Bug 910419 – dev-qt/qtbase-6.5.1-r1 emerge fail on AVX512-enabled Alder Lake CPU with march=native

• Status: UNCONFIRMED
• Product: Gentoo Linux

[Description znjameswu 2023-07-16 07:22:07 UTC]

Selected part of the error log:
```
/var/tmp/portage/dev-qt/qtbase-6.5.1-r1/work/qtbase-everywhere-src-6.5.1_build/include/QtCore/../../../qtbase-everywhere-src-6.5.1/src/corelib/global/qfloat16.h: In function ‘qfloat16 qSqrt(qfloat16)’:
/var/tmp/portage/dev-qt/qtbase-6.5.1-r1/work/qtbase-everywhere-src-6.5.1_build/include/QtCore/../../../qtbase-everywhere-src-6.5.1/src/corelib/global/qfloat16.h:266:9: error: ‘__m128h’ was not declared in this scope
  266 |         __m128h v = _mm_set_sh(f);
      |         ^~~~~~~
/var/tmp/portage/dev-qt/qtbase-6.5.1-r1/work/qtbase-everywhere-src-6.5.1_build/include/QtCore/../../../qtbase-everywhere-src-6.5.1/src/corelib/global/qfloat16.h:267:9: error: ‘v’ was not declared in this scope
  267 |         v = _mm_sqrt_sh(v, v);
      |         ^
/var/tmp/portage/dev-qt/qtbase-6.5.1-r1/work/qtbase-everywhere-src-6.5.1_build/include/QtCore/../../../qtbase-everywhere-src-6.5.1/src/corelib/global/qfloat16.h:267:13: error: ‘_mm_sqrt_sh’ was not declared in this scope
  267 |         v = _mm_sqrt_sh(v, v);
      |             ^~~~~~~~~~~
/var/tmp/portage/dev-qt/qtbase-6.5.1-r1/work/qtbase-everywhere-src-6.5.1_build/include/QtCore/../../../qtbase-everywhere-src-6.5.1/src/corelib/global/qfloat16.h:268:16: error: ‘_mm_cvtsh_h’ was not declared in this scope
  268 |         return _mm_cvtsh_h(v);
      |                ^~~~~~~~~~~
```




Reproducible: Always

Steps to Reproduce:
1. Use an AVX512-enabled Intel Alder Lake (12th gen Core) machine
2. Set "march=native" in gcc flags
Actual Results:  
Emerge failed


Suspected Cause:
in qtbase-6.5.1-r1/work/qtbase-everywhere-src-6.5.1/src/corelib/global/qfloat16.h:29: 
``` 
#if defined(QT_COMPILER_SUPPORTS_F16C) && defined(__F16C__)
#include <immintrin.h>
#endif
```
Somehow QT_COMPILER_SUPPORTS_F16C is undef on my machine. When commented out, the manual build turns out successful


Background: 
Alder Lake CPUs (or Intel 12th gen Core) do not officially support AVX512. However, a CooperLake-equivalent AVX512 support can be enabled on those CPUs by specific firmwares. Hence a very niche configuration.

[Comment 1 znjameswu 2023-07-16 07:23:36 UTC]

Created attachment 865565 [details]
lscpu

[Comment 2 znjameswu 2023-07-16 07:24:29 UTC]

Created attachment 865566 [details]
emerge --info

[Comment 3 znjameswu 2023-07-16 07:28:51 UTC]

Created attachment 865567 [details]
build.log

[Comment 4 znjameswu 2023-07-16 07:29:06 UTC]

Created attachment 865568 [details]
environment

[Comment 5 znjameswu 2023-07-16 07:31:08 UTC]

Created attachment 865569 [details]
gcc -march=native -Q --help=target

[Comment 6 znjameswu 2023-07-16 07:32:54 UTC]

Created attachment 865570 [details]
emerge --info '=dev-qt/qtbase-6.5.1-r1::gentoo'

[Comment 7 znjameswu 2023-07-16 07:34:30 UTC]

Supplementary Info: I'm not using any

[Comment 8 znjameswu 2023-07-16 07:37:22 UTC]

(In reply to znjameswu from comment #7)
Supplementary Info: I'm not using VirtualBox. The installation is on bare metal.

[Comment 9 Mike Gilbert 2023-07-29 22:29:24 UTC]

Please file a bug upstream.