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COFF: Open and map input files asynchronously on Windows.

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Profiling revealed that the majority of lld's execution time on Windows was
spent opening and mapping input files. We can reduce this cost significantly
by performing these operations asynchronously.

This change introduces a queue for all operations on input file data. When
we discover that we need to load a file (for example, when we find a lazy
archive for an undefined symbol, or when we read a linker directive to
load a file from disk), the file operation is launched using a future and
the symbol resolution operation is enqueued.  This implies another change
to symbol resolution semantics, but it seems to be harmless ("ninja All"
in Chromium still succeeds).

To measure the perf impact of this change I linked Chromium's chrome_child.dll
with both thin and fat archives.

Thin archives:

Before (median of 5 runs): 19.50s
After: 10.93s

Fat archives:

Before: 12.00s
After: 9.90s

On Linux I found that doing this asynchronously had a negative effect on
performance, probably because the cost of mapping a file is small enough that
it becomes outweighed by the cost of managing the futures. So on non-Windows
platforms I use the deferred execution strategy.

Differential Revision: https://reviews.llvm.org/D27768

llvm-svn: 289760
This commit is contained in:
Peter Collingbourne 2016-12-15 04:02:23 +00:00
parent ab5f355d8c
commit 6ee0b4e9f5
8 changed files with 223 additions and 148 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

268
lld/COFF/Driver.cpp
View File

@ -30,6 +30,13 @@
#include <algorithm>
#include <memory>
#ifdef _MSC_VER
// <future> depends on <eh.h> for __uncaught_exception.
#include <eh.h>
#endif
#include <future>
using namespace llvm;
using namespace llvm::COFF;
using llvm::sys::Process;
@ -58,33 +65,123 @@ static std::string getOutputPath(StringRef Path) {
return (S.substr(0, S.rfind('.')) + E).str();
}
// Opens a file. Path has to be resolved already.
// Newly created memory buffers are owned by this driver.
MemoryBufferRef LinkerDriver::openFile(StringRef Path) {
std::unique_ptr<MemoryBuffer> MB =
check(MemoryBuffer::getFile(Path), "could not open " + Path);
MemoryBufferRef MBRef = MB->getMemBufferRef();
OwningMBs.push_back(std::move(MB)); // take ownership
// ErrorOr is not default constructible, so it cannot be used as the type
// parameter of a future.
// FIXME: We could open the file in createFutureForFile and avoid needing to
// return an error here, but for the moment that would cost us a file descriptor
// (a limited resource on Windows) for the duration that the future is pending.
typedef std::pair<std::unique_ptr<MemoryBuffer>, std::error_code> MBErrPair;
// Create a std::future that opens and maps a file using the best strategy for
// the host platform.
static std::future<MBErrPair> createFutureForFile(std::string Path) {
#if LLVM_ON_WIN32
// On Windows, file I/O is relatively slow so it is best to do this
// asynchronously.
auto Strategy = std::launch::async;
#else
auto Strategy = std::launch::deferred;
#endif
return std::async(Strategy, [=]() {
auto MBOrErr = MemoryBuffer::getFile(Path);
if (!MBOrErr)
return MBErrPair{nullptr, MBOrErr.getError()};
return MBErrPair{std::move(*MBOrErr), std::error_code()};
});
}
MemoryBufferRef LinkerDriver::takeBuffer(std::unique_ptr<MemoryBuffer> MB) {
MemoryBufferRef MBRef = *MB;
OwningMBs.push_back(std::move(MB));
if (Driver->Cpio)
Driver->Cpio->append(relativeToRoot(MBRef.getBufferIdentifier()),
MBRef.getBuffer());
return MBRef;
}
static InputFile *createFile(MemoryBufferRef MB) {
if (Driver->Cpio)
Driver->Cpio->append(relativeToRoot(MB.getBufferIdentifier()),
MB.getBuffer());
void LinkerDriver::addBuffer(std::unique_ptr<MemoryBuffer> MB) {
MemoryBufferRef MBRef = takeBuffer(std::move(MB));
// File type is detected by contents, not by file extension.
file_magic Magic = identify_magic(MB.getBuffer());
file_magic Magic = identify_magic(MBRef.getBuffer());
if (Magic == file_magic::windows_resource) {
Resources.push_back(MBRef);
return;
}
FilePaths.push_back(MBRef.getBufferIdentifier());
if (Magic == file_magic::archive)
return make<ArchiveFile>(MB);
return Symtab.addFile(make<ArchiveFile>(MBRef));
if (Magic == file_magic::bitcode)
return make<BitcodeFile>(MB);
return Symtab.addFile(make<BitcodeFile>(MBRef));
if (Magic == file_magic::coff_cl_gl_object)
fatal(MB.getBufferIdentifier() + ": is not a native COFF file. "
fatal(MBRef.getBufferIdentifier() + ": is not a native COFF file. "
"Recompile without /GL");
Symtab.addFile(make<ObjectFile>(MBRef));
}
void LinkerDriver::enqueuePath(StringRef Path) {
auto Future =
std::make_shared<std::future<MBErrPair>>(createFutureForFile(Path));
std::string PathStr = Path;
enqueueTask([=]() {
auto MBOrErr = Future->get();
if (MBOrErr.second)
fatal(MBOrErr.second, "could not open " + PathStr);
Driver->addBuffer(std::move(MBOrErr.first));
});
if (Config->OutputFile == "")
Config->OutputFile = getOutputPath(MB.getBufferIdentifier());
return make<ObjectFile>(MB);
Config->OutputFile = getOutputPath(Path);
}
void LinkerDriver::addArchiveBuffer(MemoryBufferRef MB, StringRef SymName,
StringRef ParentName) {
file_magic Magic = identify_magic(MB.getBuffer());
if (Magic == file_magic::coff_import_library) {
Symtab.addFile(make<ImportFile>(MB));
return;
}
InputFile *Obj;
if (Magic == file_magic::coff_object)
Obj = make<ObjectFile>(MB);
else if (Magic == file_magic::bitcode)
Obj = make<BitcodeFile>(MB);
else
fatal("unknown file type: " + MB.getBufferIdentifier());
Obj->ParentName = ParentName;
Symtab.addFile(Obj);
if (Config->Verbose)
outs() << "Loaded " << toString(Obj) << " for " << SymName << "\n";
}
void LinkerDriver::enqueueArchiveMember(const Archive::Child &C,
StringRef SymName,
StringRef ParentName) {
if (!C.getParent()->isThin()) {
MemoryBufferRef MB = check(
C.getMemoryBufferRef(),
"could not get the buffer for the member defining symbol " + SymName);
enqueueTask([=]() { Driver->addArchiveBuffer(MB, SymName, ParentName); });
return;
}
auto Future = std::make_shared<std::future<MBErrPair>>(createFutureForFile(
check(C.getFullName(),
"could not get the filename for the member defining symbol " +
SymName)));
enqueueTask([=]() {
auto MBOrErr = Future->get();
if (MBOrErr.second)
fatal(MBOrErr.second,
"could not get the buffer for the member defining " + SymName);
Driver->addArchiveBuffer(takeBuffer(std::move(MBOrErr.first)), SymName,
ParentName);
});
}
static bool isDecorated(StringRef Sym) {
@ -102,10 +199,8 @@ void LinkerDriver::parseDirectives(StringRef S) {
parseAlternateName(Arg->getValue());
break;
case OPT_defaultlib:
if (Optional<StringRef> Path = findLib(Arg->getValue())) {
MemoryBufferRef MB = openFile(*Path);
Symtab.addFile(createFile(MB));
}
if (Optional<StringRef> Path = findLib(Arg->getValue()))
enqueuePath(*Path);
break;
case OPT_export: {
Export E = parseExport(Arg->getValue());
@ -255,7 +350,7 @@ static uint64_t getDefaultImageBase() {
}
static std::string createResponseFile(const opt::InputArgList &Args,
ArrayRef<MemoryBufferRef> MBs,
ArrayRef<StringRef> FilePaths,
ArrayRef<StringRef> SearchPaths) {
SmallString<0> Data;
raw_svector_ostream OS(Data);
@ -277,10 +372,8 @@ static std::string createResponseFile(const opt::InputArgList &Args,
OS << "/libpath:" << quote(RelPath) << "\n";
}
for (MemoryBufferRef MB : MBs) {
std::string InputPath = relativeToRoot(MB.getBufferIdentifier());
OS << quote(InputPath) << "\n";
}
for (StringRef Path : FilePaths)
OS << quote(relativeToRoot(Path)) << "\n";
return Data.str();
}
@ -319,6 +412,19 @@ static std::string getMapFile(const opt::InputArgList &Args) {
return (OutFile.substr(0, OutFile.rfind('.')) + ".map").str();
}
void LinkerDriver::enqueueTask(std::function<void()> Task) {
TaskQueue.push_back(std::move(Task));
}
bool LinkerDriver::run() {
bool DidWork = !TaskQueue.empty();
while (!TaskQueue.empty()) {
TaskQueue.front()();
TaskQueue.pop_front();
}
return DidWork;
}
void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
// If the first command line argument is "/lib", link.exe acts like lib.exe.
// We call our own implementation of lib.exe that understands bitcode files.
@ -544,40 +650,20 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
// Create a list of input files. Files can be given as arguments
// for /defaultlib option.
std::vector<StringRef> Paths;
std::vector<MemoryBufferRef> MBs;
for (auto *Arg : Args.filtered(OPT_INPUT))
if (Optional<StringRef> Path = findFile(Arg->getValue()))
Paths.push_back(*Path);
enqueuePath(*Path);
for (auto *Arg : Args.filtered(OPT_defaultlib))
if (Optional<StringRef> Path = findLib(Arg->getValue()))
Paths.push_back(*Path);
for (StringRef Path : Paths)
MBs.push_back(openFile(Path));
enqueuePath(*Path);
// Windows specific -- Create a resource file containing a manifest file.
if (Config->Manifest == Configuration::Embed) {
std::unique_ptr<MemoryBuffer> MB = createManifestRes();
MBs.push_back(MB->getMemBufferRef());
OwningMBs.push_back(std::move(MB)); // take ownership
}
// Windows specific -- Input files can be Windows resource files (.res files).
// We invoke cvtres.exe to convert resource files to a regular COFF file
// then link the result file normally.
std::vector<MemoryBufferRef> Resources;
auto NotResource = [](MemoryBufferRef MB) {
return identify_magic(MB.getBuffer()) != file_magic::windows_resource;
};
auto It = std::stable_partition(MBs.begin(), MBs.end(), NotResource);
if (It != MBs.end()) {
Resources.insert(Resources.end(), It, MBs.end());
MBs.erase(It, MBs.end());
}
if (Config->Manifest == Configuration::Embed)
addBuffer(createManifestRes());
// Read all input files given via the command line.
for (MemoryBufferRef MB : MBs)
Symtab.addFile(createFile(MB));
run();
// We should have inferred a machine type by now from the input files, but if
// not we assume x64.
@ -586,18 +672,15 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
Config->Machine = AMD64;
}
// Windows specific -- Convert Windows resource files to a COFF file.
if (!Resources.empty()) {
std::unique_ptr<MemoryBuffer> MB = convertResToCOFF(Resources);
Symtab.addFile(createFile(MB->getMemBufferRef()));
MBs.push_back(MB->getMemBufferRef());
OwningMBs.push_back(std::move(MB)); // take ownership
}
// Windows specific -- Input files can be Windows resource files (.res files).
// We invoke cvtres.exe to convert resource files to a regular COFF file
// then link the result file normally.
if (!Resources.empty())
addBuffer(convertResToCOFF(Resources));
if (Cpio)
Cpio->append("response.txt",
createResponseFile(Args, MBs,
createResponseFile(Args, FilePaths,
ArrayRef<StringRef>(SearchPaths).slice(1)));
// Handle /largeaddressaware
@ -640,9 +723,10 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
// Handle /def
if (auto *Arg = Args.getLastArg(OPT_deffile)) {
MemoryBufferRef MB = openFile(Arg->getValue());
// parseModuleDefs mutates Config object.
parseModuleDefs(MB);
parseModuleDefs(
takeBuffer(check(MemoryBuffer::getFile(Arg->getValue()),
Twine("could not open ") + Arg->getValue())));
}
// Handle /delayload
@ -671,40 +755,46 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
Symtab.addAbsolute(mangle("__guard_fids_count"), 0);
Symtab.addAbsolute(mangle("__guard_flags"), 0x100);
// Windows specific -- if entry point is not found,
// search for its mangled names.
if (Config->Entry)
Symtab.mangleMaybe(Config->Entry);
// This code may add new undefined symbols to the link, which may enqueue more
// symbol resolution tasks, so we need to continue executing tasks until we
// converge.
do {
// Windows specific -- if entry point is not found,
// search for its mangled names.
if (Config->Entry)
Symtab.mangleMaybe(Config->Entry);
// Windows specific -- Make sure we resolve all dllexported symbols.
for (Export &E : Config->Exports) {
if (!E.ForwardTo.empty())
continue;
E.Sym = addUndefined(E.Name);
if (!E.Directives)
Symtab.mangleMaybe(E.Sym);
}
// Windows specific -- Make sure we resolve all dllexported symbols.
for (Export &E : Config->Exports) {
if (!E.ForwardTo.empty())
continue;
E.Sym = addUndefined(E.Name);
if (!E.Directives)
Symtab.mangleMaybe(E.Sym);
}
// Add weak aliases. Weak aliases is a mechanism to give remaining
// undefined symbols final chance to be resolved successfully.
for (auto Pair : Config->AlternateNames) {
StringRef From = Pair.first;
StringRef To = Pair.second;
Symbol *Sym = Symtab.find(From);
if (!Sym)
continue;
if (auto *U = dyn_cast<Undefined>(Sym->body()))
if (!U->WeakAlias)
U->WeakAlias = Symtab.addUndefined(To);
}
// Add weak aliases. Weak aliases is a mechanism to give remaining
// undefined symbols final chance to be resolved successfully.
for (auto Pair : Config->AlternateNames) {
StringRef From = Pair.first;
StringRef To = Pair.second;
Symbol *Sym = Symtab.find(From);
if (!Sym)
continue;
if (auto *U = dyn_cast<Undefined>(Sym->body()))
if (!U->WeakAlias)
U->WeakAlias = Symtab.addUndefined(To);
}
// Windows specific -- if __load_config_used can be resolved, resolve it.
if (Symtab.findUnderscore("_load_config_used"))
addUndefined(mangle("_load_config_used"));
// Windows specific -- if __load_config_used can be resolved, resolve it.
if (Symtab.findUnderscore("_load_config_used"))
addUndefined(mangle("_load_config_used"));
} while (run());
// Do LTO by compiling bitcode input files to a set of native COFF files then
// link those files.
Symtab.addCombinedLTOObjects();
run();
// Make sure we have resolved all symbols.
Symtab.reportRemainingUndefines();

21
lld/COFF/Driver.h
View File

@ -16,6 +16,7 @@
#include "lld/Core/Reproduce.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/COFF.h"
#include "llvm/Option/Arg.h"
#include "llvm/Option/ArgList.h"
@ -65,12 +66,16 @@ public:
// Used by the resolver to parse .drectve section contents.
void parseDirectives(StringRef S);
std::unique_ptr<CpioFile> Cpio; // for /linkrepro
// Used by ArchiveFile to enqueue members.
void enqueueArchiveMember(const Archive::Child &C, StringRef SymName,
StringRef ParentName);
private:
ArgParser Parser;
SymbolTable Symtab;
std::unique_ptr<CpioFile> Cpio; // for /linkrepro
// Opens a file. Path has to be resolved already.
MemoryBufferRef openFile(StringRef Path);
@ -100,9 +105,23 @@ private:
StringRef findDefaultEntry();
WindowsSubsystem inferSubsystem();
MemoryBufferRef takeBuffer(std::unique_ptr<MemoryBuffer> MB);
void addBuffer(std::unique_ptr<MemoryBuffer> MB);
void addArchiveBuffer(MemoryBufferRef MBRef, StringRef SymName,
StringRef ParentName);
void enqueuePath(StringRef Path);
void enqueueTask(std::function<void()> Task);
bool run();
// Driver is the owner of all opened files.
// InputFiles have MemoryBufferRefs to them.
std::vector<std::unique_ptr<MemoryBuffer>> OwningMBs;
std::list<std::function<void()>> TaskQueue;
std::vector<StringRef> FilePaths;
std::vector<MemoryBufferRef> Resources;
};
void parseModuleDefs(MemoryBufferRef MB);

27
lld/COFF/InputFiles.cpp
View File

@ -61,37 +61,16 @@ void ArchiveFile::parse() {
}
// Returns a buffer pointing to a member file containing a given symbol.
InputFile *ArchiveFile::getMember(const Archive::Symbol *Sym) {
void ArchiveFile::addMember(const Archive::Symbol *Sym) {
const Archive::Child &C =
check(Sym->getMember(),
"could not get the member for symbol " + Sym->getName());
// Return an empty buffer if we have already returned the same buffer.
if (!Seen.insert(C.getChildOffset()).second)
return nullptr;
return;
MemoryBufferRef MB =
check(C.getMemoryBufferRef(),
"could not get the buffer for the member defining symbol " +
Sym->getName());
if (C.getParent()->isThin() && Driver->Cpio)
Driver->Cpio->append(relativeToRoot(check(C.getFullName())),
MB.getBuffer());
file_magic Magic = identify_magic(MB.getBuffer());
if (Magic == file_magic::coff_import_library)
return make<ImportFile>(MB);
InputFile *Obj;
if (Magic == file_magic::coff_object)
Obj = make<ObjectFile>(MB);
else if (Magic == file_magic::bitcode)
Obj = make<BitcodeFile>(MB);
else
fatal("unknown file type: " + MB.getBufferIdentifier());
Obj->ParentName = getName();
return Obj;
Driver->enqueueArchiveMember(C, Sym->getName(), getName());
}
void ObjectFile::parse() {

8
lld/COFF/InputFiles.h
View File

@ -83,10 +83,10 @@ public:
static bool classof(const InputFile *F) { return F->kind() == ArchiveKind; }
void parse() override;
// Returns an input file for a given symbol. A null pointer is returned if we
// have already returned the same input file. (So that we don't instantiate
// the same member more than once.)
InputFile *getMember(const Archive::Symbol *Sym);
// Enqueues an archive member load for the given symbol. If we've already
// enqueued a load for the same archive member, this function does nothing,
// which ensures that we don't load the same member more than once.
void addMember(const Archive::Symbol *Sym);
private:
std::unique_ptr<Archive> File;

34
lld/COFF/SymbolTable.cpp
View File

@ -122,6 +122,7 @@ std::pair<Symbol *, bool> SymbolTable::insert(StringRef Name) {
return {Sym, false};
Sym = make<Symbol>();
Sym->IsUsedInRegularObj = false;
Sym->PendingArchiveLoad = false;
return {Sym, true};
}
@ -136,8 +137,12 @@ Symbol *SymbolTable::addUndefined(StringRef Name, InputFile *F,
replaceBody<Undefined>(S, Name);
return S;
}
if (auto *L = dyn_cast<Lazy>(S->body()))
addMemberFile(L->File, L->Sym);
if (auto *L = dyn_cast<Lazy>(S->body())) {
if (!S->PendingArchiveLoad) {
S->PendingArchiveLoad = true;
L->File->addMember(&L->Sym);
}
}
return S;
}
@ -151,9 +156,10 @@ void SymbolTable::addLazy(ArchiveFile *F, const Archive::Symbol Sym) {
return;
}
auto *U = dyn_cast<Undefined>(S->body());
if (!U || U->WeakAlias)
if (!U || U->WeakAlias || S->PendingArchiveLoad)
return;
addMemberFile(F, Sym);
S->PendingArchiveLoad = true;
F->addMember(&Sym);
}
void SymbolTable::reportDuplicate(Symbol *Existing, InputFile *NewFile) {
@ -279,19 +285,6 @@ Symbol *SymbolTable::addImportThunk(StringRef Name, DefinedImportData *ID,
return S;
}
// Reads an archive member file pointed by a given symbol.
void SymbolTable::addMemberFile(ArchiveFile *F, const Archive::Symbol Sym) {
InputFile *File = F->getMember(&Sym);
// getMember returns an empty buffer if the member was already
// read from the library.
if (!File)
return;
if (Config->Verbose)
outs() << "Loaded " << toString(File) << " for " << Sym.getName() << "\n";
addFile(File);
}
std::vector<Chunk *> SymbolTable::getChunks() {
std::vector<Chunk *> Res;
for (ObjectFile *File : ObjectFiles) {
@ -371,13 +364,8 @@ void SymbolTable::addCombinedLTOObjects() {
// DefinedBitcode symbols with the definitions in the object file.
LTOCodeGenerator CG(BitcodeFile::Context);
CG.setOptLevel(Config->LTOOptLevel);
std::vector<ObjectFile *> Objs = createLTOObjects(&CG);
size_t NumBitcodeFiles = BitcodeFiles.size();
for (ObjectFile *Obj : Objs)
for (ObjectFile *Obj : createLTOObjects(&CG))
Obj->parse();
if (BitcodeFiles.size() != NumBitcodeFiles)
fatal("LTO: late loaded symbol created new bitcode reference");
}
// Combine and compile bitcode files and then return the result

6
lld/COFF/SymbolTable.h
View File

@ -17,11 +17,6 @@
#include "llvm/Support/Allocator.h"
#include "llvm/Support/raw_ostream.h"
#ifdef _MSC_VER
// <future> depends on <eh.h> for __uncaught_exception.
#include <eh.h>
#endif
namespace llvm {
struct LTOCodeGenerator;
}
@ -117,7 +112,6 @@ private:
std::pair<Symbol *, bool> insert(StringRef Name);
StringRef findByPrefix(StringRef Prefix);
void addMemberFile(ArchiveFile *F, const Archive::Symbol Sym);
void addCombinedLTOObject(ObjectFile *Obj);
std::vector<ObjectFile *> createLTOObjects(llvm::LTOCodeGenerator *CG);

5
lld/COFF/Symbols.h
View File

@ -393,6 +393,11 @@ struct Symbol {
// True if this symbol was referenced by a regular (non-bitcode) object.
unsigned IsUsedInRegularObj : 1;
// True if we've seen both a lazy and an undefined symbol with this symbol
// name, which means that we have enqueued an archive member load and should
// not load any more archive members to resolve the same symbol.
unsigned PendingArchiveLoad : 1;
// This field is used to store the Symbol's SymbolBody. This instantiation of
// AlignedCharArrayUnion gives us a struct with a char array field that is
// large and aligned enough to store any derived class of SymbolBody.

2
lld/test/COFF/order.test
View File

@ -10,6 +10,6 @@
CHECK: order.test.tmp1.obj
CHECK: order.test.tmp2.lib
CHECK: order.test.tmp2.lib(order.test.tmp2.obj) for foo
CHECK: order.test.tmp3.obj
CHECK: order.test.tmp3.lib
CHECK: order.test.tmp2.lib(order.test.tmp2.obj) for foo