[X86] NFCI : Comment updation for EVEX to VEX translation.

[jbhateja]

• Updating comment

lib/Target/X86/X86EvexToVex.cpp

 //===- X86EvexToVex.cpp ---------------------------------------------------===//
 // Compress EVEX instructions to VEX encoding when possible to reduce code size
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 /// \file
 /// This file defines the pass that goes over all AVX-512 instructions which
 /// are encoded using the EVEX prefix and if possible replaces them by their
 /// corresponding VEX encoding which is usually shorter by 2 bytes.
 /// EVEX instructions may be encoded via the VEX prefix when the AVX-512
-/// instruction has a corresponding AVX/AVX2 opcode and when it does not
-/// use the xmm or the mask registers or xmm/ymm registers with indexes
-/// higher than 15.
+/// instruction has a corresponding AVX/AVX2 opcode, when vector length 
+/// accessed by instruction is less than 512 bits and when it does not use 
+//  the xmm or the mask registers or xmm/ymm registers with indexes higher than 15.
 /// The pass applies code reduction on the generated code for AVX-512 instrs.
 //
 //===----------------------------------------------------------------------===//
 
 #include "MCTargetDesc/X86BaseInfo.h"
 #include "MCTargetDesc/X86InstComments.h"
 #include "X86.h"
 #include "X86InstrInfo.h"