[libLTO] Add support for -save-temps

[qiongsiwu1]

Summary

This patch rebases https://reviews.llvm.org/D98183 and consolidates -save-temps across libLTO, llvm-lto and llvm-lto2.

Original summary of https://reviews.llvm.org/D98183:
This patch updates LTOCodeGenerator to use addSaveTemps to support the
-save-temps option when using libLTO. At the moment, the save-temps
hooks are set up in parseCodeGenDebugOptions, because that's the
earliest the options have been parsed. I am not sure if there's a better
place, given the way libLTO's API is structured. At the moment, the
temporary files are created in the current working directory, because I
do not think there's a way to get the path for the final binary
up-front.

It also adds support for running the PostImportModuleHook just before
IR optimiztions are run. At the moment, the following temporary files
are created:

ld-temp.0.3.import.bc (before IR optimizations)
ld-temp.0.4.opt.bc (after IR optimizations)
ld-temp.0.5.precodegen.bc (before codegen)

Other hooks can be supported in the future, but the 3 IR files above
should be the most valuable ones when investigating mis-compiles or
crashes when doing full LTO using libLTO.

[qiongsiwu1]

@fhahn your original patch https://reviews.llvm.org/D98183 is very useful for us as well. I took your patch and rebased it. I tried updating the original patch but I did not find a way to do it since I am not the author. I think we have numerous existing tests for llvm-lto/llvm-lto2 -save-temps and they should be using the new option now. Let me know if this looks good! Thanks so much!

[tejohnson]

It would be better to work with @fhahn on the old patch (you can commandeer it if he is ok with that), so that comment history is preserved. But I have some comments on this version that I will add here. Looks like a test is still needed (this patch affects legacy regular LTO, the prior llvm-lto tests would have only used the existing option for ThinLTO - see thinlto-save-temps flag in llvm-lto.cpp). I'll leave a comment on the original version, I think it makes sense to common up the options used for this between thin and regular LTO in the legacy LTO API and its tool, llvm-lto.

llvm/tools/llvm-lto2/llvm-lto2.cpp

67

llvm-lto2.cpp tests the new LTO API, so it is a bit odd for it to use a flag from the legacy LTO API.

I'm not sure it makes sense to common the flag between these 2 different interfaces and their corresponding tools.

llvm/tools/lto/lto.cpp

36

Unused in this file

[qiongsiwu1]

In D153559#4441538, @tejohnson wrote:

It would be better to work with @fhahn on the old patch (you can commandeer it if he is ok with that), so that comment history is preserved. But I have some comments on this version that I will add here. Looks like a test is still needed (this patch affects legacy regular LTO, the prior llvm-lto tests would have only used the existing option for ThinLTO - see thinlto-save-temps flag in llvm-lto.cpp). I'll leave a comment on the original version, I think it makes sense to common up the options used for this between thin and regular LTO in the legacy LTO API and its tool, llvm-lto.

Thanks so much for the comment @tejohnson !! @fhahn Let me know if you are ok with me taking over the original patch https://reviews.llvm.org/D98183. I will close this patch and continue the work there (consolidating options between LTO/thinLTO and adding tests). Thanks!

[fhahn]

@qiongsiwu1 please feel free to commandeer the patch. Would be good to update the description to make this clear.

[qiongsiwu1]

Will continue in https://reviews.llvm.org/D98183.

llvm/lib/LTO/LTOCodeGenerator.cpp

 
 cl::opt<bool>
     LTORunCSIRInstr("cs-profile-generate",
                     cl::desc("Perform context sensitive PGO instrumentation"));
 
 cl::opt<std::string>
     LTOCSIRProfile("cs-profile-path",
                    cl::desc("Context sensitive profile file path"));
+
+cl::opt<bool> SaveTemps(
+    "save-temps", cl::init(false),
+    cl::desc("Save temporary LTO files in the current working directory."));
 } // namespace llvm
 
 LTOCodeGenerator::LTOCodeGenerator(LLVMContext &Context)
     : Context(Context), MergedModule(new Module("ld-temp.o", Context)),
       TheLinker(new Linker(*MergedModule)) {
   Context.setDiscardValueNames(LTODiscardValueNames);
   Context.enableDebugTypeODRUniquing();
 
bool LTOCodeGenerator::optimize() {
   this->applyScopeRestrictions();
 
   // Write LTOPostLink flag for passes that require all the modules.
   MergedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
 
   // Add an appropriate DataLayout instance for this module...
   MergedModule->setDataLayout(TargetMach->createDataLayout());
 
+  if (Config.PostImportModuleHook)
+    Config.PostImportModuleHook(0, *MergedModule);
+
   if (!SaveIRBeforeOptPath.empty()) {
     std::error_code EC;
     raw_fd_ostream OS(SaveIRBeforeOptPath, EC, sys::fs::OF_None);
     if (EC)
       report_fatal_error(Twine("Failed to open ") + SaveIRBeforeOptPath +
                          " to save optimized bitcode\n");
     WriteBitcodeToFile(*MergedModule, OS,
                        /* ShouldPreserveUseListOrder */ true);

 void LTOCodeGenerator::setCodeGenDebugOptions(ArrayRef<StringRef> Options) {
   for (StringRef Option : Options)
     CodegenOptions.push_back(Option.str());
 }
 
 void LTOCodeGenerator::parseCodeGenDebugOptions() {
   if (!CodegenOptions.empty())
     llvm::parseCommandLineOptions(CodegenOptions);
+
+  if (SaveTemps) {
+    if (Config.addSaveTemps("ld-temp.",
+                            /* UseInputModulePath */ true))
+      errs() << "Warning: failed to set up path to save temporary files\n";
+  }
 }
 
 void llvm::parseCommandLineOptions(std::vector<std::string> &Options) {
   if (!Options.empty()) {
     // ParseCommandLineOptions() expects argv[0] to be program name.
     std::vector<const char *> CodegenArgv(1, "libLLVMLTO");
     for (std::string &Arg : Options)
       CodegenArgv.push_back(Arg.c_str());

llvm/tools/llvm-lto2/llvm-lto2.cpp

 
 static cl::opt<std::string> OptPipeline("opt-pipeline",
                                         cl::desc("Optimizer Pipeline"),
                                         cl::value_desc("pipeline"));
 
 static cl::opt<std::string> AAPipeline("aa-pipeline",
                                        cl::desc("Alias Analysis Pipeline"),
                                        cl::value_desc("aapipeline"));
-
-static cl::opt<bool> SaveTemps("save-temps", cl::desc("Save temporary files"));
+namespace llvm {
+extern cl::opt<bool> SaveTemps;
+}
 
 static cl::list<std::string> SelectSaveTemps(
     "select-save-temps",
     cl::value_desc("One, or multiple of: "
                    "resolution,preopt,promote,internalize,import,opt,precodegen"
                    ",combinedindex"),
     cl::desc("Save selected temporary files. Cannot be specified together with "
              "-save-temps"),

llvm/tools/lto/lto.cpp

 #include "llvm/Support/Signals.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
 
 static codegen::RegisterCodeGenFlags CGF;
 
+namespace llvm {
+extern cl::opt<bool> SaveTemps;
+}
+
 // extra command-line flags needed for LTOCodeGenerator
 static cl::opt<char>
     OptLevel("O",
              cl::desc("Optimization level. [-O0, -O1, -O2, or -O3] "
                       "(default = '-O2')"),
              cl::Prefix, cl::init('2'));
 
 static cl::opt<bool> EnableFreestanding(