[llvm-dev] How to debug passes

[Andrzej Warzynski via llvm-dev]

Hi Iulia,

You can skip step 5 - it's not required. opt will happily work with *.ll
as well as *.bc files. Since textual form _is_ much easier to read for
humans, you can generate it directly in step 4:

clang -O3 -emit-llvm -S hello.c -c -o hello.ll

Otherwise your steps look correct (assuming that when registering your
pass with RegisterPass<> you used 'dummypass' as the name for your
pass). Did you verify that hello.ll contains any functions? And have you
tried similar steps with the Hello pass?

-Andrzej

On 16/09/2019 14:49, Iulia Stirb via llvm-dev wrote:
> Hi,
>
> Could you please confirm the following steps for debugging a pass?
>
> 1. copy your pass into llvm/lib/Transforms/Hello/Hello.cpp
>
> 2. name you pass Hello
>
> 3. insert debug messages like:|
> |
> |
> |
> |    errs() << "Vis­iting func­tion " << F.get­Name();|
> |
> |
> ||4. get LLVM bitcode:
> |
>
>      clang -O3 -emit-llvm hello.c -c -o hello.bc
>
> |
>
> |5. disassemble the bitcode:
>
> |    llvm-dis hel­lo.bc|
>
> 6. |run the pass on your program:
>
>      opt -load lib­dum­my­pass.so -dum­my­pass hel­lo.ll|
> |
>
>
> The above steps did not work because the last step does not display any
> error message that has been added in the pass.
>
> Could you please help to debug the pass by displaying the error messages?
>
> Thank you.
> Kind regards,
> Iulia
>
>
>
>
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