Hi,

This patch changes aarch64_expand_vector_init to use rtx_vector_builder,
exploiting it's internal pattern detection to find 'dup' patterns.

Bootstrapped and regression tested on aarch64-none-linux-gnu.

Is this OK for trunk or should we wait for the rest of the series?

gcc/ChangeLog:
2022-08-05  Andre Vieira  <andre.simoesdiasvieira@arm.com>

         * config/aarch64/aarch64.cc (aarch64_vec_duplicate): New.
          (aarch64_expand_vector_init): Make the existing variant construct
          a rtx_vector_builder from the list of elements and use this to 
detect
          duplicate patterns.

gcc/testesuite/ChangeLog:
2022-08-05  Andre Vieira  <andre.simoesdiasvieira@arm.com>

         * gcc.target/aarch64/ldp_stp_16.c: Modify to reflect code change.