Implement DW_OP_convert

[aprantl]

Summary

This patch adds basic support for DW_OP_convert[1] for integer types. Recent versions of LLVM's optimizer may insert this opcode into DWARF expressions. DW_OP_convert is effectively a type cast operation that takes a reference to a base type DIE (or zero) and then casts the value at the top of the DWARF stack to that type. Internally this works by changing the bit size of the APInt that is used as backing storage for LLDB's DWARF stack.

I managed to write a unit test for this by implementing a mock YAML object file / module that takes debug info sections in yaml2obj format.

[1] Typed DWARF stack. http://www.dwarfstd.org/ShowIssue.php?issue=140425.1

[jasonmolenda]

LGTM, nice job with the test case, I see myself copying that in the future. :)

lldb/source/Utility/Scalar.cpp

423 ↗

(On Diff #219422)

What about an ILP32 target like arm64_32, with lldb running on an LP64 system - are we mixing target & host type sizes here? I'm not sure if Scalar's types (e_slong etc) are in host or target terms. I mean this code might as well be if bit_size <= 32 return Scalar::e_Signed32BitType, but I wanted to check in because we're using host type sizes here.

[aprantl]

lldb/source/Utility/Scalar.cpp

423 ↗

(On Diff #219422)

As the comment on line 420 above says:
// Scalar types are always host types, hence the sizeof().

[aprantl]

lldb/source/Utility/Scalar.cpp

423 ↗

(On Diff #219422)

Note that I think the decision of making Scalar types host types very questionable and it would make much more sense for it to be target types, but the way the Scalar constructors are implemented they are definitely host types.

[JDevlieghere]

lldb/include/lldb/Utility/Scalar.h

107 ↗

(On Diff #219422)

How about GetTypeForBitSize?

lldb/source/Expression/DWARFExpression.cpp

2571 ↗

(On Diff #219422)

Can we wrap this in a lambda?

lldb/source/Utility/Scalar.cpp

442 ↗

(On Diff #219422)

llvm::unreachable?

[aprantl]

lldb/source/Expression/DWARFExpression.cpp

2571 ↗

(On Diff #219422)

Which part specifically do you mean?

[JDevlieghere]

lldb/source/Expression/DWARFExpression.cpp

2571 ↗

(On Diff #219422)

auto SetErrorString = [&](llvm::StringRef msg) { if (error_ptr) error_ptr->SetErrorString(msg); })

We could deduplicate even more code by using a macro that also covers the check around it and does the return, but I'm not sure if that's really worth it.

[vsk]

Looks good overall, especially the testing.

lldb/include/lldb/Utility/Scalar.h

107 ↗

(On Diff #219422)

nit: bool signed ?

lldb/source/Expression/DWARFExpression.cpp

2571 ↗

(On Diff #219422)

Oh, like LLDB_LOG? Seems like a nice idea. I think I need this for D67376, so I might do it if no one else has started already. It'd be great to use that here.

[aprantl]

lldb/include/lldb/Utility/Scalar.h

107 ↗

(On Diff #219422)

that name conflicts with the actual type signed.

[aprantl]

lldb/source/Expression/DWARFExpression.cpp

2571 ↗

(On Diff #219422)

I'll leave this as an NFC refactoring for later since it will affect code outside of this patch.

[labath]

The yaml object file is pretty impressive, but I am wondering if it is really necessary. Have you looked if it would be possible to reuse the existing TestFile::fromYaml functionality? I think it should be possible to reuse that by just inserting some MachO yaml blurbs around the dwarf yaml (elf yaml2obj doesn't support embedding dwarf yaml, but that's just because nobody enabled that yet).

lldb/trunk/include/lldb/Core/Section.h

public:
   typedef collection::iterator iterator;
   typedef collection::const_iterator const_iterator;
 
   const_iterator begin() const { return m_sections.begin(); }
   const_iterator end() const { return m_sections.end(); }
   const_iterator begin() { return m_sections.begin(); }
   const_iterator end() { return m_sections.end(); }
 
-  SectionList();
-
-  ~SectionList();
+  /// Create an empty list.
+  SectionList() = default;
 
   SectionList &operator=(const SectionList &rhs);
 
   size_t AddSection(const lldb::SectionSP &section_sp);
 
   size_t AddUniqueSection(const lldb::SectionSP &section_sp);
 
   size_t FindSectionIndex(const Section *sect);

lldb/trunk/include/lldb/Utility/Scalar.h

 namespace lldb_private {
 
 // A class designed to hold onto values and their corresponding types.
 // Operators are defined and Scalar objects will correctly promote their types
 // and values before performing these operations. Type promotion currently
 // follows the ANSI C type promotion rules.
 class Scalar {
 public:
+  // FIXME: These are host types which seems to be an odd choice.
   enum Type {
     e_void = 0,
     e_sint,
     e_uint,
     e_slong,
     e_ulong,
     e_slonglong,
     e_ulonglong,
Scalar(long double v, bool ieee_quad)
     else
       m_float =
           llvm::APFloat(llvm::APFloat::x87DoubleExtended(),
                         llvm::APInt(BITWIDTH_INT128, NUM_OF_WORDS_INT128,
                                     (reinterpret_cast<type128 *>(&v))->x));
   }
   Scalar(llvm::APInt v) : m_type(), m_float(static_cast<float>(0)) {
     m_integer = llvm::APInt(v);
-    switch (m_integer.getBitWidth()) {
-    case 8:
-    case 16:
-    case 32:
-      m_type = e_sint;
-      return;
-    case 64:
-      m_type = e_slonglong;
-      return;
-    case 128:
-      m_type = e_sint128;
-      return;
-    case 256:
-      m_type = e_sint256;
-      return;
-    case 512:
-      m_type = e_sint512;
-      return;
-    }
-    lldbassert(false && "unsupported bitwidth");
+    m_type = GetBestTypeForBitSize(m_integer.getBitWidth(), true);
   }
   // Scalar(const RegisterValue& reg_value);
   virtual ~Scalar();
 
+  /// Return the most efficient Scalar::Type for the requested bit size.
+  static Type GetBestTypeForBitSize(size_t bit_size, bool sign);
+
   bool SignExtend(uint32_t bit_pos);
 
   bool ExtractBitfield(uint32_t bit_size, uint32_t bit_offset);
 
   bool SetBit(uint32_t bit);
 
   bool ClearBit(uint32_t bit);
 
public:
   const char *GetTypeAsCString() const;
 
   void GetValue(Stream *s, bool show_type) const;
 
   bool IsValid() const {
     return (m_type >= e_sint) && (m_type <= e_long_double);
   }
 
+  /// Convert integer to \p type, limited to \p bits size.
+  void TruncOrExtendTo(Scalar::Type type, uint16_t bits);
+
   bool Promote(Scalar::Type type);
 
   bool MakeSigned();
 
   bool MakeUnsigned();
 
   static const char *GetValueTypeAsCString(Scalar::Type value_type);
 

lldb/trunk/source/Core/Section.cpp

 lldb::offset_t Section::GetSectionData(DataExtractor &section_data) {
   if (m_obj_file)
     return m_obj_file->ReadSectionData(this, section_data);
   return 0;
 }
 
 #pragma mark SectionList
 
-SectionList::SectionList() : m_sections() {}
-
-SectionList::~SectionList() {}
-
 SectionList &SectionList::operator=(const SectionList &rhs) {
   if (this != &rhs)
     m_sections = rhs.m_sections;
   return *this;
 }
 
 size_t SectionList::AddSection(const lldb::SectionSP &section_sp) {
   if (section_sp) {

lldb/trunk/source/Expression/DWARFExpression.cpp

     // OPERANDS: None
     // DESCRIPTION: Specifies that the object does not exist in memory but
     // rather is a constant value.  The value from the top of the stack is the
     // value to be used.  This is the actual object value and not the location.
     case DW_OP_stack_value:
       stack.back().SetValueType(Value::eValueTypeScalar);
       break;
 
+    // OPCODE: DW_OP_convert
+    // OPERANDS: 1
+    //      A ULEB128 that is either a DIE offset of a
+    //      DW_TAG_base_type or 0 for the generic (pointer-sized) type.
+    //
+    // DESCRIPTION: Pop the top stack element, convert it to a
+    // different type, and push the result.
+    case DW_OP_convert: {
+      if (stack.size() < 1) {
+        if (error_ptr)
+          error_ptr->SetErrorString(
+              "Expression stack needs at least 1 item for DW_OP_convert.");
+        return false;
+      }
+      const uint64_t die_offset = opcodes.GetULEB128(&offset);
+      Scalar::Type type = Scalar::e_void;
+      uint64_t bit_size;
+      if (die_offset == 0) {
+        // The generic type has the size of an address on the target
+        // machine and an unspecified signedness. Scalar has no
+        // "unspecified signedness", so we use unsigned types.
+        if (!module_sp) {
+          if (error_ptr)
+            error_ptr->SetErrorString("No module");
+          return false;
+        }
+        bit_size = module_sp->GetArchitecture().GetAddressByteSize() * 8;
+        if (!bit_size) {
+          if (error_ptr)
+            error_ptr->SetErrorString("unspecified architecture");
+          return false;
+        }
+        type = Scalar::GetBestTypeForBitSize(bit_size, false);
+      } else {
+        // Retrieve the type DIE that the value is being converted to.
+        // FIXME: the constness has annoying ripple effects.
+        DWARFDIE die = const_cast<DWARFUnit *>(dwarf_cu)->GetDIE(die_offset);
+        if (!die) {
+          if (error_ptr)
+            error_ptr->SetErrorString("Cannot resolve DW_OP_convert type DIE");
+          return false;
+        }
+        uint64_t encoding =
+            die.GetAttributeValueAsUnsigned(DW_AT_encoding, DW_ATE_hi_user);
+        bit_size = die.GetAttributeValueAsUnsigned(DW_AT_byte_size, 0) * 8;
+        if (!bit_size)
+          bit_size = die.GetAttributeValueAsUnsigned(DW_AT_bit_size, 0);
+        if (!bit_size) {
+          if (error_ptr)
+            error_ptr->SetErrorString("Unsupported type size in DW_OP_convert");
+          return false;
+        }
+        switch (encoding) {
+        case DW_ATE_signed:
+        case DW_ATE_signed_char:
+          type = Scalar::GetBestTypeForBitSize(bit_size, true);
+          break;
+        case DW_ATE_unsigned:
+        case DW_ATE_unsigned_char:
+          type = Scalar::GetBestTypeForBitSize(bit_size, false);
+          break;
+        default:
+          if (error_ptr)
+            error_ptr->SetErrorString("Unsupported encoding in DW_OP_convert");
+          return false;
+        }
+      }
+      if (type == Scalar::e_void) {
+        if (error_ptr)
+          error_ptr->SetErrorString("Unsupported pointer size");
+        return false;
+      }
+      Scalar &top = stack.back().ResolveValue(exe_ctx);
+      top.TruncOrExtendTo(type, bit_size);
+      break;
+    }
+
     // OPCODE: DW_OP_call_frame_cfa
     // OPERANDS: None
     // DESCRIPTION: Specifies a DWARF expression that pushes the value of
     // the canonical frame address consistent with the call frame information
     // located in .debug_frame (or in the FDEs of the eh_frame section).
     case DW_OP_call_frame_cfa:
       if (frame) {
         // Note that we don't have to parse FDEs because this DWARF expression

lldb/trunk/source/Utility/Scalar.cpp

else
       m_type = e_uint512;
     break;
   }
   return *this;
 }
 
 Scalar::~Scalar() = default;
 
+Scalar::Type Scalar::GetBestTypeForBitSize(size_t bit_size, bool sign) {
+  // Scalar types are always host types, hence the sizeof().
+  if (sign) {
+    if (bit_size <= sizeof(int)*8) return Scalar::e_sint;
+    if (bit_size <= sizeof(long)*8) return Scalar::e_slong;
+    if (bit_size <= sizeof(long long)*8) return Scalar::e_slonglong;
+    if (bit_size <= 128) return Scalar::e_sint128;
+    if (bit_size <= 256) return Scalar::e_sint256;
+    if (bit_size <= 512) return Scalar::e_sint512;
+  } else {
+    if (bit_size <= sizeof(unsigned int)*8) return Scalar::e_uint;
+    if (bit_size <= sizeof(unsigned long)*8) return Scalar::e_ulong;
+    if (bit_size <= sizeof(unsigned long long)*8) return Scalar::e_ulonglong;
+    if (bit_size <= 128) return Scalar::e_uint128;
+    if (bit_size <= 256) return Scalar::e_uint256;
+    if (bit_size <= 512) return Scalar::e_uint512;
+  }
+  return Scalar::e_void;
+};
+
+void Scalar::TruncOrExtendTo(Scalar::Type type, uint16_t bits) {
+  switch (type) {
+  case e_sint:
+  case e_slong:
+  case e_slonglong:
+  case e_sint128:
+  case e_sint256:
+  case e_sint512:
+    m_integer = m_integer.sextOrTrunc(bits);
+    break;
+  case e_uint:
+  case e_ulong:
+  case e_ulonglong:
+  case e_uint128:
+  case e_uint256:
+  case e_uint512:
+    m_integer = m_integer.zextOrTrunc(bits);
+    break;
+  default:
+    llvm_unreachable("Promoting a Scalar to a specific number of bits is only "
+                     "supported for integer types.");
+  }
+  m_type = type;
+}
+
 bool Scalar::Promote(Scalar::Type type) {
   bool success = false;
   switch (m_type) {
   case e_void:
     break;
 
   case e_sint:
     switch (type) {

lldb/trunk/unittests/Expression/DWARFExpressionTest.cpp

 //===-- DWARFExpressionTest.cpp ----------------------------------*- C++-*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "lldb/Expression/DWARFExpression.h"
+#include "../../source/Plugins/SymbolFile/DWARF/DWARFUnit.h"
+#include "../../source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h"
+#include "lldb/Core/Module.h"
+#include "lldb/Core/Section.h"
 #include "lldb/Core/Value.h"
 #include "lldb/Core/dwarf.h"
+#include "lldb/Symbol/ObjectFile.h"
 #include "lldb/Utility/StreamString.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/ObjectYAML/DWARFEmitter.h"
 #include "llvm/Testing/Support/Error.h"
 #include "gtest/gtest.h"
 
 using namespace lldb_private;
 
-static llvm::Expected<Scalar> Evaluate(llvm::ArrayRef<uint8_t> expr) {
+/// A mock module holding an object file parsed from YAML.
+class YAMLModule : public lldb_private::Module {
+public:
+  YAMLModule(ArchSpec &arch) : Module(FileSpec("test"), arch) {}
+  void SetObjectFile(lldb::ObjectFileSP obj_file) { m_objfile_sp = obj_file; }
+  ObjectFile *GetObjectFile() override { return m_objfile_sp.get(); }
+};
+
+/// A mock object file that can be parsed from YAML.
+class YAMLObjectFile : public lldb_private::ObjectFile {
+  const lldb::ModuleSP m_module_sp;
+  llvm::StringMap<std::unique_ptr<llvm::MemoryBuffer>> &m_section_map;
+  /// Because there is only one DataExtractor in the ObjectFile
+  /// interface, all sections are copied into a contiguous buffer.
+  std::vector<char> m_buffer;
+
+public:
+  YAMLObjectFile(const lldb::ModuleSP &module_sp,
+                 llvm::StringMap<std::unique_ptr<llvm::MemoryBuffer>> &map)
+      : ObjectFile(module_sp, &module_sp->GetFileSpec(), /*file_offset*/ 0,
+                   /*length*/ 0, /*data_sp*/ nullptr, /*data_offset*/ 0),
+        m_module_sp(module_sp), m_section_map(map) {}
+
+  /// Callback for initializing the module's list of sections.
+  void CreateSections(SectionList &unified_section_list) override {
+    lldb::offset_t total_bytes = 0;
+    for (auto &entry : m_section_map)
+      total_bytes += entry.getValue()->getBufferSize();
+    m_buffer.reserve(total_bytes);
+    m_data =
+        DataExtractor(m_buffer.data(), total_bytes, lldb::eByteOrderLittle, 4);
+
+    lldb::user_id_t sect_id = 1;
+    for (auto &entry : m_section_map) {
+      llvm::StringRef name = entry.getKey();
+      lldb::SectionType sect_type =
+          llvm::StringSwitch<lldb::SectionType>(name)
+              .Case("debug_info", lldb::eSectionTypeDWARFDebugInfo)
+              .Case("debug_abbrev", lldb::eSectionTypeDWARFDebugAbbrev);
+      auto &membuf = entry.getValue();
+      lldb::addr_t file_vm_addr = 0;
+      lldb::addr_t vm_size = 0;
+      lldb::offset_t file_offset = m_buffer.size();
+      lldb::offset_t file_size = membuf->getBufferSize();
+      m_buffer.resize(file_offset + file_size);
+      memcpy(m_buffer.data() + file_offset, membuf->getBufferStart(),
+             file_size);
+      uint32_t log2align = 0;
+      uint32_t flags = 0;
+      auto section_sp = std::make_shared<lldb_private::Section>(
+          m_module_sp, this, sect_id++, ConstString(name), sect_type,
+          file_vm_addr, vm_size, file_offset, file_size, log2align, flags);
+      unified_section_list.AddSection(section_sp);
+    }
+  }
+
+  /// \{
+  /// Stub methods that aren't needed here.
+  ConstString GetPluginName() override { return ConstString("YAMLObjectFile"); }
+  uint32_t GetPluginVersion() override { return 0; }
+  void Dump(Stream *s) override {}
+  uint32_t GetAddressByteSize() const override { return 8; }
+  uint32_t GetDependentModules(FileSpecList &file_list) override { return 0; }
+  bool IsExecutable() const override { return 0; }
+  ArchSpec GetArchitecture() override { return {}; }
+  Symtab *GetSymtab() override { return nullptr; }
+  bool IsStripped() override { return false; }
+  UUID GetUUID() override { return {}; }
+  lldb::ByteOrder GetByteOrder() const override {
+    return lldb::eByteOrderLittle;
+  }
+  bool ParseHeader() override { return false; }
+  Type CalculateType() override { return {}; }
+  Strata CalculateStrata() override { return {}; }
+  /// \}
+};
+
+static llvm::Expected<Scalar> Evaluate(llvm::ArrayRef<uint8_t> expr,
+                                       lldb::ModuleSP module_sp = {},
+                                       DWARFUnit *unit = nullptr) {
   DataExtractor extractor(expr.data(), expr.size(), lldb::eByteOrderLittle,
                           /*addr_size*/ 4);
-
   Value result;
   Status status;
   if (!DWARFExpression::Evaluate(
-          /*exe_ctx*/ nullptr, /*reg_ctx*/ nullptr, /*opcode_ctx*/ nullptr,
-          extractor, /*dwarf_cu*/ nullptr, lldb::eRegisterKindLLDB,
+          /*exe_ctx*/ nullptr, /*reg_ctx*/ nullptr, module_sp, extractor, unit,
+          lldb::eRegisterKindLLDB,
           /*initial_value_ptr*/ nullptr,
           /*object_address_ptr*/ nullptr, result, &status))
     return status.ToError();
 
   return result.GetScalar();
 }
 
+/// Unfortunately Scalar's operator==() is really picky.
+static Scalar GetScalar(unsigned bits, uint64_t value, bool sign) {
+  Scalar scalar;
+  auto type = Scalar::GetBestTypeForBitSize(bits, sign);
+  switch (type) {
+  case Scalar::e_sint:
+    scalar = Scalar((int)value);
+    break;
+  case Scalar::e_slong:
+    scalar = Scalar((long)value);
+    break;
+  case Scalar::e_slonglong:
+    scalar = Scalar((long long)value);
+    break;
+  case Scalar::e_uint:
+    scalar = Scalar((unsigned int)value);
+    break;
+  case Scalar::e_ulong:
+    scalar = Scalar((unsigned long)value);
+    break;
+  case Scalar::e_ulonglong:
+    scalar = Scalar((unsigned long long)value);
+    break;
+  default:
+    llvm_unreachable("not implemented");
+  }
+  scalar.TruncOrExtendTo(type, bits);
+  if (sign)
+    scalar.MakeSigned();
+  else
+    scalar.MakeUnsigned();
+  return scalar;
+}
+
 TEST(DWARFExpression, DW_OP_pick) {
   EXPECT_THAT_EXPECTED(Evaluate({DW_OP_lit1, DW_OP_lit0, DW_OP_pick, 0}),
                        llvm::HasValue(0));
   EXPECT_THAT_EXPECTED(Evaluate({DW_OP_lit1, DW_OP_lit0, DW_OP_pick, 1}),
                        llvm::HasValue(1));
   EXPECT_THAT_EXPECTED(Evaluate({DW_OP_lit1, DW_OP_lit0, DW_OP_pick, 2}),
                        llvm::Failed());
 }
+
+TEST(DWARFExpression, DW_OP_convert) {
+  /// Auxiliary debug info.
+  const char *yamldata =
+      "debug_abbrev:\n"
+      "  - Code:            0x00000001\n"
+      "    Tag:             DW_TAG_compile_unit\n"
+      "    Children:        DW_CHILDREN_yes\n"
+      "    Attributes:\n"
+      "      - Attribute:       DW_AT_language\n"
+      "        Form:            DW_FORM_data2\n"
+      "  - Code:            0x00000002\n"
+      "    Tag:             DW_TAG_base_type\n"
+      "    Children:        DW_CHILDREN_no\n"
+      "    Attributes:\n"
+      "      - Attribute:       DW_AT_encoding\n"
+      "        Form:            DW_FORM_data1\n"
+      "      - Attribute:       DW_AT_byte_size\n"
+      "        Form:            DW_FORM_data1\n"
+      "debug_info:\n"
+      "  - Length:\n"
+      "      TotalLength:     0\n"
+      "    Version:         4\n"
+      "    AbbrOffset:      0\n"
+      "    AddrSize:        8\n"
+      "    Entries:\n"
+      "      - AbbrCode:        0x00000001\n"
+      "        Values:\n"
+      "          - Value:           0x000000000000000C\n"
+      // 0x0000000e:
+      "      - AbbrCode:        0x00000002\n"
+      "        Values:\n"
+      "          - Value:           0x0000000000000007\n" // DW_ATE_unsigned
+      "          - Value:           0x0000000000000004\n"
+      // 0x00000011:
+      "      - AbbrCode:        0x00000002\n"
+      "        Values:\n"
+      "          - Value:           0x0000000000000007\n" // DW_ATE_unsigned
+      "          - Value:           0x0000000000000008\n"
+      // 0x00000014:
+      "      - AbbrCode:        0x00000002\n"
+      "        Values:\n"
+      "          - Value:           0x0000000000000005\n" // DW_ATE_signed
+      "          - Value:           0x0000000000000008\n"
+      // 0x00000017:
+      "      - AbbrCode:        0x00000002\n"
+      "        Values:\n"
+      "          - Value:           0x0000000000000008\n" // DW_ATE_unsigned_char
+      "          - Value:           0x0000000000000001\n"
+      // 0x0000001a:
+      "      - AbbrCode:        0x00000002\n"
+      "        Values:\n"
+      "          - Value:           0x0000000000000006\n" // DW_ATE_signed_char
+      "          - Value:           0x0000000000000001\n"
+      // 0x0000001d:
+      "      - AbbrCode:        0x00000002\n"
+      "        Values:\n"
+      "          - Value:           0x000000000000000b\n" // DW_ATE_numeric_string
+      "          - Value:           0x0000000000000001\n"
+      ""
+      "      - AbbrCode:        0x00000000\n"
+      "        Values:          []\n";
+  uint8_t offs_uint32_t = 0x0000000e;
+  uint8_t offs_uint64_t = 0x00000011;
+  uint8_t offs_sint64_t = 0x00000014;
+  uint8_t offs_uchar = 0x00000017;
+  uint8_t offs_schar = 0x0000001a;
+
+  //
+  // Setup. Parse the debug info sections from the YAML description.
+  //
+  auto sections_map = llvm::DWARFYAML::EmitDebugSections(yamldata, true);
+  ASSERT_TRUE((bool)sections_map);
+  ArchSpec arch("i386-unknown-linux");
+  FileSystem::Initialize();
+  auto module_sp = std::make_shared<YAMLModule>(arch);
+  lldb::ObjectFileSP objfile_sp =
+      std::make_shared<YAMLObjectFile>(module_sp, *sections_map);
+  module_sp->SetObjectFile(objfile_sp);
+  SymbolFileDWARF symfile_dwarf(objfile_sp, nullptr);
+
+  lldb::user_id_t uid = 0;
+  llvm::StringRef raw_debug_info = (*sections_map)["debug_info"]->getBuffer();
+  lldb_private::DataExtractor debug_info(
+      raw_debug_info.data(), raw_debug_info.size(), objfile_sp->GetByteOrder(),
+      objfile_sp->GetAddressByteSize());
+  lldb::offset_t offset_ptr = 0;
+  llvm::Expected<DWARFUnitSP> dwarf_unit = DWARFUnit::extract(
+      symfile_dwarf, uid,
+      *static_cast<lldb_private::DWARFDataExtractor *>(&debug_info),
+      DIERef::DebugInfo, &offset_ptr);
+  ASSERT_TRUE((bool)dwarf_unit);
+
+  //
+  // Actual tests.
+  //
+
+  // Constant is given as little-endian.
+  bool is_signed = true;
+  bool not_signed = false;
+
+  // Truncate to default unspecified (pointer-sized) type.
+  EXPECT_THAT_EXPECTED(Evaluate({DW_OP_const8u, 0x11, 0x22, 0x33, 0x44, 0x55,
+                                 0x66, 0x77, 0x88, DW_OP_convert, 0x00},
+                                module_sp, dwarf_unit->get()),
+                       llvm::HasValue(GetScalar(32, 0x44332211, not_signed)));
+  // Truncate to 32 bits.
+  EXPECT_THAT_EXPECTED(
+      Evaluate({DW_OP_const8u, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88,
+                DW_OP_convert, offs_uint32_t},
+               module_sp, dwarf_unit->get()),
+      llvm::HasValue(GetScalar(32, 0x44332211, not_signed)));
+
+  // Leave as is.
+  EXPECT_THAT_EXPECTED(
+      Evaluate({DW_OP_const8u, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88,
+                DW_OP_convert, offs_uint64_t},
+               module_sp, dwarf_unit->get()),
+      llvm::HasValue(GetScalar(64, 0x8877665544332211, not_signed)));
+
+  // Sign-extend to 64 bits.
+  EXPECT_THAT_EXPECTED(
+      Evaluate({DW_OP_const4s, 0xcc, 0xdd, 0xee, 0xff, //
+                DW_OP_convert, offs_sint64_t},
+               module_sp, dwarf_unit->get()),
+      llvm::HasValue(GetScalar(64, 0xffffffffffeeddcc, is_signed)));
+
+  // Truncate to 8 bits.
+  EXPECT_THAT_EXPECTED(
+      Evaluate({DW_OP_const4s, 'A', 'B', 'C', 'D', 0xee, 0xff, //
+                DW_OP_convert, offs_uchar},
+               module_sp, dwarf_unit->get()),
+      llvm::HasValue(GetScalar(8, 'A', not_signed)));
+
+  // Also truncate to 8 bits.
+  EXPECT_THAT_EXPECTED(
+      Evaluate({DW_OP_const4s, 'A', 'B', 'C', 'D', 0xee, 0xff, //
+                DW_OP_convert, offs_schar},
+               module_sp, dwarf_unit->get()),
+      llvm::HasValue(GetScalar(8, 'A', is_signed)));
+
+  //
+  // Errors.
+  //
+
+  // No Module.
+  EXPECT_THAT_ERROR(Evaluate({DW_OP_const1s, 'X', DW_OP_convert, 0x00}, nullptr,
+                             dwarf_unit->get())
+                        .takeError(),
+                    llvm::Failed());
+
+  // No DIE.
+  EXPECT_THAT_ERROR(Evaluate({DW_OP_const1s, 'X', DW_OP_convert, 0x01},
+                             module_sp, dwarf_unit->get())
+                        .takeError(),
+                    llvm::Failed());
+
+  // Unsupported.
+  EXPECT_THAT_ERROR(Evaluate({DW_OP_const1s, 'X', DW_OP_convert, 0x1d}, nullptr,
+                             dwarf_unit->get())
+                        .takeError(),
+                    llvm::Failed());
+
+  //
+  // Tear down.
+  //
+  FileSystem::Terminate();
+}

lldb/trunk/unittests/Utility/ScalarTest.cpp

 TEST(ScalarTest, APIntConstructor) {
   auto width_array = {8, 16, 32};
   for (auto &w : width_array) {
     Scalar A(APInt(w, 24));
     EXPECT_EQ(A.GetType(), Scalar::e_sint);
   }
 
   Scalar B(APInt(64, 42));
-  EXPECT_EQ(B.GetType(), Scalar::e_slonglong);
+  EXPECT_EQ(B.GetType(), Scalar::GetBestTypeForBitSize(64, true));
   Scalar C(APInt(128, 96));
   EXPECT_EQ(C.GetType(), Scalar::e_sint128);
   Scalar D(APInt(256, 156));
   EXPECT_EQ(D.GetType(), Scalar::e_sint256);
   Scalar E(APInt(512, 456));
   EXPECT_EQ(E.GetType(), Scalar::e_sint512);
 }