[ThinLTO] Handle bitcode without function summary sections gracefully

Summary:
Several fixes to the handling of bitcode files without function summary
sections so that they are skipped during ThinLTO processing in llvm-lto
and the gold plugin when appropriate instead of aborting.

1 Don't assert when trying to add a FunctionInfo that doesn't have
  a summary attached.
2 Skip FunctionInfo structures that don't have attached function summary
  sections when trying to create the combined function summary.
3 In both llvm-lto and gold-plugin, check whether a bitcode file has
  a function summary section before trying to parse the index, and skip
  the bitcode file if it does not.
4 Fix hasFunctionSummaryInMemBuffer in BitcodeReader, which had a bug
  where we returned to early while looking for the summary section.

Also added llvm-lto and gold-plugin based tests for cases where we
don't have function summaries in the bitcode file. I verified that
either the first couple fixes described above are enough to avoid the
crashes, or fixes 1,3,4. But have combined them all here for added
robustness.

Reviewers: joker.eph

Subscribers: llvm-commits, joker.eph

Differential Revision: http://reviews.llvm.org/D14903

llvm-svn: 253796

2 files changed, 33 insertions, 14 deletions

diff --git a/llvm/tools/gold/gold-plugin.cpp b/llvm/tools/gold/gold-plugin.cpp
index 77e4b83223c..672c4e3580d 100644
--- a/llvm/tools/gold/gold-plugin.cpp
+++ b/llvm/tools/gold/gold-plugin.cpp
@@ -620,6 +620,13 @@ getFunctionIndexForFile(claimed_file &F, ld_plugin_input_file &Info) {
 
   MemoryBufferRef BufferRef(StringRef((const char *)View, Info.filesize),
                             Info.name);
+
+  // Don't bother trying to build an index if there is no summary information
+  // in this bitcode file.
+  if (!object::FunctionIndexObjectFile::hasFunctionSummaryInMemBuffer(
+          BufferRef, diagnosticHandler))
+    return std::unique_ptr<FunctionInfoIndex>(nullptr);
+
   ErrorOr<std::unique_ptr<object::FunctionIndexObjectFile>> ObjOrErr =
       object::FunctionIndexObjectFile::create(BufferRef, diagnosticHandler);
 
@@ -911,6 +918,11 @@ static ld_plugin_status allSymbolsReadHook(raw_fd_ostream *ApiFile) {
 
       std::unique_ptr<FunctionInfoIndex> Index =
           getFunctionIndexForFile(F, File);
+
+      // Skip files without a function summary.
+      if (!Index)
+        continue;
+
       CombinedIndex.mergeFrom(std::move(Index), ++NextModuleId);
     }
 
diff --git a/llvm/tools/llvm-lto/llvm-lto.cpp b/llvm/tools/llvm-lto/llvm-lto.cpp
index aac82d31a36..e580a5df578 100644
--- a/llvm/tools/llvm-lto/llvm-lto.cpp
+++ b/llvm/tools/llvm-lto/llvm-lto.cpp
@@ -192,24 +192,27 @@ static int listSymbols(StringRef Command, const TargetOptions &Options) {
 
 /// Parse the function index out of an IR file and return the function
 /// index object if found, or nullptr if not.
-static std::unique_ptr<FunctionInfoIndex>
-getFunctionIndexForFile(StringRef Path, std::string &Error,
+static ErrorOr<std::unique_ptr<FunctionInfoIndex>>
+getFunctionIndexForFile(StringRef Path,
                         DiagnosticHandlerFunction DiagnosticHandler) {
   std::unique_ptr<MemoryBuffer> Buffer;
   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
       MemoryBuffer::getFile(Path);
-  if (std::error_code EC = BufferOrErr.getError()) {
-    Error = EC.message();
-    return nullptr;
-  }
+  if (std::error_code EC = BufferOrErr.getError())
+    return EC;
   Buffer = std::move(BufferOrErr.get());
+
+  // Don't bother trying to build an index if there is no summary information
+  // in this bitcode file.
+  if (!object::FunctionIndexObjectFile::hasFunctionSummaryInMemBuffer(
+          Buffer->getMemBufferRef(), DiagnosticHandler))
+    return std::unique_ptr<FunctionInfoIndex>(nullptr);
+
   ErrorOr<std::unique_ptr<object::FunctionIndexObjectFile>> ObjOrErr =
       object::FunctionIndexObjectFile::create(Buffer->getMemBufferRef(),
                                               DiagnosticHandler);
-  if (std::error_code EC = ObjOrErr.getError()) {
-    Error = EC.message();
-    return nullptr;
-  }
+  if (std::error_code EC = ObjOrErr.getError())
+    return EC;
   return (*ObjOrErr)->takeIndex();
 }
 
@@ -221,14 +224,18 @@ static int createCombinedFunctionIndex(StringRef Command) {
   FunctionInfoIndex CombinedIndex;
   uint64_t NextModuleId = 0;
   for (auto &Filename : InputFilenames) {
-    std::string Error;
-    std::unique_ptr<FunctionInfoIndex> Index =
-        getFunctionIndexForFile(Filename, Error, diagnosticHandler);
-    if (!Index) {
+    ErrorOr<std::unique_ptr<FunctionInfoIndex>> IndexOrErr =
+        getFunctionIndexForFile(Filename, diagnosticHandler);
+    if (std::error_code EC = IndexOrErr.getError()) {
+      std::string Error = EC.message();
       errs() << Command << ": error loading file '" << Filename
              << "': " << Error << "\n";
       return 1;
     }
+    std::unique_ptr<FunctionInfoIndex> Index = std::move(IndexOrErr.get());
+    // Skip files without a function summary.
+    if (!Index)
+      continue;
     CombinedIndex.mergeFrom(std::move(Index), ++NextModuleId);
   }
   std::error_code EC;