[llvm-dev] GSoC19: Debug Info should have no effect on codegen

[Jessica Paquette via llvm-dev]

I think an easy way to start here would probably be to use the test suite, or a subset of it.

I would recommend using the SingleSource tests to start out with. The MultiSource tests will lead you into having to bisect on object files, which is a bit more work. There are a couple of large SingleSource tests which I imagine might have a few differences in them.

A workflow like this might help you get started with finding examples of different codegen:

1) Build, but don’t execute, the tests with debug info
2) Build, but don’t execute, the tests without debug info
3) Use test-suite/utils/compare.py on the output JSON reports to check if there are any differences in, say, text size (which implies different codegen)
4) Bisect on object files if necessary 
5) Use something like bugpoint to reduce the testcase

You can build the LLVM test suite by following the instructions here:
http://llvm.org/docs/lnt/quickstart.html <http://llvm.org/docs/lnt/quickstart.html>

I find this blog post pretty useful for bugpoint stuff:
http://blog.llvm.org/2015/11/reduce-your-testcases-with-bugpoint-and.html <http://blog.llvm.org/2015/11/reduce-your-testcases-with-bugpoint-and.html>

- Jessica


> On Mar 5, 2019, at 7:54 AM, Mohamed Ali via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Dear all,
> 
> My name is Mohamed and I am a first year computer science masters student. I am writing this email because I am interested in the project idea "Debug Info Should have no effect on codegen". So far I have built llvm and clang and I was trying to reproduce the problem on simple c++ programs but I can't. Being specific this are the steps I am doing:
> 
> $ clang -g test.cc
> $ llvm-objdump -d a.out > with_debug
> $ clang  test.cc
> $ llvm-objdump -d a.out > no_debug
> $ vimdiff with_debug no_debug
>  
> I still can't reproduce the problem. In the expected results of the project you mentioned that there are already failing test cases. Can you please point me in to these cases?
> Finally, I would like to ask whether there is some qualification task I should do or I have to fix some of the open tickets? Would you please point me to such tasks or suggest some tickets/bugs that I can start working on?
> 
> Regards,
> Mohamed
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