The following one line patch improves the code generated for V8QI and V4QI
shifts when AV512BW and AVX512VL functionality is available.

For the testcase (from gcc.target/i386/vect-shiftv8qi.c):

typedef signed char v8qi __attribute__ ((__vector_size__ (8)));
v8qi foo (v8qi x) { return x >> 5; }

GCC with -O2 -march=cascadelake currently generates:

foo:    movl    $67372036, %eax
        vpsraw  $5, %xmm0, %xmm2
        vpbroadcastd    %eax, %xmm1
        movl    $117901063, %eax
        vpbroadcastd    %eax, %xmm3
        vmovdqa %xmm1, %xmm0
        vmovdqa %xmm3, -24(%rsp)
        vpternlogd      $120, -24(%rsp), %xmm2, %xmm0
        vpsubb  %xmm1, %xmm0, %xmm0
        ret

with this patch we now generate the much improved:

foo:    vpmovsxbw       %xmm0, %xmm0
        vpsraw  $5, %xmm0, %xmm0
        vpmovwb %xmm0, %xmm0
        ret

This patch also fixes the FAILs of gcc.target/i386/vect-shiftv[48]qi.c
when run with the additional -march=cascadelake flag, by splitting these
tests into two; one form testing code generation with -msse2 (and
-mno-avx512vl) as originally intended, and the other testing AVX512
code generation with an explicit -march=cascadelake.

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32}
with no new failures.  Ok for mainline?


2024-05-09  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        * config/i386/i386-expand.cc (ix86_expand_vecop_qihi_partial):
        Don't attempt ix86_expand_vec_shift_qihi_constant on AVX512.

gcc/testsuite/ChangeLog
        * gcc.target/i386/vect-shiftv4qi.c: Specify -mno-avx512vl.
        * gcc.target/i386/vect-shiftv8qi.c: Likewise.
        * gcc.target/i386/vect-shiftv4qi-2.c: New test case.
        * gcc.target/i386/vect-shiftv8qi-2.c: Likewise.


Thanks in advance,
Roger
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