[LangRef] Mention vector support for bitreverse/bswap intrinsics (PR38012)

[spatel]

LGTM - see inline for some wording/grammar nits.

docs/LangRef.rst

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integers values -> integer values

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perform -> operate?

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Run-on sentence: change comma after 'basis' to period or semi-colon.

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...family of intrinsics is used to byte swap an integer value or vector of integer values...

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...operations on data that are not...

Or just remove that sentence? Doesn't add much value IMO.

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Run-on sentence: change comma after 'basis' to period or semi-colon.

llvm/trunk/docs/LangRef.rst

 This is an overloaded intrinsic function. You can use bitreverse on any
 integer type.
 
 ::
 
       declare i16 @llvm.bitreverse.i16(i16 <id>)
       declare i32 @llvm.bitreverse.i32(i32 <id>)
       declare i64 @llvm.bitreverse.i64(i64 <id>)
+      declare <4 x i32> @llvm.bitreverse.v4i32(<4 x i32> <id>)
 
 Overview:
 """""""""
 
 The '``llvm.bitreverse``' family of intrinsics is used to reverse the
-bitpattern of an integer value; for example ``0b10110110`` becomes
-``0b01101101``.
+bitpattern of an integer value or vector of integer values; for example
+``0b10110110`` becomes ``0b01101101``.
 
 Semantics:
 """"""""""
 
 The ``llvm.bitreverse.iN`` intrinsic returns an iN value that has bit
-``M`` in the input moved to bit ``N-M`` in the output.
+``M`` in the input moved to bit ``N-M`` in the output. The vector
+intrinsics, such as ``llvm.bitreverse.v4i32``, operate on a per-element
+basis and the element order is not affected.
 
 '``llvm.bswap.*``' Intrinsics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Syntax:
 """""""
 
 This is an overloaded intrinsic function. You can use bswap on any
 integer type that is an even number of bytes (i.e. BitWidth % 16 == 0).
 
 ::
 
       declare i16 @llvm.bswap.i16(i16 <id>)
       declare i32 @llvm.bswap.i32(i32 <id>)
       declare i64 @llvm.bswap.i64(i64 <id>)
+      declare <4 x i32> @llvm.bswap.v4i32(<4 x i32> <id>)
 
 Overview:
 """""""""
 
-The '``llvm.bswap``' family of intrinsics is used to byte swap integer
-values with an even number of bytes (positive multiple of 16 bits).
-These are useful for performing operations on data that is not in the
-target's native byte order.
+The '``llvm.bswap``' family of intrinsics is used to byte swap an integer
+value or vector of integer values with an even number of bytes (positive
+multiple of 16 bits).
 
 Semantics:
 """"""""""
 
 The ``llvm.bswap.i16`` intrinsic returns an i16 value that has the high
 and low byte of the input i16 swapped. Similarly, the ``llvm.bswap.i32``
 intrinsic returns an i32 value that has the four bytes of the input i32
 swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the
 returned i32 will have its bytes in 3, 2, 1, 0 order. The
 ``llvm.bswap.i48``, ``llvm.bswap.i64`` and other intrinsics extend this
 concept to additional even-byte lengths (6 bytes, 8 bytes and more,
-respectively).
+respectively). The vector intrinsics, such as ``llvm.bswap.v4i32``,
+operate on a per-element basis and the element order is not affected.
 
 '``llvm.ctpop.*``' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Syntax:
 """""""
 
 This is an overloaded intrinsic. You can use llvm.ctpop on any integer