[documentation] Added Documentation for 'neg' unary operations

[ayushi-8102]

Summary

This patch fixes https://github.com/llvm/llvm-project/issues/19751

[craig.topper]

As noted in the PR. There is no neg instruction.

[samtebbs]

Since the instructions don't exist now, would you mind abandoning this revision? It should be an option in the right sidebar.

[ayushi-8102]

Yeah Sure I will mark it as abandoned.

llvm/docs/LangRef.rst

 Unary Operations
 -----------------
 
 Unary operators require a single operand, execute an operation on
 it, and produce a single value. The operand might represent multiple
 data, as is the case with the :ref:`vector <t_vector>` data type. The
 result value has the same type as its operand.
 
+.. _i_neg:
+
+'``neg``' Instruction
+^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+     <result> = neg [nsw] [nuw] <ty> <op1> ; yields ty:result
+
+
+Overview:
+"""""""""
+
+The 'neg' instruction is a standard instruction that performs a two's complement negation operation on an integer value.
+
+The 'neg' instruction takes a single operand, which must be an integer value, and returns its negation.
+
+
+Arguments:
+""""""""""
+
+The argument to the '``neg``' instruction must be a
+:ref:`integer-value< <t_integer>` or :ref:`vector <t_vector>`.
+
+
+Semantics:
+""""""""""
+
+For a constant integer operand, the 'neg' instruction computes the two's complement negation of the operand and returns the result as a constant integer.
+
+
+For a register or variable integer operand, the 'neg' instruction computes the two's complement negation of the operand and stores the result in the destination register or variable.
+
+
+Example:
+""""""""
+
+.. code-block:: text
+
+     <result> = neg int %val          ; yields int:result = -%var
+
 .. _i_fneg:
 
 '``fneg``' Instruction
 ^^^^^^^^^^^^^^^^^^^^^^
 
 Syntax:
 """""""