[cfe-dev] Question regarding debug information on duplicated code

[Yun Zhang]

Hi,

I ran into a problem when running clang on my code. The problem is, my 
optimization (a pass in LLVM) takes bitcode file as input, duplicate 
part of the original code, put the duplicated code in a separate 
function, then run both of them. I took the step:
1. use clang to compile .c files to bitcode files .bc, using -g flag
2. use opt from llvm to duplicate part of the code
3. use llc, compile the output of opt to assembly file .s
4. use clang to link and generate the final binary, using -g flag

The final step will abort because clang finds several identical labels 
in the program. I examined the .s file, there is no identical labels in 
assembly(output of step 3). The duplicated labels are mostly 
".Ldebug_fram_endl" etc, inserted by clang. I suspect that it is because 
the original code was annotated with debug information, after the code 
was duplicated, debug information is copied over as well, at the final 
step, the same label is generated for both. Is that right?

If that is a correct speculation, how do I solve this problem? Should I 
(and, can I) access and modify the debug information at the second step 
(opt)?  I tried to use llvm-gcc for the first step. The program 
compiles, but when I tried to debug, clang only allowed me to debug at 
assembly level (.s files).

I could have used llvm-gcc for everything, not clang, but I like clang 
for providing precise and accurate debug support. If I use llvm-gcc, I 
cannot debug the generate program at all.....

Thank you very much for any suggestion that anyone may have.

Thanks,
Yun