[Bug target/96341] New: Support mixed element widths for AArch64 "omp declare simd" functions

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96341

            Bug ID: 96341
           Summary: Support mixed element widths for AArch64 "omp declare
                    simd" functions
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rsandifo at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64*-*-*

aarch64_simd_clone_compute_vecsize_and_simdlen currently rejects
functions that operate on a mixture of element sizes.  However,
the ABI has rules to handle those cases too.  See:

https://github.com/ARM-software/abi-aa/tree/master/vfabia64

for the full specification.  We should remove the current
restriction and handle mixed sizes in accordance with the
ABI rules.