[codeview] Use comdats for debug info describing comdat functions

Summary:
This allows the linker to discard unused symbol information for comdat
functions that were discarded during the link. Before this change,
searching for the name of an inline function in the debugger would
return multiple results, one per symbol subsection in the object file.
After this change, there is only one result, the result for the function
chosen by the linker.

Reviewers: zturner, majnemer

Subscribers: aaboud, amccarth, llvm-commits

Differential Revision: http://reviews.llvm.org/D20642

llvm-svn: 270792

1 files changed, 17 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
index 53e1aa0b422..df7c85c0007 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
@@ -101,6 +101,18 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
   };
   FunctionInfo *CurFn;
 
+  /// The set of comdat .debug$S sections that we've seen so far. Each section
+  /// must start with a magic version number that must only be emitted once.
+  /// This set tracks which sections we've already opened.
+  DenseSet<MCSectionCOFF *> ComdatDebugSections;
+
+  /// Switch to the appropriate .debug$S section for GVSym. If GVSym, the symbol
+  /// of an emitted global value, is in a comdat COFF section, this will switch
+  /// to a new .debug$S section in that comdat. This method ensures that the
+  /// section starts with the magic version number on first use. If GVSym is
+  /// null, uses the main .debug$S section.
+  void switchToDebugSectionForSymbol(const MCSymbol *GVSym);
+
   /// The next available function index for use with our .cv_* directives. Not
   /// to be confused with type indices for LF_FUNC_ID records.
   unsigned NextFuncId = 0;
@@ -148,9 +160,13 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
     FileToFilepathMap.clear();
   }
 
+  /// Emit the magic version number at the start of a CodeView type or symbol
+  /// section. Appears at the front of every .debug$S or .debug$T section.
+  void emitCodeViewMagicVersion();
+
   void emitTypeInformation();
 
-  void emitInlineeFuncIdsAndLines();
+  void emitInlineeLinesSubsection();
 
   void emitDebugInfoForFunction(const Function *GV, FunctionInfo &FI);