[PATCH 2/2] [i386] For 128/256-bit vec_cond_expr, When mask operands is lt reg const0_rtx, blendv can be used instead of avx512 mask. [PR target/100648]

[Hongtao Liu via Gcc-patches]

Hi:
  This patch is about to add define_insn_and_split to convert avx512
mask mov back to pblendv instructions when mask operand is (lt: reg
const0_rtx).

  Bootstrapped and regtested on x86_64-linux-gnu{-m32,}.
  Ok for trunk?

gcc/ChangeLog:

        PR target/100648
        * config/i386/sse.md (*avx_cmp<mode>3_5): New
        define_insn_and_split.
        (*avx_cmp<mode>3_6): Ditto.
        (*avx2_pcmp<mode>3_3): Ditto.
        (*avx2_pcmp<mode>3_4): Ditto.
        (*avx2_pcmp<mode>3_5): Ditto.

gcc/testsuite/ChangeLog:

        PR target/100648
        * g++.target/i386/avx2-pr54700-2.C: Adjust testcase.
        * g++.target/i386/avx512vl-pr54700-1a.C: New test.
        * g++.target/i386/avx512vl-pr54700-1b.C: New test.
        * g++.target/i386/avx512vl-pr54700-2a.C: New test.
        * g++.target/i386/avx512vl-pr54700-2b.C: New test.
        * gcc.target/i386/avx512vl-pr100648.c: New test.