llvm-lto: Add testing coverage for local contexts

Add coverage in `llvm-lto` for the API exposed by libLTO to create
modules in local contexts.

The goal here isn't to test the symbol-related API extensively, just to
confirm that these modules work at all.  (I'll be shifting code around
soon that should be NFC and I realized there was no test coverage.)

llvm-svn: 224408

llvm/test/LTO/Inputs/list-symbols.ll

@@ -0,0 +1,4 @@
+@glob = global i32 0
+define void @bar() {
+  ret void
+}

llvm/test/LTO/list-symbols.ll

@@ -0,0 +1,15 @@
+; RUN: llvm-as -o %T/1.bc %s
+; RUN: llvm-as -o %T/2.bc %S/Inputs/list-symbols.ll
+; RUN: llvm-lto -list-symbols-only %T/1.bc %T/2.bc | FileCheck %s
+
+; CHECK-LABEL: 1.bc:
+; CHECK-DAG: foo
+; CHECK-DAG: glob
+; CHECK-LABEL: 2.bc:
+; CHECK-DAG: glob
+; CHECK-DAG: bar
+
+@glob = global i32 0
+define void @foo() {
+  ret void
+}

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

@@ -65,6 +65,10 @@ DSOSymbols("dso-symbol",
   cl::desc("Symbol to put in the symtab in the resulting dso"),
   cl::ZeroOrMore);
 
+static cl::opt<bool> ListSymbolsOnly(
+    "list-symbols-only", cl::init(false),
+    cl::desc("Instead of running LTO, list the symbols in each IR file"));
+
 namespace {
 struct ModuleInfo {
   std::vector<bool> CanBeHidden;
@@ -90,6 +94,46 @@ void handleDiagnostics(lto_codegen_diagnostic_severity_t Severity,
   errs() << Msg << "\n";
 }
 
+std::unique_ptr<LTOModule>
+getLocalLTOModule(StringRef Path, std::unique_ptr<MemoryBuffer> &Buffer,
+                  const TargetOptions &Options, std::string &Error) {
+  ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
+      MemoryBuffer::getFile(Path);
+  if (std::error_code EC = BufferOrErr.getError()) {
+    Error = EC.message();
+    return nullptr;
+  }
+  Buffer = std::move(BufferOrErr.get());
+  return std::unique_ptr<LTOModule>(LTOModule::createInLocalContext(
+      Buffer->getBufferStart(), Buffer->getBufferSize(), Options, Error, Path));
+}
+
+/// \brief List symbols in each IR file.
+///
+/// The main point here is to provide lit-testable coverage for the LTOModule
+/// functionality that's exposed by the C API to list symbols.  Moreover, this
+/// provides testing coverage for modules that have been created in their own
+/// contexts.
+int listSymbols(StringRef Command, const TargetOptions &Options) {
+  for (auto &Filename : InputFilenames) {
+    std::string Error;
+    std::unique_ptr<MemoryBuffer> Buffer;
+    std::unique_ptr<LTOModule> Module =
+        getLocalLTOModule(Filename, Buffer, Options, Error);
+    if (!Module) {
+      errs() << Command << ": error loading file '" << Filename
+             << "': " << Error << "\n";
+      return 1;
+    }
+
+    // List the symbols.
+    outs() << Filename << ":\n";
+    for (int I = 0, E = Module->getSymbolCount(); I != E; ++I)
+      outs() << Module->getSymbolName(I) << "\n";
+  }
+  return 0;
+}
+
 int main(int argc, char **argv) {
   // Print a stack trace if we signal out.
   sys::PrintStackTraceOnErrorSignal();
@@ -107,6 +151,9 @@ int main(int argc, char **argv) {
   // set up the TargetOptions for the machine
   TargetOptions Options = InitTargetOptionsFromCodeGenFlags();
 
+  if (ListSymbolsOnly)
+    return listSymbols(argv[0], Options);
+
   unsigned BaseArg = 0;
 
   LTOCodeGenerator CodeGen;