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From: "deodharvinit99 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/111683] New: Incorrect answer when using SSE2 intrinsics
 with -O3
Date: Tue, 03 Oct 2023 18:27:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111683

            Bug ID: 111683
           Summary: Incorrect answer when using SSE2 intrinsics with -O3
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: deodharvinit99 at gmail dot com
  Target Milestone: ---

Created attachment 56042
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D56042&action=3Dedit
convn_script

g++ produces incorrect answers when SSE2 intrinsics are used with -O3.=20
-O2 produces same answers compared to an equivalent code written without SS=
E2

A standalone repro shell script:

g++ -O2 convn_script.cpp
./a.out

g++ -O3 convn_script.cpp
./a.out


Target: x86_64-linux-gnu
gcc version 10.2.1 20210110 (Debian 10.2.1-6)


covn_script.cpp:

#include <cstring>
#include <emmintrin.h>
#include <iostream>

// Function Definitions
//
// Check properties of input in9
//
// Arguments    : const double in9[10]
//                const double in10[7]
//                double out5[16]
// Return Type  : void
//
void convn_script(const double in9[10], const double in10[7], double out5[1=
6])
{
  int iB;
  int iC;
  //  Check properties of input in10
  std::memset(&out5[0], 0, 16U * sizeof(double));
  iC =3D 0;
  iB =3D 0;
  for (int i{0}; i < 7; i++) {
    int b_i;
    int vectorUB;
    if (i + 10 <=3D 15) {
      b_i =3D 9;
    } else {
      b_i =3D 15 - i;
    }
    vectorUB =3D (((b_i + 1) / 2) << 1) - 2;
    for (int r{0}; r <=3D vectorUB; r +=3D 2) {
      __m128d b_r;
      b_i =3D iC + r;
      b_r =3D _mm_loadu_pd(&out5[b_i]);
      _mm_storeu_pd(&out5[b_i],
                    _mm_add_pd(b_r, _mm_mul_pd(_mm_set1_pd(in10[iB]),
                                               _mm_loadu_pd(&in9[r]))));
    }
    iC =3D iB + 1;
    iB++;
  }
}

int main() {

    double in9[10] =3D {0.8147, 0.9058, 0.1270, 0.9134,
    0.6324,
    0.0975,
    0.2785,
    0.5469,
    0.9575,
    0.9649};
    double in10[7] =3D { 0.1576,
    0.9706,
    0.9572,
    0.4854,
    0.8003,
    0.1419,
    0.4218};
    double out5[16];

    convn_script(in9, in10, out5);

    for(int i =3D 0; i < 16; i++) {

        std::cout << "Out[" << i << "] =3D " << out5[i] << "\n";
    }

}=