[llvm-dev] unable to emit vectorized code in LLVM IR (original) (raw)

Craig Topper via llvm-dev llvm-dev at lists.llvm.org
Thu Aug 17 12:28:48 PDT 2017

So your clang command line says -march=knl. Are you using a Xeon Phi to run your code? if not that's why you're failing. Try changing it to -march=native

~Craig

On Thu, Aug 17, 2017 at 12:21 PM, hameeza ahmed <hahmed2305 at gmail.com> wrote:

lli sum-vec03.ll 5 2 #0 0x0000000000c1f818 (lli+0xc1f818) #1 0x0000000000c1d90e (lli+0xc1d90e) #2 0x0000000000c1da5c (lli+0xc1da5c) _#3 0x00007f987c2c3d10 restorert (/lib/x8664-linux-gnu/ libpthread.so.0+0x10d10) #4 0x00007f987c6f0038 #5 0x0000000000989f8c (lli+0x989f8c) #6 0x00000000009383dc (lli+0x9383dc) #7 0x000000000057eedd (lli+0x57eedd) _#8 0x00007f987b464a40 libcstartmain (/lib/x8664-linux-gnu/libc. so.6+0x20a40) #9 0x00000000005a5b49 (lli+0x5a5b49) Stack dump: 0. Program arguments: lli sum-vec03.ll 5 2 Illegal instruction (core dumped)

No yet there exists no link with those new 2048 element instructions that i discussed earlier. i need to link jit with that later. presently, i am exploring jit in general to know its capabilities. 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? On Fri, Aug 18, 2017 at 12:17 AM, Craig Topper <craig.topper at gmail.com> wrote:

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::rawostream&)_ _/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 _restorert (/lib/x8664-linux-gnu/libpthr_ _ead.so.0+0x10d10)_ _#5 0x00007fcded2c3038_ _#6 0x0000000000f4a8fb llvm::MCJIT::runFunction(llvm::Function*,_ _llvm::ArrayRefllvm::GenericValue) /lib/ExecutionEngine/MCJIT/MCJ IT.cpp:538:31 #7 0x0000000000eaff23 llvm::ExecutionEngine::runFunctionAsMain(llvm::Function*, std::vector<std::_cxx11::basicstring<char, std::chartraits, std::allocator >, std::allocator<std::_cxx11::basicstring<char,_ _std::chartraits, std::allocator > > > const&, char const* const*) /lib/ExecutionEngine/ExecutionEngine.cpp:471:10 #8 0x00000000007be4e9 main /tools/lli/lli.cpp:627:18 _#9 0x00007fcdebe2fa40 libcstartmain (/lib/x8664-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: :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' sourcefilename = "sum-vec.c" target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" target triple = "x8664-unknown-linux-gnu" ; Function Attrs: norecurse nounwind readnone uwtable define i32 @main(i32, i8** nocapture readnone) localunnamedaddr #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/RELEASE400/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: :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

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