Reland "[gold] Add preliminary FatLTO support to the Gold plugin""

[paulkirth]

Summary

This reverts commit 2f34288b2476339e532a59fc43723b6de1a9ef08.

This changes the definition if isSectionBitcode to only be valid for the
.llvm.lto section, since this API is only called from LTO, and the
.llvmbc section was not intended to be used for LTO. This allows the
gold plugin to keep its existing behavior without introducing any
significant changes.

[paulkirth]

Forgot to add related revision to the reland commit message.

llvm/lib/Object/ObjectFile.cpp

Error ObjectFile::printSymbolName(raw_ostream &OS, DataRefImpl Symb) const {
   return Error::success();
 }
 
 uint32_t ObjectFile::getSymbolAlignment(DataRefImpl DRI) const { return 0; }
 
 bool ObjectFile::isSectionBitcode(DataRefImpl Sec) const {
   Expected<StringRef> NameOrErr = getSectionName(Sec);
   if (NameOrErr)
-    return *NameOrErr == ".llvmbc" || *NameOrErr == ".llvm.lto";
+    return *NameOrErr == ".llvm.lto";
   consumeError(NameOrErr.takeError());
   return false;
 }
 
 bool ObjectFile::isSectionStripped(DataRefImpl Sec) const { return false; }
 
 bool ObjectFile::isBerkeleyText(DataRefImpl Sec) const {
   return isSectionText(Sec);

llvm/test/LTO/X86/Inputs/bcsection.macho.s

 .section __FOO,__bitcode
 .asciz "Wrong Section"
 
 .section __LLVM,__bitcode
-.incbin "bcsection.bc"
+.incbin "llvm.lto.section.bc"

llvm/test/LTO/X86/Inputs/llvm.lto.section.s

+.section .llvm.lto
+.incbin "llvm.lto.section.bc"

llvm/test/LTO/X86/bcsection.ll

 ; RUN: rm -rf %t && mkdir -p %t
 ; RUN: llvm-as -o %t/bcsection.bc %s
 
 ; RUN: llvm-mc -I=%t -filetype=obj -triple=x86_64-pc-win32 -o %t/bcsection.coff.bco %p/Inputs/bcsection.s
-; RUN: llvm-nm %t/bcsection.coff.bco | FileCheck %s
-; RUN: llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/bcsection.coff.o %t/bcsection.coff.bco
-; RUN: llvm-nm %t/bcsection.coff.o | FileCheck %s
+; RUN: llvm-nm %t/bcsection.coff.bco | FileCheck %s --allow-empty
+; RUN: not llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/bcsection.coff.o %t/bcsection.coff.bco
 
 ; RUN: llvm-mc -I=%t -filetype=obj -triple=x86_64-unknown-linux-gnu -o %t/bcsection.elf.bco %p/Inputs/bcsection.s
-; RUN: llvm-nm %t/bcsection.elf.bco | FileCheck %s
-; RUN: llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/bcsection.elf.o %t/bcsection.elf.bco
-; RUN: llvm-nm %t/bcsection.elf.o | FileCheck %s
-
-; RUN: llvm-mc -I=%t -filetype=obj -triple=x86_64-apple-darwin11 -o %t/bcsection.macho.bco %p/Inputs/bcsection.macho.s
-; RUN: llvm-nm %t/bcsection.macho.bco | FileCheck %s
-; RUN: llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/bcsection.macho.o %t/bcsection.macho.bco
-; RUN: llvm-nm %t/bcsection.macho.o | FileCheck %s
+; RUN: llvm-nm %t/bcsection.elf.bco | FileCheck %s --allow-empty
+; RUN: not llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/bcsection.elf.o %t/bcsection.elf.bco
 
 target triple = "x86_64-unknown-linux-gnu"
 
-; CHECK: main
+;; The .llvmbc section is not intended for use with LTO, so there should be nothing here
+; CHECK-NOT: main
 define i32 @main() {
   ret i32 0
 }

llvm/test/LTO/X86/llvm.lto.section.ll

 ; RUN: rm -rf %t && mkdir -p %t
-; RUN: llvm-as -o %t/bcsection.bc %s
+; RUN: llvm-as -o %t/llvm.lto.section.bc %s
+
+; RUN: llvm-mc -I=%t -filetype=obj -triple=x86_64-pc-win32 -o %t/llvm.lto.section.coff.bco %p/Inputs/llvm.lto.section.s
+; RUN: llvm-nm %t/llvm.lto.section.coff.bco | FileCheck %s
+; RUN: llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/llvm.lto.section.coff.o %t/llvm.lto.section.coff.bco
+; RUN: llvm-nm %t/llvm.lto.section.coff.o | FileCheck %s
+
+; RUN: llvm-mc -I=%t -filetype=obj -triple=x86_64-unknown-linux-gnu -o %t/llvm.lto.section.elf.bco %p/Inputs/llvm.lto.section.s
+; RUN: llvm-nm %t/llvm.lto.section.elf.bco | FileCheck %s
+; RUN: llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/llvm.lto.section.elf.o %t/llvm.lto.section.elf.bco
+; RUN: llvm-nm %t/llvm.lto.section.elf.o | FileCheck %s
 
-; RUN: llvm-mc -I=%t -filetype=obj -triple=x86_64-pc-win32 -o %t/bcsection.coff.bco %p/Inputs/bcsection.s
-; RUN: llvm-nm %t/bcsection.coff.bco | FileCheck %s
-; RUN: llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/bcsection.coff.o %t/bcsection.coff.bco
-; RUN: llvm-nm %t/bcsection.coff.o | FileCheck %s
-
-; RUN: llvm-mc -I=%t -filetype=obj -triple=x86_64-unknown-linux-gnu -o %t/bcsection.elf.bco %p/Inputs/bcsection.s
-; RUN: llvm-nm %t/bcsection.elf.bco | FileCheck %s
-; RUN: llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/bcsection.elf.o %t/bcsection.elf.bco
-; RUN: llvm-nm %t/bcsection.elf.o | FileCheck %s
 
 ; RUN: llvm-mc -I=%t -filetype=obj -triple=x86_64-apple-darwin11 -o %t/bcsection.macho.bco %p/Inputs/bcsection.macho.s
 ; RUN: llvm-nm %t/bcsection.macho.bco | FileCheck %s
 ; RUN: llvm-lto -exported-symbol=main -exported-symbol=_main -o %t/bcsection.macho.o %t/bcsection.macho.bco
 ; RUN: llvm-nm %t/bcsection.macho.o | FileCheck %s
 
 target triple = "x86_64-unknown-linux-gnu"
 
 ; CHECK: main
 define i32 @main() {
   ret i32 0
 }

llvm/test/tools/gold/X86/fatlto/fatlto.invalid.s

+# REQUIRES: x86_64-linux
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: not %gold -plugin %llvmshlibdir/LLVMgold%shlibext %t -o /dev/null 2>&1 | FileCheck %s
+
+# CHECK: error:{{.*}} Invalid bitcode signature
+
+.section        .llvm.lto,"e",@progbits
+.Lllvm.embedded.object:
+        .asciz  "BC\300\3365\000"
+        .size   .Lllvm.embedded.object, 12

llvm/test/tools/gold/X86/fatlto/fatlto.test

+;; Basic FatLTO tests.
+; REQUIRES: x86_64-linux
+
+; RUN: rm -rf %t && split-file %s %t
+
+;; Ensure that input files contain .llvm.lto section
+; RUN: llc %t/a-LTO.ll --filetype=obj -o %t/a-fatLTO.o
+; RUN: opt --module-summary %t/a-LTO.ll -o %t/a-fatLTO.bc
+; RUN: llvm-objcopy --add-section=.llvm.lto=%t/a-fatLTO.bc %t/a-fatLTO.o
+; RUN: llvm-objcopy --set-section-flags=.llvm.lto=readonly,exclude %t/a-fatLTO.o
+; RUN: llvm-readobj -S %t/a-fatLTO.o | FileCheck --check-prefix=CHECK-A %s
+
+; CHECK-A: Name: .llvm.lto
+
+; RUN: llc %t/main-LTO.ll --filetype=obj -o %t/main-fatLTO.o
+; RUN: opt --module-summary %t/main-LTO.ll -o %t/main-fatLTO.bc
+; RUN: llvm-objcopy --add-section=.llvm.lto=%t/main-fatLTO.bc %t/main-fatLTO.o
+; RUN: llvm-objcopy --set-section-flags=.llvm.lto=readonly,exclude %t/main-fatLTO.o
+; RUN: llvm-readobj -S %t/main-fatLTO.o | FileCheck --check-prefix=CHECK-MAIN %s
+
+; CHECK-MAIN: Name: .llvm.lto
+
+;; Final executable should not have .llvm.lto section no matter what the target is
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext -o %t/foo-fatLTO %t/a-fatLTO.o %t/main-fatLTO.o
+; RUN: llvm-readobj -S %t/foo-fatLTO | FileCheck --check-prefix=CHECK-LTO-TARGET %s
+
+;; Check that fat objects work w/ s=--start-lib
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext -o %t/foo-fatLTO.start_lib --start-lib %t/a-fatLTO.o %t/main-fatLTO.o --end-lib
+; RUN: llvm-readobj -S %t/foo-fatLTO.start_lib | FileCheck --check-prefix=CHECK-LTO-TARGET %s
+
+;; Check if .llvm.lto section gets aggregated in LTO target
+; CHECK-LTO-TARGET-NOT: Name: .llvm.lto
+
+;; Final executable should not have .llvm.lto section no matter what the target is
+; RUN: %gold -o %t/foo-fatNoLTO %t/a-fatLTO.o %/t/main-fatLTO.o
+; RUN: llvm-readobj -S %t/foo-fatNoLTO | FileCheck --check-prefix=CHECK-NON-LTO-TARGET %s
+
+;; Check if .llvm.lto section gets aggregated in non-LTO target
+; CHECK-NON-LTO-TARGET-NOT: Name: .llvm.lto
+
+;; Check if the LTO target executable produced from FatLTO object file is
+;; identical to the one produced from LTO modules
+; RUN: opt --module-summary %t/a-LTO.ll -o %t/a-LTO.bc
+; RUN: opt --module-summary %t/main-LTO.ll -o %t/main-LTO.bc
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext -o %t/foo-LTO %t/a-LTO.bc %t/main-LTO.bc
+; RUN: cmp %t/foo-fatLTO %t/foo-LTO
+
+;; Check if the no-LTO target executable produced from FatLTO object file is
+;; identical to the one produced from regular object files
+
+; RUN: llc %t/a-LTO.ll --filetype=obj -o %t/a.o
+; RUN: llc %t/main-LTO.ll --filetype=obj -o %t/main.o
+
+; RUN: %gold -o %t/foo-noLTO %t/a.o %t/main.o
+; RUN: cmp %t/foo-fatNoLTO %t/foo-noLTO
+
+;; Check archive support
+; RUN: llvm-ar rcs %t/a.a %t/a-fatLTO.o
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext -o %t/foo-fatLTO.archive %t/main-LTO.bc %t/a.a 
+; RUN: cmp %t/foo-fatLTO.archive %t/foo-LTO
+
+;--- a-LTO.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local i32 @_start() #0 {
+entry:
+  ret i32 0
+}
+
+attributes #0 = { noinline nounwind uwtable }
+
+!llvm.module.flags = !{!0, !1, !2, !3, !4, !5, !6}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 7, !"PIC Level", i32 2}
+!2 = !{i32 7, !"PIE Level", i32 2}
+!3 = !{i32 7, !"uwtable", i32 2}
+!4 = !{i32 7, !"frame-pointer", i32 2}
+!5 = !{i32 1, !"ThinLTO", i32 0}
+!6 = !{i32 1, !"EnableSplitLTOUnit", i32 1}
+
+;--- main-LTO.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local i32 @main() #0 {
+entry:
+  %retval = alloca i32, align 4
+  store i32 0, ptr %retval, align 4
+  %call = call i32 (...) @_start()
+  ret i32 %call
+}
+
+declare i32 @_start(...)
+
+attributes #0 = { noinline nounwind uwtable }
+
+!llvm.module.flags = !{!0, !1, !2, !3, !4, !5, !6}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 7, !"PIC Level", i32 2}
+!2 = !{i32 7, !"PIE Level", i32 2}
+!3 = !{i32 7, !"uwtable", i32 2}
+!4 = !{i32 7, !"frame-pointer", i32 2}
+!5 = !{i32 1, !"ThinLTO", i32 0}
+!6 = !{i32 1, !"EnableSplitLTOUnit", i32 1}

llvm/tools/gold/gold-plugin.cpp

if (get_view) {
     if (std::error_code EC = BufferOrErr.getError()) {
       message(LDPL_ERROR, EC.message().c_str());
       return LDPS_ERR;
     }
     Buffer = std::move(BufferOrErr.get());
     BufferRef = Buffer->getMemBufferRef();
   }
 
-  // Only use bitcode files for LTO.  InputFile::create() will load bitcode
-  // from the .llvmbc section within a binary object, this bitcode is typically
-  // generated by -fembed-bitcode and is not to be used by LLVMgold.so for LTO.
-  if (identify_magic(BufferRef.getBuffer()) != file_magic::bitcode) {
-    *claimed = 0;
-    return LDPS_OK;
-  }
-
   *claimed = 1;
 
   Expected<std::unique_ptr<InputFile>> ObjOrErr = InputFile::create(BufferRef);
   if (!ObjOrErr) {
     handleAllErrors(ObjOrErr.takeError(), [&](const ErrorInfoBase &EI) {
       std::error_code EC = EI.convertToErrorCode();
       if (EC == object::object_error::invalid_file_type ||
           EC == object::object_error::bitcode_section_not_found)