This patch adds a new Clang compiler flag "-gline-tables-only".

It reduces the amount of emitted debug information:
1) DIEs in .debug_info have types DW_TAG_compile_unit, DW_TAG_subprogram,
DW_TAG_inlined_subroutine (for opt builds) and DW_TAG_lexical_block only.
2) .debug_str contains only function names.
3) No debug data for types/namespaces/variables is emitted.
4) The data in .debug_line is enough to produce valid stack traces with
function names and line numbers.

Reviewed by Eric Christopher.

llvm-svn: 156160

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -1087,7 +1087,8 @@ void CodeGenFunction::EmitDeclRefExprDbgValue(const DeclRefExpr *E,
                                               llvm::Constant *Init) {
   assert (Init && "Invalid DeclRefExpr initializer!");
   if (CGDebugInfo *Dbg = getDebugInfo())
-    Dbg->EmitGlobalVariable(E->getDecl(), Init);
+    if (CGM.getCodeGenOpts().DebugInfo >= CodeGenOptions::LimitedDebugInfo)
+      Dbg->EmitGlobalVariable(E->getDecl(), Init);
 }
 
 CodeGenFunction::PeepholeProtection