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Description: use _Float16 only when SSE2 is enabled
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The GCC documentation [1] says: “On x86 targets with SSE2 enabled, GCC
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supports half-precision (16-bit) floating point via the _Float16 type”.
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.
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On non-SSE2 x86 (such as Debian i386 baseline [2]), __FLT16_MAX__ is
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defined starting with GCC 14 [3], however any non-trivial use of the
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_Float16 type results in an error:
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.
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error: operation not permitted on type ‘_Float16’ without option ‘-msse2’
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.
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which makes some packages fail to build on i386 architecture [4].
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.
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[1]: https://gcc.gnu.org/onlinedocs/gcc/Half-Precision.html
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[2]: https://wiki.debian.org/ArchitectureSpecificsMemo#i386-1
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[3]: https://gcc.gnu.org/g:9a19fa8b616f83474c35cc5b34a3865073ced829
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[4]: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1076986
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Author: Dmitry Shachnev <mitya57@debian.org>
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Forwarded: https://codereview.qt-project.org/c/qt/qtbase/+/579205
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Last-Update: 2024-08-01
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--- a/src/corelib/global/qtypes.h
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+++ b/src/corelib/global/qtypes.h
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@@ -263,13 +263,12 @@ using NativeFloat16Type = std::float16_t
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// disabled due to https://github.com/llvm/llvm-project/issues/56963
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# define QFLOAT16_IS_NATIVE 1
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using NativeFloat16Type = decltype(__FLT16_MAX__);
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-#elif defined(Q_CC_GNU_ONLY) && defined(__FLT16_MAX__)
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+#elif defined(Q_CC_GNU_ONLY) && defined(__FLT16_MAX__) && defined(__ARM_FP16_FORMAT_IEEE)
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# define QFLOAT16_IS_NATIVE 1
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-# ifdef __ARM_FP16_FORMAT_IEEE
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using NativeFloat16Type = __fp16;
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-# else
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+#elif defined(Q_CC_GNU_ONLY) && defined(__FLT16_MAX__) && defined(__SSE2__)
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+# define QFLOAT16_IS_NATIVE 1
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using NativeFloat16Type = _Float16;
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-# endif
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#else
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# define QFLOAT16_IS_NATIVE 0
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using NativeFloat16Type = void;
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