExpression()), !dbg !91
   %this1 = load %class.B*, %class.B** %this.addr
   store i1 false, i1* %nrvo, !dbg !92
-  call void @llvm.dbg.declare(metadata %class.A* %agg.result, metadata !93, metadata !DIExpression(DW_OP_deref)), !dbg !92
+  call void @llvm.dbg.declare(metadata %class.A* %agg.result, metadata !93, metadata !DIExpression()), !dbg !92
   call void @_ZN1AC1Ei(%class.A* %agg.result, i32 12), !dbg !92
   store i1 true, i1* %nrvo, !dbg !94
   store i32 1, i32* %cleanup.dest.slot
   %nrvo.val = load i1, i1* %nrvo, !dbg !95
   br i1 %nrvo.val, label %nrvo.skipdtor, label %nrvo.unused, !dbg !95
 
 nrvo.unused:                                      ; preds = %entry
   call void @_ZN1AD2Ev(%class.A* %agg.result), !dbg !96

test/Instrumentation/AddressSanitizer/debug_info.ll

entry:
   %1 = load i32, i32* %r, align 4, !dbg !15
   ret i32 %1, !dbg !15
 }
 
 ;   CHECK: define i32 @_Z3zzzi
 ;   CHECK: entry:
 ; Verify that llvm.dbg.declare calls are in the entry basic block.
 ;   CHECK-NOT: %entry
-;   CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[ARG_ID:[0-9]+]], metadata ![[OPDEREF:[0-9]+]])
+;   CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[ARG_ID:[0-9]+]], metadata ![[EMPTY:[0-9]+]])
 ;   CHECK-NOT: %entry
-;   CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[VAR_ID:[0-9]+]], metadata ![[OPDEREF:[0-9]+]])
+;   CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[VAR_ID:[0-9]+]], metadata ![[EMPTY:[0-9]+]])
 
 declare void @llvm.dbg.declare(metadata, metadata, metadata) nounwind readnone
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!17}
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, producer: "clang version 3.3 (trunk 169314)", isOptimized: true, emissionKind: FullDebug, file: !16, enums: !1, retainedTypes: !1, globals: !1)
 !1 = !{}
 !5 = distinct !DISubprogram(name: "zzz", linkageName: "_Z3zzzi", line: 1, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: false, unit: !0, scopeLine: 1, file: !16, scope: !6, type: !7, variables: !1)
 !6 = !DIFile(filename: "a.cc", directory: "/usr/local/google/llvm_cmake_clang/tmp/debuginfo")
 !7 = !DISubroutineType(types: !8)
 !8 = !{!9, !9}
 !9 = !DIBasicType(tag: DW_TAG_base_type, name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
 !10 = !DILocalVariable(name: "p", line: 1, arg: 1, scope: !5, file: !6, type: !9)
 !11 = !DILocation(line: 1, scope: !5)
 !12 = !DILocalVariable(name: "r", line: 2, scope: !13, file: !6, type: !9)
 
 ; Verify that debug descriptors for argument and local variable will be replaced
 ; with descriptors that end with OpDeref (encoded as 2).
 ;   CHECK: ![[ARG_ID]] = !DILocalVariable(name: "p", arg: 1,{{.*}} line: 1
-;   CHECK: ![[OPDEREF]] = !DIExpression(DW_OP_deref)
+;   CHECK: ![[EMPTY]] = !DIExpression()
 ;   CHECK: ![[VAR_ID]] = !DILocalVariable(name: "r",{{.*}} line: 2
 ; Verify that there are no more variable descriptors.
 ;   CHECK-NOT: !DILocalVariable(tag: DW_TAG_arg_variable
 ;   CHECK-NOT: !DILocalVariable(tag: DW_TAG_auto_variable
 
 
 !13 = distinct !DILexicalBlock(line: 1, column: 0, file: !16, scope: !5)
 !14 = !DILocation(line: 2, scope: !13)
 !15 = !DILocation(line: 3, scope: !13)
 !16 = !DIFile(filename: "a.cc", directory: "/usr/local/google/llvm_cmake_clang/tmp/debuginfo")
 !17 = !{i32 1, !"Debug Info Version", i32 3}

test/Transforms/SafeStack/X86/debug-loc.ll

 ; CHECK:   call void @Capture
 ; CHECK:   call void @Capture
 
   ret void, !dbg !25
 }
 
 ; CHECK-DAG: ![[VAR_ARG]] = !DILocalVariable(name: "zzz"
 ; 100 aligned up to 8
-; CHECK-DAG: ![[EXPR_ARG]] = !DIExpression(DW_OP_deref, DW_OP_minus, 104
+; CHECK-DAG: ![[EXPR_ARG]] = !DIExpression(DW_OP_minus, 104)
 
 ; CHECK-DAG: ![[VAR_LOCAL]] = !DILocalVariable(name: "xxx"
-; CHECK-DAG: ![[EXPR_LOCAL]] = !DIExpression(DW_OP_deref, DW_OP_minus, 208
+; CHECK-DAG: ![[EXPR_LOCAL]] = !DIExpression(DW_OP_minus, 208)
 
 ; Function Attrs: nounwind readnone
 declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
 
 declare void @Capture(%struct.S*) #2
 
 attributes #0 = { safestack uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
 attributes #1 = { nounwind readnone }