[llvm-dev] How to debug passes

[Andrzej Warzynski via llvm-dev]

Iulia,

You need to check the contents of the hello.ll (or hello.bc) file rather
than the input *.c file - ultimately that's what opt consumes.

Try compiling without any optimisations:

clang -O0 -emit-llvm -S hello.c -c -o hello.ll

-Andrzej

On 18/09/2019 11:34, iulia_s24 wrote:
> Hi,
>
> Actually I copy-pasted step 5 from the article in which I found the
> solution, in the text of the mail so that is why dummypass appears
> instead of hello. I used hello instead of dummypass in my tries, but it
> still doesn't display nothing after recompiling the pass. The hello.c
> file contains several functions, so the module pass should display
> something (I placed a message at the verry beginning of the runOnModule
> funtion of the pass). I am compiling all the code once with ninja on
> Linux and I have seen that the hello pass is compiled as well. I have
> not compiled it separatelly.
>
> Do you have any ideas why is this?
>
> Thank you,
> Iulia
>
>
>
> Trimis de pe smartphone-ul meu Samsung Galaxy.
>
> -------- Mesaj original --------
> De la: Andrzej Warzynski <Andrzej.Warzynski at arm.com>
> Date: 17.09.2019 10:44 (GMT+02:00)
> Către: Iulia Stirb <iulia_s24 at yahoo.com>, via Llvm-dev
> <llvm-dev at lists.llvm.org>, nd <nd at arm.com>
> Subiect: Re: [llvm-dev] How to debug passes
>
> 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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