[llvm-dev] unable to emit vectorized code in LLVM IR

[hameeza ahmed via llvm-dev]

even if i make my code as follows: vectorized instructions not get emitted.
What to do?

int main(int argc, char** argv) {
int a[1000], b[1000], c[1000]; int g=0;
int aa=atoi(argv[1]), bb=atoi(argv[2]);
for (int i=0; i<1000; i++) {
a[i]=aa, b[i]=bb;
 c[i]=a[i] + b[i];
g+=c[i];
}

printf("sum: %d\n", g);

return 0;
}

On Thu, Aug 17, 2017 at 10:03 PM, Craig Topper <craig.topper at gmail.com>
wrote:

> Did you remove the printf completely? Meaning that nothing accesses 'c'
> after the loop? If so it got removed as dead code because it had no visible
> effect.
>
> ~Craig
>
> On Thu, Aug 17, 2017 at 10:01 AM, hameeza ahmed <hahmed2305 at gmail.com>
> wrote:
>
>> i removed printf from loop. Now getting no error. but the IR doesnot
>> contain vectorized code. IR Output is as follows:
>> ; ModuleID = 'sum-vec.ll'
>> source_filename = "sum-vec.c"
>> target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
>> target triple = "x86_64-unknown-linux-gnu"
>>
>> ; Function Attrs: norecurse nounwind readnone uwtable
>> define i32 @main(i32, i8** nocapture readnone) local_unnamed_addr #0 {
>>   ret i32 0
>> }
>>
>> attributes #0 = { norecurse nounwind readnone uwtable
>> "correctly-rounded-divide-sqrt-fp-math"="false"
>> "disable-tail-calls"="false" "less-precise-fpmad"="false"
>> "no-frame-pointer-elim"="false" "no-infs-fp-math"="false"
>> "no-jump-tables"="false" "no-nans-fp-math"="false"
>> "no-signed-zeros-fp-math"="false" "no-trapping-math"="false"
>> "stack-protector-buffer-size"="8" "target-cpu"="knl"
>> "target-features"="+adx,+aes,+avx,+avx2,+avx512cd,+avx512er,
>> +avx512f,+avx512pf,+bmi,+bmi2,+cx16,+f16c,+fma,+fsgsbase,+fx
>> sr,+lzcnt,+mmx,+movbe,+pclmul,+popcnt,+prefetchwt1,+rdrnd,+
>> rdseed,+rtm,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87,+xsave,+xsaveopt"
>> "unsafe-fp-math"="false" "use-soft-float"="false" }
>>
>> !llvm.ident = !{!0}
>>
>> !0 = !{!"clang version 4.0.0 (tags/RELEASE_400/final)"}
>>
>> what to do? please help.
>>
>>
>> On Thu, Aug 17, 2017 at 9:57 PM, Nemanja Ivanovic <
>> nemanja.i.ibm at gmail.com> wrote:
>>
>>> Move the printf out of the loop and it should vectorize just fine.
>>>
>>> On Thu, Aug 17, 2017 at 6:52 PM, hameeza ahmed <hahmed2305 at gmail.com>
>>> wrote:
>>>
>>>> I want to vectorize the user given inputs. when opt does vectorization
>>>> user supplied inputs (from a text file) will be added using AVX vector
>>>> instructions.
>>>>
>>>> as you pointed; When i changed my code to following:
>>>>
>>>> int main(int argc, char** argv) {
>>>> int a[1000], b[1000], c[1000];
>>>> int aa=atoi(argv[1]), bb=atoi(argv[2]);
>>>> for (int i=0; i<1000; i++) {
>>>> a[i]=aa, b[i]=bb;
>>>>  c[i]=a[i] + b[i];
>>>> printf("sum: %d\n", c[i]);
>>>>
>>>> }
>>>>
>>>> I am getting error remark: <unknown>:0:0: loop not vectorized: call
>>>> instruction cannot be vectorized.
>>>>
>>>> I am running following commands:
>>>> clang  -S -emit-llvm sum-vec.c -march=knl -O3 -mllvm
>>>> -disable-llvm-optzns -o sum-vec.ll
>>>> opt  -S -O3 -force-vector-width=64 sum-vec.ll -o sum-vec03.ll
>>>>
>>>> How to achieve this? Please help.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Thu, Aug 17, 2017 at 10:44 AM, Nemanja Ivanovic <
>>>> nemanja.i.ibm at gmail.com> wrote:
>>>>
>>>>> I'm not sure what you expect to have vectorized here. If you look at
>>>>> the emitted code, there's no loop. It's just an add and a multiply as you
>>>>> might expect when adding a loop-invariant sum 1000 times in a loop.
>>>>>
>>>>> On Wed, Aug 16, 2017 at 11:38 PM, hameeza ahmed via llvm-dev <
>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>
>>>>>> Hello,
>>>>>> I have written the following code. when i try to vectorize it through
>>>>>> opt. i am not getting vectorized instructions.
>>>>>>
>>>>>> #include <stdio.h>
>>>>>> #include<stdlib.h>
>>>>>> int main(int argc, char** argv) {
>>>>>> int sum=0; int a=atoi(argv[1]); int b=atoi(argv[2]);
>>>>>> for (int i=0;i<1000;i++)
>>>>>> {
>>>>>> sum+=a+b;
>>>>>> }
>>>>>>
>>>>>> printf("sum: %d\n", sum);
>>>>>> return 0;
>>>>>> }
>>>>>> i use following commands:
>>>>>> clang  -S -emit-llvm sum-main.c -march=knl -O3 -mllvm
>>>>>> -disable-llvm-optzns -o sum-main.ll
>>>>>> opt  -S -O3 -force-vector-width=64 sum-main.ll -o sum-main03.ll
>>>>>>
>>>>>> why is that so? where am i doing mistake? i am not getting vectorized
>>>>>> operations rather getting scalar operations.
>>>>>>
>>>>>> Please help.
>>>>>>
>>>>>> Thank You
>>>>>>
>>>>>> Regards
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> llvm-dev at lists.llvm.org
>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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