Commits on Apr 3, 2024

1. Remove useless function multiversioning features …

   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

   

   andrewcarlotti committed Apr 3, 2024
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