[ThinLTO] Fix temp file dumping, enable via llvm-lto and test it

Summary:
Fixed a bug in ThinLTOCodeGenerator's temp file dumping. The Twine
needs to be passed directly as an argument, or a copy saved into a
std::string.

It doesn't seem there are any consumers of this, so I added a new option
to llvm-lto to enable saving of temp files during ThinLTO, and augmented
a test to use it to check post-import but pre-opt bitcode.

Reviewers: mehdi_amini

Subscribers: llvm-commits, mehdi_amini

Differential Revision: https://reviews.llvm.org/D23525

llvm-svn: 278761

llvm/lib/LTO/ThinLTOCodeGenerator.cpp

@@ -78,9 +78,9 @@ static void saveTempBitcode(const Module &TheModule, StringRef TempDir,
   if (TempDir.empty())
     return;
   // User asked to save temps, let dump the bitcode file after import.
-  auto SaveTempPath = TempDir + llvm::utostr(count) + Suffix;
+  std::string SaveTempPath = (TempDir + llvm::utostr(count) + Suffix).str();
   std::error_code EC;
-  raw_fd_ostream OS(SaveTempPath.str(), EC, sys::fs::F_None);
+  raw_fd_ostream OS(SaveTempPath, EC, sys::fs::F_None);
   if (EC)
     report_fatal_error(Twine("Failed to open ") + SaveTempPath +
                        " to save optimized bitcode\n");

llvm/test/ThinLTO/X86/linkonce_resolution_comdat.ll

@@ -3,7 +3,15 @@
 ; verification error.
 ; RUN: opt -module-summary %s -o %t1.bc
 ; RUN: opt -module-summary %p/Inputs/linkonce_resolution_comdat.ll -o %t2.bc
-; RUN: llvm-lto -thinlto-action=run %t1.bc %t2.bc -exported-symbol=f -exported-symbol=g
+; RUN: llvm-lto -thinlto-action=run %t1.bc %t2.bc -exported-symbol=f -exported-symbol=g -thinlto-save-temps=%t3.
+
+; RUN: llvm-dis %t3.0.3.imported.bc -o - | FileCheck %s --check-prefix=IMPORT1
+; RUN: llvm-dis %t3.1.3.imported.bc -o - | FileCheck %s --check-prefix=IMPORT2
+; Copy from first module is prevailing and converted to weak_odr, copy
+; from second module is preempted and converted to available_externally and
+; removed from comdat.
+; IMPORT1: define weak_odr i32 @f(i8*) unnamed_addr comdat($c1) {
+; IMPORT2: define available_externally i32 @f(i8*) unnamed_addr {
 
 ; RUN: llvm-nm -o - < %t1.bc.thinlto.o | FileCheck %s --check-prefix=NM1
 ; NM1: W f

llvm/tools/llvm-lto/llvm-lto.cpp

@@ -120,6 +120,11 @@ static cl::opt<std::string> ThinLTOModuleId(
 static cl::opt<std::string>
     ThinLTOCacheDir("thinlto-cache-dir", cl::desc("Enable ThinLTO caching."));
 
+static cl::opt<std::string> ThinLTOSaveTempsPrefix(
+    "thinlto-save-temps",
+    cl::desc("Save ThinLTO temp files using filenames created by adding "
+             "suffixes to the given file path prefix."));
+
 static cl::opt<bool>
     SaveModuleFile("save-merged-module", cl::init(false),
                    cl::desc("Write merged LTO module to file before CodeGen"));
@@ -672,6 +677,8 @@ class ThinLTOProcessing {
       ThinGenerator.addModule(Filename, InputBuffers.back()->getBuffer());
     }
 
+    if (!ThinLTOSaveTempsPrefix.empty())
+      ThinGenerator.setSaveTempsDir(ThinLTOSaveTempsPrefix);
     ThinGenerator.run();
 
     auto &Binaries = ThinGenerator.getProducedBinaries();