i386: Improve V[48]QI shifts on AVX512/SSE4.1

i386: Improve V[48]QI shifts on AVX512/SSE4.1

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.

2024-05-10  Roger Sayle  <roger@nextmovesoftware.com>
	    Hongtao Liu  <hongtao.liu@intel.com>

gcc/ChangeLog
	* config/i386/i386-expand.cc (ix86_expand_vecop_qihi_partial):
	Don't attempt ix86_expand_vec_shift_qihi_constant on SSE4.1.

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.