[LLVMdev] Modifying LoopUnrollingPass

suyog sarda sardask01 at gmail.com
Mon May 4 10:55:00 PDT 2015 

Optimization passes running before LoopVectorizer should be able to combine
the two statements (this should be happening in O1. Pls check)

arr[i] = a + i
sum += arr[i]

to

sum += a + i

Not sure, why are you using the array there.

- Suyog
On 4 May 2015 23:11, "Michael Zolotukhin" <mzolotukhin at apple.com> wrote:

> Hi Yaduveer,
>
> Vectorizer probably fails because it expects a loop in a certain form, and
> to convert a loop to this form one need to run some other passes first. For
> example, when you run "opt -O3",  the following passes are invoked:
> *-targetlibinfo -tti -no-aa -tbaa -scoped-noalias
> -assumption-cache-tracker -basicaa -ipsccp -globalopt -deadargelim -domtree
> -instcombine -simplifycfg -basiccg -prune-eh -inline-cost -inline
> -functionattrs -argpromotion -sroa -domtree -early-cse -lazy-value-info
> -jump-threading -correlated-propagation -simplifycfg -domtree -instcombine
> -tailcallelim -simplifycfg -reassociate -domtree -loops -loop-simplify
> -lcssa -loop-rotate -licm -loop-unswitch -instcombine -scalar-evolution
> -loop-simplify -lcssa -indvars -loop-idiom -loop-deletion -loop-unroll
> -memdep -mldst-motion -domtree -memdep -gvn -memdep -memcpyopt -sccp
> -domtree -bdce -instcombine -lazy-value-info -jump-threading
> -correlated-propagation -domtree -memdep -dse -loops -loop-simplify -lcssa
> -licm -adce -simplifycfg -domtree -instcombine -barrier -float2int -domtree
> -loops -loop-simplify -lcssa -loop-rotate -branch-prob -block-freq
> -scalar-evolution -loop-accesses -loop-vectorize -instcombine
> -scalar-evolution -slp-vectorizer -simplifycfg -domtree -instcombine -loops
> -loop-simplify -lcssa -scalar-evolution -loop-unroll -instsimplify
> -loop-simplify -lcssa -licm -scalar-evolution -alignment-from-assumptions
> -strip-dead-prototypes -globaldce -constmerge -verify*
>
> To get this list, you can use the following command:
> llvm-as < /dev/null | opt -O3 -disable-output -debug-pass=Arguments
>
> Now, when you get a list of passes to run before the vectorizer, you need
> to get 'unoptimized' IR and run the passes on it - that should give you IR
> just before the vectorizer.
>
> To get the unoptimized IR, you could use
> clang -O3 -mllvm -disable-llvm-optzns -emit-llvm your_source.c -S -o
> unoptimized_ir.ll
> (Please note that we use "-O3 -mllvm -disable-llvm-optzns", not just "-O0"
> - that allows us to run analysis passes, but not transformations)
>
> Now you run 'opt' with passes preceding the vectorizer to get IR before
> vectorization:
> opt -targetlibinfo -tti -no-aa -tbaa ...... -scalar-evolution -loop-accesses
> unoptimized_ir.ll -S -o ir_before_loop_vectorize.ll
> (you might want to remove verifier passes from the list)
>
> And after this you are ready to run the vectorizer:
> opt -loop-vectorize ir_before_loop_vectorize.ll -S -o
> ir_after_loop_vectorize.ll
>
> Hopefully, that'll resolve the issues you are facing.
>
> Thanks,
> Michael
>
>
> On May 3, 2015, at 9:18 AM, yaduveer singh <yaduveer99 at gmail.com> wrote:
>
> Hi Michael,
>
> I tried running my sample C program using "LoopVectorizePass" but I was
> not able to get the output as I was expecting. Every time I got the message
> "LV: Not vectorizing: Cannot prove legality."
>
> Following is the scenario.
>
> c-code
>
> #include <stdio.h>
> int main()
> {
> int i;
> int a=2;
> int sum=0;
> int arr[400];
>
> for(i=0;i<400;i=i+1)
> {
> arr[i]=a+i;
> sum+=arr[i];
> }
> printf("Everything is Done for 1d\n");
> return 0;
> }
>
> following are my command:
>
> yaduveer at yaduveer-Inspiron-3542:~/RP$ clang -S -emit-llvm loop1d.c
> yaduveer at yaduveer-Inspiron-3542:~/RP$ clang -c -emit-llvm loop1d.c
> yaduveer at yaduveer-Inspiron-3542:~/RP$ opt -loop-vectorize
> -force-vector-width=4 -mem2reg -loop-rotate -indvars -debug -stats
> loop1d.ll | llvm-dis -o loop1dv1.ll
>
> we found the following message on the terminal:(Attached is the details
> found on terminal and the 2 .ll files)
>
> LV: Checking a loop in "main" from loop1d.ll
> LV: Loop hints: force=? width=4 unroll=0
> LV: Not vectorizing: Cannot prove legality.
>
> so can you please let me know if I am following correct steps.
> If not, please guide me.
>
>
> Thanks in advance.
>
>
> Regards,
> Yaduveer
>
> On Sun, May 3, 2015 at 12:32 AM, yaduveer singh <yaduveer99 at gmail.com>
> wrote:
>
>> Hi Michael,
>>
>> Thank you very much!
>> I will try this.
>>
>> Regards,
>> Yaduveer
>>
>>
>> On Sun, May 3, 2015 at 12:11 AM, Michael Zolotukhin <
>> mzolotukhin at apple.com> wrote:
>>
>>> Hi Yaduveer,
>>>
>>> As far as I remember, unroller in LoopVectorizer pass does what you want
>>> to achieve (look for a message "LV: Trying to at least unroll the loops."
>>> to locate this in the code).
>>>
>>> Michael
>>>
>>> > On May 2, 2015, at 9:00 AM, yaduveer singh <yaduveer99 at gmail.com>
>>> wrote:
>>> >
>>> > Hi Zhoulai,
>>> >
>>> > I am trying to modify "LoopUnrollPass" in llvm which produces multiple
>>> > copies of loop equal to the loop unroll factor.Currently, using
>>> multicore
>>> > architecture, say 3 for example and the execution goes like:
>>> >
>>> > for 3 cores if there are 9 iterations of loop
>>> > core          instruction
>>> > 1                   0,3,6
>>> > 2                    1,4,7
>>> > 3                    2,5,8
>>> >
>>> > But I want to to modify such that it can execute in following way:
>>> >
>>> > core          instruction
>>> > 1                   0,1,2
>>> > 2                   3,4,5
>>> > 3                   6,7,8
>>> >
>>> > I am not able to get where to modify for this. I tried creating a
>>> sample
>>> > pass using original LoopUnrollPass code and run "make", I received
>>> > following error:
>>> >
>>> > loopunrollp.cpp:210:1: error: 'void
>>> > llvm::initializeLoopUnrollpPass(llvm::PassRegistry&)' should have been
>>> > declared inside 'llvm'
>>> > /bin/rm: cannot remove
>>> >
>>> `/home/yaduveer/RP/LLVM/llvm/lib/Transforms/loopunrollp/Debug+Asserts/loopunrollp.d.tmp':
>>> > No such file or directory
>>> >
>>> >
>>> > Please help
>>> >
>>> > Thanks,
>>> > Yaduveer
>>> >
>>> > _______________________________________________
>>> > LLVM Developers mailing list
>>> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>>>
>>
> <messageOnCommandLine.txt><loop1d.c><loop1d.ll><loop1dv1.ll>
>
>
>
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