use consistent wording around the 'undefined' intrinsics, and slightly expand their docs

Author: RalfJung

crates/core_arch/src/x86/avx.rs

@@ -2815,8 +2815,9 @@ pub fn _mm256_zextpd128_pd256(a: __m128d) -> __m256d {
 }
 
 /// Returns vector of type `__m256` with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm256_undefined_ps)
 #[inline]
@@ -2828,8 +2829,9 @@ pub fn _mm256_undefined_ps() -> __m256 {
 }
 
 /// Returns vector of type `__m256d` with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm256_undefined_pd)
 #[inline]
@@ -2841,8 +2843,9 @@ pub fn _mm256_undefined_pd() -> __m256d {
 }
 
 /// Returns vector of type __m256i with with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm256_undefined_si256)
 #[inline]

crates/core_arch/src/x86/avx512f.rs

@@ -33746,8 +33746,9 @@ pub fn _mm512_mask_reduce_or_epi64(k: __mmask8, a: __m512i) -> i64 {
 }
 
 /// Returns vector of type `__m512d` with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm512_undefined_pd)
 #[inline]
@@ -33759,8 +33760,9 @@ pub fn _mm512_undefined_pd() -> __m512d {
 }
 
 /// Returns vector of type `__m512` with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm512_undefined_ps)
 #[inline]
@@ -33772,8 +33774,9 @@ pub fn _mm512_undefined_ps() -> __m512 {
 }
 
 /// Return vector of type __m512i with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm512_undefined_epi32&expand=5995)
 #[inline]
@@ -33785,8 +33788,9 @@ pub fn _mm512_undefined_epi32() -> __m512i {
 }
 
 /// Return vector of type __m512 with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm512_undefined&expand=5994)
 #[inline]

crates/core_arch/src/x86/avx512fp16.rs

@@ -262,8 +262,10 @@ pub fn _mm512_setzero_ph() -> __m512h {
     unsafe { transmute(f16x32::ZERO) }
 }
 
-/// Return vector of type `__m128h` with undefined elements. In practice, this returns the all-zero
-/// vector.
+/// Return vector of type `__m128h` with indetermination elements.
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_mm_undefined_ph)
 #[inline]
@@ -273,8 +275,10 @@ pub fn _mm_undefined_ph() -> __m128h {
     unsafe { transmute(f16x8::ZERO) }
 }
 
-/// Return vector of type `__m256h` with undefined elements. In practice, this returns the all-zero
-/// vector.
+/// Return vector of type `__m256h` with indetermination elements.
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_mm256_undefined_ph)
 #[inline]
@@ -284,8 +288,10 @@ pub fn _mm256_undefined_ph() -> __m256h {
     unsafe { transmute(f16x16::ZERO) }
 }
 
-/// Return vector of type `__m512h` with undefined elements. In practice, this returns the all-zero
-/// vector.
+/// Return vector of type `__m512h` with indetermination elements.
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_mm512_undefined_ph)
 #[inline]

crates/core_arch/src/x86/sse.rs

@@ -1884,9 +1884,10 @@ pub unsafe fn _mm_prefetch<const STRATEGY: i32>(p: *const i8) {
     prefetch(p, (STRATEGY >> 2) & 1, STRATEGY & 3, 1);
 }
 
-/// Returns vector of type __m128 with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Returns vector of type __m128 with indeterminate elements.with indetermination elements.
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm_undefined_ps)
 #[inline]

crates/core_arch/src/x86/sse2.rs

@@ -2956,9 +2956,10 @@ pub fn _mm_castsi128_ps(a: __m128i) -> __m128 {
     unsafe { transmute(a) }
 }
 
-/// Returns vector of type __m128d with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Returns vector of type __m128d with indeterminate elements.with indetermination elements.
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm_undefined_pd)
 #[inline]
@@ -2968,9 +2969,10 @@ pub fn _mm_undefined_pd() -> __m128d {
     const { unsafe { mem::zeroed() } }
 }
 
-/// Returns vector of type __m128i with indeterminate elements.
-/// Despite being "undefined", this is some valid value and not equivalent to [`mem::MaybeUninit`].
-/// In practice, this is equivalent to [`mem::zeroed`].
+/// Returns vector of type __m128i with indeterminate elements.with indetermination elements.
+/// Despite using the word "undefined" (following Intel's naming scheme), this non-deterministically
+/// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
+/// In practice, this is typically equivalent to [`mem::zeroed`].
 ///
 /// [Intel's documentation](https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm_undefined_si128)
 #[inline]