[lto] Add saving the LTO .o file to -save-temps.

[silvas]

Summary

This implements another part of -save-temps.
After this, the only remaining part is dumping the optimized bitcode. But
currently LLD's LTO doesn't have a non-intrusive place to put this.
Eventually we probably will and it will make sense to add it then.

After this patch, I have some NFC cleanups to make. I'll pull out a
maybeSaveTemp(std::string Suffix, std::function<void(raw_ostream &)>) and
simplify some of the names in the test.

[silvas]

I just checked and maybeSaveTemp is not a huge win for clarity.

[ruiu]

LGTM

test/ELF/lto/save-temps.ll

17–18 ↗

(On Diff #50178)

s/CHECK-DAG/CHECK/g

I think this test currently don't do anything.

lld/trunk/ELF/SymbolTable.cpp

void SymbolTable<ELFT>::addFile(std::unique_ptr<InputFile> File) {
   // .o file
   auto *F = cast<ObjectFile<ELFT>>(FileP);
   ObjectFiles.emplace_back(cast<ObjectFile<ELFT>>(File.release()));
   F->parse(ComdatGroups);
   for (SymbolBody *B : F->getSymbols())
     resolve(B);
 }
 
+// This is for use when debugging LTO.
+static void saveLtoObjectFile(StringRef Buffer) {
+  std::error_code EC;
+  raw_fd_ostream OS(Config->OutputFile.str() + ".lto.o", EC,
+                    sys::fs::OpenFlags::F_None);
+  check(EC);
+  OS << Buffer;
+}
+
 // Codegen the module M and returns the resulting InputFile.
 template <class ELFT>
 std::unique_ptr<InputFile> SymbolTable<ELFT>::codegen(Module &M) {
   StringRef TripleStr = M.getTargetTriple();
   Triple TheTriple(TripleStr);
 
   // FIXME: Should we have a default triple? The gold plugin uses
   // sys::getDefaultTargetTriple(), but that is probably wrong given that this
std::unique_ptr<InputFile> SymbolTable<ELFT>::codegen(Module &M) {
 
   raw_svector_ostream OS(OwningLTOData);
   legacy::PassManager CodeGenPasses;
   if (TM->addPassesToEmitFile(CodeGenPasses, OS,
                               TargetMachine::CGFT_ObjectFile))
     fatal("Failed to setup codegen");
   CodeGenPasses.run(M);
   LtoBuffer = MemoryBuffer::getMemBuffer(OwningLTOData, "", false);
+  if (Config->SaveTemps)
+    saveLtoObjectFile(LtoBuffer->getBuffer());
   return createObjectFile(*LtoBuffer);
 }
 
 static void addBitcodeFile(IRMover &Mover, BitcodeFile &F,
                            LLVMContext &Context) {
   std::unique_ptr<MemoryBuffer> Buffer =
       MemoryBuffer::getMemBuffer(F.MB, false);
   std::unique_ptr<Module> M =

lld/trunk/test/ELF/lto/save-temps.ll

 ; REQUIRES: x86
-; RUN: rm -f %t.so %t.so.lto.bc
+; RUN: rm -f %t.so %t.so.lto.bc %t.so.lto.o
 ; RUN: llvm-as %s -o %t.o
 ; RUN: llvm-as %p/Inputs/save-temps.ll -o %t2.o
 ; RUN: ld.lld -shared -m elf_x86_64 %t.o %t2.o -o %t.so -save-temps
 ; RUN: llvm-nm %t.so | FileCheck %s
 ; RUN: llvm-nm %t.so.lto.bc | FileCheck %s
+; RUN: llvm-nm %t.so.lto.o | FileCheck %s
 
 target triple = "x86_64-unknown-linux-gnu"
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 
 define void @foo() {
   ret void
 }
 
-; CHECK-DAG: T bar
-; CHECK-DAG: T foo
+; CHECK: T bar
+; CHECK: T foo