[llvm-dev] Hello

Sat Jan 9 17:22:32 PST 2021

>  This is great, thank you so much!

Np :)

>  I have read them and conceptually I understand them but I am afraid I
can't write them on my own.

I'd work a little bit more on those and godbolt can help a lot :) You can
always see what the compiler does.

> Do you know how I can learn about differences between IRs when optimizing
is turned on vs. when it is not turned on?

What do you mean ? Like, why did something happen ? Or, why is one version
faster than the other ? Or sth else ?

>  If there are many people on this list who might be interested in this
topic then we can remove spamming everyone on this list by including
llvm-dev. You guys decide.

I didn't get that... :) llvm-dev is "included", it's CC'd. In any case,
it's ok, I don't think we're spamming anyone in llvm-dev.

- Stefanos

Στις Κυρ, 10 Ιαν 2021 στις 3:06 π.μ., ο/η Mihir Sevak <mihir.sevak at gmail.com>
έγραψε:

> This is great, thank you so much! I don't have mastery over the basics
> yet. I have read them and conceptually I understand them but I am afraid I
> can't write them on my own. I also appreciate your sharing godbolt.org.
> That is a great help. Do you know how I can learn about differences between
> IRs when optimizing is turned on vs. when it is not turned on? If there are
> many people on this list who might be interested in this topic then we can
> remove spamming everyone on this list by including llvm-dev. You guys
> decide.
>
> Thanks.
>
> On Sat, Jan 9, 2021 at 4:56 PM Stefanos Baziotis <
> stefanos.baziotis at gmail.com> wrote:
>
>> Hi Mihir,
>>
>> I'm not really sure what would be the best choice given that you mention
>> that you want a source that covers LLVM IR "in depth" while previously it
>> seemed you needed
>> a beginner-like source.
>>
>> If you already know the basics, i.e.,:
>> - IR Structure (Module -> Function -> Basic Block -> Instruction)
>> - Basic operations (arithmetic, branches, calls, loads/stores,
>> conversions all that)
>> - Intrinsics / Metadata
>> - PHIs
>> - GEPs
>> - What role types play in general
>>
>> Bear in mind that when I mention these basics, I don't mean just knowing
>> sort of what they do. I also mean how knowing sort of how can you use them
>> as
>> building blocks to implement high level operations, e.g., (from simple to
>> more complicated):
>> - 1 + 2 + 3
>> - function calls
>> - if-else if-else
>> - classes / structs and operations in them
>> - virtual functions
>>
>> Maybe type conversions, pointers etc. anyway you get the point.
>>
>> If you do have the basics down, _then_ I think is the time to start
>> studying in depth. At this point, I don't think a book or any such source
>> would be useful to you. LangRef would be the way to go along
>> with writing C++ in godbolt (https://godbolt.org/) and seeing what LLVM
>> IR Clang emits (with -emit-llvm and preferably -g0 to avoid debug info as
>> cmd args).
>>
>> But if you don't have the basics down, then you probably don't need
>> something in-depth. In this case, I'd start with this video:
>> https://www.youtube.com/watch?v=m8G_S5LwlTo,
>> writing (simple) C code in godbolt and inspecting the result (eventually
>> trying to produce it myself) and maybe I'd watch a compilers course
>> (meaning 1-2 lectures covering things
>> of interest, not the whole thing and without paying - there is plenty of
>> free material from universities online).
>>
>> I hope this helps. If not, maybe you can try to direct us on what exactly
>> is your level.
>>
>> Best,
>> Stefanos
>>
>> Στις Κυρ, 10 Ιαν 2021 στις 2:39 π.μ., ο/η Mihir Sevak via llvm-dev <
>> llvm-dev at lists.llvm.org> έγραψε:
>>
>>> Ok, thanks for the reply. Lets see what other folks have to say.
>>>
>>> On Sat, Jan 9, 2021 at 4:37 PM David Blaikie <dblaikie at gmail.com> wrote:
>>>
>>>> Yeah, sorry - I haven't read any LLVM books, unfortunately. Perhaps
>>>> some other folks will be able to chime in with tips.
>>>>
>>>> On Sat, Jan 9, 2021 at 4:36 PM Mihir Sevak <mihir.sevak at gmail.com>
>>>> wrote:
>>>>
>>>>> I own this book and it doesn't cover IR in depth. I am trying to write
>>>>> an additional feature for C++ frontend and for that I want to use proper
>>>>> Intermediate Representation that doesn't become a laughing stock so I am
>>>>> looking for some in depth explanation on IR. I am aware that it changes so
>>>>> fast that a book will become outdated however for my exercise I am willing
>>>>> to go back to the version the book covers and implement it there. If you
>>>>> have used some book personally and recommend it please share with me.
>>>>>
>>>>> Thanks.
>>>>>
>>>>> On Sat, Jan 9, 2021 at 4:31 PM David Blaikie <dblaikie at gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Published books probably get out of date pretty quickly, so you'll
>>>>>> need to keep the more up-to-date code/online docs in mind even if you're
>>>>>> reading printed stuff. At a quick google this seems like the sort of thing
>>>>>> that might be useful:
>>>>>> https://www.amazon.com/Getting-Started-LLVM-Core-Libraries/dp/1782166920
>>>>>> (googling 'llvm book' shows a few results)
>>>>>>
>>>>>> On Sat, Jan 9, 2021 at 4:24 PM Mihir Sevak <mihir.sevak at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> Thanks David. Really appreciate this.
>>>>>>>
>>>>>>> Would you please kindly share those names of the books so at least I
>>>>>>> have an idea about what resources are available and in case I need more
>>>>>>> explanation than this Language Reference Manual ?
>>>>>>>
>>>>>>> Once again thanks.
>>>>>>>
>>>>>>> On Sat, Jan 9, 2021 at 3:57 PM David Blaikie <dblaikie at gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> There are some books, but if you're looking for the best reference
>>>>>>>> for LLVM IR it's online here: https://llvm.org/docs/LangRef.html
>>>>>>>>
>>>>>>>> On Sat, Jan 9, 2021 at 3:43 PM Mihir Sevak via llvm-dev <
>>>>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>>>>
>>>>>>>>> Hello LLVM group,
>>>>>>>>>      I am very new to this project. I want to develop a few things
>>>>>>>>> on LLVM platform and for that I am wondering where can I learn about
>>>>>>>>> Intermediate Representation used in LLVM project? Is there any in-depth
>>>>>>>>> instruction level guide available except online tutorials?
>>>>>>>>>
>>>>>>>>> Please advise.
>>>>>>>>>
>>>>>>>>> Thanks.
>>>>>>>>> Have a great weekend.
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> "How can anything be impossible when impossible itself says I M
>>>>>>>>> Possible???"®
>>>>>>>>> Mihir Sevak
>>>>>>>>> _______________________________________________
>>>>>>>>> LLVM Developers mailing list
>>>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> "How can anything be impossible when impossible itself says I M
>>>>>>> Possible???"®
>>>>>>> Mihir Sevak
>>>>>>>
>>>>>>
>>>>>
>>>>> --
>>>>> "How can anything be impossible when impossible itself says I M
>>>>> Possible???"®
>>>>> Mihir Sevak
>>>>>
>>>>
>>>
>>> --
>>> "How can anything be impossible when impossible itself says I M
>>> Possible???"®
>>> Mihir Sevak
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
>
> --
> "How can anything be impossible when impossible itself says I M
> Possible???"®
> Mihir Sevak
>
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