[clang] [Headers][X86] Add rounding and exception notes to conversions (PR #83447)

[Phoebe Wang via cfe-commits]

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@@ -2211,7 +2213,12 @@ _mm256_cvtpd_ps(__m256d __a)
   return (__m128)__builtin_ia32_cvtpd2ps256((__v4df) __a);
 }
 
-/// Converts a vector of [8 x float] into a vector of [8 x i32].
+/// Converts a vector of [8 x float] into a vector of [8 x i32]. Rounds inexact
+///    results according to the rounding control bits in the MXCSR register.
+///
+///    If a converted value is larger than the maximum possible result,
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phoebewang wrote:

Not only larger than, considering the negative number.

https://github.com/llvm/llvm-project/pull/83447