Supporting a feature in function multiversioning requires that the rest of the toolchain can support enabling the feature. In GCC/Binutils, this requires either that there is an equivalent feature extension available in the -march command line option, or that the feature introduces no new instructions (and therefore does not need to be enabled when passing to the assembler). However, many of the features listed in in the original function multiversioning specification do not meet this criteria. These fall into four categories:

1. Features that were originally linked to a specific architecture version (fcma, jscvt, frintts, flagm2, wfxt, rcpc2): these should get their own flags across the toolchain (and I've already added this support in Binutils).

2. Features that are combined with other features in existing command line options: these should also be merged in the function multiversioning specification.

3. Features that indicate support for hint instructions: these can be dropped, since the instructions can be used unconditionally.

4. Features that enable existing instruction behaviour to be changed when a system register flag is set: the function multiversioning resolvers don't check for runtime enablement of the control flags, so this isn't a suitable way of exploiting the behaviour enabled by those flags.

5. Features that can also be expressed as a combination of two other features.

We therefore remove support for the following features from the specification:

• sha1 (2): included within +sha2
• pmull (2): included within +aes
• dit (4)
• dgh (3)
• ebf16 (4)
• sve-bf16 (5)
• sve-ebf16 (4)
• sve-i8mm (5)
• sve2-pmull128 (2): included within +sve2-aes
• memtag2 (2): included within +memtag
• memtag3 (4)
• ssbs2 (2): included within +ssbs
• bti (3)
• ls64_v, ls64_accdata (2): included within +ls64

name: Pull request
about: Technical issues, document format problems, bugs in scripts or feature proposal.

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