[LLVMdev] Dwarf debug info misses while clang codegen

[Kevin]

I'm trying to write a llvm pass to add debug info into a non-debug-info bitcode 
file. I have been read http://llvm.org/docs/SourceLevelDebugging.html. And I use 
DIBuilder to produce the debug metadata. I know I can't get all information form 
ir code . So I add some manual info as test data. After executing my pass, I can 
find debug info metadata in my generated bitcode. Those metadata include 
"DICompileUnit" , "DIFile", "DIVariable" ,"DISubprogram", "DILexicalBlock".

Just like
------------------------------------------------------------------------------
 84 !0 = metadata !{i32 786449, i32 0, i32 4, metadata !"hello.cpp", metadata 
!"/proj/mtk04456", metadata !"clang version", i1     true, i1 true, metadata 
!"flag", i32 0, metadata !1, metadata !1, metadata !1, metadata !1} ; [ 
DW_TAG_compile_unit ] [/p    roj/mtk04456/hello.cpp] [DW_LANG_C_plus_plus]

------------------------------------------------------------------------------

First problem happen : DICompileUnit doesn't find the last four metadata (i.e. 
enums types, retained types, subprograms, global variables). But 
DIBuilder::CreateCompileUnit(...) doesn't need any MDNode* arg. It will find 
those four metadata in the function. I don't know why it can't point to right 
reference. So I use MDNode::getOperand(..)->replaceAllUseWith(...) to replace 
those four metadata with right MDNode. 

But when I compile my new bitcode to elf file. ( clang++ -g hello.bc -o exec)
I can't find my debug info when I use readelf. ( readelf -w exec > log )
There just have one TAG .

  Number TAG
   1      DW_TAG_compile_unit    [no children]
    DW_AT_producer     DW_FORM_strp
    DW_AT_language     DW_FORM_data2
    DW_AT_name         DW_FORM_strp
    DW_AT_low_pc       DW_FORM_addr
    DW_AT_stmt_list    DW_FORM_data4
    DW_AT_comp_dir     DW_FORM_strp
    Unknown AT value: 3fe1 DW_FORM_flag
    Unknown AT value: 3fe2 DW_FORM_strp

I can't find other dwarf TAG in my object file. 

Is the metadata wrong? Or I loss some step when I generate metadata?
If you need my pass's source. Please give me your mail. I will mail it for you.
Thanks!!