[DebugInfo] Introduce DW_OP_LLVM_convert

Introduce a DW_OP_LLVM_convert Dwarf expression pseudo op that allows
for a convenient way to perform type conversions on the Dwarf expression
stack. As an additional bonus it paves the way for using other Dwarf
v5 ops that need to reference a base_type.

The new DW_OP_LLVM_convert is used from lib/Transforms/Utils/Local.cpp
to perform sext/zext on debug values but mainly the patch is about
preparing terrain for adding other Dwarf v5 ops that need to reference a
base_type.

For Dwarf v5 the op maps to DW_OP_convert and for earlier versions a
complex shift & mask pattern is generated to emulate sext/zext.

This is a recommit of r356442 with trivial fixes for the failing tests.

Differential Revision: https://reviews.llvm.org/D56587

llvm-svn: 356451

14 files changed, 230 insertions, 37 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
index 7a62b6bfc6a..6fdf1451a63 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
@@ -42,11 +42,11 @@ void AsmPrinter::EmitSLEB128(int64_t Value, const char *Desc) const {
   OutStreamer->EmitSLEB128IntValue(Value);
 }
 
-void AsmPrinter::EmitULEB128(uint64_t Value, const char *Desc) const {
+void AsmPrinter::EmitULEB128(uint64_t Value, const char *Desc, unsigned PadTo) const {
   if (isVerbose() && Desc)
     OutStreamer->AddComment(Desc);
 
-  OutStreamer->EmitULEB128IntValue(Value);
+  OutStreamer->EmitULEB128IntValue(Value, PadTo);
 }
 
 /// Emit something like ".uleb128 Hi-Lo".
diff --git a/llvm/lib/CodeGen/AsmPrinter/ByteStreamer.h b/llvm/lib/CodeGen/AsmPrinter/ByteStreamer.h
index 7a2902d6807..db2ff458eb2 100644
--- a/llvm/lib/CodeGen/AsmPrinter/ByteStreamer.h
+++ b/llvm/lib/CodeGen/AsmPrinter/ByteStreamer.h
@@ -31,7 +31,7 @@ class ByteStreamer {
   // For now we're just handling the calls we need for dwarf emission/hashing.
   virtual void EmitInt8(uint8_t Byte, const Twine &Comment = "") = 0;
   virtual void EmitSLEB128(uint64_t DWord, const Twine &Comment = "") = 0;
-  virtual void EmitULEB128(uint64_t DWord, const Twine &Comment = "") = 0;
+  virtual void EmitULEB128(uint64_t DWord, const Twine &Comment = "", unsigned PadTo = 0) = 0;
 };
 
 class APByteStreamer final : public ByteStreamer {
@@ -48,7 +48,7 @@ public:
     AP.OutStreamer->AddComment(Comment);
     AP.EmitSLEB128(DWord);
   }
-  void EmitULEB128(uint64_t DWord, const Twine &Comment) override {
+  void EmitULEB128(uint64_t DWord, const Twine &Comment, unsigned PadTo) override {
     AP.OutStreamer->AddComment(Comment);
     AP.EmitULEB128(DWord);
   }
@@ -65,7 +65,7 @@ class HashingByteStreamer final : public ByteStreamer {
   void EmitSLEB128(uint64_t DWord, const Twine &Comment) override {
     Hash.addSLEB128(DWord);
   }
-  void EmitULEB128(uint64_t DWord, const Twine &Comment) override {
+  void EmitULEB128(uint64_t DWord, const Twine &Comment, unsigned PadTo) override {
     Hash.addULEB128(DWord);
   }
 };
@@ -102,9 +102,9 @@ public:
 
     }
   }
-  void EmitULEB128(uint64_t DWord, const Twine &Comment) override {
+  void EmitULEB128(uint64_t DWord, const Twine &Comment, unsigned PadTo) override {
     raw_svector_ostream OSE(Buffer);
-    unsigned Length = encodeULEB128(DWord, OSE);
+    unsigned Length = encodeULEB128(DWord, OSE, PadTo);
     if (GenerateComments) {
       Comments.push_back(Comment.str());
       // Add some empty comments to keep the Buffer and Comments vectors aligned
diff --git a/llvm/lib/CodeGen/AsmPrinter/DIE.cpp b/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
index dfc4156243d..f4134da48ca 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
@@ -506,6 +506,23 @@ LLVM_DUMP_METHOD
 void DIELabel::print(raw_ostream &O) const { O << "Lbl: " << Label->getName(); }
 
 //===----------------------------------------------------------------------===//
+// DIEBaseTypeRef Implementation
+//===----------------------------------------------------------------------===//
+
+void DIEBaseTypeRef::EmitValue(const AsmPrinter *AP, dwarf::Form Form) const {
+  uint64_t Offset = CU->ExprRefedBaseTypes[Index].Die->getOffset();
+  assert(Offset < (1ULL << (ULEB128PadSize * 7)) && "Offset wont fit");
+  AP->EmitULEB128(Offset, nullptr, ULEB128PadSize);
+}
+
+unsigned DIEBaseTypeRef::SizeOf(const AsmPrinter *AP, dwarf::Form Form) const {
+  return ULEB128PadSize;
+}
+
+LLVM_DUMP_METHOD
+void DIEBaseTypeRef::print(raw_ostream &O) const { O << "BaseTypeRef: " << Index; }
+
+//===----------------------------------------------------------------------===//
 // DIEDelta Implementation
 //===----------------------------------------------------------------------===//
 
diff --git a/llvm/lib/CodeGen/AsmPrinter/DIEHash.cpp b/llvm/lib/CodeGen/AsmPrinter/DIEHash.cpp
index 75d9430c351..bfac8850a2a 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DIEHash.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DIEHash.cpp
@@ -225,7 +225,7 @@ void DIEHash::hashLocList(const DIELocList &LocList) {
   DwarfDebug &DD = *AP->getDwarfDebug();
   const DebugLocStream &Locs = DD.getDebugLocs();
   for (const auto &Entry : Locs.getEntries(Locs.getList(LocList.getValue())))
-    DD.emitDebugLocEntry(Streamer, Entry);
+    DD.emitDebugLocEntry(Streamer, Entry, nullptr);
 }
 
 // Hash an individual attribute \param Attr based on the type of attribute and
@@ -309,6 +309,7 @@ void DIEHash::hashAttribute(const DIEValue &Value, dwarf::Tag Tag) {
     // FIXME: It's uncertain whether or not we should handle this at the moment.
   case DIEValue::isExpr:
   case DIEValue::isLabel:
+  case DIEValue::isBaseTypeRef:
   case DIEValue::isDelta:
     llvm_unreachable("Add support for additional value types.");
   }
diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h b/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
index 40360ba4d34..256a41be237 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
@@ -148,8 +148,10 @@ public:
   }
 
   /// Lower this entry into a DWARF expression.
-  void finalize(const AsmPrinter &AP, DebugLocStream::ListBuilder &List,
-                const DIBasicType *BT);
+  void finalize(const AsmPrinter &AP,
+                DebugLocStream::ListBuilder &List,
+                const DIBasicType *BT,
+                DwarfCompileUnit &TheCU);
 };
 
 /// Compare two Values for equality.
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 0a30ede2d2d..e6913bc487f 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -17,6 +17,7 @@
 #include "DwarfUnit.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/BinaryFormat/Dwarf.h"
@@ -1185,3 +1186,27 @@ void DwarfCompileUnit::addAddrTableBase() {
                                          : dwarf::DW_AT_GNU_addr_base,
                   Label, TLOF.getDwarfAddrSection()->getBeginSymbol());
 }
+
+void DwarfCompileUnit::addBaseTypeRef(DIEValueList &Die, int64_t Idx) {
+  Die.addValue(DIEValueAllocator, (dwarf::Attribute)0, dwarf::DW_FORM_udata,
+               new (DIEValueAllocator) DIEBaseTypeRef(this, Idx));
+}
+
+void DwarfCompileUnit::createBaseTypeDIEs() {
+  // Insert the base_type DIEs directly after the CU so that their offsets will
+  // fit in the fixed size ULEB128 used inside the location expressions.
+  // Maintain order by iterating backwards and inserting to the front of CU
+  // child list.
+  for (auto &Btr : reverse(ExprRefedBaseTypes)) {
+    DIE &Die = getUnitDie().addChildFront(
+      DIE::get(DIEValueAllocator, dwarf::DW_TAG_base_type));
+    SmallString<32> Str;
+    addString(Die, dwarf::DW_AT_name,
+              Twine(dwarf::AttributeEncodingString(Btr.Encoding) +
+                    "_" + Twine(Btr.BitSize)).toStringRef(Str));
+    addUInt(Die, dwarf::DW_AT_encoding, dwarf::DW_FORM_data1, Btr.Encoding);
+    addUInt(Die, dwarf::DW_AT_byte_size, None, Btr.BitSize / 8);
+
+    Btr.Die = &Die;
+  }
+}
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
index c5ec49503c6..d9addb52376 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
@@ -124,6 +124,16 @@ public:
     const DIExpression *Expr;
   };
 
+  struct BaseTypeRef {
+    BaseTypeRef(unsigned BitSize, dwarf::TypeKind Encoding) :
+      BitSize(BitSize), Encoding(Encoding) {}
+    unsigned BitSize;
+    dwarf::TypeKind Encoding;
+    DIE *Die = nullptr;
+  };
+
+  std::vector<BaseTypeRef> ExprRefedBaseTypes;
+
   /// Get or create global variable DIE.
   DIE *
   getOrCreateGlobalVariableDIE(const DIGlobalVariable *GV,
@@ -199,6 +209,8 @@ public:
                               SmallVectorImpl<DIE *> &Children,
                               bool *HasNonScopeChildren = nullptr);
 
+  void createBaseTypeDIEs();
+
   /// Construct a DIE for this subprogram scope.
   DIE &constructSubprogramScopeDIE(const DISubprogram *Sub,
                                    LexicalScope *Scope);
@@ -313,6 +325,8 @@ public:
   void setDWOId(uint64_t DwoId) { DWOId = DwoId; }
 
   bool hasDwarfPubSections() const;
+
+  void addBaseTypeRef(DIEValueList &Die, int64_t Idx);
 };
 
 } // end namespace llvm
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 1106b859859..3e60f15a22d 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -41,6 +41,8 @@
 #include "llvm/CodeGen/TargetInstrInfo.h"
 #include "llvm/CodeGen/TargetRegisterInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/DebugInfo/DWARF/DWARFExpression.h"
+#include "llvm/DebugInfo/DWARF/DWARFDataExtractor.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DebugLoc.h"
@@ -161,6 +163,7 @@ static const char *const DWARFGroupName = "dwarf";
 static const char *const DWARFGroupDescription = "DWARF Emission";
 static const char *const DbgTimerName = "writer";
 static const char *const DbgTimerDescription = "DWARF Debug Writer";
+static constexpr unsigned ULEB128PadSize = 4;
 
 void DebugLocDwarfExpression::emitOp(uint8_t Op, const char *Comment) {
   BS.EmitInt8(
@@ -176,6 +179,11 @@ void DebugLocDwarfExpression::emitUnsigned(uint64_t Value) {
   BS.EmitULEB128(Value, Twine(Value));
 }
 
+void DebugLocDwarfExpression::emitBaseTypeRef(uint64_t Idx) {
+  assert(Idx < (1ULL << (ULEB128PadSize * 7)) && "Idx wont fit");
+  BS.EmitULEB128(Idx, Twine(Idx), ULEB128PadSize);
+}
+
 bool DebugLocDwarfExpression::isFrameRegister(const TargetRegisterInfo &TRI,
                                               unsigned MachineReg) {
   // This information is not available while emitting .debug_loc entries.
@@ -940,6 +948,11 @@ void DwarfDebug::endModule() {
   assert(CurFn == nullptr);
   assert(CurMI == nullptr);
 
+  for (const auto &P : CUMap) {
+    auto &CU = *P.second;
+    CU.createBaseTypeDIEs();
+  }
+
   // If we aren't actually generating debug info (check beginModule -
   // conditionalized on !DisableDebugInfoPrinting and the presence of the
   // llvm.dbg.cu metadata node)
@@ -1369,7 +1382,7 @@ void DwarfDebug::collectEntityInfo(DwarfCompileUnit &TheCU,
 
     // Finalize the entry by lowering it into a DWARF bytestream.
     for (auto &Entry : Entries)
-      Entry.finalize(*Asm, List, BT);
+      Entry.finalize(*Asm, List, BT, TheCU);
   }
 
   // For each InlinedEntity collected from DBG_LABEL instructions, convert to
@@ -1911,13 +1924,55 @@ void DwarfDebug::emitDebugStr() {
                      StringOffsetsSection, /* UseRelativeOffsets = */ true);
 }
 
-void DwarfDebug::emitDebugLocEntry(ByteStreamer &Streamer,
-                                   const DebugLocStream::Entry &Entry) {
+void DwarfDebug::emitDebugLocEntry(ByteStreamer &Streamer, const
+                                   DebugLocStream::Entry &Entry,
+                                   const DwarfCompileUnit *CU) {
   auto &&Comments = DebugLocs.getComments(Entry);
   auto Comment = Comments.begin();
   auto End = Comments.end();
-  for (uint8_t Byte : DebugLocs.getBytes(Entry))
-    Streamer.EmitInt8(Byte, Comment != End ? *(Comment++) : "");
+
+  // The expressions are inserted into a byte stream rather early (see
+  // DwarfExpression::addExpression) so for those ops (e.g. DW_OP_convert) that
+  // need to reference a base_type DIE the offset of that DIE is not yet known.
+  // To deal with this we instead insert a placeholder early and then extract
+  // it here and replace it with the real reference.
+  unsigned PtrSize = Asm->MAI->getCodePointerSize();
+  DWARFDataExtractor Data(StringRef(DebugLocs.getBytes(Entry).data(),
+                                    DebugLocs.getBytes(Entry).size()),
+                          Asm->getDataLayout().isLittleEndian(), PtrSize);
+  DWARFExpression Expr(Data, getDwarfVersion(), PtrSize);
+
+  using Encoding = DWARFExpression::Operation::Encoding;
+  uint32_t Offset = 0;
+  for (auto &Op : Expr) {
+    assert(Op.getCode() != dwarf::DW_OP_const_type &&
+           "3 operand ops not yet supported");
+    Streamer.EmitInt8(Op.getCode(), Comment != End ? *(Comment++) : "");
+    Offset++;
+    for (unsigned I = 0; I < 2; ++I) {
+      if (Op.getDescription().Op[I] == Encoding::SizeNA)
+        continue;
+      if (Op.getDescription().Op[I] == Encoding::BaseTypeRef) {
+          if (CU) {
+            uint64_t Offset = CU->ExprRefedBaseTypes[Op.getRawOperand(I)].Die->getOffset();
+            assert(Offset < (1ULL << (ULEB128PadSize * 7)) && "Offset wont fit");
+            Asm->EmitULEB128(Offset, nullptr, ULEB128PadSize);
+          } else {
+            // Emit a reference to the 'generic type'.
+            Asm->EmitULEB128(0, nullptr, ULEB128PadSize);
+          }
+          // Make sure comments stay aligned.
+          for (unsigned J = 0; J < ULEB128PadSize; ++J)
+            if (Comment != End)
+              Comment++;
+      } else {
+        for (uint32_t J = Offset; J < Op.getOperandEndOffset(I); ++J)
+          Streamer.EmitInt8(Data.getData()[J], Comment != End ? *(Comment++) : "");
+      }
+      Offset = Op.getOperandEndOffset(I);
+    }
+    assert(Offset == Op.getEndOffset());
+  }
 }
 
 static void emitDebugLocValue(const AsmPrinter &AP, const DIBasicType *BT,
@@ -1951,11 +2006,12 @@ static void emitDebugLocValue(const AsmPrinter &AP, const DIBasicType *BT,
 
 void DebugLocEntry::finalize(const AsmPrinter &AP,
                              DebugLocStream::ListBuilder &List,
-                             const DIBasicType *BT) {
+                             const DIBasicType *BT,
+                             DwarfCompileUnit &TheCU) {
   assert(Begin != End && "unexpected location list entry with empty range");
   DebugLocStream::EntryBuilder Entry(List, Begin, End);
   BufferByteStreamer Streamer = Entry.getStreamer();
-  DebugLocDwarfExpression DwarfExpr(AP.getDwarfVersion(), Streamer);
+  DebugLocDwarfExpression DwarfExpr(AP.getDwarfVersion(), Streamer, TheCU);
   const DebugLocEntry::Value &Value = Values[0];
   if (Value.isFragment()) {
     // Emit all fragments that belong to the same variable and range.
@@ -1975,7 +2031,8 @@ void DebugLocEntry::finalize(const AsmPrinter &AP,
   DwarfExpr.finalize();
 }
 
-void DwarfDebug::emitDebugLocEntryLocation(const DebugLocStream::Entry &Entry) {
+void DwarfDebug::emitDebugLocEntryLocation(const DebugLocStream::Entry &Entry,
+                                           const DwarfCompileUnit *CU) {
   // Emit the size.
   Asm->OutStreamer->AddComment("Loc expr size");
   if (getDwarfVersion() >= 5)
@@ -1984,7 +2041,7 @@ void DwarfDebug::emitDebugLocEntryLocation(const DebugLocStream::Entry &Entry) {
     Asm->emitInt16(DebugLocs.getBytes(Entry).size());
   // Emit the entry.
   APByteStreamer Streamer(*Asm);
-  emitDebugLocEntry(Streamer, Entry);
+  emitDebugLocEntry(Streamer, Entry, CU);
 }
 
 // Emit the common part of the DWARF 5 range/locations list tables header.
@@ -2084,7 +2141,7 @@ void DwarfDebug::emitDebugLoc() {
           Asm->EmitLabelDifference(Entry.EndSym, Base, Size);
         }
 
-        emitDebugLocEntryLocation(Entry);
+        emitDebugLocEntryLocation(Entry, CU);
         continue;
       }
 
@@ -2105,7 +2162,7 @@ void DwarfDebug::emitDebugLoc() {
         Asm->OutStreamer->EmitSymbolValue(Entry.EndSym, Size);
       }
 
-      emitDebugLocEntryLocation(Entry);
+      emitDebugLocEntryLocation(Entry, CU);
     }
 
     if (IsLocLists) {
@@ -2141,7 +2198,7 @@ void DwarfDebug::emitDebugLocDWO() {
       Asm->EmitULEB128(idx);
       Asm->EmitLabelDifference(Entry.EndSym, Entry.BeginSym, 4);
 
-      emitDebugLocEntryLocation(Entry);
+      emitDebugLocEntryLocation(Entry, List.CU);
     }
     Asm->emitInt8(dwarf::DW_LLE_end_of_list);
   }
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
index f0d50a47640..ec5040f6c10 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -682,10 +682,12 @@ public:
   /// Emit an entry for the debug loc section. This can be used to
   /// handle an entry that's going to be emitted into the debug loc section.
   void emitDebugLocEntry(ByteStreamer &Streamer,
-                         const DebugLocStream::Entry &Entry);
+                         const DebugLocStream::Entry &Entry,
+                         const DwarfCompileUnit *CU);
 
   /// Emit the location for a debug loc entry, including the size header.
-  void emitDebugLocEntryLocation(const DebugLocStream::Entry &Entry);
+  void emitDebugLocEntryLocation(const DebugLocStream::Entry &Entry,
+                                 const DwarfCompileUnit *CU);
 
   /// Find the MDNode for the given reference.
   template <typename T> T *resolve(TypedDINodeRef<T> Ref) const {
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
index 558d33ac0e6..41fa45f2507 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "DwarfExpression.h"
+#include "DwarfCompileUnit.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/SmallBitVector.h"
 #include "llvm/BinaryFormat/Dwarf.h"
@@ -318,6 +319,8 @@ void DwarfExpression::addExpression(DIExpressionCursor &&ExprCursor,
   if (SubRegisterSizeInBits && N && (N->getOp() != dwarf::DW_OP_LLVM_fragment))
     maskSubRegister();
 
+  Optional<DIExpression::ExprOperand> PrevConvertOp = None;
+
   while (ExprCursor) {
     auto Op = ExprCursor.take();
     switch (Op->getOp()) {
@@ -384,6 +387,42 @@ void DwarfExpression::addExpression(DIExpressionCursor &&ExprCursor,
       assert(LocationKind != Register);
       emitConstu(Op->getArg(0));
       break;
+    case dwarf::DW_OP_LLVM_convert: {
+      unsigned BitSize = Op->getArg(0);
+      dwarf::TypeKind Encoding = static_cast<dwarf::TypeKind>(Op->getArg(1));
+      if (DwarfVersion >= 5) {
+        emitOp(dwarf::DW_OP_convert);
+        // Reuse the base_type if we already have one in this CU otherwise we
+        // create a new one.
+        unsigned I = 0, E = CU.ExprRefedBaseTypes.size();
+        for (; I != E; ++I)
+          if (CU.ExprRefedBaseTypes[I].BitSize == BitSize &&
+              CU.ExprRefedBaseTypes[I].Encoding == Encoding)
+            break;
+
+        if (I == E)
+          CU.ExprRefedBaseTypes.emplace_back(BitSize, Encoding);
+
+        // If targeting a location-list; simply emit the index into the raw
+        // byte stream as ULEB128, DwarfDebug::emitDebugLocEntry has been
+        // fitted with means to extract it later.
+        // If targeting a inlined DW_AT_location; insert a DIEBaseTypeRef
+        // (containing the index and a resolve mechanism during emit) into the
+        // DIE value list.
+        emitBaseTypeRef(I);
+      } else {
+        if (PrevConvertOp && PrevConvertOp->getArg(0) < BitSize) {
+          if (Encoding == dwarf::DW_ATE_signed)
+            emitLegacySExt(PrevConvertOp->getArg(0));
+          else if (Encoding == dwarf::DW_ATE_unsigned)
+            emitLegacyZExt(PrevConvertOp->getArg(0));
+          PrevConvertOp = None;
+        } else {
+          PrevConvertOp = Op;
+        }
+      }
+      break;
+    }
     case dwarf::DW_OP_stack_value:
       LocationKind = Implicit;
       break;
@@ -436,3 +475,25 @@ void DwarfExpression::addFragmentOffset(const DIExpression *Expr) {
     addOpPiece(FragmentOffset - OffsetInBits);
   OffsetInBits = FragmentOffset;
 }
+
+void DwarfExpression::emitLegacySExt(unsigned FromBits) {
+  // (((X >> (FromBits - 1)) * (~0)) << FromBits) | X
+  emitOp(dwarf::DW_OP_dup);
+  emitOp(dwarf::DW_OP_constu);
+  emitUnsigned(FromBits - 1);
+  emitOp(dwarf::DW_OP_shr);
+  emitOp(dwarf::DW_OP_lit0);
+  emitOp(dwarf::DW_OP_not);
+  emitOp(dwarf::DW_OP_mul);
+  emitOp(dwarf::DW_OP_constu);
+  emitUnsigned(FromBits);
+  emitOp(dwarf::DW_OP_shl);
+  emitOp(dwarf::DW_OP_or);
+}
+
+void DwarfExpression::emitLegacyZExt(unsigned FromBits) {
+  // (X & (1 << FromBits - 1))
+  emitOp(dwarf::DW_OP_constu);
+  emitUnsigned((1ULL << FromBits) - 1);
+  emitOp(dwarf::DW_OP_and);
+}
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
index 1f7b89fe5fc..18bedf0b902 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
@@ -27,7 +27,7 @@ namespace llvm {
 class AsmPrinter;
 class APInt;
 class ByteStreamer;
-class DwarfUnit;
+class DwarfCompileUnit;
 class DIELoc;
 class TargetRegisterInfo;
 
@@ -104,6 +104,8 @@ protected:
     const char *Comment;
   };
 
+  DwarfCompileUnit &CU;
+
   /// The register location, if any.
   SmallVector<Register, 2> DwarfRegs;
 
@@ -137,6 +139,8 @@ protected:
   /// Emit a raw unsigned value.
   virtual void emitUnsigned(uint64_t Value) = 0;
 
+  virtual void emitBaseTypeRef(uint64_t Idx) = 0;
+
   /// Emit a normalized unsigned constant.
   void emitConstu(uint64_t Value);
 
@@ -199,7 +203,8 @@ protected:
   ~DwarfExpression() = default;
 
 public:
-  DwarfExpression(unsigned DwarfVersion) : DwarfVersion(DwarfVersion) {}
+  DwarfExpression(unsigned DwarfVersion, DwarfCompileUnit &CU)
+    : CU(CU), DwarfVersion(DwarfVersion) {}
 
   /// This needs to be called last to commit any pending changes.
   void finalize();
@@ -247,6 +252,9 @@ public:
   /// If applicable, emit an empty DW_OP_piece / DW_OP_bit_piece to advance to
   /// the fragment described by \c Expr.
   void addFragmentOffset(const DIExpression *Expr);
+
+  void emitLegacySExt(unsigned FromBits);
+  void emitLegacyZExt(unsigned FromBits);
 };
 
 /// DwarfExpression implementation for .debug_loc entries.
@@ -256,27 +264,28 @@ class DebugLocDwarfExpression final : public DwarfExpression {
   void emitOp(uint8_t Op, const char *Comment = nullptr) override;
   void emitSigned(int64_t Value) override;
   void emitUnsigned(uint64_t Value) override;
+  void emitBaseTypeRef(uint64_t Idx) override;
   bool isFrameRegister(const TargetRegisterInfo &TRI,
                        unsigned MachineReg) override;
 
 public:
-  DebugLocDwarfExpression(unsigned DwarfVersion, ByteStreamer &BS)
-      : DwarfExpression(DwarfVersion), BS(BS) {}
+  DebugLocDwarfExpression(unsigned DwarfVersion, ByteStreamer &BS, DwarfCompileUnit &CU)
+      : DwarfExpression(DwarfVersion, CU), BS(BS) {}
 };
 
 /// DwarfExpression implementation for singular DW_AT_location.
 class DIEDwarfExpression final : public DwarfExpression {
 const AsmPrinter &AP;
-  DwarfUnit &DU;
   DIELoc &DIE;
 
   void emitOp(uint8_t Op, const char *Comment = nullptr) override;
   void emitSigned(int64_t Value) override;
   void emitUnsigned(uint64_t Value) override;
+  void emitBaseTypeRef(uint64_t Idx) override;
   bool isFrameRegister(const TargetRegisterInfo &TRI,
                        unsigned MachineReg) override;
 public:
-  DIEDwarfExpression(const AsmPrinter &AP, DwarfUnit &DU, DIELoc &DIE);
+  DIEDwarfExpression(const AsmPrinter &AP, DwarfCompileUnit &CU, DIELoc &DIE);
 
   DIELoc *finalize() {
     DwarfExpression::finalize();
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfFile.h b/llvm/lib/CodeGen/AsmPrinter/DwarfFile.h
index b3026a35b85..e550c6385b0 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfFile.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfFile.h
@@ -147,7 +147,7 @@ public:
   void emitUnits(bool UseOffsets);
 
   /// Emit the given unit to its section.
-  void emitUnit(DwarfUnit *U, bool UseOffsets);
+  void emitUnit(DwarfUnit *TheU, bool UseOffsets);
 
   /// Emit a set of abbreviations to the specific section.
   void emitAbbrevs(MCSection *);
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index b19dc4b2506..6e547469c24 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -46,21 +46,26 @@ using namespace llvm;
 
 #define DEBUG_TYPE "dwarfdebug"
 
-DIEDwarfExpression::DIEDwarfExpression(const AsmPrinter &AP, DwarfUnit &DU,
+DIEDwarfExpression::DIEDwarfExpression(const AsmPrinter &AP,
+                                       DwarfCompileUnit &CU,
                                        DIELoc &DIE)
-    : DwarfExpression(AP.getDwarfVersion()), AP(AP), DU(DU),
+    : DwarfExpression(AP.getDwarfVersion(), CU), AP(AP),
       DIE(DIE) {}
 
 void DIEDwarfExpression::emitOp(uint8_t Op, const char* Comment) {
-  DU.addUInt(DIE, dwarf::DW_FORM_data1, Op);
+  CU.addUInt(DIE, dwarf::DW_FORM_data1, Op);
 }
 
 void DIEDwarfExpression::emitSigned(int64_t Value) {
-  DU.addSInt(DIE, dwarf::DW_FORM_sdata, Value);
+  CU.addSInt(DIE, dwarf::DW_FORM_sdata, Value);
 }
 
 void DIEDwarfExpression::emitUnsigned(uint64_t Value) {
-  DU.addUInt(DIE, dwarf::DW_FORM_udata, Value);
+  CU.addUInt(DIE, dwarf::DW_FORM_udata, Value);
+}
+
+void DIEDwarfExpression::emitBaseTypeRef(uint64_t Idx) {
+  CU.addBaseTypeRef(DIE, Idx);
 }
 
 bool DIEDwarfExpression::isFrameRegister(const TargetRegisterInfo &TRI,
diff --git a/llvm/lib/CodeGen/AsmPrinter/LLVMBuild.txt b/llvm/lib/CodeGen/AsmPrinter/LLVMBuild.txt
index 88d7c13ce03..56449269681 100644
--- a/llvm/lib/CodeGen/AsmPrinter/LLVMBuild.txt
+++ b/llvm/lib/CodeGen/AsmPrinter/LLVMBuild.txt
@@ -18,4 +18,4 @@
 type = Library
 name = AsmPrinter
 parent = Libraries
-required_libraries = Analysis BinaryFormat CodeGen Core DebugInfoCodeView DebugInfoMSF MC MCParser Support Target
+required_libraries = Analysis BinaryFormat CodeGen Core DebugInfoCodeView DebugInfoDWARF DebugInfoMSF MC MCParser Support Target