[FMV] Unify aes with pmull and sve2-aes with sve2-pmull128.

[labrinea]

I originally tried splitting these features (see relevant pull request llvm/llvm-project#110816), but the following came to my attention:

According to https://developer.arm.com/documentation/ddi0487/latest Arm Architecture Reference Manual for A-profile architecture:

D23.2.83 ID_AA64ZFR0_EL1, SVE Feature ID Register 0

ID_AA64ZFR0_EL1.AES, bits [7:4]

FEAT_SVE_AES implements the functionality identified by the value 0b0001.
FEAT_SVE_PMULL128 implements the functionality identified by the value 0b0010.
The permitted values are 0b0000 and 0b0010.

Andrew Carlotti suggests that the same applies for ID_AA64ISAR0_EL1.AES (llvm/llvm-project#110816 (comment))

D19.2.61 ID_AA64ISAR0_EL1, AArch64 Instruction Set Attribute Register 0

ID_AA64ISAR0_EL1.AES, bits [7:4]

FEAT_AES implements the functionality identified by the value 0b0001.
FEAT_PMULL implements the functionality identified by the value 0b0010.
From Armv8, the permitted values are 0b0000 and 0b0010.

This was removed from the latest release of the Arm Architecture Reference Manual, but it appears to be a mistake that was not intended to relax the architecture constraints. The discrepancy has been reported.

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[labrinea]

@vhscampos @andrewcarlotti @tmatheson-arm

[labrinea]

Ping

[DanielKristofKiss]

IMHO from the user(developer) point of view the 'pmull' feature could be useful outside of aes so in cases it could be more expressive to say pmull instead of aes when really only pmull is used actually from the feature set.
(it would be fine if that is just an alias to aes internally)

[andrewcarlotti]

This looks good to me. I don't think there's any point creating aliases when the corresponding command line flags have existed without any need for aliases for many years.

[labrinea]

This case is similar to feat_sha1 and feat_sha256 (you can't have one without having the other), which we decided to unify: #347. I think we should do the same here.

[tmatheson-arm]

This case is similar to feat_sha1 and feat_sha256 (you can't have one without having the other), which we decided to unify: #347. I think we should do the same here.

Agree, now that we have set the precedent for keeping FMV aligned with the command line options, we should stick with it. If a need arises for specifying pmull without aes then they can be added to both (command line and FMV) later.