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

[Craig Topper via llvm-dev]

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,+
> fxsr,+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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