public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug c++/111306] New: macro-fusion makes error on conjugate complex multiplication
@ 2023-09-06 12:18 joony.wie at samsung dot com
  2023-09-08  2:18 ` [Bug target/111306] [12,13] macro-fusion makes error on conjugate complex multiplication fp16 pinskia at gcc dot gnu.org
                   ` (8 more replies)
  0 siblings, 9 replies; 10+ messages in thread
From: joony.wie at samsung dot com @ 2023-09-06 12:18 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111306

            Bug ID: 111306
           Summary: macro-fusion makes error on conjugate complex
                    multiplication
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: joony.wie at samsung dot com
  Target Milestone: ---

It seems that the operands src1 and src2 of "_mm512_fcmul_pch" are swapped for
macro-fusion with optimize option.

If the operands are swapped, the imag value of result will have incorrect sign
bit.

So, the operands should not be swapped in these conjugate complex
multiplication intrinsics.

Let me show the example and the output.

output: 
3.000000 -4.000000 // w/o optimize.
3.000000 4.000000 // w/ optimize.

https://godbolt.org/z/df9Gz18hc // but may not executable
```
#include <immintrin.h>
#include <cstdio>

__attribute__((optimize("O0")))
auto func0(_Float16 *a, _Float16 *b, int n, _Float16 *c) {
  __m512h rA = _mm512_loadu_ph(a);
  for (int i = 0; i < n; i += 32) {
    __m512h rB = _mm512_loadu_ph(b + i);
    _mm512_storeu_ph(c + i, _mm512_fcmul_pch(rB, rA));
  }
}

__attribute__((optimize("O")))
auto func1(_Float16 *a, _Float16 *b, int n, _Float16 *c) {
  __m512h rA = _mm512_loadu_ph(a);
  for (int i = 0; i < n; i += 32) {
    __m512h rB = _mm512_loadu_ph(b + i);
    _mm512_storeu_ph(c + i, _mm512_fcmul_pch(rB, rA));
  }
}

int main() {
  int n = 32;

  _Float16 a[n], b[n], c[n];
  for (int i = 1; i <= n; i++) {
    a[i - 1] = i & 1 ? -i : i;
    b[i - 1] = i;
  }

  func0(a, b, n, c);
    for (int i = 0; i < n / 32 * 2; i++) {
      printf("%f ", (float)c[i]);
    }
    printf("\n");

  func1(a, b, n, c);
    for (int i = 0; i < n / 32 * 2; i++) {
      printf("%f ", (float)c[i]);
    }
    printf("\n");

  return 0;
}
```

^ permalink raw reply	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2023-09-12 11:09 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-09-06 12:18 [Bug c++/111306] New: macro-fusion makes error on conjugate complex multiplication joony.wie at samsung dot com
2023-09-08  2:18 ` [Bug target/111306] [12,13] macro-fusion makes error on conjugate complex multiplication fp16 pinskia at gcc dot gnu.org
2023-09-08  2:19 ` pinskia at gcc dot gnu.org
2023-09-08  3:24 ` crazylht at gmail dot com
2023-09-08  6:02 ` crazylht at gmail dot com
2023-09-11  1:17 ` cvs-commit at gcc dot gnu.org
2023-09-11  1:20 ` cvs-commit at gcc dot gnu.org
2023-09-11  1:22 ` cvs-commit at gcc dot gnu.org
2023-09-11  1:23 ` crazylht at gmail dot com
2023-09-12 11:09 ` rguenth at gcc dot gnu.org

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).