i386: psrlq is not used for PERM<a,{0},1,2,3,4> [PR113871]

i386: psrlq is not used for PERM<a,{0},1,2,3,4> [PR113871]

Introduce vec_shl_<mode> and vec_shr_<mode> expanders to improve

	'*a = __builtin_shufflevector(*a, (vect64){0}, 1, 2, 3, 4);'

and
	'*a = __builtin_shufflevector((vect64){0}, *a, 3, 4, 5, 6);'

shuffles.  The generated code improves from:

	movzwl  6(%rdi), %eax
	movzwl  4(%rdi), %edx
	salq    $16, %rax
	orq     %rdx, %rax
	movzwl  2(%rdi), %edx
	salq    $16, %rax
	orq     %rdx, %rax
	movq    %rax, (%rdi)

to:
	movq    (%rdi), %xmm0
	psrlq   $16, %xmm0
	movq    %xmm0, (%rdi)

and to:
	movq    (%rdi), %xmm0
	psllq   $16, %xmm0
	movq    %xmm0, (%rdi)

in the second case.

The patch handles 32-bit vectors as well and improves generated code from:

	movd    (%rdi), %xmm0
	pxor    %xmm1, %xmm1
	punpcklwd       %xmm1, %xmm0
	pshuflw $230, %xmm0, %xmm0
	movd    %xmm0, (%rdi)

to:
	movd    (%rdi), %xmm0
	psrld   $16, %xmm0
	movd    %xmm0, (%rdi)

and to:
	movd    (%rdi), %xmm0
	pslld   $16, %xmm0
	movd    %xmm0, (%rdi)

	PR target/113871

gcc/ChangeLog:

	* config/i386/mmx.md (V248FI): New mode iterator.
	(V24FI_32): DItto.
	(vec_shl_<V248FI:mode>): New expander.
	(vec_shl_<V24FI_32:mode>): Ditto.
	(vec_shr_<V248FI:mode>): Ditto.
	(vec_shr_<V24FI_32:mode>): Ditto.
	* config/i386/sse.md (vec_shl_<V_128:mode>): Simplify expander.
	(vec_shr_<V248FI:mode>): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr113871-1a.c: New test.
	* gcc.target/i386/pr113871-1b.c: New test.
	* gcc.target/i386/pr113871-2a.c: New test.
	* gcc.target/i386/pr113871-2b.c: New test.
	* gcc.target/i386/pr113871-3a.c: New test.
	* gcc.target/i386/pr113871-3b.c: New test.
	* gcc.target/i386/pr113871-4a.c: New test.