[LLVMdev] How to use LLVM optimizations with clang

Abdul Wahid Memon engrwahidmemon at gmail.com
Fri Jun 8 10:21:37 PDT 2012 

Hello Duncan

Sorry for the mistake. Actually that error occurred when I was
compiling all the files at once, NOT in for loop.

The for loop is working perfectly as it is dealing with individual
files. I have now one new issue. Let me specify it briefly.

If I compile the program using the following command line i.e.

$ clang -O3 -lm *.c

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.

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

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

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