[llvm] r341998 - [object] Improve the performance of getSymbols used by ArchiveWriter

[Alexander Shaposhnikov via llvm-commits]

Author: alexshap
Date: Tue Sep 11 15:00:47 2018
New Revision: 341998

URL: http://llvm.org/viewvc/llvm-project?rev=341998&view=rev
Log:
[object] Improve the performance of getSymbols used by ArchiveWriter

In this diff we adjust the code of getSymbols to avoid creating LLVMContext when it's not necessary.
Without this patch when the function getSymbols was called on a MachO object with a __bitcode section
it was parsing the embedded bitcode and then ignoring the result.

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D51759

Modified:
    llvm/trunk/lib/Object/ArchiveWriter.cpp

Modified: llvm/trunk/lib/Object/ArchiveWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Object/ArchiveWriter.cpp?rev=341998&r1=341997&r2=341998&view=diff
==============================================================================
--- llvm/trunk/lib/Object/ArchiveWriter.cpp (original)
+++ llvm/trunk/lib/Object/ArchiveWriter.cpp Tue Sep 11 15:00:47 2018
@@ -372,20 +372,32 @@ static void writeSymbolTable(raw_ostream
 static Expected<std::vector<unsigned>>
 getSymbols(MemoryBufferRef Buf, raw_ostream &SymNames, bool &HasObject) {
   std::vector<unsigned> Ret;
-  LLVMContext Context;
 
-  Expected<std::unique_ptr<object::SymbolicFile>> ObjOrErr =
-      object::SymbolicFile::createSymbolicFile(Buf, llvm::file_magic::unknown,
-                                               &Context);
-  if (!ObjOrErr) {
-    // FIXME: check only for "not an object file" errors.
-    consumeError(ObjOrErr.takeError());
-    return Ret;
+  // In the scenario when LLVMContext is populated SymbolicFile will contain a
+  // reference to it, thus SymbolicFile should be destroyed first.
+  LLVMContext Context;
+  std::unique_ptr<object::SymbolicFile> Obj;
+  if (identify_magic(Buf.getBuffer()) == file_magic::bitcode) {
+    auto ObjOrErr = object::SymbolicFile::createSymbolicFile(
+        Buf, file_magic::bitcode, &Context);
+    if (!ObjOrErr) {
+      // FIXME: check only for "not an object file" errors.
+      consumeError(ObjOrErr.takeError());
+      return Ret;
+    }
+    Obj = std::move(*ObjOrErr);
+  } else {
+    auto ObjOrErr = object::SymbolicFile::createSymbolicFile(Buf);
+    if (!ObjOrErr) {
+      // FIXME: check only for "not an object file" errors.
+      consumeError(ObjOrErr.takeError());
+      return Ret;
+    }
+    Obj = std::move(*ObjOrErr);
   }
 
   HasObject = true;
-  object::SymbolicFile &Obj = *ObjOrErr.get();
-  for (const object::BasicSymbolRef &S : Obj.symbols()) {
+  for (const object::BasicSymbolRef &S : Obj->symbols()) {
     if (!isArchiveSymbol(S))
       continue;
     Ret.push_back(SymNames.tell());
@@ -470,7 +482,7 @@ Error llvm::writeArchive(StringRef ArcNa
   if (WriteSymtab) {
     uint64_t MaxOffset = 0;
     uint64_t LastOffset = MaxOffset;
-    for (const auto& M : Data) {
+    for (const auto &M : Data) {
       // Record the start of the member's offset
       LastOffset = MaxOffset;
       // Account for the size of each part associated with the member.