[LLVMdev] How to use LLVM optimizations with clang

[Abdul Wahid Memon]

Hello Duncan

On Fri, Jun 8, 2012 at 2:58 PM, Duncan Sands <baldrick at free.fr> wrote:
> Hi Shahzad,
>
>
>> I tried your method and it works fine. What would be the next step to
>> produce the final executable? I have tried the following but it is
>> producing an error
>>
>> $ gcc -fplugin=/path/to/dragonegg.so -S *.c
>> -fplugin-arg-dragonegg-emit-ir | opt -adce
>
>
> this won't work because you aren't passing the IR to opt (you need -o - for
> that if using a pipe) and you aren't doing anything with opt output.  What's
> more, you are trying to compile multiple files at once.  Probably something
> like this would work:
I tried it with -o - but its producing an error

gcc: fatal error: cannot specify -o with -c, -S or -E with multiple files

What you suggest?

Regards

Abdul

>
>  for F in *.c ; do B=`basename $F .c` ; gcc -fplugin=/path/to/dragonegg.so
> -S -o - $F -fplugin-arg-dragonegg-emit-ir | opt -adce -o $B.ll ; done
>  clang *.ll
>
> Ciao, Duncan.
>
>
>>
>> $ clang *.s
>>
>> Regards
>>
>> Shahzad
>>
>> On Fri, Jun 8, 2012 at 9:10 AM, Duncan Sands<baldrick at free.fr>  wrote:
>>>
>>> Hi Shahzad,
>>>
>>>
>>>> Is it possible that we can use LLVM optimization beside O1, O2, O3
>>>> along with dragonegg plugin?
>>>
>>>
>>>
>>> sure, try this:
>>>
>>>  gcc -fplugin=path/dragonegg.so ...other_options_here... -S -o -
>>> -fplugin-arg-dragonegg-emit-ir -fplugin-arg-dragonegg-llvm-ir-optimize=0
>>> |
>>> opt -pass1 -pass2 ...
>>>
>>> Here -fplugin-arg-dragonegg-emit-ir tells it to output LLVM IR rather
>>> than
>>> target assembler.  You can also use -flto here.
>>>
>>> -fplugin-arg-dragonegg-llvm-ir-optimize=0 disables the standard set of
>>> LLVM
>>> optimizations.
>>>
>>> In general, if a front-end can produce LLVM IR then you can do this, by
>>> outputting the IR and passing it to "opt".
>>>
>>> Ciao, Duncan.
>>>
>>>
>>>>
>>>> Regards
>>>>
>>>> Shahzad
>>>>
>>>> On Thu, Jun 7, 2012 at 10:59 PM, Abdul Wahid Memon
>>>> <engrwahidmemon at gmail.com>    wrote:
>>>>>
>>>>>
>>>>> Thanks alot Chad for these quick and fine responses.
>>>>>
>>>>> Regards
>>>>>
>>>>> Abdul
>>>>>
>>>>> On Thu, Jun 7, 2012 at 10:57 PM, Chad Rosier<mcrosier at apple.com>
>>>>>  wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Jun 7, 2012, at 1:53 PM, Abdul Wahid Memon wrote:
>>>>>>
>>>>>>> Thanks again chad. One more question please.
>>>>>>>
>>>>>>> Is it possible that I can use these optimization using dragonegg
>>>>>>> plugin
>>>>>>> somehow?
>>>>>>
>>>>>>
>>>>>>
>>>>>> I haven't a clue.  Maybe Duncan can answer that?
>>>>>>
>>>>>>  Chad
>>>>>>
>>>>>>>
>>>>>>> Regards
>>>>>>>
>>>>>>> Shahzad
>>>>>>>
>>>>>>> On Thu, Jun 7, 2012 at 10:51 PM, Chad Rosier<mcrosier at apple.com>
>>>>>>>  wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Jun 7, 2012, at 1:48 PM, Abdul Wahid Memon wrote:
>>>>>>>>
>>>>>>>>> On Thu, Jun 7, 2012 at 10:44 PM, Chad Rosier<mcrosier at apple.com>
>>>>>>>>>  wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Jun 7, 2012, at 1:39 PM, Abdul Wahid Memon wrote:
>>>>>>>>>>
>>>>>>>>>>> Thanks alot Chad for quick response. Does this means that, we can
>>>>>>>>>>> not
>>>>>>>>>>> use LLVM optimizations except O1, O2, O3, O4 and unroll-loops
>>>>>>>>>>> with
>>>>>>>>>>> clang?
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Try using the -debug-pass=Arguments options to see what passes are
>>>>>>>>>> being run at each optimization level.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Yes, I have seen those optimization but I want to disable all the
>>>>>>>>> default optimization (-O0) and specify them individually to test
>>>>>>>>> their
>>>>>>>>> effect.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> 1. Generate the bitcode/ir with -O0
>>>>>>>> 2. Run opt with the optimization in question.  You should be able to
>>>>>>>> specify most any pass with opt.
>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> E.g.,
>>>>>>>>>> clang -O[0-3] -mllvm -debug-pass=Arguments foo.c.
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> One more thing I would like to know that If I want to process
>>>>>>>>>>> multiple
>>>>>>>>>>> modules with opt at the same time like
>>>>>>>>>>>
>>>>>>>>>>> opt -adce *.bc
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> I don't think this will work.
>>>>>>>>>>
>>>>>>>>> ok.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> then how is it possible with opt in one go, if I process all the
>>>>>>>>>>> bytecode files within Makefile.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> You should be able to define a rule in the Makefile to compile
>>>>>>>>>> your
>>>>>>>>>> bitcode/IR files.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> ok. I got the point.
>>>>>>>>>
>>>>>>>>> Thanks alot
>>>>>>>>>
>>>>>>>>> Shahzad
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>  Chad
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Thanks.
>>>>>>>>>>>
>>>>>>>>>>> Shahzad
>>>>>>>>>>>
>>>>>>>>>>> On Thu, Jun 7, 2012 at 9:22 PM, Chad Rosier<mcrosier at apple.com>
>>>>>>>>>>>  wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On Jun 7, 2012, at 10:59 AM, Abdul Wahid Memon wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> Hello everyone
>>>>>>>>>>>>>
>>>>>>>>>>>>> I am trying to use some LLVM optimizations like -die or -adce.
>>>>>>>>>>>>> Is
>>>>>>>>>>>>> it
>>>>>>>>>>>>> possible to use them along clang?
>>>>>>>>>>>>>
>>>>>>>>>>>>> Or is there a way where these optimization can be passed on to
>>>>>>>>>>>>> "opt"
>>>>>>>>>>>>> tool through clang, if opt is being used by clang behind the
>>>>>>>>>>>>> scenes?
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> No, opt only works on llvm IR/bitcode.  You can generate it like
>>>>>>>>>>>> this:
>>>>>>>>>>>> clang -c foo.c -emit-llvm -o foo.bc
>>>>>>>>>>>> or
>>>>>>>>>>>> clang -S foo.c -emit-llvm -o foo.ll
>>>>>>>>>>>>
>>>>>>>>>>>> Then you can run the optimization(s):
>>>>>>>>>>>> opt -adce foo.bc -o foo-adce.bc
>>>>>>>>>>>>
>>>>>>>>>>>> Then you can compile using clang
>>>>>>>>>>>> clang -c foo-adce.bc -o foo-adce.o
>>>>>>>>>>>>
>>>>>>>>>>>>  Chad
>>>>>>>>>>>>
>>>>>>>>>>>>> Thanks alot
>>>>>>>>>>>>>
>>>>>>>>>>>>> Regards
>>>>>>>>>>>>>
>>>>>>>>>>>>> Shahzad
>>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>>> LLVM Developers mailing list
>>>>>>>>>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>>>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>
>>>>>>
>>>
>