Always evaluate the second argument for CHECK() lazily.

[ruiu]

Summary

This patch is to rename check CHECK and make it a C macro, so that
we can evaluate the second argument lazily.

[pcc]

lld/include/lld/Common/ErrorHandler.h

117

Perhaps it would be better to support only the two-argument form via the CHECK macro? That would not only simplify the macro definition, but also if I look at a check call with a single argument, I can tell from the name that it is just a straightforward function call.

[ruiu]

• Use llvm::function_ref instead of std::function

[ruiu]

lld/include/lld/Common/ErrorHandler.h

117

Yeah that probably makes more sense. I thought that this macro isn't that bad, but we should avoid this sort of hack.

[ruiu]

• Use C macro only for the arity 2 check function.

[pcc]

LGTM

lld/COFF/Driver.cpp

void LinkerDriver::addBuffer(std::unique_ptr<MemoryBuffer> MB,
   switch (identify_magic(MBRef.getBuffer())) {
   case file_magic::windows_resource:
     Resources.push_back(MBRef);
     break;
 
   case file_magic::archive:
     if (WholeArchive) {
       std::unique_ptr<Archive> File =
-          check(Archive::create(MBRef),
+          CHECK(Archive::create(MBRef),
                 MBRef.getBufferIdentifier() + ": failed to parse archive");
 
       for (MemoryBufferRef M : getArchiveMembers(File.get()))
         addArchiveBuffer(M, "<whole-archive>", MBRef.getBufferIdentifier());
       return;
     }
     Symtab->addFile(make<ArchiveFile>(MBRef));
     break;
void LinkerDriver::addArchiveBuffer(MemoryBufferRef MB, StringRef SymName,
   Symtab->addFile(Obj);
   log("Loaded " + toString(Obj) + " for " + SymName);
 }
 
 void LinkerDriver::enqueueArchiveMember(const Archive::Child &C,
                                         StringRef SymName,
                                         StringRef ParentName) {
   if (!C.getParent()->isThin()) {
-    MemoryBufferRef MB = check(
+    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(),
+      CHECK(C.getFullName(),
             "could not get the filename for the member defining symbol " +
                 SymName)));
   enqueueTask([=]() {
     auto MBOrErr = Future->get();
     if (MBOrErr.second)
       fatal("could not get the buffer for the member defining " + SymName +
             ": " + MBOrErr.second.message());
     Driver->addArchiveBuffer(takeBuffer(std::move(MBOrErr.first)), SymName,
static void createImportLibrary(bool AsLib) {
 
   auto E = writeImportLibrary(getImportName(AsLib), getImplibPath(), Exports,
                               Config->Machine, false);
   handleAllErrors(std::move(E),
                   [&](ErrorInfoBase &EIB) { error(EIB.message()); });
 }
 
 static void parseModuleDefs(StringRef Path) {
-  std::unique_ptr<MemoryBuffer> MB = check(
+  std::unique_ptr<MemoryBuffer> MB = CHECK(
       MemoryBuffer::getFile(Path, -1, false, true), "could not open " + Path);
   COFFModuleDefinition M = check(parseCOFFModuleDefinition(
       MB->getMemBufferRef(), Config->Machine, Config->MinGW));
 
   if (Config->OutputFile.empty())
     Config->OutputFile = Saver.save(M.OutputFile);
   Config->ImportName = Saver.save(M.ImportName);
   if (M.ImageBase)
     Config->ImageBase = M.ImageBase;
static void parseModuleDefs(StringRef Path) {
   }
 }
 
 // A helper function for filterBitcodeFiles.
 static bool needsRebuilding(MemoryBufferRef MB) {
   // The MSVC linker doesn't support thin archives, so if it's a thin
   // archive, we always need to rebuild it.
   std::unique_ptr<Archive> File =
-      check(Archive::create(MB), "Failed to read " + MB.getBufferIdentifier());
+      CHECK(Archive::create(MB), "Failed to read " + MB.getBufferIdentifier());
   if (File->isThin())
     return true;
 
   // Returns true if the archive contains at least one bitcode file.
   for (MemoryBufferRef Member : getArchiveMembers(File.get()))
     if (identify_magic(Member.getBuffer()) == file_magic::bitcode)
       return true;
   return false;
 }
 
 // Opens a given path as an archive file and removes bitcode files
 // from them if exists. This function is to appease the MSVC linker as
 // their linker doesn't like archive files containing non-native
 // object files.
 //
 // If a given archive doesn't contain bitcode files, the archive path
 // is returned as-is. Otherwise, a new temporary file is created and
 // its path is returned.
 static Optional<std::string>
 filterBitcodeFiles(StringRef Path, std::vector<std::string> &TemporaryFiles) {
-  std::unique_ptr<MemoryBuffer> MB = check(
+  std::unique_ptr<MemoryBuffer> MB = CHECK(
       MemoryBuffer::getFile(Path, -1, false, true), "could not open " + Path);
   MemoryBufferRef MBRef = MB->getMemBufferRef();
   file_magic Magic = identify_magic(MBRef.getBuffer());
 
   if (Magic == file_magic::bitcode)
     return None;
   if (Magic != file_magic::archive)
     return Path.str();
   if (!needsRebuilding(MBRef))
     return Path.str();
 
   std::unique_ptr<Archive> File =
-      check(Archive::create(MBRef),
+      CHECK(Archive::create(MBRef),
             MBRef.getBufferIdentifier() + ": failed to parse archive");
 
   std::vector<NewArchiveMember> New;
   for (MemoryBufferRef Member : getArchiveMembers(File.get()))
     if (identify_magic(Member.getBuffer()) != file_magic::bitcode)
       New.emplace_back(Member);
 
   if (New.empty())
if (Args.hasArg(OPT_lldsavetemps))
     Config->SaveTemps = true;
 
   // Handle /lldltocache
   if (auto *Arg = Args.getLastArg(OPT_lldltocache))
     Config->LTOCache = Arg->getValue();
 
   // Handle /lldsavecachepolicy
   if (auto *Arg = Args.getLastArg(OPT_lldltocachepolicy))
-    Config->LTOCachePolicy = check(
+    Config->LTOCachePolicy = CHECK(
         parseCachePruningPolicy(Arg->getValue()),
         Twine("/lldltocachepolicy: invalid cache policy: ") + Arg->getValue());
 
   // Handle /failifmismatch
   for (auto *Arg : Args.filtered(OPT_failifmismatch))
     checkFailIfMismatch(Arg->getValue());
 
   // Handle /merge

lld/COFF/DriverUtils.cpp

public:
   }
 
   // Returns a memory buffer of this temporary file.
   // Note that this function does not leave the file open,
   // so it is safe to remove the file immediately after this function
   // is called (you cannot remove an opened file on Windows.)
   std::unique_ptr<MemoryBuffer> getMemoryBuffer() {
     // IsVolatileSize=true forces MemoryBuffer to not use mmap().
-    return check(MemoryBuffer::getFile(Path, /*FileSize=*/-1,
+    return CHECK(MemoryBuffer::getFile(Path, /*FileSize=*/-1,
                                        /*RequiresNullTerminator=*/false,
                                        /*IsVolatileSize=*/true),
                  "could not open " + Path);
   }
 
   std::string Path;
 };
 }
static std::string createManifestXmlWithExternalMt(StringRef DefaultXml) {
   for (StringRef Filename : Config->ManifestInput) {
     E.add("/manifest");
     E.add(Filename);
   }
   E.add("/nologo");
   E.add("/out:" + StringRef(User.Path));
   E.run();
 
-  return check(MemoryBuffer::getFile(User.Path), "could not open " + User.Path)
+  return CHECK(MemoryBuffer::getFile(User.Path), "could not open " + User.Path)
       .get()
       ->getBuffer();
 }
 
 static std::string createManifestXml() {
   std::string DefaultXml = createDefaultXml();
   if (Config->ManifestInput.empty())
     return DefaultXml;

lld/COFF/InputFiles.cpp

if (auto *U = dyn_cast<Undefined>(Source)) {
     U->WeakAlias = Target;
   }
 }
 
 ArchiveFile::ArchiveFile(MemoryBufferRef M) : InputFile(ArchiveKind, M) {}
 
 void ArchiveFile::parse() {
   // Parse a MemoryBufferRef as an archive file.
-  File = check(Archive::create(MB), toString(this));
+  File = CHECK(Archive::create(MB), toString(this));
 
   // Read the symbol table to construct Lazy objects.
   for (const Archive::Symbol &Sym : File->symbols())
     Symtab->addLazy(this, Sym);
 }
 
 // Returns a buffer pointing to a member file containing a given symbol.
 void ArchiveFile::addMember(const Archive::Symbol *Sym) {
   const Archive::Child &C =
-      check(Sym->getMember(),
+      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;
 
   Driver->enqueueArchiveMember(C, Sym->getName(), getName());
 }
 
 std::vector<MemoryBufferRef> getArchiveMembers(Archive *File) {
   std::vector<MemoryBufferRef> V;
   Error Err = Error::success();
   for (const ErrorOr<Archive::Child> &COrErr : File->children(Err)) {
     Archive::Child C =
-        check(COrErr,
+        CHECK(COrErr,
               File->getFileName() + ": could not get the child of the archive");
     MemoryBufferRef MBRef =
-        check(C.getMemoryBufferRef(),
+        CHECK(C.getMemoryBufferRef(),
               File->getFileName() +
                   ": could not get the buffer for a child of the archive");
     V.push_back(MBRef);
   }
   if (Err)
     fatal(File->getFileName() +
           ": Archive::children failed: " + toString(std::move(Err)));
   return V;
 }
 
 void ObjFile::parse() {
   // Parse a memory buffer as a COFF file.
-  std::unique_ptr<Binary> Bin = check(createBinary(MB), toString(this));
+  std::unique_ptr<Binary> Bin = CHECK(createBinary(MB), toString(this));
 
   if (auto *Obj = dyn_cast<COFFObjectFile>(Bin.get())) {
     Bin.release();
     COFFObj.reset(Obj);
   } else {
     fatal(toString(this) + " is not a COFF file");
   }
 

lld/COFF/Writer.cpp

template <typename PEHeaderTy> void Writer::writeHeader() {
   // The first 4 bytes is length including itself.
   Buf = reinterpret_cast<uint8_t *>(&SymbolTable[NumberOfSymbols]);
   write32le(Buf, Strtab.size() + 4);
   if (!Strtab.empty())
     memcpy(Buf + 4, Strtab.data(), Strtab.size());
 }
 
 void Writer::openFile(StringRef Path) {
-  Buffer = check(
+  Buffer = CHECK(
       FileOutputBuffer::create(Path, FileSize, FileOutputBuffer::F_executable),
       "failed to open " + Path);
 }
 
 void Writer::createSEHTable(OutputSection *RData) {
   // Create SEH table. x86-only.
   if (Config->Machine != I386)
     return;

lld/ELF/Driver.cpp

static std::tuple<ELFKind, uint16_t, uint8_t> parseEmulation(StringRef Emul) {
   return std::make_tuple(Ret.first, Ret.second, OSABI);
 }
 
 // Returns slices of MB by parsing MB as an archive file.
 // Each slice consists of a member file in the archive.
 std::vector<std::pair<MemoryBufferRef, uint64_t>> static getArchiveMembers(
     MemoryBufferRef MB) {
   std::unique_ptr<Archive> File =
-      check(Archive::create(MB),
+      CHECK(Archive::create(MB),
             MB.getBufferIdentifier() + ": failed to parse archive");
 
   std::vector<std::pair<MemoryBufferRef, uint64_t>> V;
   Error Err = Error::success();
   bool AddToTar = File->isThin() && Tar;
   for (const ErrorOr<Archive::Child> &COrErr : File->children(Err)) {
     Archive::Child C =
-        check(COrErr, MB.getBufferIdentifier() +
+        CHECK(COrErr, MB.getBufferIdentifier() +
                           ": could not get the child of the archive");
     MemoryBufferRef MBRef =
-        check(C.getMemoryBufferRef(),
+        CHECK(C.getMemoryBufferRef(),
               MB.getBufferIdentifier() +
                   ": could not get the buffer for a child of the archive");
     if (AddToTar)
       Tar->append(relativeToRoot(check(C.getFullName())), MBRef.getBuffer());
     V.push_back(std::make_pair(MBRef, C.getChildOffset()));
   }
   if (Err)
     fatal(MB.getBufferIdentifier() + ": Archive::children failed: " +
case file_magic::archive: {
     // Handle -whole-archive.
     if (InWholeArchive) {
       for (const auto &P : getArchiveMembers(MBRef))
         Files.push_back(createObjectFile(P.first, Path, P.second));
       return;
     }
 
     std::unique_ptr<Archive> File =
-        check(Archive::create(MBRef), Path + ": failed to parse archive");
+        CHECK(Archive::create(MBRef), Path + ": failed to parse archive");
 
     // If an archive file has no symbol table, it is likely that a user
     // is attempting LTO and using a default ar command that doesn't
     // understand the LLVM bitcode file. It is a pretty common error, so
     // we'll handle it as if it had a symbol table.
     if (!File->isEmpty() && !File->hasSymbolTable()) {
       for (const auto &P : getArchiveMembers(MBRef))
         Files.push_back(make<LazyObjFile>(P.first, Path, P.second));
void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->SingleRoRx = Args.hasArg(OPT_no_rosegment);
   Config->SoName = Args.getLastArgValue(OPT_soname);
   Config->SortSection = getSortSection(Args);
   Config->Strip = getStrip(Args);
   Config->Sysroot = Args.getLastArgValue(OPT_sysroot);
   Config->Target1Rel = Args.hasFlag(OPT_target1_rel, OPT_target1_abs, false);
   Config->Target2 = getTarget2(Args);
   Config->ThinLTOCacheDir = Args.getLastArgValue(OPT_thinlto_cache_dir);
-  Config->ThinLTOCachePolicy = check(
+  Config->ThinLTOCachePolicy = CHECK(
       parseCachePruningPolicy(Args.getLastArgValue(OPT_thinlto_cache_policy)),
       "--thinlto-cache-policy: invalid cache policy");
   Config->ThinLTOJobs = args::getInteger(Args, OPT_thinlto_jobs, -1u);
   ThreadsEnabled = Args.hasFlag(OPT_threads, OPT_no_threads, true);
   Config->Trace = Args.hasArg(OPT_trace);
   Config->Undefined = args::getStrings(Args, OPT_undefined);
   Config->UnresolvedSymbols = getUnresolvedSymbolPolicy(Args);
   Config->Verbose = Args.hasArg(OPT_verbose);

lld/ELF/InputFiles.cpp

 
 template <class ELFT>
 typename ELFT::SymRange ELFFileBase<ELFT>::getGlobalELFSyms() {
   return makeArrayRef(ELFSyms.begin() + FirstNonLocal, ELFSyms.end());
 }
 
 template <class ELFT>
 uint32_t ELFFileBase<ELFT>::getSectionIndex(const Elf_Sym &Sym) const {
-  return checkLazy(getObj().getSectionIndex(&Sym, ELFSyms, SymtabSHNDX),
-                   [=]() { return toString(this); });
+  return CHECK(getObj().getSectionIndex(&Sym, ELFSyms, SymtabSHNDX),
+               toString(this));
 }
 
 template <class ELFT>
 void ELFFileBase<ELFT>::initSymtab(ArrayRef<Elf_Shdr> Sections,
                                    const Elf_Shdr *Symtab) {
   FirstNonLocal = Symtab->sh_info;
-  ELFSyms = check(getObj().symbols(Symtab), toString(this));
+  ELFSyms = CHECK(getObj().symbols(Symtab), toString(this));
   if (FirstNonLocal == 0 || FirstNonLocal > ELFSyms.size())
     fatal(toString(this) + ": invalid sh_info in symbol table");
 
-  StringTable = check(getObj().getStringTableForSymtab(*Symtab, Sections),
+  StringTable = CHECK(getObj().getStringTableForSymtab(*Symtab, Sections),
                       toString(this));
 }
 
 template <class ELFT>
 ObjFile<ELFT>::ObjFile(MemoryBufferRef M, StringRef ArchiveName)
     : ELFFileBase<ELFT>(Base::ObjKind, M) {
   this->ArchiveName = ArchiveName;
 }

 // They are identified and deduplicated by group name. This function
 // returns a group name.
 template <class ELFT>
 StringRef ObjFile<ELFT>::getShtGroupSignature(ArrayRef<Elf_Shdr> Sections,
                                               const Elf_Shdr &Sec) {
   // Group signatures are stored as symbol names in object files.
   // sh_info contains a symbol index, so we fetch a symbol and read its name.
   if (this->ELFSyms.empty())
-    this->initSymtab(Sections,
-                     checkLazy(object::getSection<ELFT>(Sections, Sec.sh_link),
-                               [=]() { return toString(this); }));
-
-  const Elf_Sym *Sym =
-      checkLazy(object::getSymbol<ELFT>(this->ELFSyms, Sec.sh_info),
-                [=]() { return toString(this); });
-  StringRef Signature = checkLazy(Sym->getName(this->StringTable),
-                                  [=]() { return toString(this); });
+    this->initSymtab(
+        Sections,
+        CHECK(object::getSection<ELFT>(Sections, Sec.sh_link), toString(this)));
+
+  const Elf_Sym *Sym = CHECK(
+      object::getSymbol<ELFT>(this->ELFSyms, Sec.sh_info), toString(this));
+  StringRef Signature = CHECK(Sym->getName(this->StringTable), toString(this));
 
   // As a special case, if a symbol is a section symbol and has no name,
   // we use a section name as a signature.
   //
   // Such SHT_GROUP sections are invalid from the perspective of the ELF
   // standard, but GNU gold 1.14 (the neweset version as of July 2017) or
   // older produce such sections as outputs for the -r option, so we need
   // a bug-compatibility.
   if (Signature.empty() && Sym->getType() == STT_SECTION)
     return getSectionName(Sec);
   return Signature;
 }
 
 template <class ELFT>
 ArrayRef<typename ObjFile<ELFT>::Elf_Word>
 ObjFile<ELFT>::getShtGroupEntries(const Elf_Shdr &Sec) {
   const ELFFile<ELFT> &Obj = this->getObj();
-  ArrayRef<Elf_Word> Entries =
-      checkLazy(Obj.template getSectionContentsAsArray<Elf_Word>(&Sec),
-                [=]() { return toString(this); });
+  ArrayRef<Elf_Word> Entries = CHECK(
+      Obj.template getSectionContentsAsArray<Elf_Word>(&Sec), toString(this));
   if (Entries.empty() || Entries[0] != GRP_COMDAT)
     fatal(toString(this) + ": unsupported SHT_GROUP format");
   return Entries.slice(1);
 }
 
 template <class ELFT> bool ObjFile<ELFT>::shouldMerge(const Elf_Shdr &Sec) {
   // We don't merge sections if -O0 (default is -O1). This makes sometimes
   // the linker significantly faster, although the output will be bigger.

 }
 
 template <class ELFT>
 void ObjFile<ELFT>::initializeSections(
     DenseSet<CachedHashStringRef> &ComdatGroups) {
   const ELFFile<ELFT> &Obj = this->getObj();
 
   ArrayRef<Elf_Shdr> ObjSections =
-      check(this->getObj().sections(), toString(this));
+      CHECK(this->getObj().sections(), toString(this));
   uint64_t Size = ObjSections.size();
   this->Sections.resize(Size);
   this->SectionStringTable =
-      check(Obj.getSectionStringTable(ObjSections), toString(this));
+      CHECK(Obj.getSectionStringTable(ObjSections), toString(this));
 
   for (size_t I = 0, E = ObjSections.size(); I < E; I++) {
     if (this->Sections[I] == &InputSection::Discarded)
       continue;
     const Elf_Shdr &Sec = ObjSections[I];
 
     // SHF_EXCLUDE'ed sections are discarded by the linker. However,
     // if -r is given, we'll let the final link discard such sections.
case SHT_GROUP: {
       }
       break;
     }
     case SHT_SYMTAB:
       this->initSymtab(ObjSections, &Sec);
       break;
     case SHT_SYMTAB_SHNDX:
       this->SymtabSHNDX =
-          check(Obj.getSHNDXTable(Sec, ObjSections), toString(this));
+          CHECK(Obj.getSHNDXTable(Sec, ObjSections), toString(this));
       break;
     case SHT_STRTAB:
     case SHT_NULL:
       break;
     default:
       this->Sections[I] = createInputSection(Sec);
     }
 
case SHT_REL: {
     // sections with relocations as non-mergeable.
     if (auto *MS = dyn_cast<MergeInputSection>(Target)) {
       Target = toRegularSection(MS);
       this->Sections[Sec.sh_info] = Target;
     }
 
     size_t NumRelocations;
     if (Sec.sh_type == SHT_RELA) {
-      ArrayRef<Elf_Rela> Rels = checkLazy(this->getObj().relas(&Sec),
-                                          [=]() { return toString(this); });
+      ArrayRef<Elf_Rela> Rels =
+          CHECK(this->getObj().relas(&Sec), toString(this));
       Target->FirstRelocation = Rels.begin();
       NumRelocations = Rels.size();
       Target->AreRelocsRela = true;
     } else {
-      ArrayRef<Elf_Rel> Rels = checkLazy(this->getObj().rels(&Sec),
-                                         [=]() { return toString(this); });
+      ArrayRef<Elf_Rel> Rels = CHECK(this->getObj().rels(&Sec), toString(this));
       Target->FirstRelocation = Rels.begin();
       NumRelocations = Rels.size();
       Target->AreRelocsRela = false;
     }
     assert(isUInt<31>(NumRelocations));
     Target->NumRelocations = NumRelocations;
 
     // Relocation sections processed by the linker are usually removed
InputSectionBase *ObjFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
 
   if (shouldMerge(Sec))
     return make<MergeInputSection>(this, &Sec, Name);
   return make<InputSection>(this, &Sec, Name);
 }
 
 template <class ELFT>
 StringRef ObjFile<ELFT>::getSectionName(const Elf_Shdr &Sec) {
-  return checkLazy(this->getObj().getSectionName(&Sec, SectionStringTable),
-                   [=]() { return toString(this); });
+  return CHECK(this->getObj().getSectionName(&Sec, SectionStringTable),
+               toString(this));
 }
 
 template <class ELFT> void ObjFile<ELFT>::initializeSymbols() {
   this->Symbols.reserve(this->ELFSyms.size());
   for (const Elf_Sym &Sym : this->ELFSyms)
     this->Symbols.push_back(createSymbol(&Sym));
 }
 
template <class ELFT> Symbol *ObjFile<ELFT>::createSymbol(const Elf_Sym *Sym) {
 
   uint8_t StOther = Sym->st_other;
   uint8_t Type = Sym->getType();
   uint64_t Value = Sym->st_value;
   uint64_t Size = Sym->st_size;
 
   if (Binding == STB_LOCAL) {
     if (Sym->getType() == STT_FILE)
-      SourceFile = check(Sym->getName(this->StringTable), toString(this));
+      SourceFile = CHECK(Sym->getName(this->StringTable), toString(this));
 
     if (this->StringTable.size() <= Sym->st_name)
       fatal(toString(this) + ": invalid symbol name offset");
 
     StringRefZ Name = this->StringTable.data() + Sym->st_name;
     if (Sym->st_shndx == SHN_UNDEF)
       return make<Undefined>(this, Name, Binding, StOther, Type);
 
     return make<Defined>(this, Name, Binding, StOther, Type, Value, Size, Sec);
   }
 
-  StringRef Name = checkLazy(Sym->getName(this->StringTable),
-                             [=]() { return toString(this); });
+  StringRef Name = CHECK(Sym->getName(this->StringTable), toString(this));
 
   switch (Sym->st_shndx) {
   case SHN_UNDEF:
     return Symtab->addUndefined<ELFT>(Name, Binding, StOther, Type,
                                       /*CanOmitFromDynSym=*/false, this);
   case SHN_COMMON:
     if (Value == 0 || Value >= UINT32_MAX)
       fatal(toString(this) + ": common symbol '" + Name +
template <class ELFT> void ArchiveFile::parse() {
   for (const Archive::Symbol &Sym : File->symbols())
     Symbols.push_back(Symtab->addLazyArchive<ELFT>(Sym.getName(), this, Sym));
 }
 
 // Returns a buffer pointing to a member file containing a given symbol.
 std::pair<MemoryBufferRef, uint64_t>
 ArchiveFile::getMember(const Archive::Symbol *Sym) {
   Archive::Child C =
-      check(Sym->getMember(), toString(this) +
+      CHECK(Sym->getMember(), toString(this) +
                                   ": could not get the member for symbol " +
                                   Sym->getName());
 
   if (!Seen.insert(C.getChildOffset()).second)
     return {MemoryBufferRef(), 0};
 
   MemoryBufferRef Ret =
-      check(C.getMemoryBufferRef(),
+      CHECK(C.getMemoryBufferRef(),
             toString(this) +
                 ": could not get the buffer for the member defining symbol " +
                 Sym->getName());
 
   if (C.getParent()->isThin() && Tar)
-    Tar->append(relativeToRoot(check(C.getFullName(), toString(this))),
+    Tar->append(relativeToRoot(CHECK(C.getFullName(), toString(this))),
                 Ret.getBuffer());
   if (C.getParent()->isThin())
     return {Ret, 0};
   return {Ret, C.getChildOffset()};
 }
 
 template <class ELFT>
 SharedFile<ELFT>::SharedFile(MemoryBufferRef M, StringRef DefaultSoName)
     : ELFFileBase<ELFT>(Base::SharedKind, M), SoName(DefaultSoName),
       IsNeeded(!Config->AsNeeded) {}
 
 // Partially parse the shared object file so that we can call
 // getSoName on this object.
 template <class ELFT> void SharedFile<ELFT>::parseSoName() {
   const Elf_Shdr *DynamicSec = nullptr;
   const ELFFile<ELFT> Obj = this->getObj();
-  ArrayRef<Elf_Shdr> Sections = check(Obj.sections(), toString(this));
+  ArrayRef<Elf_Shdr> Sections = CHECK(Obj.sections(), toString(this));
 
   // Search for .dynsym, .dynamic, .symtab, .gnu.version and .gnu.version_d.
   for (const Elf_Shdr &Sec : Sections) {
     switch (Sec.sh_type) {
     default:
       continue;
     case SHT_DYNSYM:
       this->initSymtab(Sections, &Sec);
       break;
     case SHT_DYNAMIC:
       DynamicSec = &Sec;
       break;
     case SHT_SYMTAB_SHNDX:
       this->SymtabSHNDX =
-          check(Obj.getSHNDXTable(Sec, Sections), toString(this));
+          CHECK(Obj.getSHNDXTable(Sec, Sections), toString(this));
       break;
     case SHT_GNU_versym:
       this->VersymSec = &Sec;
       break;
     case SHT_GNU_verdef:
       this->VerdefSec = &Sec;
       break;
     }
   }
 
   if (this->VersymSec && this->ELFSyms.empty())
     error("SHT_GNU_versym should be associated with symbol table");
 
   // Search for a DT_SONAME tag to initialize this->SoName.
   if (!DynamicSec)
     return;
   ArrayRef<Elf_Dyn> Arr =
-      check(Obj.template getSectionContentsAsArray<Elf_Dyn>(DynamicSec),
+      CHECK(Obj.template getSectionContentsAsArray<Elf_Dyn>(DynamicSec),
             toString(this));
   for (const Elf_Dyn &Dyn : Arr) {
     if (Dyn.d_tag == DT_SONAME) {
       uint64_t Val = Dyn.getVal();
       if (Val >= this->StringTable.size())
         fatal(toString(this) + ": invalid DT_SONAME entry");
       SoName = this->StringTable.data() + Val;
       return;

 
 // Fully parse the shared object file. This must be called after parseSoName().
 template <class ELFT> void SharedFile<ELFT>::parseRest() {
   // Create mapping from version identifiers to Elf_Verdef entries.
   const Elf_Versym *Versym = nullptr;
   std::vector<const Elf_Verdef *> Verdefs = parseVerdefs(Versym);
 
   ArrayRef<Elf_Shdr> Sections =
-      check(this->getObj().sections(), toString(this));
+      CHECK(this->getObj().sections(), toString(this));
 
   // Add symbols to the symbol table.
   Elf_Sym_Range Syms = this->getGlobalELFSyms();
   for (const Elf_Sym &Sym : Syms) {
     unsigned VersymIndex = 0;
     if (Versym) {
       VersymIndex = Versym->vs_index;
       ++Versym;
     }
     bool Hidden = VersymIndex & VERSYM_HIDDEN;
     VersymIndex = VersymIndex & ~VERSYM_HIDDEN;
 
-    StringRef Name = check(Sym.getName(this->StringTable), toString(this));
+    StringRef Name = CHECK(Sym.getName(this->StringTable), toString(this));
     if (Sym.isUndefined()) {
       Undefs.push_back(Name);
       continue;
     }
 
     // Ignore local symbols.
     if (Versym && VersymIndex == VER_NDX_LOCAL)
       continue;
BitcodeFile::BitcodeFile(MemoryBufferRef MB, StringRef ArchiveName,
   // ThinLTO uses the MemoryBufferRef identifier to access its internal
   // data structures and if two archives define two members with the same name,
   // this causes a collision which result in only one of the objects being
   // taken into consideration at LTO time (which very likely causes undefined
   // symbols later in the link stage).
   MemoryBufferRef MBRef(MB.getBuffer(),
                         Saver.save(ArchiveName + MB.getBufferIdentifier() +
                                    utostr(OffsetInArchive)));
-  Obj = check(lto::InputFile::create(MBRef), toString(this));
+  Obj = CHECK(lto::InputFile::create(MBRef), toString(this));
 
   Triple T(Obj->getTargetTriple());
   EKind = getBitcodeELFKind(T);
   EMachine = getBitcodeMachineKind(MB.getBufferIdentifier(), T);
 }
 
 static uint8_t mapVisibility(GlobalValue::VisibilityTypes GvVisibility) {
   switch (GvVisibility) {

 }
 
 template <class ELFT> std::vector<StringRef> LazyObjFile::getElfSymbols() {
   typedef typename ELFT::Shdr Elf_Shdr;
   typedef typename ELFT::Sym Elf_Sym;
   typedef typename ELFT::SymRange Elf_Sym_Range;
 
   ELFFile<ELFT> Obj = check(ELFFile<ELFT>::create(this->MB.getBuffer()));
-  ArrayRef<Elf_Shdr> Sections = check(Obj.sections(), toString(this));
+  ArrayRef<Elf_Shdr> Sections = CHECK(Obj.sections(), toString(this));
   for (const Elf_Shdr &Sec : Sections) {
     if (Sec.sh_type != SHT_SYMTAB)
       continue;
 
-    Elf_Sym_Range Syms = check(Obj.symbols(&Sec), toString(this));
+    Elf_Sym_Range Syms = CHECK(Obj.symbols(&Sec), toString(this));
     uint32_t FirstNonLocal = Sec.sh_info;
     StringRef StringTable =
-        check(Obj.getStringTableForSymtab(Sec, Sections), toString(this));
+        CHECK(Obj.getStringTableForSymtab(Sec, Sections), toString(this));
     std::vector<StringRef> V;
 
     for (const Elf_Sym &Sym : Syms.slice(FirstNonLocal))
       if (Sym.st_shndx != SHN_UNDEF)
-        V.push_back(check(Sym.getName(StringTable), toString(this)));
+        V.push_back(CHECK(Sym.getName(StringTable), toString(this)));
     return V;
   }
   return {};
 }
 
 std::vector<StringRef> LazyObjFile::getBitcodeSymbols() {
   std::unique_ptr<lto::InputFile> Obj =
-      check(lto::InputFile::create(this->MB), toString(this));
+      CHECK(lto::InputFile::create(this->MB), toString(this));
   std::vector<StringRef> V;
   for (const lto::InputFile::Symbol &Sym : Obj->symbols())
     if (!Sym.isUndefined())
       V.push_back(Saver.save(Sym.getName()));
   return V;
 }
 
 // Returns a vector of globally-visible defined symbol names.

lld/include/lld/Common/ErrorHandler.h

 }
 inline void log(const Twine &Msg) { errorHandler().log(Msg); }
 inline void message(const Twine &Msg) { errorHandler().message(Msg); }
 inline void warn(const Twine &Msg) { errorHandler().warn(Msg); }
 inline uint64_t errorCount() { return errorHandler().ErrorCount; }
 
 LLVM_ATTRIBUTE_NORETURN void exitLld(int Val);
 
-// check() functions are convenient functions to strip errors
+// check functions are convenient functions to strip errors
 // from error-or-value objects.
 template <class T> T check(ErrorOr<T> E) {
   if (auto EC = E.getError())
     fatal(EC.message());
   return std::move(*E);
 }
 
 template <class T> T check(Expected<T> E) {
   if (!E)
     fatal(llvm::toString(E.takeError()));
   return std::move(*E);
 }
 
-template <class T> T check(ErrorOr<T> E, const Twine &Prefix) {
+template <class T>
+T check2(ErrorOr<T> E, llvm::function_ref<std::string()> Prefix) {
   if (auto EC = E.getError())
-    fatal(Prefix + ": " + EC.message());
-  return std::move(*E);
-}
-
-template <class T> T check(Expected<T> E, const Twine &Prefix) {
-  if (!E)
-    fatal(Prefix + ": " + toString(E.takeError()));
+    fatal(Prefix() + ": " + EC.message());
   return std::move(*E);
 }
 
-// A lazy variant that only allocates error messages when there is an error.
 template <class T>
-T checkLazy(Expected<T> E, llvm::function_ref<std::string()> getPrefix) {
+T check2(Expected<T> E, llvm::function_ref<std::string()> Prefix) {
   if (!E)
-    fatal(getPrefix() + ": " + toString(E.takeError()));
+    fatal(Prefix() + ": " + toString(E.takeError()));
   return std::move(*E);
 }
+
+inline std::string checkToString(const Twine &S) { return S.str(); }
+inline std::string checkToString(std::string S) { return S; }
+inline std::string checkToString(const char *S) { return S; }
+
+// To evaluate the second argument lazily, we use C macro.
+#define CHECK(E, S) check2(E, [&] { return checkToString(S); })
+
 } // namespace lld
 
 #endif

lld/wasm/InputFiles.cpp

uint32_t ObjFile::relocateGlobalIndex(uint32_t Original) const {
 
   DEBUG(dbgs() << " -> " << Index << "\n");
   return Index;
 }
 
 void ObjFile::parse() {
   // Parse a memory buffer as a wasm file.
   DEBUG(dbgs() << "Parsing object: " << toString(this) << "\n");
-  std::unique_ptr<Binary> Bin = check(createBinary(MB), toString(this));
+  std::unique_ptr<Binary> Bin = CHECK(createBinary(MB), toString(this));
 
   auto *Obj = dyn_cast<WasmObjectFile>(Bin.get());
   if (!Obj)
     fatal(toString(this) + ": not a wasm file");
   if (!Obj->isRelocatableObject())
     fatal(toString(this) + ": not a relocatable wasm file");
 
   Bin.release();
if (Sym.isLocal()) {
     return S;
   }
   return Symtab->addDefined(this, &Sym, Segment);
 }
 
 void ArchiveFile::parse() {
   // Parse a MemoryBufferRef as an archive file.
   DEBUG(dbgs() << "Parsing library: " << toString(this) << "\n");
-  File = check(Archive::create(MB), toString(this));
+  File = CHECK(Archive::create(MB), toString(this));
 
   // Read the symbol table to construct Lazy symbols.
   int Count = 0;
   for (const Archive::Symbol &Sym : File->symbols()) {
     Symtab->addLazy(this, &Sym);
     ++Count;
   }
   DEBUG(dbgs() << "Read " << Count << " symbols\n");
 }
 
 void ArchiveFile::addMember(const Archive::Symbol *Sym) {
   const Archive::Child &C =
-      check(Sym->getMember(),
+      CHECK(Sym->getMember(),
             "could not get the member for symbol " + Sym->getName());
 
   // Don't try to load the same member twice (this can happen when members
   // mutually reference each other).
   if (!Seen.insert(C.getChildOffset()).second)
     return;
 
   DEBUG(dbgs() << "loading lazy: " << Sym->getName() << "\n");
   DEBUG(dbgs() << "from archive: " << toString(this) << "\n");
 
   MemoryBufferRef MB =
-      check(C.getMemoryBufferRef(),
+      CHECK(C.getMemoryBufferRef(),
             "could not get the buffer for the member defining symbol " +
                 Sym->getName());
 
   if (identify_magic(MB.getBuffer()) != file_magic::wasm_object) {
     error("unknown file type: " + MB.getBufferIdentifier());
     return;
   }