[PATCH] NEON instructions were erroneously decoded from certain invalid encodings

[Artyom Skrobov]

Hello,

We have found that certain invalid encodings were erroneously decoded as NEON/Crypto instructions.
ThumbDisassembler::getInstruction didn't validate that an instruction's bits 26:27 are 11, before resetting them to 00 to match an ARM NEON encoding.

As an example:
==========
$ echo 0x00 0xfc 0x40 0x0c | llvm-mc -disassemble -triple thumbv8 -show-encoding
                .text
                sha256h.32         q0, q0, q0      @ encoding: [0x00,0xff,0x40,0x0c]
==========
Here, [0x00 0xfc 0x40 0x0c] has been decoded into an MCInst whose encoding is [0x00,0xff,0x40,0x0c].

OK to commit this fix?

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