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hameeza ahmed via llvm-dev

2017-Aug-17 17:09 UTC

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

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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hameeza ahmed via llvm-dev

2017-Aug-17 18:37 UTC

head link

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

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
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
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Craig Topper via llvm-dev

2017-Aug-17 18:44 UTC

head link

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

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
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
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