]> git.saurik.com Git - apple/ld64.git/blobdiff - src/ld/parsers/lto_file.cpp
ld64-351.8.tar.gz
[apple/ld64.git] / src / ld / parsers / lto_file.cpp
index 460dcf0b837da5d9751a7bcb76f0b06c91c073bd..811b6b308d5a69e87db75d465df6cbab90eaf270 100644 (file)
 #include <stdlib.h>
 #include <sys/param.h>
 #include <sys/fcntl.h>
+#include <sys/mman.h>
 #include <sys/stat.h>
 #include <errno.h>
 #include <pthread.h>
 #include <mach-o/dyld.h>
 #include <vector>
+#include <map>
 #include <unordered_set>
 #include <unordered_map>
+#include <iostream>
+#include <fstream>
 
 #include "MachOFileAbstraction.hpp"
 #include "Architectures.hpp"
 #include "macho_relocatable_file.h"
 #include "lto_file.h"
 
-// #defines are a work around for <rdar://problem/8760268>
-#define __STDC_LIMIT_MACROS 1
-#define __STDC_CONSTANT_MACROS 1
 #include "llvm-c/lto.h"
 
-
 namespace lto {
          
 
@@ -63,19 +63,18 @@ class InternalAtom : public ld::Atom
 public:
                                                                                                InternalAtom(class File& f);
        // overrides of ld::Atom
-       virtual ld::File*                                                       file() const            { return &_file; }
-       virtual const char*                                                     name() const            { return "import-atom"; }
-       virtual uint64_t                                                        size() const            { return 0; }
-       virtual uint64_t                                                        objectAddress() const { return 0; }
-       virtual void                                                            copyRawContent(uint8_t buffer[]) const { }
-       virtual void                                                            setScope(Scope)         { }
-       virtual ld::Fixup::iterator                                     fixupsBegin() const     { return &_undefs[0]; }
-       virtual ld::Fixup::iterator                                     fixupsEnd()     const   { return &_undefs[_undefs.size()]; }
+       ld::File*                                                       file() const override           { return &_file; }
+       const char*                                                     name() const override           { return "import-atom"; }
+       uint64_t                                                        size() const override           { return 0; }
+       uint64_t                                                        objectAddress() const override { return 0; }
+       void                                                            copyRawContent(uint8_t buffer[]) const override { }
+       ld::Fixup::iterator                                     fixupsBegin() const override    { return &_undefs[0]; }
+       ld::Fixup::iterator                                     fixupsEnd()     const override  { return &_undefs[_undefs.size()]; }
 
        // for adding references to symbols outside bitcode file
        void                                                                            addReference(const char* nm)
                                                                                                                                        { _undefs.push_back(ld::Fixup(0, ld::Fixup::k1of1, 
-                                                                                                                                                               ld::Fixup::kindNone, false, nm)); }
+                                                                                                                                                               ld::Fixup::kindNone, false, strdup(nm))); }
 private:
 
        ld::File&                                                                       _file;
@@ -91,24 +90,27 @@ class File : public ld::relocatable::File
 public:
                                                                                        File(const char* path, time_t mTime, ld::File::Ordinal ordinal, 
                                                                                                         const uint8_t* content, uint32_t contentLength, cpu_type_t arch);
-       virtual                                                                 ~File();
+                                                                                       ~File() override;
 
        // overrides of ld::File
-       virtual bool                                                                            forEachAtom(ld::File::AtomHandler&) const;
-       virtual bool                                                                            justInTimeforEachAtom(const char* name, ld::File::AtomHandler&) const 
+       bool                                                                            forEachAtom(ld::File::AtomHandler&) const override;
+       bool                                                                            justInTimeforEachAtom(const char* name, ld::File::AtomHandler&) const override
                                                                                                                                                                        { return false; }
-       virtual uint32_t                                                                        cpuSubType() const                      { return _cpuSubType; }
+       uint32_t                                                                        cpuSubType() const override                     { return _cpuSubType; }
        
        // overrides of ld::relocatable::File 
-       virtual DebugInfoKind                                                           debugInfo()     const                   { return _debugInfo; }
-       virtual const char*                                                                     debugInfoPath() const           { return _debugInfoPath; }
-       virtual time_t                                                                          debugInfoModificationTime() const 
+       DebugInfoKind                                                           debugInfo()     const override                  { return _debugInfo; }
+       const char*                                                                     debugInfoPath() const override          { return _debugInfoPath; }
+       time_t                                                                          debugInfoModificationTime() const override
                                                                                                                                                                        { return _debugInfoModTime; }
-       virtual const std::vector<ld::relocatable::File::Stab>* stabs() const                   { return NULL; }
-       virtual bool                                                                            canScatterAtoms() const         { return true; }
-       virtual LinkerOptionsList*                                                      linkerOptions() const           { return NULL; }
-
-
+       const std::vector<ld::relocatable::File::Stab>* stabs() const override                  { return NULL; }
+       bool                                                                            canScatterAtoms() const override                { return true; }
+       LinkerOptionsList*                                                      linkerOptions() const override          { return NULL; }
+       const ToolVersionList&                                          toolVersions() const override           { return _toolVersions; }
+       bool                                                                                            isThinLTO() const                       { return _isThinLTO; }
+       void                                                                                            setIsThinLTO(bool ThinLTO)      { _isThinLTO = ThinLTO; }
+       // fixme rdar://24734472 objCConstraint() and objcHasCategoryClassProperties()
+       void                                                                                            release();
        lto_module_t                                                                            module()                                        { return _module; }
        class InternalAtom&                                                                     internalAtom()                          { return _internalAtom; }
        void                                                                                            setDebugInfo(ld::relocatable::File::DebugInfoKind k,
@@ -118,22 +120,33 @@ public:
                                                                                                                                                                                _debugInfoModTime = modTime; 
                                                                                                                                                                                _cpuSubType = subtype;}
 
+    static bool                                         sSupportsLocalContext;
+    static bool                                         sHasTriedLocalContext;
+    bool                                                mergeIntoGenerator(lto_code_gen_t generator, bool useSetModule);
+#if LTO_API_VERSION >= 18
+       void                                                addToThinGenerator(thinlto_code_gen_t generator, int id);
+#endif
 private:
        friend class Atom;
        friend class InternalAtom;
        friend class Parser;
-       
+
+       bool                                                                    _isThinLTO;
        cpu_type_t                                                              _architecture;
        class InternalAtom                                              _internalAtom;
        class Atom*                                                             _atomArray;
        uint32_t                                                                _atomArrayCount;
        lto_module_t                                                    _module;
+       const char*                             _path;
+       const uint8_t*                          _content;
+       uint32_t                                _contentLength;
        const char*                                                             _debugInfoPath;
        time_t                                                                  _debugInfoModTime;
        ld::Section                                                             _section;
        ld::Fixup                                                               _fixupToInternal;
        ld::relocatable::File::DebugInfoKind    _debugInfo; 
        uint32_t                                                                _cpuSubType;
+       ToolVersionList                                                 _toolVersions;  // unused, may some day contain version of clang the created bitcode
 };
 
 //
@@ -150,31 +163,32 @@ public:
                                                                                                ld::Atom::Definition d, ld::Atom::Combine c, ld::Atom::Alignment a, bool ah);
 
        // overrides of ld::Atom
-       virtual ld::File*                                       file() const            { return &_file; }
-       virtual const char*                                     translationUnitSource() const
+       const ld::File*                         file() const override           { return (_compiledAtom ? _compiledAtom->file() : &_file ); }
+       const ld::File*                         originalFile() const override   { return &_file; }
+       const char*                                     translationUnitSource() const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->translationUnitSource() : NULL); }
-       virtual const char*                                     name() const            { return _name; }
-       virtual uint64_t                                        size() const            { return (_compiledAtom ? _compiledAtom->size() : 0); }
-       virtual uint64_t                                        objectAddress() const { return (_compiledAtom ? _compiledAtom->objectAddress() : 0); }
-       virtual void                                            copyRawContent(uint8_t buffer[]) const 
+       const char*                                     name() const override           { return _name; }
+       uint64_t                                        size() const override           { return (_compiledAtom ? _compiledAtom->size() : 0); }
+       uint64_t                                        objectAddress() const override { return (_compiledAtom ? _compiledAtom->objectAddress() : 0); }
+       void                                            copyRawContent(uint8_t buffer[]) const override
                                                                                                                        { if (_compiledAtom) _compiledAtom->copyRawContent(buffer); }
-       virtual const uint8_t*                          rawContentPointer() const 
+       const uint8_t*                          rawContentPointer() const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->rawContentPointer() : NULL);  }
-       virtual unsigned long                           contentHash(const class ld::IndirectBindingTable& ibt) const 
+       unsigned long                           contentHash(const class ld::IndirectBindingTable& ibt) const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->contentHash(ibt) : 0);  }
-       virtual bool                                            canCoalesceWith(const ld::Atom& rhs, const class ld::IndirectBindingTable& ibt) const 
+       bool                                            canCoalesceWith(const ld::Atom& rhs, const class ld::IndirectBindingTable& ibt) const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->canCoalesceWith(rhs,ibt) : false); }
-       virtual ld::Fixup::iterator                             fixupsBegin() const     
+       ld::Fixup::iterator                             fixupsBegin() const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->fixupsBegin() : (ld::Fixup*)&_file._fixupToInternal); }
-       virtual ld::Fixup::iterator                             fixupsEnd() const       
+       ld::Fixup::iterator                             fixupsEnd() const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->fixupsEnd() : &((ld::Fixup*)&_file._fixupToInternal)[1]); }
-       virtual ld::Atom::UnwindInfo::iterator  beginUnwind() const 
+       ld::Atom::UnwindInfo::iterator  beginUnwind() const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->beginUnwind() : NULL); }
-       virtual ld::Atom::UnwindInfo::iterator  endUnwind() const       
+       ld::Atom::UnwindInfo::iterator  endUnwind() const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->endUnwind() : NULL); }
-       virtual ld::Atom::LineInfo::iterator    beginLineInfo() const 
+       ld::Atom::LineInfo::iterator    beginLineInfo() const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->beginLineInfo() : NULL); }
-       virtual ld::Atom::LineInfo::iterator    endLineInfo() const 
+       ld::Atom::LineInfo::iterator    endLineInfo() const override
                                                                                                                        { return (_compiledAtom ? _compiledAtom->endLineInfo() : NULL); }
                                                                                                                        
        const ld::Atom*                                         compiledAtom()          { return _compiledAtom; }
@@ -199,7 +213,8 @@ public:
        static bool                                             validFile(const uint8_t* fileContent, uint64_t fileLength, cpu_type_t architecture, cpu_subtype_t subarch);
        static const char*                              fileKind(const uint8_t* fileContent, uint64_t fileLength);
        static File*                                    parse(const uint8_t* fileContent, uint64_t fileLength, const char* path, 
-                                                                                       time_t modTime, ld::File::Ordinal ordinal, cpu_type_t architecture, cpu_subtype_t subarch, bool logAllFiles);
+                                                                                       time_t modTime, ld::File::Ordinal ordinal, cpu_type_t architecture, cpu_subtype_t subarch,
+                                                                                       bool logAllFiles, bool verboseOptimizationHints);
        static bool                                             libLTOisLoaded() { return (::lto_get_version() != NULL); }
        static bool                                             optimize(   const std::vector<const ld::Atom*>& allAtoms,
                                                                                                ld::Internal&                                           state,
@@ -208,11 +223,16 @@ public:
                                                                                                std::vector<const ld::Atom*>&           newAtoms, 
                                                                                                std::vector<const char*>&                       additionalUndefines);
 
-       static const char*                      ltoVersion()    { return ::lto_get_version(); }
+       static const char*                              ltoVersion()    { return ::lto_get_version(); }
 
 private:
+
        static const char*                              tripletPrefixForArch(cpu_type_t arch);
-       static ld::relocatable::File*   parseMachOFile(const uint8_t* p, size_t len, const OptimizeOptions& options);
+       static ld::relocatable::File*   parseMachOFile(const uint8_t* p, size_t len, const std::string &path, const OptimizeOptions& options,
+                                                                                                  ld::File::Ordinal ordinal);
+#if LTO_API_VERSION >= 7
+       static void ltoDiagnosticHandler(lto_codegen_diagnostic_severity_t, const char*, void*);
+#endif
 
        typedef std::unordered_set<const char*, ld::CStringHash, ld::CStringEquals>  CStringSet;
        typedef std::unordered_map<const char*, Atom*, ld::CStringHash, ld::CStringEquals> CStringToAtom;
@@ -220,22 +240,72 @@ private:
        class AtomSyncer : public ld::File::AtomHandler {
        public:
                                                        AtomSyncer(std::vector<const char*>& a, std::vector<const ld::Atom*>&na,
-                                                                               CStringToAtom la, CStringToAtom dla, const OptimizeOptions& options) :
-                                                                               _options(options), _additionalUndefines(a), _newAtoms(na), _llvmAtoms(la), _deadllvmAtoms(dla) { }
-               virtual void            doAtom(const class ld::Atom&);
-               virtual void            doFile(const class ld::File&) { }
+                                                                               const CStringToAtom &la, const CStringToAtom &dla, const OptimizeOptions& options) :
+                                                                               _options(options), _additionalUndefines(a), _newAtoms(na), _llvmAtoms(la), _deadllvmAtoms(dla), _lastProxiedAtom(NULL), _lastProxiedFile(NULL) {}
+               void            doAtom(const class ld::Atom&) override;
+               void            doFile(const class ld::File&) override { }
                
                const OptimizeOptions&                  _options;
                std::vector<const char*>&               _additionalUndefines;
                std::vector<const ld::Atom*>&   _newAtoms;
-               CStringToAtom                                   _llvmAtoms;
-               CStringToAtom                                   _deadllvmAtoms;
+               const CStringToAtom                                     &_llvmAtoms;
+               const CStringToAtom                                     &_deadllvmAtoms;
+               const ld::Atom*                                 _lastProxiedAtom;
+               const ld::File*                                 _lastProxiedFile;
        };
 
+       static void                                             setPreservedSymbols(const std::vector<const ld::Atom*>& allAtoms,
+                                                                                                               ld::Internal&                                           state,
+                                                                                                               const OptimizeOptions&                          options,
+                                                                                                               CStringToAtom &deadllvmAtoms,
+                                                                                                               CStringToAtom &llvmAtoms,
+                                                                                                               lto_code_gen_t generator);
+
+       static std::tuple<uint8_t *, size_t> codegen(const OptimizeOptions& options,
+                                                                                                ld::Internal&                  state,
+                                                                                                lto_code_gen_t                 generator,
+                                                                                            std::string&           object_path);
+
+
+       static void loadMachO(ld::relocatable::File*                            machoFile,
+                                                 const OptimizeOptions&                options,
+                                                 ld::File::AtomHandler&                handler,
+                                                 std::vector<const ld::Atom*>& newAtoms,
+                                                 std::vector<const char*>&             additionalUndefines,
+                                                 CStringToAtom                                 &llvmAtoms,
+                                                 CStringToAtom                                 &deadllvmAtoms);
+
+       static bool optimizeLTO(const std::vector<File*> files,
+                                                       const std::vector<const ld::Atom*>&     allAtoms,
+                                                       ld::Internal&                                           state,
+                                                       const OptimizeOptions&                          options,
+                                                       ld::File::AtomHandler&                          handler,
+                                                       std::vector<const ld::Atom*>&           newAtoms,
+                                                       std::vector<const char*>&                       additionalUndefines);
+
+       static bool optimizeThinLTO(const std::vector<File*>&              Files,
+                                                           const std::vector<const ld::Atom*>& allAtoms,
+                                                               ld::Internal&                                           state,
+                                                               const OptimizeOptions&                          options,
+                                                               ld::File::AtomHandler&                          handler,
+                                                               std::vector<const ld::Atom*>&           newAtoms,
+                                                               std::vector<const char*>&                       additionalUndefines);
+
+#if LTO_API_VERSION >= 18
+       static thinlto_code_gen_t init_thinlto_codegen(const std::vector<File*>&           files,
+                                                                                                  const std::vector<const ld::Atom*>& allAtoms,
+                                                                                                  ld::Internal&                                       state,
+                                                                                                  const OptimizeOptions&                          options,
+                                                                                                  CStringToAtom&                      deadllvmAtoms,
+                                                                                                  CStringToAtom&                      llvmAtoms);
+#endif
+
        static std::vector<File*>               _s_files;
+       static bool                                             _s_llvmOptionsProcessed;
 };
 
 std::vector<File*> Parser::_s_files;
+bool Parser::_s_llvmOptionsProcessed = false;
 
 
 bool Parser::validFile(const uint8_t* fileContent, uint64_t fileLength, cpu_type_t architecture, cpu_subtype_t subarch)
@@ -276,7 +346,7 @@ const char* Parser::fileKind(const uint8_t* p, uint64_t fileLength)
 }
 
 File* Parser::parse(const uint8_t* fileContent, uint64_t fileLength, const char* path, time_t modTime, ld::File::Ordinal ordinal,
-                                                                                                       cpu_type_t architecture, cpu_subtype_t subarch, bool logAllFiles) 
+                                                                                                       cpu_type_t architecture, cpu_subtype_t subarch, bool logAllFiles, bool verboseOptimizationHints
 {
        File* f = new File(path, modTime, ordinal, fileContent, fileLength, architecture);
        _s_files.push_back(f);
@@ -286,7 +356,8 @@ File* Parser::parse(const uint8_t* fileContent, uint64_t fileLength, const char*
 }
 
 
-ld::relocatable::File* Parser::parseMachOFile(const uint8_t* p, size_t len, const OptimizeOptions& options) 
+ld::relocatable::File* Parser::parseMachOFile(const uint8_t* p, size_t len, const std::string &path, const OptimizeOptions& options,
+                                                                                         ld::File::Ordinal ordinal)
 {
        mach_o::relocatable::ParserOptions objOpts;
        objOpts.architecture            = options.arch;
@@ -295,19 +366,29 @@ ld::relocatable::File* Parser::parseMachOFile(const uint8_t* p, size_t len, cons
        objOpts.warnUnwindConversionProblems    = options.needsUnwindInfoSection;
        objOpts.keepDwarfUnwind         = options.keepDwarfUnwind;
        objOpts.forceDwarfConversion = false;
+       objOpts.neverConvertDwarf   = false;
+       objOpts.verboseOptimizationHints = options.verboseOptimizationHints;
+       objOpts.armUsesZeroCostExceptions = options.armUsesZeroCostExceptions;
+       objOpts.simulator                       = options.simulator;
+       objOpts.ignoreMismatchPlatform = options.ignoreMismatchPlatform;
+       objOpts.platform                        = options.platform;
+       objOpts.minOSVersion            = options.minOSVersion;
        objOpts.subType                         = 0;
-       
-       // mach-o parsing is done in-memory, but need path for debug notes
-       const char* path = "/tmp/lto.o";
+       objOpts.srcKind                         = ld::relocatable::File::kSourceLTO;
+       objOpts.treateBitcodeAsData = false;
+       objOpts.usingBitcode            = options.bitcodeBundle;
+       objOpts.maxDefaultCommonAlignment = options.maxDefaultCommonAlignment;
+
+       const char *object_path = path.c_str();
+       if (path.empty())
+               object_path = "/tmp/lto.o";
+
        time_t modTime = 0;
-       if ( options.tmpObjectFilePath != NULL ) {
-               path = options.tmpObjectFilePath;
-               struct stat statBuffer;
-               if ( stat(options.tmpObjectFilePath, &statBuffer) == 0 )
-                       modTime = statBuffer.st_mtime;
-       }
-       
-       ld::relocatable::File* result = mach_o::relocatable::parse(p, len, path, modTime, ld::File::Ordinal::LTOOrdinal(), objOpts);
+       struct stat statBuffer;
+       if ( stat(object_path, &statBuffer) == 0 )
+               modTime = statBuffer.st_mtime;
+
+       ld::relocatable::File* result = mach_o::relocatable::parse(p, len, strdup(object_path), modTime, ordinal, objOpts);
        if ( result != NULL )
                return result;
        throw "LLVM LTO, file is not of required architecture";
@@ -316,8 +397,9 @@ ld::relocatable::File* Parser::parseMachOFile(const uint8_t* p, size_t len, cons
 
 
 File::File(const char* pth, time_t mTime, ld::File::Ordinal ordinal, const uint8_t* content, uint32_t contentLength, cpu_type_t arch) 
-       : ld::relocatable::File(pth,mTime,ordinal), _architecture(arch), _internalAtom(*this), 
-       _atomArray(NULL), _atomArrayCount(0), _module(NULL), _debugInfoPath(pth), 
+       : ld::relocatable::File(pth,mTime,ordinal), _isThinLTO(false), _architecture(arch), _internalAtom(*this),
+       _atomArray(NULL), _atomArrayCount(0), _module(NULL), _path(pth),
+       _content(content), _contentLength(contentLength), _debugInfoPath(pth),
        _section("__TEXT_", "__tmp_lto", ld::Section::typeTempLTO),
        _fixupToInternal(0, ld::Fixup::k1of1, ld::Fixup::kindNone, &_internalAtom),
        _debugInfo(ld::relocatable::File::kDebugInfoNone), _cpuSubType(0)
@@ -325,12 +407,30 @@ File::File(const char* pth, time_t mTime, ld::File::Ordinal ordinal, const uint8
        const bool log = false;
        
        // create llvm module
+#if LTO_API_VERSION >= 11
+       if ( sSupportsLocalContext || !sHasTriedLocalContext ) {
+               _module = ::lto_module_create_in_local_context(content, contentLength, pth);
+       }
+       if ( !sHasTriedLocalContext ) {
+               sHasTriedLocalContext = true;
+               sSupportsLocalContext = (_module != NULL);
+       }
+       if ( (_module == NULL) && !sSupportsLocalContext )
+#endif
+#if LTO_API_VERSION >= 9
+       _module = ::lto_module_create_from_memory_with_path(content, contentLength, pth);
+       if ( _module == NULL && !sSupportsLocalContext )
+#endif
        _module = ::lto_module_create_from_memory(content, contentLength);
     if ( _module == NULL )
                throwf("could not parse object file %s: '%s', using libLTO version '%s'", pth, ::lto_get_error_message(), ::lto_get_version());
 
        if ( log ) fprintf(stderr, "bitcode file: %s\n", pth);
-       
+
+#if LTO_API_VERSION >= 18
+       _isThinLTO = ::lto_module_is_thinlto(_module);
+#endif
+
        // create atom for each global symbol in module
        uint32_t count = ::lto_module_get_num_symbols(_module);
        _atomArray = (Atom*)malloc(sizeof(Atom)*count);
@@ -404,12 +504,60 @@ File::File(const char* pth, time_t mTime, ld::File::Ordinal ordinal, const uint8
                        if ( log ) fprintf(stderr, "\t%s (undefined)\n", name);
                }
        }
+
+#if LTO_API_VERSION >= 11
+       if ( sSupportsLocalContext )
+               this->release();
+#endif
 }
 
 File::~File()
+{
+       this->release();
+}
+
+bool File::mergeIntoGenerator(lto_code_gen_t generator, bool useSetModule) {
+#if LTO_API_VERSION >= 11
+    if ( sSupportsLocalContext ) {
+        assert(!_module && "Expected module to be disposed");
+        _module = ::lto_module_create_in_codegen_context(_content, _contentLength,
+                                                        _path, generator);
+        if ( _module == NULL )
+            throwf("could not reparse object file %s: '%s', using libLTO version '%s'",
+                  _path, ::lto_get_error_message(), ::lto_get_version());
+    }
+#endif
+    assert(_module && "Expected module to stick around");
+#if LTO_API_VERSION >= 13
+    if (useSetModule) {
+        // lto_codegen_set_module will transfer ownership of the module to LTO code generator,
+        // so we don't need to release the module here.
+        ::lto_codegen_set_module(generator, _module);
+        return false;
+    }
+#endif
+    if ( ::lto_codegen_add_module(generator, _module) )
+        return true;
+
+    // <rdar://problem/15471128> linker should release module as soon as possible
+    this->release();
+    return false;
+}
+
+#if LTO_API_VERSION >= 18
+void File::addToThinGenerator(thinlto_code_gen_t generator, int id) {
+       assert(!_module && "Expected module to be disposed");
+       std::string pathWithID = _path;
+       pathWithID += std::to_string(id);
+       ::thinlto_codegen_add_module(generator, strdup(pathWithID.c_str()), (const char *)_content, _contentLength);
+}
+#endif
+
+void File::release()
 {
        if ( _module != NULL )
                ::lto_module_dispose(_module);
+       _module = NULL;
 }
 
 bool File::forEachAtom(ld::File::AtomHandler& handler) const
@@ -432,7 +580,7 @@ Atom::Atom(File& f, const char* nm, ld::Atom::Scope s, ld::Atom::Definition d, l
                        ld::Atom::Alignment a, bool ah)
        : ld::Atom(f._section, d, c, s, ld::Atom::typeLTOtemporary, 
                                ld::Atom::symbolTableIn, false, false, false, a),
-               _file(f), _name(nm), _compiledAtom(NULL)
+               _file(f), _name(strdup(nm)), _compiledAtom(NULL)
 {
        if ( ah )
                this->setAutoHide();
@@ -461,61 +609,46 @@ struct CommandLineOrderFileSorter
 };
 
 
-bool Parser::optimize(  const std::vector<const ld::Atom*>&    allAtoms,
-                                               ld::Internal&                                           state,
-                                               const OptimizeOptions&                          options,
-                                               ld::File::AtomHandler&                          handler,
-                                               std::vector<const ld::Atom*>&           newAtoms, 
-                                               std::vector<const char*>&                       additionalUndefines)
+#if LTO_API_VERSION >= 7
+void Parser::ltoDiagnosticHandler(lto_codegen_diagnostic_severity_t severity, const char* message, void*) 
 {
-       const bool logMustPreserve = false;
-       const bool logExtraOptions = false;
-       const bool logBitcodeFiles = false;
-       const bool logAtomsBeforeSync = false;
-
-       // exit quickly if nothing to do
-       if ( _s_files.size() == 0 ) 
-               return false;
-       
-       // print out LTO version string if -v was used
-       if ( options.verbose )
-               fprintf(stderr, "%s\n", ::lto_get_version());
-       
-       // create optimizer and add each Reader
-       lto_code_gen_t generator = ::lto_codegen_create();
-       // <rdar://problem/12379604> The order that files are merged must match command line order
-       std::sort(_s_files.begin(), _s_files.end(), CommandLineOrderFileSorter());
-       ld::File::Ordinal lastOrdinal;
-       for (std::vector<File*>::iterator it=_s_files.begin(); it != _s_files.end(); ++it) {
-               File* f = *it;
-               assert(f->ordinal() > lastOrdinal);
-               if ( logBitcodeFiles ) fprintf(stderr, "lto_codegen_add_module(%s)\n", f->path());
-               if ( ::lto_codegen_add_module(generator, f->module()) )
-                       throwf("lto: could not merge in %s because '%s', using libLTO version '%s'", f->path(), ::lto_get_error_message(), ::lto_get_version());
-               lastOrdinal = f->ordinal();
+       switch ( severity ) {
+#if LTO_API_VERSION >= 10
+               case LTO_DS_REMARK:
+                       fprintf(stderr, "ld: LTO remark: %s\n", message);
+                       break;
+#endif
+               case LTO_DS_NOTE:
+               case LTO_DS_WARNING:
+                       warning("%s", message);
+                       break;
+               case LTO_DS_ERROR:
+                       throwf("%s", message);
        }
+}
+#endif
 
-       // add any -mllvm command line options
-       for (std::vector<const char*>::const_iterator it=options.llvmOptions->begin(); it != options.llvmOptions->end(); ++it) {
-               if ( logExtraOptions ) fprintf(stderr, "passing option to llvm: %s\n", *it);
-               ::lto_codegen_debug_options(generator, *it);
-       }
 
-       // <rdar://problem/13687397> Need a way for LTO to get cpu variants (until that info is in bitcode)
-       if ( options.mcpu != NULL )
-               ::lto_codegen_set_cpu(generator, options.mcpu);
+/// Instruct libLTO about the list of symbols to preserve, compute deadllvmAtoms and llvmAtoms
+void Parser::setPreservedSymbols(      const std::vector<const ld::Atom*>&     allAtoms,
+                                                                       ld::Internal&                                           state,
+                                                                       const OptimizeOptions&                          options,
+                                                                       CStringToAtom &deadllvmAtoms,
+                                                                       CStringToAtom &llvmAtoms,
+                                                                       lto_code_gen_t generator) {
+       const bool logMustPreserve = false;
 
-       // The atom graph uses directed edges (references). Collect all references where 
-       // originating atom is not part of any LTO Reader. This allows optimizer to optimize an 
-       // external (i.e. not originated from same .o file) reference if all originating atoms are also 
+       // The atom graph uses directed edges (references). Collect all references where
+       // originating atom is not part of any LTO Reader. This allows optimizer to optimize an
+       // external (i.e. not originated from same .o file) reference if all originating atoms are also
        // defined in llvm bitcode file.
        CStringSet nonLLVMRefs;
-       CStringToAtom llvmAtoms;
-    bool hasNonllvmAtoms = false;
+       bool hasNonllvmAtoms = false;
        for (std::vector<const ld::Atom*>::const_iterator it = allAtoms.begin(); it != allAtoms.end(); ++it) {
                const ld::Atom* atom = *it;
-               // only look at references that come from an atom that is not an llvm atom
-               if ( atom->contentType() != ld::Atom::typeLTOtemporary ) {
+               // only look at references that come from an atom that is not an LTO atom
+               if (atom->contentType() != ld::Atom::typeLTOtemporary ||
+                       ((lto::File *)atom->file())->isThinLTO()) {
                        if ( (atom->section().type() != ld::Section::typeMachHeader) && (atom->definition() != ld::Atom::definitionProxy) ) {
                                hasNonllvmAtoms = true;
                        }
@@ -524,36 +657,32 @@ bool Parser::optimize(  const std::vector<const ld::Atom*>&       allAtoms,
                                switch ( fit->binding ) {
                                        case ld::Fixup::bindingDirectlyBound:
                                                // that reference an llvm atom
-                                               if ( fit->u.target->contentType() == ld::Atom::typeLTOtemporary ) 
+                                               if ( fit->u.target->contentType() == ld::Atom::typeLTOtemporary )
                                                        nonLLVMRefs.insert(fit->u.target->name());
                                                break;
                                        case ld::Fixup::bindingsIndirectlyBound:
                                                target = state.indirectBindingTable[fit->u.bindingIndex];
-                                               if ( target == NULL )
-                                                       throwf("'%s' in %s contains undefined reference", atom->name(), atom->file()->path());
-                                               assert(target != NULL);
-                                               if ( target->contentType() == ld::Atom::typeLTOtemporary )
+                                               if ( (target != NULL) && (target->contentType() == ld::Atom::typeLTOtemporary) )
                                                        nonLLVMRefs.insert(target->name());
                                        default:
                                                break;
                                }
                        }
                }
-               else {
+               else if ( atom->scope() >= ld::Atom::scopeLinkageUnit ) {
                        llvmAtoms[atom->name()] = (Atom*)atom;
                }
        }
        // if entry point is in a llvm bitcode file, it must be preserved by LTO
        if ( state.entryPoint!= NULL ) {
-               if ( state.entryPoint->contentType() == ld::Atom::typeLTOtemporary ) 
+               if ( state.entryPoint->contentType() == ld::Atom::typeLTOtemporary )
                        nonLLVMRefs.insert(state.entryPoint->name());
        }
-       
+
        // deadAtoms are the atoms that the linker coalesced.  For instance weak or tentative definitions
        // overriden by another atom.  If any of these deadAtoms are llvm atoms and they were replaced
-       // with a mach-o atom, we need to tell the lto engine to preserve (not optimize away) its dead 
+       // with a mach-o atom, we need to tell the lto engine to preserve (not optimize away) its dead
        // atom so that the linker can replace it with the mach-o one later.
-       CStringToAtom deadllvmAtoms;
        for (std::vector<const ld::Atom*>::const_iterator it = allAtoms.begin(); it != allAtoms.end(); ++it) {
                const ld::Atom* atom = *it;
                if ( atom->coalescedAway() && (atom->contentType() == ld::Atom::typeLTOtemporary) ) {
@@ -570,7 +699,7 @@ bool Parser::optimize(  const std::vector<const ld::Atom*>& allAtoms,
                        if ( llvmAtom->coalescedAway()  ) {
                                const char* name = llvmAtom->name();
                                if ( deadllvmAtoms.find(name) == deadllvmAtoms.end() ) {
-                                       if ( logMustPreserve ) 
+                                       if ( logMustPreserve )
                                                fprintf(stderr, "lto_codegen_add_must_preserve_symbol(%s) because linker coalesce away and replace with a mach-o atom\n", name);
                                        ::lto_codegen_add_must_preserve_symbol(generator, name);
                                        deadllvmAtoms[name] = (Atom*)llvmAtom;
@@ -582,7 +711,7 @@ bool Parser::optimize(  const std::vector<const ld::Atom*>& allAtoms,
                        }
                }
        }
-       
+
        // tell code generator about symbols that must be preserved
        for (CStringToAtom::iterator it = llvmAtoms.begin(); it != llvmAtoms.end(); ++it) {
                const char* name = it->first;
@@ -591,7 +720,7 @@ bool Parser::optimize(  const std::vector<const ld::Atom*>& allAtoms,
                // 1 - atom scope is global (and not linkage unit).
                // 2 - included in nonLLVMRefs set.
                // If a symbol is not listed in exportList then LTO is free to optimize it away.
-               if ( (atom->scope() == ld::Atom::scopeGlobal) && options.preserveAllGlobals ) { 
+               if ( (atom->scope() == ld::Atom::scopeGlobal) && options.preserveAllGlobals ) {
                        if ( logMustPreserve ) fprintf(stderr, "lto_codegen_add_must_preserve_symbol(%s) because global symbol\n", name);
                        ::lto_codegen_add_must_preserve_symbol(generator, name);
                }
@@ -599,50 +728,85 @@ bool Parser::optimize(  const std::vector<const ld::Atom*>&       allAtoms,
                        if ( logMustPreserve ) fprintf(stderr, "lto_codegen_add_must_preserve_symbol(%s) because referenced by a mach-o atom\n", name);
                        ::lto_codegen_add_must_preserve_symbol(generator, name);
                }
+               else if ( options.relocatable && hasNonllvmAtoms ) {
+                       // <rdar://problem/14334895> ld -r mode but merging in some mach-o files, so need to keep libLTO from optimizing away anything
+                       if ( logMustPreserve ) fprintf(stderr, "lto_codegen_add_must_preserve_symbol(%s) because -r mode disable LTO dead stripping\n", name);
+                       ::lto_codegen_add_must_preserve_symbol(generator, name);
+               }
        }
-       
-    // special case running ld -r on all bitcode files to produce another bitcode file (instead of mach-o)
-    if ( options.relocatable && !hasNonllvmAtoms ) {
+
+       // <rdar://problem/16165191> tell code generator to preserve initial undefines
+       for( std::vector<const char*>::const_iterator it=options.initialUndefines->begin(); it != options.initialUndefines->end(); ++it) {
+               if ( logMustPreserve ) fprintf(stderr, "lto_codegen_add_must_preserve_symbol(%s) because it is an initial undefine\n", *it);
+               ::lto_codegen_add_must_preserve_symbol(generator, *it);
+       }
+
+       // special case running ld -r on all bitcode files to produce another bitcode file (instead of mach-o)
+       if ( options.relocatable && !hasNonllvmAtoms ) {
+#if LTO_API_VERSION >= 15
+               ::lto_codegen_set_should_embed_uselists(generator, false);
+#endif
                if ( ! ::lto_codegen_write_merged_modules(generator, options.outputFilePath) ) {
                        // HACK, no good way to tell linker we are all done, so just quit
                        exit(0);
                }
                warning("could not produce merged bitcode file");
-    }
-    
-       // set code-gen model
-       lto_codegen_model model = LTO_CODEGEN_PIC_MODEL_DYNAMIC;
+       }
+
+}
+
+// Retrieve the codegen model from the options
+static lto_codegen_model getCodeModel(const OptimizeOptions& options) {
        if ( options.mainExecutable ) {
                if ( options.staticExecutable ) {
                        // x86_64 "static" or any "-static -pie" is really dynamic code model
                        if ( (options.arch == CPU_TYPE_X86_64) || options.pie )
-                               model = LTO_CODEGEN_PIC_MODEL_DYNAMIC;
+                               return LTO_CODEGEN_PIC_MODEL_DYNAMIC;
                        else
-                               model = LTO_CODEGEN_PIC_MODEL_STATIC;
+                               return LTO_CODEGEN_PIC_MODEL_STATIC;
+               }
+               else if ( options.preload ) {
+                       if ( options.pie )
+                               return LTO_CODEGEN_PIC_MODEL_DYNAMIC;
+                       else
+                               return LTO_CODEGEN_PIC_MODEL_STATIC;
                }
                else {
                        if ( options.pie )
-                               model = LTO_CODEGEN_PIC_MODEL_DYNAMIC;
+                               return LTO_CODEGEN_PIC_MODEL_DYNAMIC;
                        else
-                               model = LTO_CODEGEN_PIC_MODEL_DYNAMIC_NO_PIC;
+                               return LTO_CODEGEN_PIC_MODEL_DYNAMIC_NO_PIC;
                }
        }
        else {
                if ( options.allowTextRelocs )
-                       model = LTO_CODEGEN_PIC_MODEL_DYNAMIC_NO_PIC;
+                       return LTO_CODEGEN_PIC_MODEL_DYNAMIC_NO_PIC;
                else
-                       model = LTO_CODEGEN_PIC_MODEL_DYNAMIC;
+                       return LTO_CODEGEN_PIC_MODEL_DYNAMIC;
        }
-       if ( ::lto_codegen_set_pic_model(generator, model) )
+
+}
+
+std::tuple<uint8_t *, size_t> Parser::codegen(const OptimizeOptions& options,
+                                                                                         ld::Internal&                  state,
+                                                                                         lto_code_gen_t                 generator,
+                                                                                         std::string&           object_path) {
+       uint8_t *machOFile;
+       size_t machOFileLen;
+
+       if ( ::lto_codegen_set_pic_model(generator, getCodeModel(options)) )
                throwf("could not create set codegen model: %s", lto_get_error_message());
 
-    // if requested, save off merged bitcode file
-    if ( options.saveTemps ) {
-        char tempBitcodePath[MAXPATHLEN];
-        strcpy(tempBitcodePath, options.outputFilePath);
-        strcat(tempBitcodePath, ".lto.bc");
-        ::lto_codegen_write_merged_modules(generator, tempBitcodePath);
-    }
+       // if requested, save off merged bitcode file
+       if ( options.saveTemps ) {
+               char tempBitcodePath[MAXPATHLEN];
+               strcpy(tempBitcodePath, options.outputFilePath);
+               strcat(tempBitcodePath, ".lto.bc");
+#if LTO_API_VERSION >= 15
+               ::lto_codegen_set_should_embed_uselists(generator, true);
+#endif
+               ::lto_codegen_write_merged_modules(generator, tempBitcodePath);
+       }
 
 #if LTO_API_VERSION >= 3
        // find assembler next to linker
@@ -658,66 +822,205 @@ bool Parser::optimize(  const std::vector<const ld::Atom*>&      allAtoms,
                }
        }
 #endif
-       // run code generator
-       size_t machOFileLen;
-       const uint8_t* machOFile = (uint8_t*)::lto_codegen_compile(generator, &machOFileLen);
-       if ( machOFile == NULL ) 
-               throwf("could not do LTO codegen: '%s', using libLTO version '%s'", ::lto_get_error_message(), ::lto_get_version());
-       
-    // if requested, save off temp mach-o file
-    if ( options.saveTemps ) {
-        char tempMachoPath[MAXPATHLEN];
-        strcpy(tempMachoPath, options.outputFilePath);
-        strcat(tempMachoPath, ".lto.o");
-        int fd = ::open(tempMachoPath, O_CREAT | O_WRONLY | O_TRUNC, 0666);
+
+       // When lto API version is greater than or equal to 12, we use lto_codegen_optimize and lto_codegen_compile_optimized
+       // instead of lto_codegen_compile, and we save the merged bitcode file in between.
+       bool useSplitAPI = false;
+#if LTO_API_VERSION >= 12
+       if ( ::lto_api_version() >= 12)
+               useSplitAPI = true;
+#endif
+
+       if ( useSplitAPI) {
+#if LTO_API_VERSION >= 12
+#if LTO_API_VERSION >= 14
+               if ( ::lto_api_version() >= 14 && options.ltoCodegenOnly)
+                       lto_codegen_set_should_internalize(generator, false);
+#endif
+               // run optimizer
+               if ( !options.ltoCodegenOnly && ::lto_codegen_optimize(generator) )
+                       throwf("could not do LTO optimization: '%s', using libLTO version '%s'", ::lto_get_error_message(), ::lto_get_version());
+
+               if ( options.saveTemps || options.bitcodeBundle ) {
+                       // save off merged bitcode file
+                       char tempOptBitcodePath[MAXPATHLEN];
+                       strcpy(tempOptBitcodePath, options.outputFilePath);
+                       strcat(tempOptBitcodePath, ".lto.opt.bc");
+#if LTO_API_VERSION >= 15
+                       ::lto_codegen_set_should_embed_uselists(generator, true);
+#endif
+                       ::lto_codegen_write_merged_modules(generator, tempOptBitcodePath);
+                       if ( options.bitcodeBundle )
+                               state.ltoBitcodePath.push_back(tempOptBitcodePath);
+               }
+
+               // run code generator
+               machOFile = (uint8_t*)::lto_codegen_compile_optimized(generator, &machOFileLen);
+#endif
+               if ( machOFile == NULL )
+                       throwf("could not do LTO codegen: '%s', using libLTO version '%s'", ::lto_get_error_message(), ::lto_get_version());
+       }
+       else {
+               // run optimizer and code generator
+               machOFile = (uint8_t*)::lto_codegen_compile(generator, &machOFileLen);
+               if ( machOFile == NULL )
+                       throwf("could not do LTO codegen: '%s', using libLTO version '%s'", ::lto_get_error_message(), ::lto_get_version());
+               if ( options.saveTemps ) {
+                       // save off merged bitcode file
+                       char tempOptBitcodePath[MAXPATHLEN];
+                       strcpy(tempOptBitcodePath, options.outputFilePath);
+                       strcat(tempOptBitcodePath, ".lto.opt.bc");
+#if LTO_API_VERSION >= 15
+                       ::lto_codegen_set_should_embed_uselists(generator, true);
+#endif
+                       ::lto_codegen_write_merged_modules(generator, tempOptBitcodePath);
+               }
+       }
+
+       // if requested, save off temp mach-o file
+       if ( options.saveTemps ) {
+               char tempMachoPath[MAXPATHLEN];
+               strcpy(tempMachoPath, options.outputFilePath);
+               strcat(tempMachoPath, ".lto.o");
+               int fd = ::open(tempMachoPath, O_CREAT | O_WRONLY | O_TRUNC, 0666);
                if ( fd != -1) {
                        ::write(fd, machOFile, machOFileLen);
                        ::close(fd);
                }
-               //      save off merged bitcode file
-               char tempOptBitcodePath[MAXPATHLEN];
-        strcpy(tempOptBitcodePath, options.outputFilePath);
-        strcat(tempOptBitcodePath, ".lto.opt.bc");
-        ::lto_codegen_write_merged_modules(generator, tempOptBitcodePath);
        }
 
        // if needed, save temp mach-o file to specific location
-       if ( options.tmpObjectFilePath != NULL ) {
-               int fd = ::open(options.tmpObjectFilePath, O_CREAT | O_WRONLY | O_TRUNC, 0666);
+       if ( !object_path.empty() ) {
+               int fd = ::open(object_path.c_str(), O_CREAT | O_WRONLY | O_TRUNC, 0666);
                if ( fd != -1) {
                        ::write(fd, machOFile, machOFileLen);
                        ::close(fd);
                }
                else {
-                       warning("could not write LTO temp file '%s', errno=%d", options.tmpObjectFilePath, errno);
+                       warning("could not write LTO temp file '%s', errno=%d", object_path.c_str(), errno);
                }
        }
-       
-       // parse generated mach-o file into a MachOReader
-       ld::relocatable::File* machoFile = parseMachOFile(machOFile, machOFileLen, options);
-       
+       return std::make_tuple(machOFile, machOFileLen);
+}
+
+/// Load the MachO located in buffer \p machOFile with size \p machOFileLen.
+/// The loaded atoms are sync'ed using all the supplied lists.
+void Parser::loadMachO(ld::relocatable::File*                          machoFile,
+                                          const OptimizeOptions&                               options,
+                                          ld::File::AtomHandler&                               handler,
+                                          std::vector<const ld::Atom*>&                newAtoms,
+                                          std::vector<const char*>&                    additionalUndefines,
+                                          CStringToAtom                                                &llvmAtoms,
+                                          CStringToAtom                                                &deadllvmAtoms) {
+       const bool logAtomsBeforeSync = false;
+
        // sync generated mach-o atoms with existing atoms ld knows about
        if ( logAtomsBeforeSync ) {
                fprintf(stderr, "llvmAtoms:\n");
                for (CStringToAtom::iterator it = llvmAtoms.begin(); it != llvmAtoms.end(); ++it) {
                        const char* name = it->first;
-                       //Atom* atom = it->second;
-                       fprintf(stderr, "\t%s\n", name);
+                       Atom* atom = it->second;
+                       fprintf(stderr, "\t%p\t%s\n", atom, name);
                }
                fprintf(stderr, "deadllvmAtoms:\n");
                for (CStringToAtom::iterator it = deadllvmAtoms.begin(); it != deadllvmAtoms.end(); ++it) {
                        const char* name = it->first;
-                       //Atom* atom = it->second;
-                       fprintf(stderr, "\t%s\n", name);
+                       Atom* atom = it->second;
+                       fprintf(stderr, "\t%p\t%s\n", atom, name);
                }
        }
        AtomSyncer syncer(additionalUndefines, newAtoms, llvmAtoms, deadllvmAtoms, options);
        machoFile->forEachAtom(syncer);
-                       
-       // Remove InternalAtoms from ld
-       for (std::vector<File*>::iterator it=_s_files.begin(); it != _s_files.end(); ++it) {
-               (*it)->internalAtom().setCoalescedAway();
+
+       // notify about file level attributes
+       handler.doFile(*machoFile);
+}
+
+// Full LTO processing
+bool Parser::optimizeLTO(const std::vector<File*>                              files,
+                                                const std::vector<const ld::Atom*>&    allAtoms,
+                                                ld::Internal&                                                  state,
+                                                const OptimizeOptions&                                 options,
+                                                ld::File::AtomHandler&                                 handler,
+                                                std::vector<const ld::Atom*>&                  newAtoms,
+                                                std::vector<const char*>&                              additionalUndefines) {
+       const bool logExtraOptions = false;
+       const bool logBitcodeFiles = false;
+
+       if (files.empty())
+               return true;
+
+       // create optimizer and add each Reader
+       lto_code_gen_t generator = NULL;
+#if LTO_API_VERSION >= 11
+       if ( File::sSupportsLocalContext )
+               generator = ::lto_codegen_create_in_local_context();
+       else
+#endif
+               generator = ::lto_codegen_create();
+#if LTO_API_VERSION >= 7
+       lto_codegen_set_diagnostic_handler(generator, ltoDiagnosticHandler, NULL);
+#endif
+
+       ld::File::Ordinal lastOrdinal;
+
+       // When flto_codegen_only is on and we have a single .bc file, use lto_codegen_set_module instead of
+       // lto_codegen_add_module, to make sure the the destination module will be the same as the input .bc file.
+       bool useSetModule = false;
+#if LTO_API_VERSION >= 13
+       useSetModule = (files.size() == 1) && options.ltoCodegenOnly && (::lto_api_version() >= 13);
+#endif
+       for (auto *f : files) {
+               assert(f->ordinal() > lastOrdinal);
+               if ( logBitcodeFiles && !useSetModule ) fprintf(stderr, "lto_codegen_add_module(%s)\n", f->path());
+               if ( logBitcodeFiles && useSetModule ) fprintf(stderr, "lto_codegen_set_module(%s)\n", f->path());
+               if ( f->mergeIntoGenerator(generator, useSetModule) )
+                       throwf("lto: could not merge in %s because '%s', using libLTO version '%s'", f->path(), ::lto_get_error_message(), ::lto_get_version());
+               lastOrdinal = f->ordinal();
+       }
+
+       // add any -mllvm command line options
+       if ( !_s_llvmOptionsProcessed ) {
+               for (const char* opt : *options.llvmOptions) {
+                       if ( logExtraOptions ) fprintf(stderr, "passing option to llvm: %s\n", opt);
+                       ::lto_codegen_debug_options(generator, opt);
+               }
+               _s_llvmOptionsProcessed = true;
        }
+
+       // <rdar://problem/13687397> Need a way for LTO to get cpu variants (until that info is in bitcode)
+       if ( options.mcpu != NULL )
+               ::lto_codegen_set_cpu(generator, options.mcpu);
+
+       // Compute the preserved symbols
+       CStringToAtom deadllvmAtoms, llvmAtoms;
+       setPreservedSymbols(allAtoms, state, options, deadllvmAtoms, llvmAtoms, generator);
+
+       size_t machOFileLen = 0;
+       const uint8_t* machOFile = NULL;
+
+       // mach-o parsing is done in-memory, but need path for debug notes
+       std::string object_path;
+       if ( options.tmpObjectFilePath != NULL ) {
+               object_path = options.tmpObjectFilePath;
+               // If the path exists and is a directory (for instance if some files
+               // were processed with ThinLTO before), we create the LTO file inside
+               // the directory.
+               struct stat statBuffer;
+               if( stat(object_path.c_str(), &statBuffer) == 0 && S_ISDIR(statBuffer.st_mode) ) {
+                       object_path += "/lto.o";
+               }
+       }
+
+       // Codegen Now
+       std::tie(machOFile, machOFileLen) = codegen(options, state, generator, object_path);
+
+       // parse generated mach-o file into a MachOReader
+       ld::relocatable::File* machoFile = parseMachOFile(machOFile, machOFileLen, object_path, options, ld::File::Ordinal::LTOOrdinal());
+
+       // Load the generated MachO file
+       loadMachO(machoFile, options, handler, newAtoms, additionalUndefines, llvmAtoms, deadllvmAtoms);
+
        // Remove Atoms from ld if code generator optimized them away
        for (CStringToAtom::iterator li = llvmAtoms.begin(), le = llvmAtoms.end(); li != le; ++li) {
                // check if setRealAtom() called on this Atom
@@ -726,58 +1029,498 @@ bool Parser::optimize(  const std::vector<const ld::Atom*>&     allAtoms,
                        li->second->setCoalescedAway();
                }
        }
-       
-       // notify about file level attributes
-       handler.doFile(*machoFile);
-       
+
        // if final mach-o file has debug info, update original bitcode files to match
-       for (std::vector<File*>::iterator it=_s_files.begin(); it != _s_files.end(); ++it) {
-               (*it)->setDebugInfo(machoFile->debugInfo(), machoFile->path(),
-                                                       machoFile->modificationTime(), machoFile->cpuSubType());
+       for (auto *f : files) {
+               f->setDebugInfo(machoFile->debugInfo(), machoFile->path(), machoFile->modificationTime(), machoFile->cpuSubType());
        }
-       
+
        return true;
 }
 
+#if LTO_API_VERSION >= 18
+// Create the ThinLTO codegenerator
+thinlto_code_gen_t Parser::init_thinlto_codegen(const std::vector<File*>&           files,
+                                                                                   const std::vector<const ld::Atom*>& allAtoms,
+                                                                                               ld::Internal&                                  state,
+                                                                                               const OptimizeOptions&                     options,
+                                                                                           CStringToAtom&                      deadllvmAtoms,
+                                                                                           CStringToAtom&                      llvmAtoms) {
+       const bool logMustPreserve = false;
+
+    thinlto_code_gen_t thingenerator = ::thinlto_create_codegen();
+
+       // Caching control
+       if (options.ltoCachePath && !options.bitcodeBundle) {
+               struct stat statBuffer;
+               if( stat(options.ltoCachePath, &statBuffer) != 0 || !S_ISDIR(statBuffer.st_mode) ) {
+                       if ( mkdir(options.ltoCachePath, 0700) !=0 ) {
+                               warning("unable to create ThinLTO cache directory: %s", options.ltoCachePath);
+                       }
+               }
+               thinlto_codegen_set_cache_dir(thingenerator, options.ltoCachePath);
+               thinlto_codegen_set_cache_pruning_interval(thingenerator, options.ltoPruneInterval);
+               thinlto_codegen_set_cache_entry_expiration(thingenerator, options.ltoPruneAfter);
+               thinlto_codegen_set_final_cache_size_relative_to_available_space(thingenerator, options.ltoMaxCacheSize);
+       }
+
+       // if requested, ask the code generator to save off intermediate bitcode files
+       if ( options.saveTemps ) {
+               std::string tempPath = options.outputFilePath;
+               tempPath += ".thinlto.bcs/";
+               struct stat statBuffer;
+               if( stat(tempPath.c_str(), &statBuffer) != 0 || !S_ISDIR(statBuffer.st_mode) ) {
+                       if ( mkdir(tempPath.c_str(), 0700) !=0 ) {
+                               warning("unable to create ThinLTO output directory for temporary bitcode files: %s", tempPath.c_str());
+                       }
+               }
+               thinlto_codegen_set_savetemps_dir(thingenerator, tempPath.c_str());
+       }
+
+       // Set some codegen options
+       if ( thinlto_codegen_set_pic_model(thingenerator, getCodeModel(options)) )
+               throwf("could not create set codegen model: %s", lto_get_error_message());
+
+       // Expose reachability informations for internalization in LTO
+
+       // The atom graph uses directed edges (references). Collect all references where
+       // originating atom is not part of any LTO Reader. This allows optimizer to optimize an
+       // external (i.e. not originated from same .o file) reference if all originating atoms are also
+       // defined in llvm bitcode file.
+       CStringSet nonLLVMRefs;
+       CStringSet LLVMRefs;
+       for (std::vector<const ld::Atom*>::const_iterator it = allAtoms.begin(); it != allAtoms.end(); ++it) {
+               const ld::Atom* atom = *it;
+               const ld::Atom* target;
+               for (ld::Fixup::iterator fit=atom->fixupsBegin(); fit != atom->fixupsEnd(); ++fit) {
+                       switch ( fit->binding ) {
+                               case ld::Fixup::bindingDirectlyBound:
+                                       // that reference a ThinLTO llvm atom
+                                       target = fit->u.target;
+                                       if ( target->contentType() == ld::Atom::typeLTOtemporary &&
+                                               ((lto::File *)target->file())->isThinLTO() &&
+                                               atom->file() != target->file()
+                                               ) {
+                                               if (atom->contentType() != ld::Atom::typeLTOtemporary ||
+                                                       !((lto::File *)atom->file())->isThinLTO())
+                                                       nonLLVMRefs.insert(target->name());
+                                               else
+                                                       LLVMRefs.insert(target->name());
+                                               if ( logMustPreserve )
+                                                       fprintf(stderr, "Found a reference from %s -> %s\n", atom->name(), target->name());
+                                       }
+                                       break;
+                               case ld::Fixup::bindingsIndirectlyBound:
+                                       target = state.indirectBindingTable[fit->u.bindingIndex];
+                                       if ( (target != NULL) && (target->contentType() == ld::Atom::typeLTOtemporary)  &&
+                                               ((lto::File *)target->file())->isThinLTO() &&
+                                               atom->file() != target->file()
+                                               ) {
+                                               if (atom->contentType() != ld::Atom::typeLTOtemporary ||
+                                                       !((lto::File *)atom->file())->isThinLTO())
+                                                       nonLLVMRefs.insert(target->name());
+                                               else
+                                                       LLVMRefs.insert(target->name());
+                                               if ( logMustPreserve )
+                                                       fprintf(stderr, "Found a reference from %s -> %s\n", atom->name(), target->name());
+                                       }
+                               default:
+                                       break;
+                       }
+               }
+               if (atom->contentType() == ld::Atom::typeLTOtemporary &&
+                       ((lto::File *)atom->file())->isThinLTO()) {
+                       llvmAtoms[atom->name()] = (Atom*)atom;
+               }
+       }
+       // if entry point is in a llvm bitcode file, it must be preserved by LTO
+       if ( state.entryPoint != NULL ) {
+               if ( state.entryPoint->contentType() == ld::Atom::typeLTOtemporary )
+                       nonLLVMRefs.insert(state.entryPoint->name());
+       }
+       for (auto file : files) {
+               for(uint32_t i=0; i < file->_atomArrayCount; ++i) {
+                       Atom* llvmAtom = &file->_atomArray[i];
+                       if ( llvmAtom->coalescedAway()  ) {
+                               const char* name = llvmAtom->name();
+                               if ( deadllvmAtoms.find(name) == deadllvmAtoms.end() ) {
+                                       if ( logMustPreserve )
+                                               fprintf(stderr, "thinlto_codegen_add_must_preserve_symbol(%s) because linker coalesce away and replace with a mach-o atom\n", name);
+                                       ::thinlto_codegen_add_must_preserve_symbol(thingenerator, name, strlen(name));
+                                       deadllvmAtoms[name] = (Atom*)llvmAtom;
+                               }
+                       }
+                       else if ( options.linkerDeadStripping && !llvmAtom->live() ) {
+                               const char* name = llvmAtom->name();
+                               deadllvmAtoms[name] = (Atom*)llvmAtom;
+                       }
+               }
+       }
+
+       // tell code generator about symbols that must be preserved
+       for (CStringToAtom::iterator it = llvmAtoms.begin(); it != llvmAtoms.end(); ++it) {
+               const char* name = it->first;
+               Atom* atom = it->second;
+               // Include llvm Symbol in export list if it meets one of following two conditions
+               // 1 - atom scope is global (and not linkage unit).
+               // 2 - included in nonLLVMRefs set.
+               // If a symbol is not listed in exportList then LTO is free to optimize it away.
+               if ( (atom->scope() == ld::Atom::scopeGlobal) && options.preserveAllGlobals ) {
+                       if ( logMustPreserve ) fprintf(stderr, "thinlto_codegen_add_must_preserve_symbol(%s) because global symbol\n", name);
+                       ::thinlto_codegen_add_must_preserve_symbol(thingenerator, name, strlen(name));
+               }
+               else if ( nonLLVMRefs.find(name) != nonLLVMRefs.end() ) {
+                       if ( logMustPreserve ) fprintf(stderr, "thinlto_codegen_add_must_preserve_symbol(%s) because referenced from outside of ThinLTO\n", name);
+                       ::thinlto_codegen_add_must_preserve_symbol(thingenerator, name, strlen(name));
+               }
+               else if ( LLVMRefs.find(name) != LLVMRefs.end() ) {
+                       if ( logMustPreserve ) fprintf(stderr, "thinlto_codegen_add_cross_referenced_symbol(%s) because referenced from another file\n", name);
+                       ::thinlto_codegen_add_cross_referenced_symbol(thingenerator, name, strlen(name));
+               } else {
+                       if ( logMustPreserve ) fprintf(stderr, "NOT preserving(%s)\n", name);
+               }
+// FIXME: to be implemented
+//             else if ( options.relocatable && hasNonllvmAtoms ) {
+//                     // <rdar://problem/14334895> ld -r mode but merging in some mach-o files, so need to keep libLTO from optimizing away anything
+//                     if ( logMustPreserve ) fprintf(stderr, "lto_codegen_add_must_preserve_symbol(%s) because -r mode disable LTO dead stripping\n", name);
+//                     ::thinlto_codegen_add_must_preserve_symbol(thingenerator, name, strlen(name));
+//             }
+       }
+
+       return thingenerator;
+}
+#endif
+
+// Full LTO processing
+bool Parser::optimizeThinLTO(const std::vector<File*>&              files,
+                                                        const std::vector<const ld::Atom*>&    allAtoms,
+                                                        ld::Internal&                                                  state,
+                                                        const OptimizeOptions&                                 options,
+                                                        ld::File::AtomHandler&                                 handler,
+                                                        std::vector<const ld::Atom*>&                  newAtoms,
+                                                        std::vector<const char*>&                              additionalUndefines) {
+       const bool logBitcodeFiles = false;
+
+       if (files.empty())
+               return true;
+
+#if LTO_API_VERSION >= 18
+
+       if (::lto_api_version() < 18)
+               throwf("lto: could not use -thinlto because libLTO is too old (version '%d', >=18 is required)", ::lto_api_version());
+
+       // Handle -mllvm options
+       if ( !_s_llvmOptionsProcessed ) {
+               thinlto_debug_options(options.llvmOptions->data(), options.llvmOptions->size());
+               _s_llvmOptionsProcessed = true;
+       }
+
+       // Create the ThinLTO codegenerator
+       CStringToAtom                     deadllvmAtoms;
+       CStringToAtom                     llvmAtoms;
+       thinlto_code_gen_t thingenerator = init_thinlto_codegen(files, allAtoms, state, options, deadllvmAtoms, llvmAtoms);
+
+
+       ld::File::Ordinal lastOrdinal;
+       int FileId = 0;
+       for (auto *f : files) {
+               if ( logBitcodeFiles) fprintf(stderr, "thinlto_codegen_add_module(%s)\n", f->path());
+               f->addToThinGenerator(thingenerator, FileId++);
+               lastOrdinal = f->ordinal();
+       }
+
+#if LTO_API_VERSION >= 19
+       // In the bitcode bundle case, we first run the generator with codegen disabled
+       // and get the bitcode output. These files are added for later bundling, and a
+       // new codegenerator is setup with these as input, and the optimizer disabled.
+       if (options.bitcodeBundle) {
+               // Bitcode Bundle case
+               thinlto_codegen_disable_codegen(thingenerator, true);
+               // Process the optimizer only
+               thinlto_codegen_process(thingenerator);
+               auto numObjects = thinlto_module_get_num_objects(thingenerator);
+               // Save the codegenerator
+               thinlto_code_gen_t bitcode_generator = thingenerator;
+               // Create a new codegen generator for the codegen part.
+               thingenerator = init_thinlto_codegen(files, allAtoms, state, options, deadllvmAtoms, llvmAtoms);
+               // Disable the optimizer
+               thinlto_codegen_set_codegen_only(thingenerator, true);
+
+               // Save bitcode files for later, and add them to the codegen generator.
+               for (unsigned bufID = 0; bufID < numObjects; ++bufID) {
+                       auto machOFile = thinlto_module_get_object(bitcode_generator, bufID);
+                       std::string tempMachoPath = options.outputFilePath;
+                       tempMachoPath += ".";
+                       tempMachoPath += std::to_string(bufID);
+                       tempMachoPath += ".thinlto.o.bc";
+                       state.ltoBitcodePath.push_back(tempMachoPath);
+                       int fd = ::open(tempMachoPath.c_str(), O_CREAT | O_WRONLY | O_TRUNC, 0666);
+                       if ( fd != -1 ) {
+                               ::write(fd, machOFile.Buffer, machOFile.Size);
+                               ::close(fd);
+                       } else {
+                               throwf("unable to write temporary ThinLTO output: %s", tempMachoPath.c_str());
+                       }
+
+                       // Add the optimized bitcode to the codegen generator now.
+                       ::thinlto_codegen_add_module(thingenerator, strdup(tempMachoPath.c_str()), (const char *)machOFile.Buffer, machOFile.Size);
+               }
+       }
+
+       if (options.ltoCodegenOnly)
+               // Disable the optimizer
+               thinlto_codegen_set_codegen_only(thingenerator, true);
+#endif
+
+       // If object_path_lto is used, we switch to a file-based API: libLTO will
+       // generate the files on disk and we'll map them on-demand.
+
+#if LTO_API_VERSION >= 21
+       bool useFileBasedAPI = (options.tmpObjectFilePath && ::lto_api_version() >= 21);
+       if ( useFileBasedAPI )
+               thinlto_set_generated_objects_dir(thingenerator, options.tmpObjectFilePath);
+#endif
+
+       // run code generator
+       thinlto_codegen_process(thingenerator);
+
+       unsigned numObjects;
+#if LTO_API_VERSION >= 21
+       if ( useFileBasedAPI )
+               numObjects = thinlto_module_get_num_object_files(thingenerator);
+       else
+#endif
+               numObjects = thinlto_module_get_num_objects(thingenerator);
+       if ( numObjects == 0 )
+               throwf("could not do ThinLTO codegen (thinlto_codegen_process didn't produce any object): '%s', using libLTO version '%s'", ::lto_get_error_message(), ::lto_get_version());
+
+       auto get_thinlto_buffer_or_load_file = [&] (unsigned ID) {
+#if LTO_API_VERSION >= 21
+               if ( useFileBasedAPI ) {
+                       const char* path = thinlto_module_get_object_file(thingenerator, ID);
+                       // map in whole file
+                       struct stat stat_buf;
+                       int fd = ::open(path, O_RDONLY, 0);
+                       if ( fd == -1 )
+                               throwf("can't open thinlto file '%s', errno=%d", path, errno);
+                       if ( ::fstat(fd, &stat_buf) != 0 )
+                               throwf("fstat thinlto file '%s' failed, errno=%d\n", path, errno);
+                       size_t len = stat_buf.st_size;
+                       if ( len < 20 )
+                               throwf("ThinLTO file '%s' too small (length=%zu)", path, len);
+                       const char* p = (const char*)::mmap(NULL, len, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, 0);
+                       if ( p == (const char*)(-1) )
+                               throwf("can't map file, errno=%d", errno);
+                       ::close(fd);
+                       return LTOObjectBuffer{ p, len };
+               }
+#endif
+               return thinlto_module_get_object(thingenerator, ID);
+       };
+
+       // if requested, save off objects files
+       if ( options.saveTemps ) {
+               for (unsigned bufID = 0; bufID < numObjects; ++bufID) {
+                       auto machOFile = get_thinlto_buffer_or_load_file(bufID);
+                       std::string tempMachoPath = options.outputFilePath;
+                       tempMachoPath += ".";
+                       tempMachoPath += std::to_string(bufID);
+                       tempMachoPath += ".thinlto.o";
+                       int fd = ::open(tempMachoPath.c_str(), O_CREAT | O_WRONLY | O_TRUNC, 0666);
+                       if ( fd != -1 ) {
+                               ::write(fd, machOFile.Buffer, machOFile.Size);
+                               ::close(fd);
+                       }
+                       else {
+                               warning("unable to write temporary ThinLTO output: %s", tempMachoPath.c_str());
+                       }
+               }
+       }
+
+       // mach-o parsing is done in-memory, but need path for debug notes
+       std::string macho_dirpath = "/tmp/thinlto.o";
+       if ( options.tmpObjectFilePath != NULL ) {
+               macho_dirpath = options.tmpObjectFilePath;
+               struct stat statBuffer;
+               if( stat(macho_dirpath.c_str(), &statBuffer) != 0 || !S_ISDIR(statBuffer.st_mode) ) {
+                       unlink(macho_dirpath.c_str());
+                       if ( mkdir(macho_dirpath.c_str(), 0700) !=0 ) {
+                               warning("unable to create ThinLTO output directory for temporary object files: %s", macho_dirpath.c_str());
+                       }
+               }
+       }
+
+       auto ordinal = ld::File::Ordinal::LTOOrdinal().nextFileListOrdinal();
+       for (unsigned bufID = 0; bufID < numObjects; ++bufID) {
+               auto machOFile = get_thinlto_buffer_or_load_file(bufID);
+               if (!machOFile.Size) {
+                       warning("Ignoring empty buffer generated by ThinLTO");
+                       continue;
+               }
+
+               // mach-o parsing is done in-memory, but need path for debug notes
+               std::string tmp_path;
+#if LTO_API_VERSION >= 21
+               if ( useFileBasedAPI ) {
+                       tmp_path = thinlto_module_get_object_file(thingenerator, bufID);
+               }
+               else
+#endif
+               if ( options.tmpObjectFilePath != NULL) {
+                       tmp_path = macho_dirpath + "/" + std::to_string(bufID) + ".o";
+                       // if needed, save temp mach-o file to specific location
+                       int fd = ::open(tmp_path.c_str(), O_CREAT | O_WRONLY | O_TRUNC, 0666);
+                       if ( fd != -1) {
+                               ::write(fd, (const uint8_t *)machOFile.Buffer, machOFile.Size);
+                               ::close(fd);
+                       }
+                       else {
+                               warning("could not write ThinLTO temp file '%s', errno=%d", tmp_path.c_str(), errno);
+                       }
+               }
+
+               // parse generated mach-o file into a MachOReader
+               ld::relocatable::File* machoFile = parseMachOFile((const uint8_t *)machOFile.Buffer, machOFile.Size, tmp_path, options, ordinal);
+               ordinal = ordinal.nextFileListOrdinal();
+
+               // Load the generated MachO file
+               loadMachO(machoFile, options, handler, newAtoms, additionalUndefines, llvmAtoms, deadllvmAtoms);
+       }
+
+       // Remove Atoms from ld if code generator optimized them away
+       for (CStringToAtom::iterator li = llvmAtoms.begin(), le = llvmAtoms.end(); li != le; ++li) {
+               // check if setRealAtom() called on this Atom
+               if ( li->second->compiledAtom() == NULL ) {
+                       //fprintf(stderr, "llvm optimized away %p %s\n", li->second, li->second->name());
+                       li->second->setCoalescedAway();
+               }
+       }
+
+       return true;
+#else // ! (LTO_API_VERSION >= 18)
+       throwf("lto: could not use -thinlto because ld was built against a version of libLTO too old (version '%d', >=18 is required)", LTO_API_VERSION);
+#endif
+}
+
+bool Parser::optimize(  const std::vector<const ld::Atom*>&    allAtoms,
+                                               ld::Internal&                                           state,
+                                               const OptimizeOptions&                          options,
+                                               ld::File::AtomHandler&                          handler,
+                                               std::vector<const ld::Atom*>&           newAtoms,
+                                               std::vector<const char*>&                       additionalUndefines)
+{
+
+       // exit quickly if nothing to do
+       if ( _s_files.size() == 0 )
+               return false;
+
+       // print out LTO version string if -v was used
+       if ( options.verbose )
+               fprintf(stderr, "%s\n", ::lto_get_version());
+
+       // <rdar://problem/12379604> The order that files are merged must match command line order
+       std::sort(_s_files.begin(), _s_files.end(), CommandLineOrderFileSorter());
+
+#if LTO_API_VERSION >= 19
+       // If ltoCodegenOnly is set, we don't want to merge any bitcode files and perform FullLTO
+       // we just take the ThinLTO path (optimization will be disabled anyway).
+       if (options.ltoCodegenOnly) {
+               for (auto *file : _s_files) {
+                       file->setIsThinLTO(true);
+               }
+       }
+#endif
+
+       std::vector<File *> theLTOFiles;
+       std::vector<File *> theThinLTOFiles;
+       for (auto *file : _s_files) {
+               if (file->isThinLTO()) {
+                       theThinLTOFiles.push_back(file);
+               } else {
+                       theLTOFiles.push_back(file);
+               }
+       }
+
+       auto result =  optimizeThinLTO(theThinLTOFiles, allAtoms, state, options, handler, newAtoms, additionalUndefines) &&
+                                  optimizeLTO(theLTOFiles, allAtoms, state, options, handler, newAtoms, additionalUndefines);
+
+       // Remove InternalAtoms from ld
+       for (std::vector<File*>::iterator it=_s_files.begin(); it != _s_files.end(); ++it) {
+               (*it)->internalAtom().setCoalescedAway();
+       }
+
+       return result;
+}
+
 
 void Parser::AtomSyncer::doAtom(const ld::Atom& machoAtom)
 {
+       static const bool log = false;
        // update proxy atoms to point to real atoms and find new atoms
        const char* name = machoAtom.name();
-       if ( machoAtom.scope() >= ld::Atom::scopeLinkageUnit ) {
-               CStringToAtom::iterator pos = _llvmAtoms.find(name);
-               if ( pos != _llvmAtoms.end() ) {
-                       // turn Atom into a proxy for this mach-o atom
-                       pos->second->setCompiledAtom(machoAtom);
+       CStringToAtom::const_iterator pos = _llvmAtoms.find(name);
+       if ( (pos != _llvmAtoms.end()) && (machoAtom.scope() != ld::Atom::scopeTranslationUnit) ) {
+               // turn Atom into a proxy for this mach-o atom
+               if (pos->second->scope() == ld::Atom::scopeLinkageUnit) {
+                       if (log) fprintf(stderr, "demote %s to hidden after LTO\n", name);
+                       (const_cast<ld::Atom*>(&machoAtom))->setScope(ld::Atom::scopeLinkageUnit);
                }
-               else {
-                       // an atom of this name was not in the allAtoms list the linker gave us
-                       if ( _deadllvmAtoms.find(name) != _deadllvmAtoms.end() ) {
-                               // this corresponding to an atom that the linker coalesced away or marked not-live
-                               if ( _options.linkerDeadStripping ) {
-                                       // llvm seems to want this atom and -dead_strip is enabled, so it will be deleted if not needed, so add back
-                                       Atom* llvmAtom = _deadllvmAtoms[name];
-                                       llvmAtom->setCompiledAtom(machoAtom);
-                                       _newAtoms.push_back(&machoAtom);
-                               }
-                               else {
-                                       // Don't pass it back as a new atom
-                               } 
-                       }
-                       else
-                       {
-                               // this is something new that lto conjured up, tell ld its new
+               pos->second->setCompiledAtom(machoAtom);
+               _lastProxiedAtom = &machoAtom;
+               _lastProxiedFile = pos->second->file();
+               if (log) fprintf(stderr, "AtomSyncer, mach-o atom %p synced to lto atom %p (name=%s)\n", &machoAtom, pos->second, machoAtom.name());
+       }
+       else {
+               // an atom of this name was not in the allAtoms list the linker gave us
+               auto llvmAtom = _deadllvmAtoms.find(name);
+               if ( llvmAtom != _deadllvmAtoms.end() ) {
+                       // this corresponding to an atom that the linker coalesced away or marked not-live
+                       if ( _options.linkerDeadStripping ) {
+                               // llvm seems to want this atom and -dead_strip is enabled, so it will be deleted if not needed, so add back
+                               llvmAtom->second->setCompiledAtom(machoAtom);
                                _newAtoms.push_back(&machoAtom);
+                               if (log) fprintf(stderr, "AtomSyncer, mach-o atom %p matches dead lto atom %p but adding back (name=%s)\n", &machoAtom, llvmAtom->second, machoAtom.name());
                        }
+                       else {
+                               // Don't pass it back as a new atom
+                               if (log) fprintf(stderr, "AtomSyncer, mach-o atom %p matches dead lto atom %p (name=%s)\n", &machoAtom, llvmAtom->second, machoAtom.name());
+                               if ( llvmAtom->second->coalescedAway() ) {
+                                       if (log) fprintf(stderr, "AtomSyncer: dead coalesced atom %s\n", machoAtom.name());
+                                       // <rdar://problem/28269547>
+                                       // We told libLTO to keep a weak atom that will replaced by an native mach-o atom.
+                                       // We also need to remove any atoms directly dependent on this (FDE, LSDA).
+                                       for (ld::Fixup::iterator fit=machoAtom.fixupsBegin(), fend=machoAtom.fixupsEnd(); fit != fend; ++fit) {
+                                               switch ( fit->kind ) {
+                                                       case ld::Fixup::kindNoneGroupSubordinate:
+                                                       case ld::Fixup::kindNoneGroupSubordinateFDE:
+                                                       case ld::Fixup::kindNoneGroupSubordinateLSDA:
+                                                               assert(fit->binding == ld::Fixup::bindingDirectlyBound);
+                                                               (const_cast<ld::Atom*>(fit->u.target))->setCoalescedAway();
+                                                               if (log) fprintf(stderr, "AtomSyncer: mark coalesced-away subordinate atom %s\n", fit->u.target->name());
+                                                               break;
+                                                       default:
+                                                               break;
+                                               }
+                                       }
+                               }
+                       } 
+               }
+               else
+               {
+                       // this is something new that lto conjured up, tell ld its new
+                       _newAtoms.push_back(&machoAtom);
+                       // <rdar://problem/15469363> if new static atom in same section as previous non-static atom, assign to same file as previous
+                       if ( (_lastProxiedAtom != NULL) && (_lastProxiedAtom->section() == machoAtom.section()) ) {
+                               ld::Atom* ma = const_cast<ld::Atom*>(&machoAtom);
+                               ma->setFile(_lastProxiedFile);
+                               if (log) fprintf(stderr, "AtomSyncer, mach-o atom %s is proxied to %s (path=%s)\n", machoAtom.name(), _lastProxiedAtom->name(), _lastProxiedFile->path());
+                       }
+                       if (log) fprintf(stderr, "AtomSyncer, mach-o atom %p is totally new (name=%s)\n", &machoAtom, machoAtom.name());
                }
-       }
-       else {
-               // ld only knew about non-static atoms, so this one must be new
-               _newAtoms.push_back(&machoAtom);
        }
        
        // adjust fixups to go through proxy atoms
-       //fprintf(stderr, "adjusting fixups in atom: %s\n", machoAtom.name());
+       if (log) fprintf(stderr, "  adjusting fixups in atom: %s\n", machoAtom.name());
        for (ld::Fixup::iterator fit=machoAtom.fixupsBegin(); fit != machoAtom.fixupsEnd(); ++fit) {
                switch ( fit->binding ) {
                        case ld::Fixup::bindingNone:
@@ -786,21 +1529,24 @@ void Parser::AtomSyncer::doAtom(const ld::Atom& machoAtom)
                                // don't know if this target has been seen by linker before or if it is new
                                // be conservative and tell linker it is new
                                _additionalUndefines.push_back(fit->u.name);
-                               //fprintf(stderr, "    by name ref to: %s\n", fit->u.name);
+                               if (log) fprintf(stderr, "    adding by-name symbol %s\n", fit->u.name);
                                break;
                        case ld::Fixup::bindingDirectlyBound:
                                // If mach-o atom is referencing another mach-o atom then 
                                // reference is not going through Atom proxy. Fix it here to ensure that all
                                // llvm symbol references always go through Atom proxy.
-                               if (  fit->u.target->scope() != ld::Atom::scopeTranslationUnit ) {
+                               if ( fit->u.target->scope() != ld::Atom::scopeTranslationUnit )
+                               {
                                        const char* targetName = fit->u.target->name();
-                                       CStringToAtom::iterator pos = _llvmAtoms.find(targetName);
-                                       if ( pos != _llvmAtoms.end() ) {
-                                               fit->u.target = pos->second;
+                                       CStringToAtom::const_iterator post = _llvmAtoms.find(targetName);
+                                       if ( post != _llvmAtoms.end() ) {
+                                               const ld::Atom* t = post->second;
+                                               if (log) fprintf(stderr, "    updating direct reference to %p to be ref to %p: %s\n", fit->u.target, t, targetName);
+                                               fit->u.target = t;
                                        }
                                        else {
                                                // <rdar://problem/12859831> Don't unbind follow-on reference into by-name reference 
-                                               if ( (_deadllvmAtoms.find(targetName) != _deadllvmAtoms.end()) && (fit->kind != ld::Fixup::kindNoneFollowOn) ) {
+                                               if ( (_deadllvmAtoms.find(targetName) != _deadllvmAtoms.end()) && (fit->kind != ld::Fixup::kindNoneFollowOn) && (fit->u.target->scope() != ld::Atom::scopeTranslationUnit) ) {
                                                        // target was coalesed away and replace by mach-o atom from a non llvm .o file
                                                        fit->binding = ld::Fixup::bindingByNameUnbound;
                                                        fit->u.name = targetName;
@@ -828,6 +1574,8 @@ public:
        ~Mutex() { pthread_mutex_unlock(&lto_lock); }
 };
 pthread_mutex_t Mutex::lto_lock = PTHREAD_MUTEX_INITIALIZER;
+bool File::sSupportsLocalContext = false;
+bool File::sHasTriedLocalContext = false;
 
 //
 // Used by archive reader to see if member is an llvm bitcode file
@@ -838,19 +1586,53 @@ bool isObjectFile(const uint8_t* fileContent, uint64_t fileLength, cpu_type_t ar
        return Parser::validFile(fileContent, fileLength, architecture, subarch);
 }
 
+//
+// Used by archive reader to see if member defines a Category (for -ObjC semantics)
+//
+bool hasObjCCategory(const uint8_t* fileContent, uint64_t fileLength)
+{
+#if LTO_API_VERSION >= 20
+       // note: if run with older libLTO.dylib that does not implement
+       // lto_module_has_objc_category, the call will return 0 which is "false"
+       return lto_module_has_objc_category(fileContent, fileLength);
+#else
+       return false;
+#endif
+}
+
+
+static ld::relocatable::File *parseImpl(
+          const uint8_t *fileContent, uint64_t fileLength, const char *path,
+          time_t modTime, ld::File::Ordinal ordinal, cpu_type_t architecture,
+          cpu_subtype_t subarch, bool logAllFiles,
+          bool verboseOptimizationHints)
+{
+       if ( Parser::validFile(fileContent, fileLength, architecture, subarch) )
+               return Parser::parse(fileContent, fileLength, path, modTime, ordinal, architecture, subarch, logAllFiles, verboseOptimizationHints);
+       else
+               return NULL;
+}
 
 //
 // main function used by linker to instantiate ld::Files
 //
 ld::relocatable::File* parse(const uint8_t* fileContent, uint64_t fileLength, 
                                                                const char* path, time_t modTime, ld::File::Ordinal ordinal,
-                                                               cpu_type_t architecture, cpu_subtype_t subarch, bool logAllFiles)
+                                                               cpu_type_t architecture, cpu_subtype_t subarch, bool logAllFiles,
+                                                               bool verboseOptimizationHints)
 {
-       Mutex lock;
-       if ( Parser::validFile(fileContent, fileLength, architecture, subarch) )
-               return Parser::parse(fileContent, fileLength, path, modTime, ordinal, architecture, subarch, logAllFiles);
-       else
+       // do light weight check before acquiring lock
+       if ( fileLength < 4 )
+               return NULL;
+       if ( (fileContent[0] != 0xDE) || (fileContent[1] != 0xC0) || (fileContent[2] != 0x17) || (fileContent[3] != 0x0B) )
                return NULL;
+
+       // Note: Once lto_module_create_in_local_context() and friends are thread safe
+       // this lock can be removed.
+       Mutex lock;
+       return parseImpl(fileContent, fileLength, path, modTime, ordinal,
+                                       architecture, subarch, logAllFiles,
+                                       verboseOptimizationHints);
 }
 
 //
@@ -862,6 +1644,22 @@ const char* version()
        return ::lto_get_version();
 }
 
+//
+// used by "ld -v" to report static version of libLTO.dylib API being compiled
+//
+unsigned int static_api_version()
+{
+       return LTO_API_VERSION;
+}
+
+//
+// used by "ld -v" to report version of libLTO.dylib being used
+//
+unsigned int runtime_api_version()
+{
+       return ::lto_api_version();
+}
+
 
 //
 // used by ld for error reporting