[LLVMdev] How to use LLVM optimizations with clang

[Abdul Wahid Memon]

Thanks Duncan

It was really helpful.

Regards

Abdul

On Fri, Jun 8, 2012 at 7:23 PM, Duncan Sands <baldrick at free.fr> wrote:
> Hi,
>
>
>> If I compile the program using the following command line i.e.
>>
>> $ clang -O3 -lm *.c
>
>
> this may be doing link time optimization.
>
>
>>
>> then
>>
>> $ time ./a.out
>>
>> real    0m2.606s
>> user    0m2.584s
>> sys     0m0.012s
>>
>> BUT, if I use all the optimizations enabled with -O3 but specify them
>> explicity i.e.
>
>
> you can just use "opt -O3" here.
>
>
>>
>> for F in *.c ; do B=`basename $F .c` ; gcc
>> -fplugin=/damm/compilers/dragonegg-3.1.src/dragonegg.so -S -o - $F
>> -fplugin-arg-dragonegg-emit-ir | opt -targetlibinfo -no-aa -tbaa
>> -basicaa -globalopt -ipsccp -deadargelim -instcombine -simplifycfg
>> -basiccg -prune-eh -inline -functionattrs -argpromotion
>> -scalarrepl-ssa -domtree -early-cse -simplify-libcalls
>> -lazy-value-info -jump-threading -correlated-propagation -simplifycfg
>> -instcombine -tailcallelim -simplifycfg -reassociate -domtree -loops
>> -loop-simplify -lcssa -loop-rotate -licm -lcssa -loop-unswitch
>> -instcombine -scalar-evolution -loop-simplify -lcssa -indvars
>> -loop-idiom -loop-deletion -loop-unroll -memdep -gvn -memdep
>> -memcpyopt -sccp -instcombine -lazy-value-info -jump-threading
>> -correlated-propagation -domtree -memdep -dse -adce -simplifycfg
>> -instcombine -strip-dead-prototypes -globaldce -constmerge -preverify
>> -domtree -verify -o $B.ll ; done
>>
>> $ clang *.ll
>
>
> Try clang -O3 *.ll
>
> If it makes a difference then that means that clang is linking all these
> files
> together to form one mega file which it is then optimizing.
>
> Ciao, Duncan.
>
>
>>
>> then
>>
>> time ./a.out
>>
>> real    0m7.791s
>> user    0m7.760s
>> sys     0m0.008s
>>
>> Am I missing something here?
>>
>> Though directly compiling files i.e.
>>
>> $ clang *.c
>>
>> results in
>>
>> time ./a.out
>>
>> real    0m10.167s
>> user    0m10.121s
>> sys     0m0.016s
>>
>> Regards
>>
>> Shahzad
>>
>> On Fri, Jun 8, 2012 at 7:00 PM, Duncan Sands<baldrick at free.fr>  wrote:
>>>
>>> Hi,
>>>
>>>
>>>> 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?
>>>
>>>
>>>
>>> what I wrote:
>>>
>>>>>  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
>>>
>>>
>>>
>>> Thanks to the for loop and passing $F to gcc, you are no longer using gcc
>>> with
>>> multiple files.  So if you are getting that message then you are don't
>>> what
>>> I
>>> suggested.
>>>
>>> Ciao, Duncan.
>>>
>>>
>>>>>
>>>>> 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
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>
>>>>>
>>>
>