[clang] [X86][Headers] Specify result of NaN comparisons (PR #85862)

[Simon Pilgrim via cfe-commits]

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@@ -207,6 +207,8 @@ _mm256_div_ps(__m256 __a, __m256 __b)
 /// Compares two 256-bit vectors of [4 x double] and returns the greater
 ///    of each pair of values.
 ///
+///    If either value in a comparison is NaN, returns the value from \a __b.
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RKSimon wrote:

I don't think so either - we don't need to start explaining general fp comparison behaviour, just any x86/sse quirks.

https://github.com/llvm/llvm-project/pull/85862