[llvm-dev] unable to emit vectorized code in LLVM IR
Craig Topper via llvm-dev
llvm-dev at lists.llvm.org
Thu Aug 17 12:17:13 PDT 2017
What was your lli command line? Is this based on your code where you
created 2048-bit instructions in the x86 backend?
~Craig
On Thu, Aug 17, 2017 at 12:12 PM, hameeza ahmed <hahmed2305 at gmail.com>
wrote:
> Ok. I have managed to vectorize the second loop in the following code. But
> the first loop is still not vectorized? Why?
>
> 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+i, b[i]=bb+i;}
>
> for (int i=0; i<1000; i++) {
> c[i]=a[i] + b[i];
> g+=c[i];
> }
>
> printf("sum: %d\n", g);
>
> return 0;
> }
>
> When i executed the optimized IR through jit (lli sum-vec03.ll 5 2) i am
> getting following error:
>
> #0 0x00000000013f965c llvm::sys::PrintStackTrace(llvm::raw_ostream&)
> /lib/Support/Unix/Signals.inc:402:11
> #1 0x00000000013f9b49 PrintStackTraceSignalHandler(void*)
> /lib/Support/Unix/Signals.inc:466:1
> #2 0x00000000013f7ec3 llvm::sys::RunSignalHandlers()
> /lib/Support/Signals.cpp:0:5
> #3 0x00000000013f9ea4 SignalHandler(int) /lib/Support/Unix/Signals.inc:
> 256:1
> #4 0x00007fcdece96d10 __restore_rt (/lib/x86_64-linux-gnu/
> libpthread.so.0+0x10d10)
> #5 0x00007fcded2c3038
> #6 0x0000000000f4a8fb llvm::MCJIT::runFunction(llvm::Function*,
> llvm::ArrayRef<llvm::GenericValue>) /lib/ExecutionEngine/MCJIT/
> MCJIT.cpp:538:31
> #7 0x0000000000eaff23 llvm::ExecutionEngine::runFunctionAsMain(llvm::Function*,
> std::vector<std::__cxx11::basic_string<char, std::char_traits<char>,
> std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char,
> std::char_traits<char>, std::allocator<char> > > > const&, char const*
> const*) /lib/ExecutionEngine/ExecutionEngine.cpp:471:10
> #8 0x00000000007be4e9 main /tools/lli/lli.cpp:627:18
> #9 0x00007fcdebe2fa40 __libc_start_main (/lib/x86_64-linux-gnu/libc.
> so.6+0x20a40)
> #10 0x00000000007bc169 _start (/bin/lli+0x7bc169)
> Stack dump:
> 0. Program arguments:lli sum-vec03.ll 5 2
> Illegal instruction (core dumped)
>
>
> What is wrong here? please help.
>
>
>
>
>
>
>
>
>
> On Thu, Aug 17, 2017 at 11:51 PM, hameeza ahmed <hahmed2305 at gmail.com>
> wrote:
>
>> 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
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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