[gold] Add preliminary FatLTO support to the Gold plugin

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.

Depends on D146778

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D152973

llvm/lib/Object/ObjectFile.cpp

@@ -79,7 +79,7 @@ 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;
 }

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

@@ -2,4 +2,4 @@
 .asciz "Wrong Section"
 
 .section __LLVM,__bitcode
-.incbin "bcsection.bc"
+.incbin "llvm.lto.section.bc"

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

@@ -0,0 +1,2 @@
+.section .llvm.lto
+.incbin "llvm.lto.section.bc"

llvm/test/LTO/X86/bcsection.ll

@@ -2,23 +2,17 @@
 ; 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

@@ -0,0 +1,25 @@
+; RUN: rm -rf %t && mkdir -p %t
+; 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-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

@@ -0,0 +1,9 @@
+# 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

@@ -0,0 +1,108 @@
+;; Basic FatLTO tests.
+
+; 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

@@ -538,14 +538,6 @@ static ld_plugin_status claim_file_hook(const ld_plugin_input_file *file,
     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);