[LLVMdev] How to use LLVM optimizations with clang

[Abdul Wahid Memon]

Hello Duncan

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

$ 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
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>
>>>>>>
>>>>
>