i386: Two minor tweaks to ix86_expand_move.

i386: Two minor tweaks to ix86_expand_move.

This patch splits out two (independent) minor changes to i386-expand.cc's
ix86_expand_move from a larger patch, given that it's better to review
and commit these independent pieces separately from a more complex patch.

The first change is to test for CONST_WIDE_INT_P before calling
ix86_convert_const_wide_int_to_broadcast.  Whilst stepping through
this function in gdb, I was surprised that the code was continually
jumping into this function with operands that obviously weren't
appropriate.

The second change is to generalize the optimization for efficiently
moving a TImode value to V1TImode (via V2DImode), to cover all 128-bit
vector modes.

Hence for the test case:

typedef unsigned long uv2di __attribute__ ((__vector_size__ (16)));
uv2di foo2(__int128 x) { return (uv2di)x; }

we'd previously move via memory with:

foo2:   movq    %rdi, -24(%rsp)
        movq    %rsi, -16(%rsp)
        movdqa  -24(%rsp), %xmm0
        ret

with this patch we now generate with -O2 (the same as V1TImode):

foo2:   movq    %rdi, %xmm0
        movq    %rsi, %xmm1
        punpcklqdq      %xmm1, %xmm0
        ret

and with -O2 -msse4 the even better:

foo2:   movq    %rdi, %xmm0
        pinsrq  $1, %rsi, %xmm0
        ret

The new test case is unimaginatively called sse2-v1ti-mov-2.c given
the original test case just for V1TI mode was called sse2-v1ti-mov-1.c.

2023-06-17  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386-expand.cc (ix86_expand_move): Check that OP1 is
	CONST_WIDE_INT_P before calling ix86_convert_wide_int_to_broadcast.
	Generalize special case for converting TImode to V1TImode to handle
	all 128-bit vector conversions.

gcc/testsuite/ChangeLog
	* gcc.target/i386/sse2-v1ti-mov-2.c: New test case.