[lld] r303920 - [lld] Fix a bug where we continually re-follow type servers.

[Zachary Turner via llvm-commits]

Author: zturner
Date: Thu May 25 16:16:03 2017
New Revision: 303920

URL: http://llvm.org/viewvc/llvm-project?rev=303920&view=rev
Log:
[lld] Fix a bug where we continually re-follow type servers.

Originally this was intended to be set up so that when linking
a PDB which refers to a type server, it would only visit the
PDB once, and on subsequent visitations it would just skip it
since all the records had already been added.

Due to some C++ scoping issues, this was not occurring and it
was revisiting the type server every time, which caused every
record to end up being thrown away on all subsequent visitations.

This doesn't affect the performance of linking clang-cl generated
object files because we don't use type servers, but when linking
object files and libraries generated with /Zi via MSVC, this means
only 1 object file has to be linked instead of N object files, so
the speedup is quite large.

Modified:
    lld/trunk/COFF/PDB.cpp

Modified: lld/trunk/COFF/PDB.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/PDB.cpp?rev=303920&r1=303919&r2=303920&view=diff
==============================================================================
--- lld/trunk/COFF/PDB.cpp (original)
+++ lld/trunk/COFF/PDB.cpp Thu May 25 16:16:03 2017
@@ -99,6 +99,12 @@ static void addTypeInfo(pdb::TpiStreamBu
 static void mergeDebugT(SymbolTable *Symtab, pdb::PDBFileBuilder &Builder,
                         codeview::TypeTableBuilder &TypeTable,
                         codeview::TypeTableBuilder &IDTable) {
+  // Follow type servers.  If the same type server is encountered more than
+  // once for this instance of `PDBTypeServerHandler` (for example if many
+  // object files reference the same TypeServer), the types from the
+  // TypeServer will only be visited once.
+  pdb::PDBTypeServerHandler Handler;
+
   // Visit all .debug$T sections to add them to Builder.
   for (ObjectFile *File : Symtab->ObjectFiles) {
     ArrayRef<uint8_t> Data = getDebugSection(File, ".debug$T");
@@ -109,11 +115,6 @@ static void mergeDebugT(SymbolTable *Sym
     codeview::CVTypeArray Types;
     BinaryStreamReader Reader(Stream);
     SmallVector<TypeIndex, 128> SourceToDest;
-    // Follow type servers.  If the same type server is encountered more than
-    // once for this instance of `PDBTypeServerHandler` (for example if many
-    // object files reference the same TypeServer), the types from the
-    // TypeServer will only be visited once.
-    pdb::PDBTypeServerHandler Handler;
     Handler.addSearchPath(llvm::sys::path::parent_path(File->getName()));
     if (auto EC = Reader.readArray(Types, Reader.getLength()))
       fatal(EC, "Reader::readArray failed");