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

Thu Aug 17 11:51:00 PDT 2017

when i change it to following: then get error: remark: <unknown>:0:0: loop
not vectorized: call instruction cannot be vectorized
int main(int argc, char** argv) {
int a[1000], b[1000], c[1000]; int g=0;
for (int i=0; i<1000; i++) {
a[i]=atoi(argv[1]), b[i]=atoi(argv[2]);
 c[i]=a[i] + b[i];
g+=c[i];
}

Here my main goal is that i need to use JIT to perform operations on user
input file supplied at run time using vector instructions. is it possible
and achievable through JIT?
Please help.

On Thu, Aug 17, 2017 at 11:44 PM, Craig Topper <craig.topper at gmail.com>
wrote:

> I assume compiler knows that your only have 2 input values that you just
> added together 1000 times.
>
> Despite the fact that you stored to a[i] and b[i] here, nothing reads them
> other than the addition in the same loop iteration. So the compiler easily
> removed the a and b arrays. Same with 'c', it's not read outside the loop
> so it doesn't need to exist. So the compiler turned your loop body back
> into g+= aa + bb; And since the loop is 1000 iterations and aa and bb never
> change this got further simplified to (aa+bb)*1000.
>
> 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];
> }
>
> ~Craig
>
> On Thu, Aug 17, 2017 at 11:37 AM, hameeza ahmed <hahmed2305 at gmail.com>
> wrote:
>
>> why is it happening? is there any way to solve this?
>>
>> On Thu, Aug 17, 2017 at 10:09 PM, hameeza ahmed <hahmed2305 at gmail.com>
>> wrote:
>>
>>> 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,+r
>>>>> dseed,+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
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20170817/75d77f4a/attachment-0001.html>