valarray with exp instruction error in Intel OneApi Developer Tools 2021.4?

[JerzyP]

Hi,
I found that Intel OneApi Developer Tools 2021.4 (from w_BaseKit_p_2021.4.0.3421_offline.exe + w_HPCKit_p_2021.4.0.3340_offline.exe packages) has a problem with the generation of good code when valarrays type is used together with exp instructions, i.e. generate the bad results.
This problem appears, when we use /O2 and /fp:fast options using Intel oneAPI DPC++/C++ Compiler 2021 (but does not appear when we use Intel C++ Compiler Clasic 19.2 from Intel OneApi Developer Tools 2021.4 package).
See the “textexp.cpp” code:
-----------------------
#include <iostream>
#include <cmath>
#include <valarray>
#include <random>
int main() {
  using namespace std;
  mt19937_64 engine;
  engine.seed(0); //0 to have reproducible results
  uniform_real_distribution<double> uniform0_1(0, 1);

// Random size is used to protect from unrolling loop instructions (e.g. for "for" instructions)
// If replace this line by "int size = 20;", compiler unrolls "for" instructions.
  int size = 20 + int(0.001 * uniform0_1(engine)); //size=20.

  valarray<double> x, y;
  x.resize(size);
  y.resize(size);
  for (int i = 0; i < y.size(); ++i)
    y[i] = x[i] = 1.0;

  for (int i = 0; i < y.size(); ++i)
    y[i] *= exp(-x[i]); //All y[i] should be equal to 0.367978...
  //... but for i equal to 2, 3, 6, 7, 10, 11, 14, 15 and so on y[i]=1.44467 !!!???
  //if program is compiled by oneAPI DPC++/C++ Compiler from Intel OneApi Developer Tools 2021.4
  //(w_BaseKit_p_2021.4.0.3421_offline.exe + w_HPCKit_p_2021.4.0.3340_offline.exe) using MS Visual Studio 2019 envirenment.

  for (int i = 0; i < y.size(); ++i)
    cout << y[i] << endl; //We obtain 0.367978, 0.367978, 1.44467, 1.44467, 0.367978, 0.367978, 1.44467, 1.44467, 0.367978, 0.367978, 1.44467, 1.44467...???
  return 0;
}
-----------------
Compile options: /GS /W3 /Gy /Zi /O2 /fp:fast /D "NDEBUG" /D "_CONSOLE" /D "_UNICODE" /D "UNICODE" /Qipo /Zc:forScope /std:c17 /Oi /MT /Fa"x64\Release\" /EHsc /nologo /Fo"x64\Release\" //fprofile-instr-use "x64\Release\" /Fp"x64\Release\testexp.pch"

Please help me,
Thanks a lot.
Jerzy

[JerzyP]

The program was compiled and run on a PC with Windows 10 (i7 3770K processor).

Jerzy

[VarshaS_Intel]

Hi,

Thanks for reporting us.

We are able to reproduce your issue using "release" mode. However, we observed that with "debug" mode we are getting expected/correct results.

We are working on your issue internally and will get back to you soon.

Thanks & Regards

Varsha

[Alex_Y_Intel]

The issue has been escalated our engineers and we will work on it internally. We will get back to you when update is available.

[Alex_Y_Intel]

The problem cannot be reproduced for icx compiler 2022.0 in oneAPI Base Toolkit 2022.1.2. I'm closing this issue as fixed. Please feel free to reopen or file a new issue if you find any more problems.