Remove ignore-empty-index-file option

[tejohnson]

Summary

As discussed in the D32195 review thread and on IRC, remove this option
and replace with parameter, which will be set to true when invoked
from clang in the context of a ThinLTO distributed backend.

[pcc]

LGTM, thanks for taking care of this

include/llvm/Bitcode/BitcodeReader.h

namespace llvm {
 
   /// Parse the specified bitcode buffer and merge the index into CombinedIndex.
   Error readModuleSummaryIndex(MemoryBufferRef Buffer,
                                ModuleSummaryIndex &CombinedIndex,
                                unsigned ModuleId);
 
   /// Parse the module summary index out of an IR file and return the module
   /// summary index object if found, or an empty summary if not. If Path refers
-  /// to an empty file and the -ignore-empty-index-file cl::opt flag is passed
+  /// to an empty file and IgnoreEmptyThinLTOIndexFile is true, then
   /// this function will return nullptr.
   Expected<std::unique_ptr<ModuleSummaryIndex>>
-  getModuleSummaryIndexForFile(StringRef Path);
+  getModuleSummaryIndexForFile(StringRef Path,
+                               bool IgnoreEmptyThinLTOIndexFile = false);
 
   /// isBitcodeWrapper - Return true if the given bytes are the magic bytes
   /// for an LLVM IR bitcode wrapper.
   ///
   inline bool isBitcodeWrapper(const unsigned char *BufPtr,
                                const unsigned char *BufEnd) {
     // See if you can find the hidden message in the magic bytes :-).
     // (Hint: it's a little-endian encoding.)

lib/Bitcode/Reader/BitcodeReader.cpp

 
 using namespace llvm;
 
 static cl::opt<bool> PrintSummaryGUIDs(
     "print-summary-global-ids", cl::init(false), cl::Hidden,
     cl::desc(
         "Print the global id for each value when reading the module summary"));
 
-// FIXME: This flag should either be removed or moved to clang as a driver flag.
-static llvm::cl::opt<bool> IgnoreEmptyThinLTOIndexFile(
-    "ignore-empty-index-file", llvm::cl::ZeroOrMore,
-    llvm::cl::desc(
-        "Ignore an empty index file and perform non-ThinLTO compilation"),
-    llvm::cl::init(false));
-
 namespace {
 
 enum {
   SWITCH_INST_MAGIC = 0x4B5 // May 2012 => 1205 => Hex
 };
 
 Error error(const Twine &Message) {
   return make_error<StringError>(
Expected<bool> llvm::hasGlobalValueSummary(MemoryBufferRef Buffer) {
   Expected<BitcodeModule> BM = getSingleModule(Buffer);
   if (!BM)
     return BM.takeError();
 
   return BM->hasSummary();
 }
 
 Expected<std::unique_ptr<ModuleSummaryIndex>>
-llvm::getModuleSummaryIndexForFile(StringRef Path) {
+llvm::getModuleSummaryIndexForFile(StringRef Path,
+                                   bool IgnoreEmptyThinLTOIndexFile) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> FileOrErr =
       MemoryBuffer::getFileOrSTDIN(Path);
   if (!FileOrErr)
     return errorCodeToError(FileOrErr.getError());
   if (IgnoreEmptyThinLTOIndexFile && !(*FileOrErr)->getBufferSize())
     return nullptr;
   return getModuleSummaryIndex(**FileOrErr);
 }