[llvm-dev] LLVM log file

[Stefanos Baziotis via llvm-dev]

Hi  Sudakshina,

> The optimization applied in the optimization pass depends on the source
program; hence, the number of optimizations applied differs from source
program to source program.

"applied" is still ambiguous, at least to me. If by "applied" you mean
"attempted", then no, that does not depend on the source program. It
depends on the optimization level (e.g., O1, O2, ...) or the individual
passes that you may request yourself.
That is, for -O1 for example, there is a predetermined sequence of passes
that _attempt_ to optimize the program and you can see that with the
options I mentioned above (e.g., `-mllvm -opt-bisect-limit=-1`)

If by applied you mean "actually changed the code", then yes, this differs
from program to program. You can see that with `print-changed`, it'll show
you the IR after every transformation that changed your program.

Finally, if you want to see why a transformation could or not change the
code, you can use the related comments about remarks.

Best,
Stefanos

Στις Κυρ, 24 Ιαν 2021 στις 7:24 π.μ., ο/η Sudakshina Dutta <
sudakshina at iitgoa.ac.in> έγραψε:

> Dear all,
>
> In the optimization phase, the compiler applies some optimization to
> generate an optimized program. The optimization applied in the optimization
> pass depends on the source program; hence, the number of optimizations
> applied differs from source program to source program. By mentioning
> "applied" transformation, I wanted to know what all transformations are
> applied for a specific input program when subjected to the LLVM optimizer.
>
> Thanks,
> Sudakshina
>
>
> On Sun, 24 Jan 2021, 09:27 Stefanos Baziotis, <stefanos.baziotis at gmail.com>
> wrote:
>
>> Hi Sudakshina,
>>
>> Not really sure what you mean by "applied", so, let me offer some more
>> ideas other than Brian's and Adrian's great suggestions. First, there are
>> some
>> diagnostics / remarks flags in Clang like the -R family [1] or some -f
>> flags about printing optimization reports [2] from Clang. They can be
>> useful or useless depending
>> on your case. They can also be parsed relatively easily.
>>
>> If you just want to see a list of passes that were attempted in your
>> code, you can do it with: `-mllvm -opt-bisect-limit=-1`
>> You can also use `-mllvm-debug-pass=Arguments` to see the arguments that
>> were passed.
>>
>> Moving into opt, you can use something like `print-after-all`, which was
>> already mentioned. If you don't know what these flags do, is they show you
>> the IR in different stages in the pipeline (e.g., `print-after-all` shows
>> you each pass attempted and how the IR is after it).
>>
>> Hope it helps,
>> Stefanos
>>
>> [1]
>> https://clang.llvm.org/docs/ClangCommandLineReference.html#diagnostic-flags
>> [2]
>> https://clang.llvm.org/docs/UsersManual.html#cmdoption-f-no-save-optimization-record
>>
>> Στις Κυρ, 24 Ιαν 2021 στις 5:47 π.μ., ο/η Adrian Vogelsgesang via
>> llvm-dev <llvm-dev at lists.llvm.org> έγραψε:
>>
>>> I used “-print-changed”, “-print-before-all”, “print-after-all” last
>>> time I wanted to see the passes together with their inout/output IR modules.
>>>
>>> In my case, I used them through “clang++”, i.e. I had to prefix them
>>> with “-mllvm”
>>> > clang++ test_file.cpp -mllvm -print-after-all
>>>
>>>
>>>
>>> *From: *llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Brian
>>> Cain via llvm-dev <llvm-dev at lists.llvm.org>
>>> *Date: *Sunday, 24. January 2021 at 04:40
>>> *To: *Sudakshina Dutta <sudakshina at iitgoa.ac.in>
>>> *Cc: *LLVM Development List <llvm-dev at lists.llvm.org>
>>> *Subject: *Re: [llvm-dev] LLVM log file
>>>
>>> I don't know if it's exhaustive but there's the "remarks" feature:
>>>
>>>
>>>
>>>
>>> https://llvm.org/docs/Remarks.html#introduction-to-the-llvm-remark-diagnostics
>>>
>>>
>>>
>>> On Sat, Jan 23, 2021 at 9:20 PM Sudakshina Dutta via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>> Dear all,
>>>
>>>
>>>
>>> Good morning. I want to know whether LLVM creates any log file
>>> consisting of applied optimizations in the optimization phase. It will be
>>> really useful for the researchers who work on compilers, formal methods,
>>> etc.
>>>
>>>
>>>
>>> Thanks,
>>>
>>> Sudakshina
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>>
>>>
>>> --
>>>
>>> -Brian
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
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