[LLVMdev] How to use LLVM optimizations with clang
Duncan Sands
baldrick at free.fr
Tue Jun 12 03:28:16 PDT 2012
Hi,
> Yes, they both are exactly the same.
then I don't know what is going on. I suggest you send a copy of comb.ll to the
list so that we can see for ourselves.
Ciao, Duncan.
>
> Regards
>
> Shahzad
>
> On Tue, Jun 12, 2012 at 9:38 AM, Duncan Sands<baldrick at free.fr> wrote:
>> Hi, is the comb.ll used here:
>>
>>
>>> $ time lli ./comb.ll
>>>
>>> then the runtime is
>>>
>>> real 0m2.671s
>>> user 0m2.640s
>>> sys 0m0.020s
>>>
>>> But, if I convert this same file comb,ll in to native binary
>>
>>
>> the same as the comb.ll used here:
>>
>>> $ clang comb.ll
>>
>>
>> ?
>>
>> Ciao, Duncan.
>>
>>
>>>
>>> and execute it, then the runtime increases alot
>>>
>>> $ time ./a.out
>>>
>>> real 0m8.008s
>>> user 0m7.964s
>>>
>>> The binary generated directly by clang have runtime of around 2
>>> seconds while generated after LLVM IR have around 8 secs but LLVM
>>> bytecode having same optimizations when executed with lli have runtime
>>> of around 2 secs.
>>>
>>> What steps are exactly taken by clang to produce the binary in order
>>> to achieve the runtime of around 2 secs. If it is a question of link
>>> time optimizations then how can we achieve that?
>>>
>>> Best Regards
>>>
>>> Shahzad
>>>
>>> On Fri, Jun 8, 2012 at 7:29 PM, Abdul Wahid Memon
>>> <engrwahidmemon at gmail.com> wrote:
>>>>
>>>> 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
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>
>>>>>>>
>>>>>
>>
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