<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">LLVM is very smart about deleting useless code.<div class=""><br class=""></div><div class="">If you want to see vectorized code, I would suggest to write such a function.</div><div class=""><br class=""></div><div class="">int f(int* a, int* b, int n) {</div><div class=""> int ans = 0;</div><div class=""> for (int i = 0; i < n; ++i) {</div><div class=""> ans += a[i] * b[i];</div><div class=""> }</div><div class=""> return ans;</div><div class="">}</div><div class=""><br class=""></div><div class="">That way, the compiler knows nothing about the values of a and b and cannot optimize anything. Also, beware of pointer aliasing which might prevent vectorization or create 2 different paths : one vectorized, one not vectorized.</div><div class=""><br class=""></div><div class=""><div class="">
<div style="color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">François Fayard<br class=""></div></div>
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<br class=""><div><blockquote type="cite" class=""><div class="">On Aug 17, 2017, at 7:01 PM, hameeza ahmed via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">i removed printf from loop. Now getting no error. but the IR doesnot contain vectorized code. IR Output is as follows:<div class=""><div class="">; ModuleID = 'sum-vec.ll'</div><div class="">source_filename = "sum-vec.c"</div><div class="">target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"</div><div class="">target triple = "x86_64-unknown-linux-gnu"</div><div class=""><br class=""></div><div class="">; Function Attrs: norecurse nounwind readnone uwtable</div><div class="">define i32 @main(i32, i8** nocapture readnone) local_unnamed_addr #0 {</div><div class=""> ret i32 0</div><div class="">}</div><div class=""><br class=""></div><div class="">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" }</div><div class=""><br class=""></div><div class="">!llvm.ident = !{!0}</div><div class=""><br class=""></div><div class="">!0 = !{!"clang version 4.0.0 (tags/RELEASE_400/final)"}</div></div><div class=""><br class=""></div><div class="">what to do? please help.</div><div class=""><br class=""></div></div><div class="gmail_extra"><br class=""><div class="gmail_quote">On Thu, Aug 17, 2017 at 9:57 PM, Nemanja Ivanovic <span dir="ltr" class=""><<a href="mailto:nemanja.i.ibm@gmail.com" target="_blank" class="">nemanja.i.ibm@gmail.com</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr" class="">Move the printf out of the loop and it should vectorize just fine.<br class=""></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br class=""><div class="gmail_quote">On Thu, Aug 17, 2017 at 6:52 PM, hameeza ahmed <span dir="ltr" class=""><<a href="mailto:hahmed2305@gmail.com" target="_blank" class="">hahmed2305@gmail.com</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr" class="">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.<div class=""><br class=""></div><div class="">as you pointed; When i changed my code to following:</div><div class=""><br class=""></div><div class=""><div class="">int main(int argc, char** argv) {</div><div class="">int a[1000], b[1000], c[1000];</div><div class="">int aa=atoi(argv[1]), bb=atoi(argv[2]);</div><div class="">for (int i=0; i<1000; i++) {</div><div class="">a[i]=aa, b[i]=bb;</div><div class=""> c[i]=a[i] + b[i];</div><div class="">printf("sum: %d\n", c[i]);</div><div class=""><br class=""></div><div class="">}</div></div><div class=""><br class=""></div><div class="">I am getting error remark: <unknown>:0:0: loop not vectorized: call instruction cannot be vectorized.</div><div class=""><br class=""></div><div class="">I am running following commands:</div><div class="">clang -S -emit-llvm sum-vec.c -march=knl -O3 -mllvm -disable-llvm-optzns -o sum-vec.ll<br class=""></div><div class="">opt -S -O3 -force-vector-width=64 sum-vec.ll -o sum-vec03.ll<br class=""></div><div class=""><br class=""></div><div class="">How to achieve this? Please help.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div></div><div class="gmail_extra"><br class=""><div class="gmail_quote">On Thu, Aug 17, 2017 at 10:44 AM, Nemanja Ivanovic <span dir="ltr" class=""><<a href="mailto:nemanja.i.ibm@gmail.com" target="_blank" class="">nemanja.i.ibm@gmail.com</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr" class="">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.<br class=""></div><div class="gmail_extra"><br class=""><div class="gmail_quote"><div class=""><div class="m_-9083316128729032069m_-5426776120835238504h5">On Wed, Aug 16, 2017 at 11:38 PM, hameeza ahmed via llvm-dev <span dir="ltr" class=""><<a href="mailto:llvm-dev@lists.llvm.org" target="_blank" class="">llvm-dev@lists.llvm.org</a>></span> wrote:<br class=""></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class=""><div class="m_-9083316128729032069m_-5426776120835238504h5"><div dir="ltr" class="">Hello, <div class="">I have written the following code. when i try to vectorize it through opt. i am not getting vectorized instructions.</div><div class=""><br class=""></div><div class=""><div class="">#include <stdio.h></div><div class="">#include<stdlib.h></div><div class="">int main(int argc, char** argv) {</div><div class="">int sum=0; int a=atoi(argv[1]); int b=atoi(argv[2]);</div><div class="">for (int i=0;i<1000;i++)</div><div class="">{</div><div class="">sum+=a+b;<br class=""></div><div class="">}</div><div class=""><br class=""></div><div class="">printf("sum: %d\n", sum);</div><div class="">return 0;</div><div class="">}</div></div><div class="">i use following commands:</div><div class=""><div class="">clang -S -emit-llvm sum-main.c -march=knl -O3 -mllvm -disable-llvm-optzns -o sum-main.ll</div></div><div class=""><div class="">opt -S -O3 -force-vector-width=64 sum-main.ll -o sum-main03.ll</div></div><div class=""><br class=""></div><div class="">why is that so? where am i doing mistake? i am not getting vectorized operations rather getting scalar operations.</div><div class=""><br class=""></div><div class="">Please help.</div><div class=""><br class=""></div><div class="">Thank You</div><div class=""><br class=""></div><div class="">Regards</div><div class=""><br class=""></div></div>
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