Hi:
  For v{,p}expand* When mask is 0, -1, or has all all one bits in its
lower part, it can be optimized to simple mov or mask mov.
  Bootstrapped and regtested on x86_64-linux-gnu{-m32,}  and
x86_64-linux-gnu{m32\ -march=cascadelake,-m64\ -march=cascadelake},

gcc/ChangeLog:

        * config/i386/i386-builtin.def (BDESC): Adjust builtin name.
        * config/i386/sse.md (<avx512>_expand<mode>_mask): Rename to ..
        (expand<mode>_mask): this ..
        (*expand<mode>_mask): New pre_reload splitter to transform
        * v{,p}expand* to vmov* when mask is zero, all ones, or has
        all ones in its lower part, otherwise still generate v{,p}expand*.

gcc/testsuite/ChangeLog:

        * gcc.target/i386/avx512bw-pr100267-1.c: New test.
        * gcc.target/i386/avx512bw-pr100267-b-2.c: New test.
        * gcc.target/i386/avx512bw-pr100267-d-2.c: New test.
        * gcc.target/i386/avx512bw-pr100267-q-2.c: New test.
        * gcc.target/i386/avx512bw-pr100267-w-2.c: New test.
        * gcc.target/i386/avx512f-pr100267-1.c: New test.
        * gcc.target/i386/avx512f-pr100267-pd-2.c: New test.
        * gcc.target/i386/avx512f-pr100267-ps-2.c: New test.
        * gcc.target/i386/avx512vl-pr100267-1.c: New test.
        * gcc.target/i386/avx512vl-pr100267-pd-2.c: New test.
        * gcc.target/i386/avx512vl-pr100267-ps-2.c: New test.
        * gcc.target/i386/avx512vlbw-pr100267-1.c: New test.
        * gcc.target/i386/avx512vlbw-pr100267-b-2.c: New test.
        * gcc.target/i386/avx512vlbw-pr100267-d-2.c: New test.
        * gcc.target/i386/avx512vlbw-pr100267-q-2.c: New test.
        * gcc.target/i386/avx512vlbw-pr100267-w-2.c: New test.