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Use _Float16 only when SSE2 is enabled

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The GCC documentation [1] says: “On x86 targets with SSE2 enabled, GCC
supports half-precision (16-bit) floating point via the _Float16 type”.

On non-SSE2 x86 (such as Debian i386 baseline [2]), __FLT16_MAX__ is
defined starting with GCC 14 [3], however any non-trivial use of the
_Float16 type results in an error:

error: operation not permitted on type ‘_Float16’ without option ‘-msse2’

which makes some packages fail to build on i386 architecture [4].

[1]: https://gcc.gnu.org/onlinedocs/gcc/Half-Precision.html
[2]: https://wiki.debian.org/ArchitectureSpecificsMemo#i386-1
[3]: https://gcc.gnu.org/g:9a19fa8b616f83474c35cc5b34a3865073ced829
[4]: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1076986

Pick-to: 6.7 6.5
Change-Id: I393ee83eb8e8888f5fc9e3b349dc8b063eef6f5a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
(cherry picked from commit 39fa7e7bef90be2940c5f736935f963e3969e0bd)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Dmitry Shachnev 2024-07-27 23:03:07 +03:00 committed by Qt Cherry-pick Bot
parent a58abfec1c
commit f2601a27b0
1 changed files with 3 additions and 4 deletions
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7
src/corelib/global/qtypes.h
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@ -263,13 +263,12 @@ using NativeFloat16Type = std::float16_t;
// disabled due to https://github.com/llvm/llvm-project/issues/56963
# define QFLOAT16_IS_NATIVE 1
using NativeFloat16Type = decltype(__FLT16_MAX__);
#elif defined(Q_CC_GNU_ONLY) && defined(__FLT16_MAX__)
#elif defined(Q_CC_GNU_ONLY) && defined(__FLT16_MAX__) && defined(__ARM_FP16_FORMAT_IEEE)
# define QFLOAT16_IS_NATIVE 1
# ifdef __ARM_FP16_FORMAT_IEEE
using NativeFloat16Type = __fp16;
# else
#elif defined(Q_CC_GNU_ONLY) && defined(__FLT16_MAX__) && defined(__SSE2__)
# define QFLOAT16_IS_NATIVE 1
using NativeFloat16Type = _Float16;
# endif
#else
# define QFLOAT16_IS_NATIVE 0
using NativeFloat16Type = void;