Rewrite ix86_expand_vecop_qihi2 to expand fo 2x-wider (e.g. V16QI -> V16HImode)
instructions when available.  Currently, the compiler generates following
assembly for V16QImode multiplication (-mavx2):

    vpunpcklbw      %xmm0, %xmm0, %xmm3
    vpunpcklbw      %xmm1, %xmm1, %xmm2
    vpunpckhbw      %xmm0, %xmm0, %xmm0
    movl    $255, %eax
    vpunpckhbw      %xmm1, %xmm1, %xmm1
    vpmullw %xmm3, %xmm2, %xmm2
    vmovd   %eax, %xmm3
    vpmullw %xmm0, %xmm1, %xmm1
    vpbroadcastw    %xmm3, %xmm3
    vpand   %xmm2, %xmm3, %xmm0
    vpand   %xmm1, %xmm3, %xmm3
    vpackuswb       %xmm3, %xmm0, %xmm0

and only with -mavx512bw -mavx512vl generates:

    vpmovzxbw       %xmm1, %ymm1
    vpmovzxbw       %xmm0, %ymm0
    vpmullw %ymm1, %ymm0, %ymm0
    vpmovwb %ymm0, %xmm0

Patched compiler generates more optimized code involving multiplication
in 2x-wider mode in cases where missing truncate instruction has to be
emulated with a permutation (-mavx2):

    vpmovzxbw       %xmm0, %ymm0
    vpmovzxbw       %xmm1, %ymm1
    movl    $255, %eax
    vpmullw %ymm1, %ymm0, %ymm1
    vmovd   %eax, %xmm0
    vpbroadcastw    %xmm0, %ymm0
    vpand   %ymm1, %ymm0, %ymm0
    vpackuswb       %ymm0, %ymm0, %ymm0
    vpermq  $216, %ymm0, %ymm0

The patch also adjusts cost calculation of V*QImode emulations to account
for generation of 2x-wider mode instructions.

gcc/ChangeLog:

    * config/i386/i386-expand.cc (ix86_expand_vecop_qihi2):
    Rewrite to expand to 2x-wider (e.g. V16QI -> V16HImode)
    instructions when available.  Emulate truncation via
    ix86_expand_vec_perm_const_1 when native truncate insn
    is not available.
    (ix86_expand_vecop_qihi_partial) <case MULT>: Use pmovzx
    when available.  Trivially rename some variables.
    (ix86_expand_vecop_qihi): Unconditionally call ix86_expand_vecop_qihi2.
    * config/i386/i386.cc (ix86_multiplication_cost): Rewrite cost
    calculation of V*QImode emulations to account for generation of
    2x-wider mode instructions.
    (ix86_shift_rotate_cost): Update cost calculation of V*QImode
    emulations to account for generation of 2x-wider mode instructions.

gcc/testsuite/ChangeLog:

    * gcc.target/i386/avx512vl-pr95488-1.c: Revert 2023-05-18 change.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Uros.