[LLVMdev] How to use LLVM optimizations with clang

[Duncan Sands]

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:

   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
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>
>>>>>>>
>>>>>
>>