llvm/lib/CodeGen/AsmPrinter/DIEHash.cpp - toolchain/llvm-project - Gitiles

 //===-- llvm/CodeGen/DIEHash.cpp - Dwarf Hashing Framework ----------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains support for DWARF4 hashing of DIEs.
 //
 //===----------------------------------------------------------------------===//

 #include "DIEHash.h"
 #include "ByteStreamer.h"
 #include "DwarfDebug.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/CodeGen/AsmPrinter.h"
 #include "llvm/CodeGen/DIE.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/MD5.h"
 #include "llvm/Support/raw_ostream.h"

 using namespace llvm;

 #define DEBUG_TYPE "dwarfdebug"

 /// Grabs the string in whichever attribute is passed in and returns
 /// a reference to it.
 static StringRef getDIEStringAttr(const DIE &Die, uint16_t Attr) {
   // Iterate through all the attributes until we find the one we're
   // looking for, if we can't find it return an empty string.
   for (const auto &V : Die.values())
     if (V.getAttribute() == Attr)
       return V.getDIEString().getString();

   return StringRef("");
 }

 /// Adds the string in \p Str to the hash. This also hashes
 /// a trailing NULL with the string.
 void DIEHash::addString(StringRef Str) {
   LLVM_DEBUG(dbgs() << "Adding string " << Str << " to hash.\n");
   Hash.update(Str);
   Hash.update(makeArrayRef((uint8_t)'\0'));
 }

 // FIXME: The LEB128 routines are copied and only slightly modified out of
 // LEB128.h.

 /// Adds the unsigned in \p Value to the hash encoded as a ULEB128.
 void DIEHash::addULEB128(uint64_t Value) {
   LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
   do {
     uint8_t Byte = Value & 0x7f;
     Value >>= 7;
     if (Value != 0)
       Byte |= 0x80; // Mark this byte to show that more bytes will follow.
     Hash.update(Byte);
   } while (Value != 0);
 }

 void DIEHash::addSLEB128(int64_t Value) {
   LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
   bool More;
   do {
     uint8_t Byte = Value & 0x7f;
     Value >>= 7;
     More = !((((Value == 0) && ((Byte & 0x40) == 0)) ||
               ((Value == -1) && ((Byte & 0x40) != 0))));
     if (More)
       Byte |= 0x80; // Mark this byte to show that more bytes will follow.
     Hash.update(Byte);
   } while (More);
 }

 /// Including \p Parent adds the context of Parent to the hash..
 void DIEHash::addParentContext(const DIE &Parent) {

   LLVM_DEBUG(dbgs() << "Adding parent context to hash...\n");

   // [7.27.2] For each surrounding type or namespace beginning with the
   // outermost such construct...
   SmallVector<const DIE *, 1> Parents;
   const DIE *Cur = &Parent;
   while (Cur->getParent()) {
     Parents.push_back(Cur);
     Cur = Cur->getParent();
   }
   assert(Cur->getTag() == dwarf::DW_TAG_compile_unit ||
          Cur->getTag() == dwarf::DW_TAG_type_unit);

   // Reverse iterate over our list to go from the outermost construct to the
   // innermost.
   for (SmallVectorImpl<const DIE *>::reverse_iterator I = Parents.rbegin(),
                                                       E = Parents.rend();
        I != E; ++I) {
     const DIE &Die = **I;

     // ... Append the letter "C" to the sequence...
     addULEB128('C');

     // ... Followed by the DWARF tag of the construct...
     addULEB128(Die.getTag());

     // ... Then the name, taken from the DW_AT_name attribute.
     StringRef Name = getDIEStringAttr(Die, dwarf::DW_AT_name);
     LLVM_DEBUG(dbgs() << "... adding context: " << Name << "\n");
     if (!Name.empty())
       addString(Name);
   }
 }

 // Collect all of the attributes for a particular DIE in single structure.
 void DIEHash::collectAttributes(const DIE &Die, DIEAttrs &Attrs) {

   for (const auto &V : Die.values()) {
     LLVM_DEBUG(dbgs() << "Attribute: "
                       << dwarf::AttributeString(V.getAttribute())
                       << " added.\n");
     switch (V.getAttribute()) {
 #define HANDLE_DIE_HASH_ATTR(NAME)                                             \
   case dwarf::NAME:                                                            \
     Attrs.NAME = V;                                                            \
     break;
 #include "DIEHashAttributes.def"
     default:
       break;
     }
   }
 }

 void DIEHash::hashShallowTypeReference(dwarf::Attribute Attribute,
                                        const DIE &Entry, StringRef Name) {
   // append the letter 'N'
   addULEB128('N');

   // the DWARF attribute code (DW_AT_type or DW_AT_friend),
   addULEB128(Attribute);

   // the context of the tag,
   if (const DIE *Parent = Entry.getParent())
     addParentContext(*Parent);

   // the letter 'E',
   addULEB128('E');

   // and the name of the type.
   addString(Name);

   // Currently DW_TAG_friends are not used by Clang, but if they do become so,
   // here's the relevant spec text to implement:
   //
   // For DW_TAG_friend, if the referenced entry is the DW_TAG_subprogram,
   // the context is omitted and the name to be used is the ABI-specific name
   // of the subprogram (e.g., the mangled linker name).
 }

 void DIEHash::hashRepeatedTypeReference(dwarf::Attribute Attribute,
                                         unsigned DieNumber) {
   // a) If T is in the list of [previously hashed types], use the letter
   // 'R' as the marker
   addULEB128('R');

   addULEB128(Attribute);

   // and use the unsigned LEB128 encoding of [the index of T in the
   // list] as the attribute value;
   addULEB128(DieNumber);
 }

 void DIEHash::hashDIEEntry(dwarf::Attribute Attribute, dwarf::Tag Tag,
                            const DIE &Entry) {
   assert(Tag != dwarf::DW_TAG_friend && "No current LLVM clients emit friend "
                                         "tags. Add support here when there's "
                                         "a use case");
   // Step 5
   // If the tag in Step 3 is one of [the below tags]
   if ((Tag == dwarf::DW_TAG_pointer_type ||
        Tag == dwarf::DW_TAG_reference_type ||
        Tag == dwarf::DW_TAG_rvalue_reference_type ||
        Tag == dwarf::DW_TAG_ptr_to_member_type) &&
       // and the referenced type (via the [below attributes])
       // FIXME: This seems overly restrictive, and causes hash mismatches
       // there's a decl/def difference in the containing type of a
       // ptr_to_member_type, but it's what DWARF says, for some reason.
       Attribute == dwarf::DW_AT_type) {
     // ... has a DW_AT_name attribute,
     StringRef Name = getDIEStringAttr(Entry, dwarf::DW_AT_name);
     if (!Name.empty()) {
       hashShallowTypeReference(Attribute, Entry, Name);
       return;
     }
   }

   unsigned &DieNumber = Numbering[&Entry];
   if (DieNumber) {
     hashRepeatedTypeReference(Attribute, DieNumber);
     return;
   }

   // otherwise, b) use the letter 'T' as the marker, ...
   addULEB128('T');

   addULEB128(Attribute);

   // ... process the type T recursively by performing Steps 2 through 7, and
   // use the result as the attribute value.
   DieNumber = Numbering.size();
   computeHash(Entry);
 }

 // Hash all of the values in a block like set of values. This assumes that
 // all of the data is going to be added as integers.
 void DIEHash::hashBlockData(const DIE::const_value_range &Values) {
   for (const auto &V : Values)
     Hash.update((uint64_t)V.getDIEInteger().getValue());
 }

 // Hash the contents of a loclistptr class.
 void DIEHash::hashLocList(const DIELocList &LocList) {
   HashingByteStreamer Streamer(*this);
   DwarfDebug &DD = *AP->getDwarfDebug();
   const DebugLocStream &Locs = DD.getDebugLocs();
   for (const auto &Entry : Locs.getEntries(Locs.getList(LocList.getValue())))
     DD.emitDebugLocEntry(Streamer, Entry);
 }

 // Hash an individual attribute \param Attr based on the type of attribute and
 // the form.
 void DIEHash::hashAttribute(const DIEValue &Value, dwarf::Tag Tag) {
   dwarf::Attribute Attribute = Value.getAttribute();

   // Other attribute values use the letter 'A' as the marker, and the value
   // consists of the form code (encoded as an unsigned LEB128 value) followed by
   // the encoding of the value according to the form code. To ensure
   // reproducibility of the signature, the set of forms used in the signature
   // computation is limited to the following: DW_FORM_sdata, DW_FORM_flag,
   // DW_FORM_string, and DW_FORM_block.

   switch (Value.getType()) {
   case DIEValue::isNone:
     llvm_unreachable("Expected valid DIEValue");

     // 7.27 Step 3
     // ... An attribute that refers to another type entry T is processed as
     // follows:
   case DIEValue::isEntry:
     hashDIEEntry(Attribute, Tag, Value.getDIEEntry().getEntry());
     break;
   case DIEValue::isInteger: {
     addULEB128('A');
     addULEB128(Attribute);
     switch (Value.getForm()) {
     case dwarf::DW_FORM_data1:
     case dwarf::DW_FORM_data2:
     case dwarf::DW_FORM_data4:
     case dwarf::DW_FORM_data8:
     case dwarf::DW_FORM_udata:
     case dwarf::DW_FORM_sdata:
       addULEB128(dwarf::DW_FORM_sdata);
       addSLEB128((int64_t)Value.getDIEInteger().getValue());
       break;
     // DW_FORM_flag_present is just flag with a value of one. We still give it a
     // value so just use the value.
     case dwarf::DW_FORM_flag_present:
     case dwarf::DW_FORM_flag:
       addULEB128(dwarf::DW_FORM_flag);
       addULEB128((int64_t)Value.getDIEInteger().getValue());
       break;
     default:
       llvm_unreachable("Unknown integer form!");
     }
     break;
   }
   case DIEValue::isString:
     addULEB128('A');
     addULEB128(Attribute);
     addULEB128(dwarf::DW_FORM_string);
     addString(Value.getDIEString().getString());
     break;
   case DIEValue::isInlineString:
     addULEB128('A');
     addULEB128(Attribute);
     addULEB128(dwarf::DW_FORM_string);
     addString(Value.getDIEInlineString().getString());
     break;
   case DIEValue::isBlock:
   case DIEValue::isLoc:
   case DIEValue::isLocList:
     addULEB128('A');
     addULEB128(Attribute);
     addULEB128(dwarf::DW_FORM_block);
     if (Value.getType() == DIEValue::isBlock) {
       addULEB128(Value.getDIEBlock().ComputeSize(AP));
       hashBlockData(Value.getDIEBlock().values());
     } else if (Value.getType() == DIEValue::isLoc) {
       addULEB128(Value.getDIELoc().ComputeSize(AP));
       hashBlockData(Value.getDIELoc().values());
     } else {
       // We could add the block length, but that would take
       // a bit of work and not add a lot of uniqueness
       // to the hash in some way we could test.
       hashLocList(Value.getDIELocList());
     }
     break;
     // FIXME: It's uncertain whether or not we should handle this at the moment.
   case DIEValue::isExpr:
   case DIEValue::isLabel:
   case DIEValue::isDelta:
     llvm_unreachable("Add support for additional value types.");
   }
 }

 // Go through the attributes from \param Attrs in the order specified in 7.27.4
 // and hash them.
 void DIEHash::hashAttributes(const DIEAttrs &Attrs, dwarf::Tag Tag) {
 #define HANDLE_DIE_HASH_ATTR(NAME)                                             \
   {                                                                            \
     if (Attrs.NAME)                                                           \
       hashAttribute(Attrs.NAME, Tag);                                         \
   }
 #include "DIEHashAttributes.def"
   // FIXME: Add the extended attributes.
 }

 // Add all of the attributes for \param Die to the hash.
 void DIEHash::addAttributes(const DIE &Die) {
   DIEAttrs Attrs = {};
   collectAttributes(Die, Attrs);
   hashAttributes(Attrs, Die.getTag());
 }

 void DIEHash::hashNestedType(const DIE &Die, StringRef Name) {
   // 7.27 Step 7
   // ... append the letter 'S',
   addULEB128('S');

   // the tag of C,
   addULEB128(Die.getTag());

   // and the name.
   addString(Name);
 }

 // Compute the hash of a DIE. This is based on the type signature computation
 // given in section 7.27 of the DWARF4 standard. It is the md5 hash of a
 // flattened description of the DIE.
 void DIEHash::computeHash(const DIE &Die) {
   // Append the letter 'D', followed by the DWARF tag of the DIE.
   addULEB128('D');
   addULEB128(Die.getTag());

   // Add each of the attributes of the DIE.
   addAttributes(Die);

   // Then hash each of the children of the DIE.
   for (auto &C : Die.children()) {
     // 7.27 Step 7
     // If C is a nested type entry or a member function entry, ...
     if (isType(C.getTag()) || C.getTag() == dwarf::DW_TAG_subprogram) {
       StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name);
       // ... and has a DW_AT_name attribute
       if (!Name.empty()) {
         hashNestedType(C, Name);
         continue;
       }
     }
     computeHash(C);
   }

   // Following the last (or if there are no children), append a zero byte.
   Hash.update(makeArrayRef((uint8_t)'\0'));
 }

 /// This is based on the type signature computation given in section 7.27 of the
 /// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
 /// with the inclusion of the full CU and all top level CU entities.
 // TODO: Initialize the type chain at 0 instead of 1 for CU signatures.
 uint64_t DIEHash::computeCUSignature(StringRef DWOName, const DIE &Die) {
   Numbering.clear();
   Numbering[&Die] = 1;

   if (!DWOName.empty())
     Hash.update(DWOName);
   // Hash the DIE.
   computeHash(Die);

   // Now return the result.
   MD5::MD5Result Result;
   Hash.final(Result);

   // ... take the least significant 8 bytes and return those. Our MD5
   // implementation always returns its results in little endian, so we actually
   // need the "high" word.
   return Result.high();
 }

 /// This is based on the type signature computation given in section 7.27 of the
 /// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
 /// with the inclusion of additional forms not specifically called out in the
 /// standard.
 uint64_t DIEHash::computeTypeSignature(const DIE &Die) {
   Numbering.clear();
   Numbering[&Die] = 1;

   if (const DIE *Parent = Die.getParent())
     addParentContext(*Parent);

   // Hash the DIE.
   computeHash(Die);

   // Now return the result.
   MD5::MD5Result Result;
   Hash.final(Result);

   // ... take the least significant 8 bytes and return those. Our MD5
   // implementation always returns its results in little endian, so we actually
   // need the "high" word.
   return Result.high();
 }
	//===-- llvm/CodeGen/DIEHash.cpp - Dwarf Hashing Framework ----------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This file contains support for DWARF4 hashing of DIEs.
	//
	//===----------------------------------------------------------------------===//

	#include "DIEHash.h"
	#include "ByteStreamer.h"
	#include "DwarfDebug.h"
	#include "llvm/ADT/ArrayRef.h"
	#include "llvm/ADT/StringRef.h"
	#include "llvm/BinaryFormat/Dwarf.h"
	#include "llvm/CodeGen/AsmPrinter.h"
	#include "llvm/CodeGen/DIE.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/Support/Endian.h"
	#include "llvm/Support/MD5.h"
	#include "llvm/Support/raw_ostream.h"

	using namespace llvm;

	#define DEBUG_TYPE "dwarfdebug"

	/// Grabs the string in whichever attribute is passed in and returns
	/// a reference to it.
	static StringRef getDIEStringAttr(const DIE &Die, uint16_t Attr) {
	// Iterate through all the attributes until we find the one we're
	// looking for, if we can't find it return an empty string.
	for (const auto &V : Die.values())
	if (V.getAttribute() == Attr)
	return V.getDIEString().getString();

	return StringRef("");
	}

	/// Adds the string in \p Str to the hash. This also hashes
	/// a trailing NULL with the string.
	void DIEHash::addString(StringRef Str) {
	LLVM_DEBUG(dbgs() << "Adding string " << Str << " to hash.\n");
	Hash.update(Str);
	Hash.update(makeArrayRef((uint8_t)'\0'));
	}

	// FIXME: The LEB128 routines are copied and only slightly modified out of
	// LEB128.h.

	/// Adds the unsigned in \p Value to the hash encoded as a ULEB128.
	void DIEHash::addULEB128(uint64_t Value) {
	LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
	do {
	uint8_t Byte = Value & 0x7f;
	Value >>= 7;
	if (Value != 0)
	Byte \|= 0x80; // Mark this byte to show that more bytes will follow.
	Hash.update(Byte);
	} while (Value != 0);
	}

	void DIEHash::addSLEB128(int64_t Value) {
	LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
	bool More;
	do {
	uint8_t Byte = Value & 0x7f;
	Value >>= 7;
	More = !((((Value == 0) && ((Byte & 0x40) == 0)) \|\|
	((Value == -1) && ((Byte & 0x40) != 0))));
	if (More)
	Byte \|= 0x80; // Mark this byte to show that more bytes will follow.
	Hash.update(Byte);
	} while (More);
	}

	/// Including \p Parent adds the context of Parent to the hash..
	void DIEHash::addParentContext(const DIE &Parent) {

	LLVM_DEBUG(dbgs() << "Adding parent context to hash...\n");

	// [7.27.2] For each surrounding type or namespace beginning with the
	// outermost such construct...
	SmallVector<const DIE *, 1> Parents;
	const DIE *Cur = &Parent;
	while (Cur->getParent()) {
	Parents.push_back(Cur);
	Cur = Cur->getParent();
	}
	assert(Cur->getTag() == dwarf::DW_TAG_compile_unit \|\|
	Cur->getTag() == dwarf::DW_TAG_type_unit);

	// Reverse iterate over our list to go from the outermost construct to the
	// innermost.
	for (SmallVectorImpl<const DIE *>::reverse_iterator I = Parents.rbegin(),
	E = Parents.rend();
	I != E; ++I) {
	const DIE &Die = **I;

	// ... Append the letter "C" to the sequence...
	addULEB128('C');

	// ... Followed by the DWARF tag of the construct...
	addULEB128(Die.getTag());

	// ... Then the name, taken from the DW_AT_name attribute.
	StringRef Name = getDIEStringAttr(Die, dwarf::DW_AT_name);
	LLVM_DEBUG(dbgs() << "... adding context: " << Name << "\n");
	if (!Name.empty())
	addString(Name);
	}
	}

	// Collect all of the attributes for a particular DIE in single structure.
	void DIEHash::collectAttributes(const DIE &Die, DIEAttrs &Attrs) {

	for (const auto &V : Die.values()) {
	LLVM_DEBUG(dbgs() << "Attribute: "
	<< dwarf::AttributeString(V.getAttribute())
	<< " added.\n");
	switch (V.getAttribute()) {
	#define HANDLE_DIE_HASH_ATTR(NAME) \
	case dwarf::NAME: \
	Attrs.NAME = V; \
	break;
	#include "DIEHashAttributes.def"
	default:
	break;
	}
	}
	}

	void DIEHash::hashShallowTypeReference(dwarf::Attribute Attribute,
	const DIE &Entry, StringRef Name) {
	// append the letter 'N'
	addULEB128('N');

	// the DWARF attribute code (DW_AT_type or DW_AT_friend),
	addULEB128(Attribute);

	// the context of the tag,
	if (const DIE *Parent = Entry.getParent())
	addParentContext(*Parent);

	// the letter 'E',
	addULEB128('E');

	// and the name of the type.
	addString(Name);

	// Currently DW_TAG_friends are not used by Clang, but if they do become so,
	// here's the relevant spec text to implement:
	//
	// For DW_TAG_friend, if the referenced entry is the DW_TAG_subprogram,
	// the context is omitted and the name to be used is the ABI-specific name
	// of the subprogram (e.g., the mangled linker name).
	}

	void DIEHash::hashRepeatedTypeReference(dwarf::Attribute Attribute,
	unsigned DieNumber) {
	// a) If T is in the list of [previously hashed types], use the letter
	// 'R' as the marker
	addULEB128('R');

	addULEB128(Attribute);

	// and use the unsigned LEB128 encoding of [the index of T in the
	// list] as the attribute value;
	addULEB128(DieNumber);
	}

	void DIEHash::hashDIEEntry(dwarf::Attribute Attribute, dwarf::Tag Tag,
	const DIE &Entry) {
	assert(Tag != dwarf::DW_TAG_friend && "No current LLVM clients emit friend "
	"tags. Add support here when there's "
	"a use case");
	// Step 5
	// If the tag in Step 3 is one of [the below tags]
	if ((Tag == dwarf::DW_TAG_pointer_type \|\|
	Tag == dwarf::DW_TAG_reference_type \|\|
	Tag == dwarf::DW_TAG_rvalue_reference_type \|\|
	Tag == dwarf::DW_TAG_ptr_to_member_type) &&
	// and the referenced type (via the [below attributes])
	// FIXME: This seems overly restrictive, and causes hash mismatches
	// there's a decl/def difference in the containing type of a
	// ptr_to_member_type, but it's what DWARF says, for some reason.
	Attribute == dwarf::DW_AT_type) {
	// ... has a DW_AT_name attribute,
	StringRef Name = getDIEStringAttr(Entry, dwarf::DW_AT_name);
	if (!Name.empty()) {
	hashShallowTypeReference(Attribute, Entry, Name);
	return;
	}
	}

	unsigned &DieNumber = Numbering[&Entry];
	if (DieNumber) {
	hashRepeatedTypeReference(Attribute, DieNumber);
	return;
	}

	// otherwise, b) use the letter 'T' as the marker, ...
	addULEB128('T');

	addULEB128(Attribute);

	// ... process the type T recursively by performing Steps 2 through 7, and
	// use the result as the attribute value.
	DieNumber = Numbering.size();
	computeHash(Entry);
	}

	// Hash all of the values in a block like set of values. This assumes that
	// all of the data is going to be added as integers.
	void DIEHash::hashBlockData(const DIE::const_value_range &Values) {
	for (const auto &V : Values)
	Hash.update((uint64_t)V.getDIEInteger().getValue());
	}

	// Hash the contents of a loclistptr class.
	void DIEHash::hashLocList(const DIELocList &LocList) {
	HashingByteStreamer Streamer(*this);
	DwarfDebug &DD = *AP->getDwarfDebug();
	const DebugLocStream &Locs = DD.getDebugLocs();
	for (const auto &Entry : Locs.getEntries(Locs.getList(LocList.getValue())))
	DD.emitDebugLocEntry(Streamer, Entry);
	}

	// Hash an individual attribute \param Attr based on the type of attribute and
	// the form.
	void DIEHash::hashAttribute(const DIEValue &Value, dwarf::Tag Tag) {
	dwarf::Attribute Attribute = Value.getAttribute();

	// Other attribute values use the letter 'A' as the marker, and the value
	// consists of the form code (encoded as an unsigned LEB128 value) followed by
	// the encoding of the value according to the form code. To ensure
	// reproducibility of the signature, the set of forms used in the signature
	// computation is limited to the following: DW_FORM_sdata, DW_FORM_flag,
	// DW_FORM_string, and DW_FORM_block.

	switch (Value.getType()) {
	case DIEValue::isNone:
	llvm_unreachable("Expected valid DIEValue");

	// 7.27 Step 3
	// ... An attribute that refers to another type entry T is processed as
	// follows:
	case DIEValue::isEntry:
	hashDIEEntry(Attribute, Tag, Value.getDIEEntry().getEntry());
	break;
	case DIEValue::isInteger: {
	addULEB128('A');
	addULEB128(Attribute);
	switch (Value.getForm()) {
	case dwarf::DW_FORM_data1:
	case dwarf::DW_FORM_data2:
	case dwarf::DW_FORM_data4:
	case dwarf::DW_FORM_data8:
	case dwarf::DW_FORM_udata:
	case dwarf::DW_FORM_sdata:
	addULEB128(dwarf::DW_FORM_sdata);
	addSLEB128((int64_t)Value.getDIEInteger().getValue());
	break;
	// DW_FORM_flag_present is just flag with a value of one. We still give it a
	// value so just use the value.
	case dwarf::DW_FORM_flag_present:
	case dwarf::DW_FORM_flag:
	addULEB128(dwarf::DW_FORM_flag);
	addULEB128((int64_t)Value.getDIEInteger().getValue());
	break;
	default:
	llvm_unreachable("Unknown integer form!");
	}
	break;
	}
	case DIEValue::isString:
	addULEB128('A');
	addULEB128(Attribute);
	addULEB128(dwarf::DW_FORM_string);
	addString(Value.getDIEString().getString());
	break;
	case DIEValue::isInlineString:
	addULEB128('A');
	addULEB128(Attribute);
	addULEB128(dwarf::DW_FORM_string);
	addString(Value.getDIEInlineString().getString());
	break;
	case DIEValue::isBlock:
	case DIEValue::isLoc:
	case DIEValue::isLocList:
	addULEB128('A');
	addULEB128(Attribute);
	addULEB128(dwarf::DW_FORM_block);
	if (Value.getType() == DIEValue::isBlock) {
	addULEB128(Value.getDIEBlock().ComputeSize(AP));
	hashBlockData(Value.getDIEBlock().values());
	} else if (Value.getType() == DIEValue::isLoc) {
	addULEB128(Value.getDIELoc().ComputeSize(AP));
	hashBlockData(Value.getDIELoc().values());
	} else {
	// We could add the block length, but that would take
	// a bit of work and not add a lot of uniqueness
	// to the hash in some way we could test.
	hashLocList(Value.getDIELocList());
	}
	break;
	// FIXME: It's uncertain whether or not we should handle this at the moment.
	case DIEValue::isExpr:
	case DIEValue::isLabel:
	case DIEValue::isDelta:
	llvm_unreachable("Add support for additional value types.");
	}
	}

	// Go through the attributes from \param Attrs in the order specified in 7.27.4
	// and hash them.
	void DIEHash::hashAttributes(const DIEAttrs &Attrs, dwarf::Tag Tag) {
	#define HANDLE_DIE_HASH_ATTR(NAME) \
	{ \
	if (Attrs.NAME) \
	hashAttribute(Attrs.NAME, Tag); \
	}
	#include "DIEHashAttributes.def"
	// FIXME: Add the extended attributes.
	}

	// Add all of the attributes for \param Die to the hash.
	void DIEHash::addAttributes(const DIE &Die) {
	DIEAttrs Attrs = {};
	collectAttributes(Die, Attrs);
	hashAttributes(Attrs, Die.getTag());
	}

	void DIEHash::hashNestedType(const DIE &Die, StringRef Name) {
	// 7.27 Step 7
	// ... append the letter 'S',
	addULEB128('S');

	// the tag of C,
	addULEB128(Die.getTag());

	// and the name.
	addString(Name);
	}

	// Compute the hash of a DIE. This is based on the type signature computation
	// given in section 7.27 of the DWARF4 standard. It is the md5 hash of a
	// flattened description of the DIE.
	void DIEHash::computeHash(const DIE &Die) {
	// Append the letter 'D', followed by the DWARF tag of the DIE.
	addULEB128('D');
	addULEB128(Die.getTag());

	// Add each of the attributes of the DIE.
	addAttributes(Die);

	// Then hash each of the children of the DIE.
	for (auto &C : Die.children()) {
	// 7.27 Step 7
	// If C is a nested type entry or a member function entry, ...
	if (isType(C.getTag()) \|\| C.getTag() == dwarf::DW_TAG_subprogram) {
	StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name);
	// ... and has a DW_AT_name attribute
	if (!Name.empty()) {
	hashNestedType(C, Name);
	continue;
	}
	}
	computeHash(C);
	}

	// Following the last (or if there are no children), append a zero byte.
	Hash.update(makeArrayRef((uint8_t)'\0'));
	}

	/// This is based on the type signature computation given in section 7.27 of the
	/// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
	/// with the inclusion of the full CU and all top level CU entities.
	// TODO: Initialize the type chain at 0 instead of 1 for CU signatures.
	uint64_t DIEHash::computeCUSignature(StringRef DWOName, const DIE &Die) {
	Numbering.clear();
	Numbering[&Die] = 1;

	if (!DWOName.empty())
	Hash.update(DWOName);
	// Hash the DIE.
	computeHash(Die);

	// Now return the result.
	MD5::MD5Result Result;
	Hash.final(Result);

	// ... take the least significant 8 bytes and return those. Our MD5
	// implementation always returns its results in little endian, so we actually
	// need the "high" word.
	return Result.high();
	}

	/// This is based on the type signature computation given in section 7.27 of the
	/// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
	/// with the inclusion of additional forms not specifically called out in the
	/// standard.
	uint64_t DIEHash::computeTypeSignature(const DIE &Die) {
	Numbering.clear();
	Numbering[&Die] = 1;

	if (const DIE *Parent = Die.getParent())
	addParentContext(*Parent);

	// Hash the DIE.
	computeHash(Die);

	// Now return the result.
	MD5::MD5Result Result;
	Hash.final(Result);

	// ... take the least significant 8 bytes and return those. Our MD5
	// implementation always returns its results in little endian, so we actually
	// need the "high" word.
	return Result.high();
	}