Revert "[lld] Preliminary fat-lto-object support"

This reverts commit c9953d9 and a
forward fix in 3a45b84.

D14677 causes some failure on windows bots that the forward fix did not
address. Thus I'm reverting until the underlying cause can me triaged.

Author: ilovepi

lld/ELF/Config.h

@@ -125,8 +125,7 @@ class LinkerDriver {
   void inferMachineType();
   void link(llvm::opt::InputArgList &args);
   template <class ELFT> void compileBitcodeFiles(bool skipLinkedOutput);
-  bool tryAddFatLTOFile(MemoryBufferRef mb, StringRef archiveName,
-                        uint64_t offsetInArchive, bool lazy);
+
   // True if we are in --whole-archive and --no-whole-archive.
   bool inWholeArchive = false;
 
@@ -206,7 +205,6 @@ struct Config {
       callGraphProfile;
   bool cmseImplib = false;
   bool allowMultipleDefinition;
-  bool fatLTOObjects;
   bool androidPackDynRelocs = false;
   bool armHasBlx = false;
   bool armHasMovtMovw = false;

lld/ELF/Driver.cpp

@@ -52,7 +52,6 @@
 #include "llvm/Config/llvm-config.h"
 #include "llvm/LTO/LTO.h"
 #include "llvm/Object/Archive.h"
-#include "llvm/Object/IRObjectFile.h"
 #include "llvm/Remarks/HotnessThresholdParser.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compression.h"
@@ -238,19 +237,6 @@ static bool isBitcode(MemoryBufferRef mb) {
   return identify_magic(mb.getBuffer()) == llvm::file_magic::bitcode;
 }
 
-bool LinkerDriver::tryAddFatLTOFile(MemoryBufferRef mb, StringRef archiveName,
-                                    uint64_t offsetInArchive, bool lazy) {
-  if (!config->fatLTOObjects)
-    return false;
-  Expected<MemoryBufferRef> fatLTOData =
-      IRObjectFile::findBitcodeInMemBuffer(mb);
-  if (errorToBool(fatLTOData.takeError()))
-    return false;
-  files.push_back(
-      make<BitcodeFile>(*fatLTOData, archiveName, offsetInArchive, lazy));
-  return true;
-}
-
 // Opens a file and create a file object. Path has to be resolved already.
 void LinkerDriver::addFile(StringRef path, bool withLOption) {
   using namespace sys::fs;
@@ -275,7 +261,7 @@ void LinkerDriver::addFile(StringRef path, bool withLOption) {
       for (const std::pair<MemoryBufferRef, uint64_t> &p : members) {
         if (isBitcode(p.first))
           files.push_back(make<BitcodeFile>(p.first, path, p.second, false));
-        else if (!tryAddFatLTOFile(p.first, path, p.second, false))
+        else
           files.push_back(createObjFile(p.first, path));
       }
       return;
@@ -299,10 +285,9 @@ void LinkerDriver::addFile(StringRef path, bool withLOption) {
     InputFile::isInGroup = true;
     for (const std::pair<MemoryBufferRef, uint64_t> &p : members) {
       auto magic = identify_magic(p.first.getBuffer());
-      if (magic == file_magic::elf_relocatable) {
-        if (!tryAddFatLTOFile(p.first, path, p.second, true))
-          files.push_back(createObjFile(p.first, path, true));
-      } else if (magic == file_magic::bitcode)
+      if (magic == file_magic::elf_relocatable)
+        files.push_back(createObjFile(p.first, path, true));
+      else if (magic == file_magic::bitcode)
         files.push_back(make<BitcodeFile>(p.first, path, p.second, true));
       else
         warn(path + ": archive member '" + p.first.getBufferIdentifier() +
@@ -334,8 +319,7 @@ void LinkerDriver::addFile(StringRef path, bool withLOption) {
     files.push_back(make<BitcodeFile>(mbref, "", 0, inLib));
     break;
   case file_magic::elf_relocatable:
-    if (!tryAddFatLTOFile(mbref, "", 0, inLib))
-      files.push_back(createObjFile(mbref, "", inLib));
+    files.push_back(createObjFile(mbref, "", inLib));
     break;
   default:
     error(path + ": unknown file type");
@@ -1154,8 +1138,6 @@ static void readConfigs(opt::InputArgList &args) {
       args.hasFlag(OPT_android_memtag_heap, OPT_no_android_memtag_heap, false);
   config->androidMemtagStack = args.hasFlag(OPT_android_memtag_stack,
                                             OPT_no_android_memtag_stack, false);
-  config->fatLTOObjects =
-      args.hasFlag(OPT_fat_lto_objects, OPT_no_fat_lto_objects, false);
   config->androidMemtagMode = getMemtagMode(args);
   config->auxiliaryList = args::getStrings(args, OPT_auxiliary);
   config->armBe8 = args.hasArg(OPT_be8);

lld/ELF/Options.td

@@ -647,10 +647,6 @@ def thinlto_prefix_replace_eq: JJ<"thinlto-prefix-replace=">;
 def thinlto_single_module_eq: JJ<"thinlto-single-module=">,
   HelpText<"Specify a single module to compile in ThinLTO mode, for debugging only">;
 
-defm fat_lto_objects: BB<"fat-lto-objects",
-    "Use the .llvm.lto section, which contains LLVM bitcode, in fat LTO object files to perform LTO.",
-    "Ignore the .llvm.lto section in relocatable object files (default).">;
-
 def: J<"plugin-opt=O">, Alias<lto_O>, HelpText<"Alias for --lto-O">;
 def: F<"plugin-opt=debug-pass-manager">,
   Alias<lto_debug_pass_manager>, HelpText<"Alias for --lto-debug-pass-manager">;

lld/docs/ReleaseNotes.rst

@@ -31,10 +31,6 @@ ELF Improvements
 * ``PT_RISCV_ATTRIBUTES`` is added to include the SHT_RISCV_ATTRIBUTES section.
   (`D152065 <https://reviews.llvm.org/D152065>`_)
 
-- ``--fat-lto-objects`` option is added to support LLVM FatLTO.
-  Without ``--fat-lto-objects``, LLD will link LLVM FatLTO objects using the
-  relocatable object file. (`D146778 <https://reviews.llvm.org/D146778>`_)
-
 Breaking changes
 ----------------
 

lld/docs/ld.lld.1

@@ -621,10 +621,6 @@ Number of threads.
 (default) means all of concurrent threads supported.
 .Cm 1
 disables multi-threading.
-.It Fl -fat-lto-objects
-Use the .llvm.lto section, which contains LLVM bitcode, in fat LTO object files to perform LTO.
-.It Fl -no-fat-lto-objects
-Ignore the .llvm.lto section in relocatable object files (default).
 .It Fl -time-trace
 Record time trace.
 .It Fl -time-trace-file Ns = Ns Ar file