Merge clang, llvm, lld, lldb, compiler-rt and libc++ 5.0.0 release.

MFC r309126 (by emaste):

  Correct lld llvm-tblgen dependency file name

MFC r309169:

  Get rid of separate Subversion mergeinfo properties for llvm-dwarfdump
  and llvm-lto.  The mergeinfo confuses Subversion enormously, and these
  directories will just use the mergeinfo for llvm itself.

MFC r312765:

  Pull in r276136 from upstream llvm trunk (by Wei Mi):

    Use ValueOffsetPair to enhance value reuse during SCEV expansion.

    In D12090, the ExprValueMap was added to reuse existing value during
    SCEV expansion. However, const folding and sext/zext distribution can
    make the reuse still difficult.

    A simplified case is: suppose we know S1 expands to V1 in
    ExprValueMap, and
      S1 = S2 + C_a
      S3 = S2 + C_b
    where C_a and C_b are different SCEVConstants. Then we'd like to
    expand S3 as V1 - C_a + C_b instead of expanding S2 literally. It is
    helpful when S2 is a complex SCEV expr and S2 has no entry in
    ExprValueMap, which is usually caused by the fact that S3 is
    generated from S1 after const folding.

    In order to do that, we represent ExprValueMap as a mapping from SCEV
    to ValueOffsetPair. We will save both S1->{V1, 0} and S2->{V1, C_a}
    into the ExprValueMap when we create SCEV for V1. When S3 is
    expanded, it will first expand S2 to V1 - C_a because of S2->{V1,
    C_a} in the map, then expand S3 to V1 - C_a + C_b.

    Differential Revision: https://reviews.llvm.org/D21313

  This should fix assertion failures when building OpenCV >= 3.1.

  PR:		215649

MFC r312831:

  Revert r312765 for now, since it causes assertions when building
  lang/spidermonkey24.

  Reported by:	antoine
  PR:		215649

MFC r316511 (by jhb):

  Add an implementation of __ffssi2() derived from __ffsdi2().

  Newer versions of GCC include an __ffssi2() symbol in libgcc and the
  compiler can emit calls to it in generated code.  This is true for at
  least GCC 6.2 when compiling world for mips and mips64.

  Reviewed by:	jmallett, dim
  Sponsored by:	DARPA / AFRL
  Differential Revision:	https://reviews.freebsd.org/D10086

MFC r318601 (by adrian):

  [libcompiler-rt] add bswapdi2/bswapsi2

  This is required for mips gcc 6.3 userland to build/run.

  Reviewed by:	emaste, dim
  Approved by:	emaste
  Differential Revision:	https://reviews.freebsd.org/D10838

MFC r318884 (by emaste):

  lldb: map TRAP_CAP to a trace trap

  In the absense of a more specific handler for TRAP_CAP (generated by
  ENOTCAPABLE or ECAPMODE while in capability mode) treat it as a trace
  trap.

  Example usage (testing the bug in PR219173):

  % proccontrol -m trapcap lldb usr.bin/hexdump/obj/hexdump -- -Cv -s 1 /bin/ls
  ...
  (lldb) run
  Process 12980 launching
  Process 12980 launched: '.../usr.bin/hexdump/obj/hexdump' (x86_64)
  Process 12980 stopped
  * thread #1, stop reason = trace
      frame #0: 0x0000004b80c65f1a libc.so.7`__sys_lseek + 10
  ...

  In the future we should have LLDB control the trapcap procctl itself
  (as it does with ASLR), as well as report a specific stop reason.
  This change eliminates an assertion failure from LLDB for now.

MFC r319796:

  Remove a few unneeded files from libllvm, libclang and liblldb.

MFC r319885 (by emaste):

  lld: ELF: Fix ICF crash on absolute symbol relocations.

  If two sections contained relocations to absolute symbols with the same
  value we would crash when trying to access their sections. Add a check that
  both symbols point to sections before accessing their sections, and treat
  absolute symbols as equal if their values are equal.

  Obtained from:	LLD commit r292578

MFC r319918:

  Revert r319796 for now, it can cause undefined references when linking
  in some circumstances.

  Reported by:	Shawn Webb <shawn.webb@hardenedbsd.org>

MFC r319957 (by emaste):

  lld: Add armelf emulation mode

  Obtained from:	LLD r305375

MFC r321369:

  Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
  5.0.0 (trunk r308421).  Upstream has branched for the 5.0.0 release,
  which should be in about a month.  Please report bugs and regressions,
  so we can get them into the release.

  Please note that from 3.5.0 onwards, clang, llvm and lldb require C++11
  support to build; see UPDATING for more information.

MFC r321420:

  Add a few more object files to liblldb, which should solve errors when
  linking the lldb executable in some cases.  In particular, when the
  -ffunction-sections -fdata-sections options are turned off, or
  ineffective.

  Reported by:	Shawn Webb, Mark Millard

MFC r321433:

  Cleanup stale Options.inc files from the previous libllvm build for
  clang 4.0.0.  Otherwise, these can get included before the two newly
  generated ones (which are different) for clang 5.0.0.

  Reported by:	Mark Millard

MFC r321439 (by bdrewery):

  Move llvm Options.inc hack from r321433 for NO_CLEAN to lib/clang/libllvm.

  The files are only ever generated to .OBJDIR, not to WORLDTMP (as a
  sysroot) and are only ever included from a compilation.  So using
  a beforebuild target here removes the file before the compilation
  tries to include it.

MFC r321664:

  Pull in r308891 from upstream llvm trunk (by Benjamin Kramer):

    [CodeGenPrepare] Cut off FindAllMemoryUses if there are too many uses.

    This avoids excessive compile time. The case I'm looking at is
    Function.cpp from an old version of LLVM that still had the giant
    memcmp string matcher in it. Before r308322 this compiled in about 2
    minutes, after it, clang takes infinite* time to compile it. With
    this patch we're at 5 min, which is still bad but this is a
    pathological case.

    The cut off at 20 uses was chosen by looking at other cut-offs in LLVM
    for user scanning. It's probably too high, but does the job and is
    very unlikely to regress anything.

    Fixes PR33900.

    * I'm impatient and aborted after 15 minutes, on the bug report it was
      killed after 2h.

  Pull in r308986 from upstream llvm trunk (by Simon Pilgrim):

    [X86][CGP] Reduce memcmp() expansion to 2 load pairs (PR33914)

    D35067/rL308322 attempted to support up to 4 load pairs for memcmp
    inlining which resulted in regressions for some optimized libc memcmp
    implementations (PR33914).

    Until we can match these more optimal cases, this patch reduces the
    memcmp expansion to a maximum of 2 load pairs (which matches what we
    do for -Os).

    This patch should be considered for the 5.0.0 release branch as well

    Differential Revision: https://reviews.llvm.org/D35830

  These fix a hang (or extremely long compile time) when building older
  LLVM ports.

  Reported by:    antoine
  PR:             219139

MFC r321719:

  Pull in r309503 from upstream clang trunk (by Richard Smith):

    PR33902: Invalidate line number cache when adding more text to
    existing buffer.

    This led to crashes as the line number cache would report a bogus
    line number for a line of code, and we'd try to find a nonexistent
    column within the line when printing diagnostics.

  This fixes an assertion when building the graphics/champlain port.

  Reported by:	antoine, kwm
  PR:		219139

MFC r321723:

  Upgrade our copies of clang, llvm, lld and lldb to r309439 from the
  upstream release_50 branch.  This is just after upstream's 5.0.0-rc1.

MFC r322320:

  Upgrade our copies of clang, llvm and libc++ to r310316 from the
  upstream release_50 branch.

MFC r322326 (by emaste):

  lldb: Make i386-*-freebsd expression work on JIT path

  * Enable i386 ABI creation for freebsd
  * Added an extra argument in ABISysV_i386::PrepareTrivialCall for mmap
    syscall
  * Unlike linux, the last argument of mmap is actually 64-bit(off_t).
    This requires us to push an additional word for the higher order bits.
  * Prior to this change, ktrace dump will show mmap failures due to
    invalid argument coming from the 6th mmap argument.

  Submitted by:	Karnajit Wangkhem
  Differential Revision:	https://reviews.llvm.org/D34776

MFC r322360 (by emaste):

  lldb: Report inferior signals as signals, not exceptions, on FreeBSD

  This is the FreeBSD equivalent of LLVM r238549.

  This serves 2 purposes:

  * LLDB should handle inferior process signals SIGSEGV/SIGILL/SIGBUS/
    SIGFPE the way it is suppose to be handled. Prior to this fix these
    signals will neither create a coredump, nor exit from the debugger
    or work for signal handling scenario.
  * eInvalidCrashReason need not report "unknown crash reason" if we have
    a valid si_signo

  llvm.org/pr23699

  Patch by Karnajit Wangkhem

  Differential Revision:  https://reviews.llvm.org/D35223

  Submitted by:	Karnajit Wangkhem
  Obtained from:	LLVM r310591

MFC r322474 (by emaste):

  lld: Add `-z muldefs` option.

  Obtained from:	LLVM r310757

MFC r322740:

  Upgrade our copies of clang, llvm, lld and libc++ to r311219 from the
  upstream release_50 branch.

MFC r322855:

  Upgrade our copies of clang, llvm, lldb and compiler-rt to r311606 from
  the upstream release_50 branch.

  As of this version, lib/msun's trig test should also work correctly
  again (see bug 220989 for more information).

  PR:		220989

MFC r323112:

  Upgrade our copies of clang, llvm, lldb and compiler-rt to r312293 from
  the upstream release_50 branch.  This corresponds to 5.0.0 rc4.

  As of this version, the cad/stepcode port should now compile in a more
  reasonable time on i386 (see bug 221836 for more information).

  PR:		221836

MFC r323245:

  Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
  5.0.0 release (upstream r312559).

  Release notes for llvm, clang and lld will be available here soon:
  <http://releases.llvm.org/5.0.0/docs/ReleaseNotes.html>
  <http://releases.llvm.org/5.0.0/tools/clang/docs/ReleaseNotes.html>
  <http://releases.llvm.org/5.0.0/tools/lld/docs/ReleaseNotes.html>

  Relnotes:	yes

1 files changed, 237 insertions, 178 deletions

diff --git a/contrib/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/contrib/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 91a3d09..f1b4d9f 100644
--- a/contrib/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/contrib/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -22,6 +22,7 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Triple.h"
+#include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/CodeGen/DIE.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
@@ -38,8 +39,6 @@
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
-#include "llvm/Support/Dwarf.h"
-#include "llvm/Support/Endian.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FormattedStream.h"
 #include "llvm/Support/LEB128.h"
@@ -72,6 +71,10 @@ static cl::opt<bool> GenerateARangeSection("generate-arange-section",
                                            cl::desc("Generate dwarf aranges"),
                                            cl::init(false));
 
+static cl::opt<bool> SplitDwarfCrossCuReferences(
+    "split-dwarf-cross-cu-references", cl::Hidden,
+    cl::desc("Enable cross-cu references in DWO files"), cl::init(false));
+
 namespace {
 enum DefaultOnOff { Default, Enable, Disable };
 }
@@ -92,14 +95,6 @@ DwarfAccelTables("dwarf-accel-tables", cl::Hidden,
                  cl::init(Default));
 
 static cl::opt<DefaultOnOff>
-SplitDwarf("split-dwarf", cl::Hidden,
-           cl::desc("Output DWARF5 split debug info."),
-           cl::values(clEnumVal(Default, "Default for platform"),
-                      clEnumVal(Enable, "Enabled"),
-                      clEnumVal(Disable, "Disabled")),
-           cl::init(Default));
-
-static cl::opt<DefaultOnOff>
 DwarfPubSections("generate-dwarf-pub-sections", cl::Hidden,
                  cl::desc("Generate DWARF pubnames and pubtypes sections"),
                  cl::values(clEnumVal(Default, "Default for platform"),
@@ -127,17 +122,17 @@ static const char *const DWARFGroupDescription = "DWARF Emission";
 static const char *const DbgTimerName = "writer";
 static const char *const DbgTimerDescription = "DWARF Debug Writer";
 
-void DebugLocDwarfExpression::EmitOp(uint8_t Op, const char *Comment) {
+void DebugLocDwarfExpression::emitOp(uint8_t Op, const char *Comment) {
   BS.EmitInt8(
       Op, Comment ? Twine(Comment) + " " + dwarf::OperationEncodingString(Op)
                   : dwarf::OperationEncodingString(Op));
 }
 
-void DebugLocDwarfExpression::EmitSigned(int64_t Value) {
+void DebugLocDwarfExpression::emitSigned(int64_t Value) {
   BS.EmitSLEB128(Value, Twine(Value));
 }
 
-void DebugLocDwarfExpression::EmitUnsigned(uint64_t Value) {
+void DebugLocDwarfExpression::emitUnsigned(uint64_t Value) {
   BS.EmitULEB128(Value, Twine(Value));
 }
 
@@ -200,6 +195,12 @@ const DIType *DbgVariable::getType() const {
 }
 
 ArrayRef<DbgVariable::FrameIndexExpr> DbgVariable::getFrameIndexExprs() const {
+  if (FrameIndexExprs.size() == 1)
+    return FrameIndexExprs;
+
+  assert(all_of(FrameIndexExprs,
+                [](const FrameIndexExpr &A) { return A.Expr->isFragment(); }) &&
+         "multiple FI expressions without DW_OP_LLVM_fragment");
   std::sort(FrameIndexExprs.begin(), FrameIndexExprs.end(),
             [](const FrameIndexExpr &A, const FrameIndexExpr &B) -> bool {
               return A.Expr->getFragmentInfo()->OffsetInBits <
@@ -248,17 +249,8 @@ DwarfDebug::DwarfDebug(AsmPrinter *A, Module *M)
 
   HasAppleExtensionAttributes = tuneForLLDB();
 
-  // Handle split DWARF. Off by default for now.
-  if (SplitDwarf == Default)
-    HasSplitDwarf = false;
-  else
-    HasSplitDwarf = SplitDwarf == Enable;
-
-  // Pubnames/pubtypes on by default for GDB.
-  if (DwarfPubSections == Default)
-    HasDwarfPubSections = tuneForGDB();
-  else
-    HasDwarfPubSections = DwarfPubSections == Enable;
+  // Handle split DWARF.
+  HasSplitDwarf = !Asm->TM.Options.MCOptions.SplitDwarfFile.empty();
 
   // SCE defaults to linkage names only for abstract subprograms.
   if (DwarfLinkageNames == DefaultLinkageNames)
@@ -368,25 +360,49 @@ template <typename Func> static void forBothCUs(DwarfCompileUnit &CU, Func F) {
       F(*SkelCU);
 }
 
-void DwarfDebug::constructAbstractSubprogramScopeDIE(LexicalScope *Scope) {
+bool DwarfDebug::shareAcrossDWOCUs() const {
+  return SplitDwarfCrossCuReferences;
+}
+
+void DwarfDebug::constructAbstractSubprogramScopeDIE(DwarfCompileUnit &SrcCU,
+                                                     LexicalScope *Scope) {
   assert(Scope && Scope->getScopeNode());
   assert(Scope->isAbstractScope());
   assert(!Scope->getInlinedAt());
 
   auto *SP = cast<DISubprogram>(Scope->getScopeNode());
 
-  ProcessedSPNodes.insert(SP);
-
   // Find the subprogram's DwarfCompileUnit in the SPMap in case the subprogram
   // was inlined from another compile unit.
-  auto &CU = *CUMap.lookup(SP->getUnit());
-  forBothCUs(CU, [&](DwarfCompileUnit &CU) {
-    CU.constructAbstractSubprogramScopeDIE(Scope);
-  });
+  if (useSplitDwarf() && !shareAcrossDWOCUs() && !SP->getUnit()->getSplitDebugInlining())
+    // Avoid building the original CU if it won't be used
+    SrcCU.constructAbstractSubprogramScopeDIE(Scope);
+  else {
+    auto &CU = getOrCreateDwarfCompileUnit(SP->getUnit());
+    if (auto *SkelCU = CU.getSkeleton()) {
+      (shareAcrossDWOCUs() ? CU : SrcCU)
+          .constructAbstractSubprogramScopeDIE(Scope);
+      if (CU.getCUNode()->getSplitDebugInlining())
+        SkelCU->constructAbstractSubprogramScopeDIE(Scope);
+    } else
+      CU.constructAbstractSubprogramScopeDIE(Scope);
+  }
+}
+
+bool DwarfDebug::hasDwarfPubSections(bool includeMinimalInlineScopes) const {
+  // Opting in to GNU Pubnames/types overrides the default to ensure these are
+  // generated for things like Gold's gdb_index generation.
+  if (GenerateGnuPubSections)
+    return true;
+
+  if (DwarfPubSections == Default)
+    return tuneForGDB() && !includeMinimalInlineScopes;
+
+  return DwarfPubSections == Enable;
 }
 
-void DwarfDebug::addGnuPubAttributes(DwarfUnit &U, DIE &D) const {
-  if (!GenerateGnuPubSections)
+void DwarfDebug::addGnuPubAttributes(DwarfCompileUnit &U, DIE &D) const {
+  if (!hasDwarfPubSections(U.includeMinimalInlineScopes()))
     return;
 
   U.addFlag(D, dwarf::DW_AT_GNU_pubnames);
@@ -395,7 +411,9 @@ void DwarfDebug::addGnuPubAttributes(DwarfUnit &U, DIE &D) const {
 // Create new DwarfCompileUnit for the given metadata node with tag
 // DW_TAG_compile_unit.
 DwarfCompileUnit &
-DwarfDebug::constructDwarfCompileUnit(const DICompileUnit *DIUnit) {
+DwarfDebug::getOrCreateDwarfCompileUnit(const DICompileUnit *DIUnit) {
+  if (auto *CU = CUMap.lookup(DIUnit))
+    return *CU;
   StringRef FN = DIUnit->getFilename();
   CompilationDir = DIUnit->getDirectory();
 
@@ -407,7 +425,7 @@ DwarfDebug::constructDwarfCompileUnit(const DICompileUnit *DIUnit) {
   if (useSplitDwarf()) {
     NewCU.setSkeleton(constructSkeletonCU(NewCU));
     NewCU.addString(Die, dwarf::DW_AT_GNU_dwo_name,
-                    DIUnit->getSplitDebugFilename());
+                  Asm->TM.Options.MCOptions.SplitDwarfFile);
   }
 
   // LTO with assembly output shares a single line table amongst multiple CUs.
@@ -418,7 +436,14 @@ DwarfDebug::constructDwarfCompileUnit(const DICompileUnit *DIUnit) {
     Asm->OutStreamer->getContext().setMCLineTableCompilationDir(
         NewCU.getUniqueID(), CompilationDir);
 
-  NewCU.addString(Die, dwarf::DW_AT_producer, DIUnit->getProducer());
+  StringRef Producer = DIUnit->getProducer();
+  StringRef Flags = DIUnit->getFlags();
+  if (!Flags.empty()) {
+    std::string ProducerWithFlags = Producer.str() + " " + Flags.str();
+    NewCU.addString(Die, dwarf::DW_AT_producer, ProducerWithFlags);
+  } else
+    NewCU.addString(Die, dwarf::DW_AT_producer, Producer);
+
   NewCU.addUInt(Die, dwarf::DW_AT_language, dwarf::DW_FORM_data2,
                 DIUnit->getSourceLanguage());
   NewCU.addString(Die, dwarf::DW_AT_name, FN);
@@ -521,7 +546,12 @@ void DwarfDebug::beginModule() {
   }
 
   for (DICompileUnit *CUNode : M->debug_compile_units()) {
-    DwarfCompileUnit &CU = constructDwarfCompileUnit(CUNode);
+    if (CUNode->getEnumTypes().empty() && CUNode->getRetainedTypes().empty() &&
+        CUNode->getGlobalVariables().empty() &&
+        CUNode->getImportedEntities().empty() && CUNode->getMacros().empty())
+      continue;
+
+    DwarfCompileUnit &CU = getOrCreateDwarfCompileUnit(CUNode);
     for (auto *IE : CUNode->getImportedEntities())
       CU.addImportedEntity(IE);
 
@@ -544,7 +574,6 @@ void DwarfDebug::beginModule() {
       // The retained types array by design contains pointers to
       // MDNodes rather than DIRefs. Unique them here.
       if (DIType *RT = dyn_cast<DIType>(Ty))
-        if (!RT->isExternalTypeRef())
           // There is no point in force-emitting a forward declaration.
           CU.getOrCreateTypeDIE(RT);
     }
@@ -564,22 +593,17 @@ void DwarfDebug::finishVariableDefinitions() {
     // DIE::getUnit isn't simple - it walks parent pointers, etc.
     DwarfCompileUnit *Unit = CUDieMap.lookup(VariableDie->getUnitDie());
     assert(Unit);
-    DbgVariable *AbsVar = getExistingAbstractVariable(
-        InlinedVariable(Var->getVariable(), Var->getInlinedAt()));
-    if (AbsVar && AbsVar->getDIE()) {
-      Unit->addDIEEntry(*VariableDie, dwarf::DW_AT_abstract_origin,
-                        *AbsVar->getDIE());
-    } else
-      Unit->applyVariableAttributes(*Var, *VariableDie);
+    Unit->finishVariableDefinition(*Var);
   }
 }
 
 void DwarfDebug::finishSubprogramDefinitions() {
-  for (const DISubprogram *SP : ProcessedSPNodes)
-    if (SP->getUnit()->getEmissionKind() != DICompileUnit::NoDebug)
-      forBothCUs(*CUMap.lookup(SP->getUnit()), [&](DwarfCompileUnit &CU) {
-        CU.finishSubprogramDefinition(SP);
-      });
+  for (const DISubprogram *SP : ProcessedSPNodes) {
+    assert(SP->getUnit()->getEmissionKind() != DICompileUnit::NoDebug);
+    forBothCUs(
+        getOrCreateDwarfCompileUnit(SP->getUnit()),
+        [&](DwarfCompileUnit &CU) { CU.finishSubprogramDefinition(SP); });
+  }
 }
 
 void DwarfDebug::finalizeModuleInfo() {
@@ -589,6 +613,13 @@ void DwarfDebug::finalizeModuleInfo() {
 
   finishVariableDefinitions();
 
+  // Include the DWO file name in the hash if there's more than one CU.
+  // This handles ThinLTO's situation where imported CUs may very easily be
+  // duplicate with the same CU partially imported into another ThinLTO unit.
+  StringRef DWOName;
+  if (CUMap.size() > 1)
+    DWOName = Asm->TM.Options.MCOptions.SplitDwarfFile;
+
   // Handle anything that needs to be done on a per-unit basis after
   // all other generation.
   for (const auto &P : CUMap) {
@@ -603,7 +634,8 @@ void DwarfDebug::finalizeModuleInfo() {
     auto *SkCU = TheCU.getSkeleton();
     if (useSplitDwarf()) {
       // Emit a unique identifier for this CU.
-      uint64_t ID = DIEHash(Asm).computeCUSignature(TheCU.getUnitDie());
+      uint64_t ID =
+          DIEHash(Asm).computeCUSignature(DWOName, TheCU.getUnitDie());
       TheCU.addUInt(TheCU.getUnitDie(), dwarf::DW_AT_GNU_dwo_id,
                     dwarf::DW_FORM_data8, ID);
       SkCU->addUInt(SkCU->getUnitDie(), dwarf::DW_AT_GNU_dwo_id,
@@ -712,63 +744,40 @@ void DwarfDebug::endModule() {
   }
 
   // Emit the pubnames and pubtypes sections if requested.
-  if (HasDwarfPubSections) {
+  // The condition is optimistically correct - any CU not using GMLT (&
+  // implicit/default pubnames state) might still have pubnames.
+  if (hasDwarfPubSections(/* gmlt */ false)) {
     emitDebugPubNames(GenerateGnuPubSections);
     emitDebugPubTypes(GenerateGnuPubSections);
   }
 
   // clean up.
-  AbstractVariables.clear();
-}
-
-// Find abstract variable, if any, associated with Var.
-DbgVariable *
-DwarfDebug::getExistingAbstractVariable(InlinedVariable IV,
-                                        const DILocalVariable *&Cleansed) {
-  // More then one inlined variable corresponds to one abstract variable.
-  Cleansed = IV.first;
-  auto I = AbstractVariables.find(Cleansed);
-  if (I != AbstractVariables.end())
-    return I->second.get();
-  return nullptr;
+  // FIXME: AbstractVariables.clear();
 }
 
-DbgVariable *DwarfDebug::getExistingAbstractVariable(InlinedVariable IV) {
-  const DILocalVariable *Cleansed;
-  return getExistingAbstractVariable(IV, Cleansed);
-}
-
-void DwarfDebug::createAbstractVariable(const DILocalVariable *Var,
-                                        LexicalScope *Scope) {
-  auto AbsDbgVariable = make_unique<DbgVariable>(Var, /* IA */ nullptr);
-  InfoHolder.addScopeVariable(Scope, AbsDbgVariable.get());
-  AbstractVariables[Var] = std::move(AbsDbgVariable);
-}
-
-void DwarfDebug::ensureAbstractVariableIsCreated(InlinedVariable IV,
+void DwarfDebug::ensureAbstractVariableIsCreated(DwarfCompileUnit &CU, InlinedVariable IV,
                                                  const MDNode *ScopeNode) {
   const DILocalVariable *Cleansed = nullptr;
-  if (getExistingAbstractVariable(IV, Cleansed))
+  if (CU.getExistingAbstractVariable(IV, Cleansed))
     return;
 
-  createAbstractVariable(Cleansed, LScopes.getOrCreateAbstractScope(
+  CU.createAbstractVariable(Cleansed, LScopes.getOrCreateAbstractScope(
                                        cast<DILocalScope>(ScopeNode)));
 }
 
-void DwarfDebug::ensureAbstractVariableIsCreatedIfScoped(
+void DwarfDebug::ensureAbstractVariableIsCreatedIfScoped(DwarfCompileUnit &CU,
     InlinedVariable IV, const MDNode *ScopeNode) {
   const DILocalVariable *Cleansed = nullptr;
-  if (getExistingAbstractVariable(IV, Cleansed))
+  if (CU.getExistingAbstractVariable(IV, Cleansed))
     return;
 
   if (LexicalScope *Scope =
           LScopes.findAbstractScope(cast_or_null<DILocalScope>(ScopeNode)))
-    createAbstractVariable(Cleansed, Scope);
+    CU.createAbstractVariable(Cleansed, Scope);
 }
-
 // Collect variable information from side table maintained by MF.
 void DwarfDebug::collectVariableInfoFromMFTable(
-    DenseSet<InlinedVariable> &Processed) {
+    DwarfCompileUnit &TheCU, DenseSet<InlinedVariable> &Processed) {
   for (const auto &VI : Asm->MF->getVariableDbgInfo()) {
     if (!VI.Var)
       continue;
@@ -783,7 +792,7 @@ void DwarfDebug::collectVariableInfoFromMFTable(
     if (!Scope)
       continue;
 
-    ensureAbstractVariableIsCreatedIfScoped(Var, Scope->getScopeNode());
+    ensureAbstractVariableIsCreatedIfScoped(TheCU, Var, Scope->getScopeNode());
     auto RegVar = make_unique<DbgVariable>(Var.first, Var.second);
     RegVar->initializeMMI(VI.Expr, VI.Slot);
     if (InfoHolder.addScopeVariable(Scope, RegVar.get()))
@@ -954,24 +963,71 @@ DwarfDebug::buildLocationList(SmallVectorImpl<DebugLocEntry> &DebugLoc,
   }
 }
 
-DbgVariable *DwarfDebug::createConcreteVariable(LexicalScope &Scope,
+DbgVariable *DwarfDebug::createConcreteVariable(DwarfCompileUnit &TheCU,
+                                                LexicalScope &Scope,
                                                 InlinedVariable IV) {
-  ensureAbstractVariableIsCreatedIfScoped(IV, Scope.getScopeNode());
+  ensureAbstractVariableIsCreatedIfScoped(TheCU, IV, Scope.getScopeNode());
   ConcreteVariables.push_back(make_unique<DbgVariable>(IV.first, IV.second));
   InfoHolder.addScopeVariable(&Scope, ConcreteVariables.back().get());
   return ConcreteVariables.back().get();
 }
 
-// Determine whether this DBG_VALUE is valid at the beginning of the function.
-static bool validAtEntry(const MachineInstr *MInsn) {
-  auto MBB = MInsn->getParent();
-  // Is it in the entry basic block?
-  if (!MBB->pred_empty())
+/// Determine whether a *singular* DBG_VALUE is valid for the entirety of its
+/// enclosing lexical scope. The check ensures there are no other instructions
+/// in the same lexical scope preceding the DBG_VALUE and that its range is
+/// either open or otherwise rolls off the end of the scope.
+static bool validThroughout(LexicalScopes &LScopes,
+                            const MachineInstr *DbgValue,
+                            const MachineInstr *RangeEnd) {
+  assert(DbgValue->getDebugLoc() && "DBG_VALUE without a debug location");
+  auto MBB = DbgValue->getParent();
+  auto DL = DbgValue->getDebugLoc();
+  auto *LScope = LScopes.findLexicalScope(DL);
+  // Scope doesn't exist; this is a dead DBG_VALUE.
+  if (!LScope)
     return false;
-  for (MachineBasicBlock::const_reverse_iterator I(MInsn); I != MBB->rend(); ++I)
-    if (!(I->isDebugValue() || I->getFlag(MachineInstr::FrameSetup)))
+  auto &LSRange = LScope->getRanges();
+  if (LSRange.size() == 0)
+    return false;
+
+  // Determine if the DBG_VALUE is valid at the beginning of its lexical block.
+  const MachineInstr *LScopeBegin = LSRange.front().first;
+  // Early exit if the lexical scope begins outside of the current block.
+  if (LScopeBegin->getParent() != MBB)
+    return false;
+  MachineBasicBlock::const_reverse_iterator Pred(DbgValue);
+  for (++Pred; Pred != MBB->rend(); ++Pred) {
+    if (Pred->getFlag(MachineInstr::FrameSetup))
+      break;
+    auto PredDL = Pred->getDebugLoc();
+    if (!PredDL || Pred->isMetaInstruction())
+      continue;
+    // Check whether the instruction preceding the DBG_VALUE is in the same
+    // (sub)scope as the DBG_VALUE.
+    if (DL->getScope() == PredDL->getScope())
       return false;
-  return true;
+    auto *PredScope = LScopes.findLexicalScope(PredDL);
+    if (!PredScope || LScope->dominates(PredScope))
+      return false;
+  }
+
+  // If the range of the DBG_VALUE is open-ended, report success.
+  if (!RangeEnd)
+    return true;
+
+  // Fail if there are instructions belonging to our scope in another block.
+  const MachineInstr *LScopeEnd = LSRange.back().second;
+  if (LScopeEnd->getParent() != MBB)
+    return false;
+
+  // Single, constant DBG_VALUEs in the prologue are promoted to be live
+  // throughout the function. This is a hack, presumably for DWARF v2 and not
+  // necessarily correct. It would be much better to use a dbg.declare instead
+  // if we know the constant is live throughout the scope.
+  if (DbgValue->getOperand(0).isImm() && MBB->pred_empty())
+    return true;
+
+  return false;
 }
 
 // Find variables for each lexical scope.
@@ -979,7 +1035,7 @@ void DwarfDebug::collectVariableInfo(DwarfCompileUnit &TheCU,
                                      const DISubprogram *SP,
                                      DenseSet<InlinedVariable> &Processed) {
   // Grab the variable info that was squirreled away in the MMI side-table.
-  collectVariableInfoFromMFTable(Processed);
+  collectVariableInfoFromMFTable(TheCU, Processed);
 
   for (const auto &I : DbgValues) {
     InlinedVariable IV = I.first;
@@ -1001,16 +1057,14 @@ void DwarfDebug::collectVariableInfo(DwarfCompileUnit &TheCU,
       continue;
 
     Processed.insert(IV);
-    DbgVariable *RegVar = createConcreteVariable(*Scope, IV);
+    DbgVariable *RegVar = createConcreteVariable(TheCU, *Scope, IV);
 
     const MachineInstr *MInsn = Ranges.front().first;
     assert(MInsn->isDebugValue() && "History must begin with debug value");
 
-    // Check if there is a single DBG_VALUE, valid throughout the function.
-    // A single constant is also considered valid for the entire function.
+    // Check if there is a single DBG_VALUE, valid throughout the var's scope.
     if (Ranges.size() == 1 &&
-        (MInsn->getOperand(0).isImm() ||
-         (validAtEntry(MInsn) && Ranges.front().second == nullptr))) {
+        validThroughout(LScopes, MInsn, Ranges.front().second)) {
       RegVar->initializeDbgValue(MInsn);
       continue;
     }
@@ -1037,7 +1091,7 @@ void DwarfDebug::collectVariableInfo(DwarfCompileUnit &TheCU,
   for (const DILocalVariable *DV : SP->getVariables()) {
     if (Processed.insert(InlinedVariable(DV, nullptr)).second)
       if (LexicalScope *Scope = LScopes.findLexicalScope(DV->getScope()))
-        createConcreteVariable(*Scope, InlinedVariable(DV, nullptr));
+        createConcreteVariable(TheCU, *Scope, InlinedVariable(DV, nullptr));
   }
 }
 
@@ -1046,8 +1100,12 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
   DebugHandlerBase::beginInstruction(MI);
   assert(CurMI);
 
+  const auto *SP = MI->getParent()->getParent()->getFunction()->getSubprogram();
+  if (!SP || SP->getUnit()->getEmissionKind() == DICompileUnit::NoDebug)
+    return;
+
   // Check if source location changes, but ignore DBG_VALUE and CFI locations.
-  if (MI->isDebugValue() || MI->isCFIInstruction())
+  if (MI->isMetaInstruction())
     return;
   const DebugLoc &DL = MI->getDebugLoc();
   // When we emit a line-0 record, we don't update PrevInstLoc; so look at
@@ -1129,7 +1187,7 @@ static DebugLoc findPrologueEndLoc(const MachineFunction *MF) {
   // the beginning of the function body.
   for (const auto &MBB : *MF)
     for (const auto &MI : MBB)
-      if (!MI.isDebugValue() && !MI.getFlag(MachineInstr::FrameSetup) &&
+      if (!MI.isMetaInstruction() && !MI.getFlag(MachineInstr::FrameSetup) &&
           MI.getDebugLoc())
         return MI.getDebugLoc();
   return DebugLoc();
@@ -1137,75 +1195,50 @@ static DebugLoc findPrologueEndLoc(const MachineFunction *MF) {
 
 // Gather pre-function debug information.  Assumes being called immediately
 // after the function entry point has been emitted.
-void DwarfDebug::beginFunction(const MachineFunction *MF) {
+void DwarfDebug::beginFunctionImpl(const MachineFunction *MF) {
   CurFn = MF;
 
-  // If there's no debug info for the function we're not going to do anything.
-  if (!MMI->hasDebugInfo())
+  auto *SP = MF->getFunction()->getSubprogram();
+  assert(LScopes.empty() || SP == LScopes.getCurrentFunctionScope()->getScopeNode());
+  if (SP->getUnit()->getEmissionKind() == DICompileUnit::NoDebug)
     return;
 
-  auto DI = MF->getFunction()->getSubprogram();
-  if (!DI)
-    return;
-
-  // Grab the lexical scopes for the function, if we don't have any of those
-  // then we're not going to be able to do anything.
-  DebugHandlerBase::beginFunction(MF);
-  if (LScopes.empty())
-    return;
+  DwarfCompileUnit &CU = getOrCreateDwarfCompileUnit(SP->getUnit());
 
   // Set DwarfDwarfCompileUnitID in MCContext to the Compile Unit this function
   // belongs to so that we add to the correct per-cu line table in the
   // non-asm case.
-  LexicalScope *FnScope = LScopes.getCurrentFunctionScope();
-  // FnScope->getScopeNode() and DI->second should represent the same function,
-  // though they may not be the same MDNode due to inline functions merged in
-  // LTO where the debug info metadata still differs (either due to distinct
-  // written differences - two versions of a linkonce_odr function
-  // written/copied into two separate files, or some sub-optimal metadata that
-  // isn't structurally identical (see: file path/name info from clang, which
-  // includes the directory of the cpp file being built, even when the file name
-  // is absolute (such as an <> lookup header)))
-  auto *SP = cast<DISubprogram>(FnScope->getScopeNode());
-  DwarfCompileUnit *TheCU = CUMap.lookup(SP->getUnit());
-  if (!TheCU) {
-    assert(SP->getUnit()->getEmissionKind() == DICompileUnit::NoDebug &&
-           "DICompileUnit missing from llvm.dbg.cu?");
-    return;
-  }
   if (Asm->OutStreamer->hasRawTextSupport())
     // Use a single line table if we are generating assembly.
     Asm->OutStreamer->getContext().setDwarfCompileUnitID(0);
   else
-    Asm->OutStreamer->getContext().setDwarfCompileUnitID(TheCU->getUniqueID());
+    Asm->OutStreamer->getContext().setDwarfCompileUnitID(CU.getUniqueID());
 
   // Record beginning of function.
   PrologEndLoc = findPrologueEndLoc(MF);
-  if (DILocation *L = PrologEndLoc) {
+  if (PrologEndLoc) {
     // We'd like to list the prologue as "not statements" but GDB behaves
     // poorly if we do that. Revisit this with caution/GDB (7.5+) testing.
-    auto *SP = L->getInlinedAtScope()->getSubprogram();
+    auto *SP = PrologEndLoc->getInlinedAtScope()->getSubprogram();
     recordSourceLine(SP->getScopeLine(), 0, SP, DWARF2_FLAG_IS_STMT);
   }
 }
 
+void DwarfDebug::skippedNonDebugFunction() {
+  // If we don't have a subprogram for this function then there will be a hole
+  // in the range information. Keep note of this by setting the previously used
+  // section to nullptr.
+  PrevCU = nullptr;
+  CurFn = nullptr;
+}
+
 // Gather and emit post-function debug information.
-void DwarfDebug::endFunction(const MachineFunction *MF) {
+void DwarfDebug::endFunctionImpl(const MachineFunction *MF) {
+  const DISubprogram *SP = MF->getFunction()->getSubprogram();
+
   assert(CurFn == MF &&
       "endFunction should be called with the same function as beginFunction");
 
-  const DISubprogram *SP = MF->getFunction()->getSubprogram();
-  if (!MMI->hasDebugInfo() || !SP ||
-      SP->getUnit()->getEmissionKind() == DICompileUnit::NoDebug) {
-    // If we don't have a subprogram for this function then there will be a hole
-    // in the range information. Keep note of this by setting the previously
-    // used section to nullptr.
-    PrevCU = nullptr;
-    CurFn = nullptr;
-    DebugHandlerBase::endFunction(MF);
-    return;
-  }
-
   // Set DwarfDwarfCompileUnitID in MCContext to default value.
   Asm->OutStreamer->getContext().setDwarfCompileUnitID(0);
 
@@ -1220,17 +1253,14 @@ void DwarfDebug::endFunction(const MachineFunction *MF) {
   TheCU.addRange(RangeSpan(Asm->getFunctionBegin(), Asm->getFunctionEnd()));
 
   // Under -gmlt, skip building the subprogram if there are no inlined
-  // subroutines inside it.
-  if (TheCU.getCUNode()->getEmissionKind() == DICompileUnit::LineTablesOnly &&
+  // subroutines inside it. But with -fdebug-info-for-profiling, the subprogram
+  // is still needed as we need its source location.
+  if (!TheCU.getCUNode()->getDebugInfoForProfiling() &&
+      TheCU.getCUNode()->getEmissionKind() == DICompileUnit::LineTablesOnly &&
       LScopes.getAbstractScopesList().empty() && !IsDarwin) {
     assert(InfoHolder.getScopeVariables().empty());
-    assert(DbgValues.empty());
-    // FIXME: This wouldn't be true in LTO with a -g (with inlining) CU followed
-    // by a -gmlt CU. Add a test and remove this assertion.
-    assert(AbstractVariables.empty());
     PrevLabel = nullptr;
     CurFn = nullptr;
-    DebugHandlerBase::endFunction(MF);
     return;
   }
 
@@ -1244,12 +1274,12 @@ void DwarfDebug::endFunction(const MachineFunction *MF) {
     for (const DILocalVariable *DV : SP->getVariables()) {
       if (!ProcessedVars.insert(InlinedVariable(DV, nullptr)).second)
         continue;
-      ensureAbstractVariableIsCreated(InlinedVariable(DV, nullptr),
+      ensureAbstractVariableIsCreated(TheCU, InlinedVariable(DV, nullptr),
                                       DV->getScope());
       assert(LScopes.getAbstractScopesList().size() == NumAbstractScopes
              && "ensureAbstractVariableIsCreated inserted abstract scopes");
     }
-    constructAbstractSubprogramScopeDIE(AScope);
+    constructAbstractSubprogramScopeDIE(TheCU, AScope);
   }
 
   ProcessedSPNodes.insert(SP);
@@ -1266,7 +1296,6 @@ void DwarfDebug::endFunction(const MachineFunction *MF) {
   InfoHolder.getScopeVariables().clear();
   PrevLabel = nullptr;
   CurFn = nullptr;
-  DebugHandlerBase::endFunction(MF);
 }
 
 // Register a source line with debug info. Returns the  unique label that was
@@ -1361,6 +1390,18 @@ void DwarfDebug::emitAccelTypes() {
 /// computeIndexValue - Compute the gdb index value for the DIE and CU.
 static dwarf::PubIndexEntryDescriptor computeIndexValue(DwarfUnit *CU,
                                                         const DIE *Die) {
+  // Entities that ended up only in a Type Unit reference the CU instead (since
+  // the pub entry has offsets within the CU there's no real offset that can be
+  // provided anyway). As it happens all such entities (namespaces and types,
+  // types only in C++ at that) are rendered as TYPE+EXTERNAL. If this turns out
+  // not to be true it would be necessary to persist this information from the
+  // point at which the entry is added to the index data structure - since by
+  // the time the index is built from that, the original type/namespace DIE in a
+  // type unit has already been destroyed so it can't be queried for properties
+  // like tag, etc.
+  if (Die->getTag() == dwarf::DW_TAG_compile_unit)
+    return dwarf::PubIndexEntryDescriptor(dwarf::GIEK_TYPE,
+                                          dwarf::GIEL_EXTERNAL);
   dwarf::GDBIndexEntryLinkage Linkage = dwarf::GIEL_STATIC;
 
   // We could have a specification DIE that has our most of our knowledge,
@@ -1418,7 +1459,7 @@ void DwarfDebug::emitDebugPubSection(
 
     const auto &Globals = (TheU->*Accessor)();
 
-    if (Globals.empty())
+    if (!hasDwarfPubSections(TheU->includeMinimalInlineScopes()))
       continue;
 
     if (auto *Skeleton = TheU->getSkeleton())
@@ -1498,27 +1539,36 @@ static void emitDebugLocValue(const AsmPrinter &AP, const DIBasicType *BT,
                               ByteStreamer &Streamer,
                               const DebugLocEntry::Value &Value,
                               DwarfExpression &DwarfExpr) {
-  DIExpressionCursor ExprCursor(Value.getExpression());
-  DwarfExpr.addFragmentOffset(Value.getExpression());
+  auto *DIExpr = Value.getExpression();
+  DIExpressionCursor ExprCursor(DIExpr);
+  DwarfExpr.addFragmentOffset(DIExpr);
   // Regular entry.
   if (Value.isInt()) {
     if (BT && (BT->getEncoding() == dwarf::DW_ATE_signed ||
                BT->getEncoding() == dwarf::DW_ATE_signed_char))
-      DwarfExpr.AddSignedConstant(Value.getInt());
+      DwarfExpr.addSignedConstant(Value.getInt());
     else
-      DwarfExpr.AddUnsignedConstant(Value.getInt());
+      DwarfExpr.addUnsignedConstant(Value.getInt());
   } else if (Value.isLocation()) {
-    MachineLocation Loc = Value.getLoc();
+    MachineLocation Location = Value.getLoc();
+    if (Location.isIndirect())
+      DwarfExpr.setMemoryLocationKind();
+    SmallVector<uint64_t, 8> Ops;
+    if (Location.isIndirect() && Location.getOffset()) {
+      Ops.push_back(dwarf::DW_OP_plus_uconst);
+      Ops.push_back(Location.getOffset());
+    }
+    Ops.append(DIExpr->elements_begin(), DIExpr->elements_end());
+    DIExpressionCursor Cursor(Ops);
     const TargetRegisterInfo &TRI = *AP.MF->getSubtarget().getRegisterInfo();
-    if (Loc.getOffset())
-      DwarfExpr.AddMachineRegIndirect(TRI, Loc.getReg(), Loc.getOffset());
-    else
-      DwarfExpr.AddMachineRegExpression(TRI, ExprCursor, Loc.getReg());
+    if (!DwarfExpr.addMachineRegExpression(TRI, Cursor, Location.getReg()))
+      return;
+    return DwarfExpr.addExpression(std::move(Cursor));
   } else if (Value.isConstantFP()) {
     APInt RawBytes = Value.getConstantFP()->getValueAPF().bitcastToAPInt();
-    DwarfExpr.AddUnsignedConstant(RawBytes);
+    DwarfExpr.addUnsignedConstant(RawBytes);
   }
-  DwarfExpr.AddExpression(std::move(ExprCursor));
+  DwarfExpr.addExpression(std::move(ExprCursor));
 }
 
 void DebugLocEntry::finalize(const AsmPrinter &AP,
@@ -1558,10 +1608,13 @@ void DwarfDebug::emitDebugLocEntryLocation(const DebugLocStream::Entry &Entry) {
 
 // Emit locations into the debug loc section.
 void DwarfDebug::emitDebugLoc() {
+  if (DebugLocs.getLists().empty())
+    return;
+
   // Start the dwarf loc section.
   Asm->OutStreamer->SwitchSection(
       Asm->getObjFileLowering().getDwarfLocSection());
-  unsigned char Size = Asm->getDataLayout().getPointerSize();
+  unsigned char Size = Asm->MAI->getCodePointerSize();
   for (const auto &List : DebugLocs.getLists()) {
     Asm->OutStreamer->EmitLabel(List.Label);
     const DwarfCompileUnit *CU = List.CU;
@@ -1691,7 +1744,7 @@ void DwarfDebug::emitDebugARanges() {
   Asm->OutStreamer->SwitchSection(
       Asm->getObjFileLowering().getDwarfARangesSection());
 
-  unsigned PtrSize = Asm->getDataLayout().getPointerSize();
+  unsigned PtrSize = Asm->MAI->getCodePointerSize();
 
   // Build a list of CUs used.
   std::vector<DwarfCompileUnit *> CUs;
@@ -1769,12 +1822,15 @@ void DwarfDebug::emitDebugARanges() {
 
 /// Emit address ranges into a debug ranges section.
 void DwarfDebug::emitDebugRanges() {
+  if (CUMap.empty())
+    return;
+
   // Start the dwarf ranges section.
   Asm->OutStreamer->SwitchSection(
       Asm->getObjFileLowering().getDwarfRangesSection());
 
   // Size for our labels.
-  unsigned char Size = Asm->getDataLayout().getPointerSize();
+  unsigned char Size = Asm->MAI->getCodePointerSize();
 
   // Grab the specific ranges for the compile units in the module.
   for (const auto &I : CUMap) {
@@ -1848,6 +1904,9 @@ void DwarfDebug::emitMacroFile(DIMacroFile &F, DwarfCompileUnit &U) {
 
 /// Emit macros into a debug macinfo section.
 void DwarfDebug::emitDebugMacinfo() {
+  if (CUMap.empty())
+    return;
+
   // Start the dwarf macinfo section.
   Asm->OutStreamer->SwitchSection(
       Asm->getObjFileLowering().getDwarfMacinfoSection());
@@ -1869,7 +1928,7 @@ void DwarfDebug::emitDebugMacinfo() {
 void DwarfDebug::initSkeletonUnit(const DwarfUnit &U, DIE &Die,
                                   std::unique_ptr<DwarfCompileUnit> NewU) {
   NewU->addString(Die, dwarf::DW_AT_GNU_dwo_name,
-                  U.getCUNode()->getSplitDebugFilename());
+                  Asm->TM.Options.MCOptions.SplitDwarfFile);
 
   if (!CompilationDir.empty())
     NewU->addString(Die, dwarf::DW_AT_comp_dir, CompilationDir);
@@ -1940,11 +1999,11 @@ uint64_t DwarfDebug::makeTypeSignature(StringRef Identifier) {
   MD5 Hash;
   Hash.update(Identifier);
   // ... take the least significant 8 bytes and return those. Our MD5
-  // implementation always returns its results in little endian, swap bytes
-  // appropriately.
+  // implementation always returns its results in little endian, so we actually
+  // need the "high" word.
   MD5::MD5Result Result;
   Hash.final(Result);
-  return support::endian::read64le(Result + 8);
+  return Result.high();
 }
 
 void DwarfDebug::addDwarfTypeUnitType(DwarfCompileUnit &CU,