[LLVMdev] How to use LLVM optimizations with clang
Duncan Sands
baldrick at free.fr
Tue Jun 12 00:38:56 PDT 2012
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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