[llvm-dev] LLVM Loop vectorizer - 2 vector.body blocks appear

[Alex Susu via llvm-dev]

   Hello.
     Michael, thank you for your answer - indeed, your command generates only 1 vector.body.

     I give the following commands to compile:
         $(LLVM_PATH)/clang -fvectorize -mllvm -force-vector-width=8 src.c -S -emit-llvm
         $(LLVM_PATH)/opt -debug -O3 -loop-vectorize -force-vector-width=8 src.ll -S 
 >3better_after_opt.ll
         $(LLVM_PATH)/llc -print-after-all -debug -march=connex -O0 -asm-show-inst 
-asm-verbose src_after_opt.ll

    I'd like to mention I am using the version of LoopVectorize.cpp from beginning of Jul 
2016.

   Best regards,
     Alex

On 8/6/2016 2:15 AM, Michael Zolotukhin wrote:
> Hi Alex,
>
> How do you compile this program? I compile it as follows, and don’t see extra vector-bodies:
>
>> bin/clang -O3 vec.c -S -o - |grep "##"
>
>     _foo:                                   ## @foo
>     ## BB#0:                                ## %entry
>     ## BB#1:                                ## %for.body.preheader
>     ## BB#8:                                ## %min.iters.checked
>     ## BB#9:                                ## %vector.memcheck
>     ## BB#10:                               ## %vector.memcheck
>     ## BB#11:                               ## %vector.body.preheader
>     ## BB#12:                               ## %vector.body.prol
>     LBB0_13:                                ## %vector.body.prol.loopexit
>     ## BB#14:                               ## %vector.body.preheader.new
>     LBB0_15:                                ## %vector.body
>                                              ## =>This Inner Loop Header: Depth=1
>     LBB0_16:                                ## %middle.block
>     LBB0_2:                                 ## %for.body.preheader27
>     ## BB#3:                                ## %for.body.prol.preheader
>     LBB0_4:                                 ## %for.body.prol
>                                              ## =>This Inner Loop Header: Depth=1
>     LBB0_5:                                 ## %for.body.prol.loopexit
>     ## BB#6:                                ## %for.body.preheader27.new
>     LBB0_7:                                 ## %for.body
>                                              ## =>This Inner Loop Header: Depth=1
>     LBB0_17:                                ## %for.cond.cleanup
>
>
>
> Best regards,
> Michael
>
>
>> On Jul 31, 2016, at 5:29 PM, Alex Susu <alex.e.susu at gmail.com
>> <mailto:alex.e.susu at gmail.com>> wrote:
>>
>>  Hello.
>>    Mikhail, with the more recent version of the LoopVectorize.cpp code (retrieved at the
>> beginning of July 2016) I ran the following piece of C code:
>>    void foo(long *A, long *B, long *C, long N) {
>>      for (long i = 0; i < N; ++i) {
>>        C[i] = A[i] + B[i];
>>      }
>>    }
>>
>>    The vectorized LLVM program I obtain contains 2 vector.body blocks - one named
>> "vector.body" and the other "vector.body34" for example. The code seems correct - the
>> first "vector.body" block is responsible for the vector add of a number of vector
>> elements multiple of VF * UF. There are 2 epilogues which makes things a bit strange - I
>> am still trying to understand the code.
>>
>>
>>    Is it possible to explain to me where in LoopVectorize.cpp are created 2 vector.body
>> blocks? I know that InnerLoopVectorizer::vectorize() calls
>> InnerLoopVectorizer::createEmptyLoop() which creates the blocks required for
>> vectorization, but I have difficulties to follow the classes instantiations.
>>    I ask because in fact, I would prefer having only one "vector.body" block for the
>> above C program, as it was happening with LoopVectorize.cpp version of Nov 2015.
>>
>>  Thank you very much,
>>    Alex
>