i386: More TImode parameter passing improvements.

i386: More TImode parameter passing improvements.

This patch is the next piece of a solution to the x86_64 ABI issues in
PR 88873.  This splits the *concat<mode><dwi>3_3 define_insn_and_split
into two patterns, a TARGET_64BIT *concatditi3_3 and a !TARGET_64BIT
*concatsidi3_3. This allows us to add an additional alternative to the
the 64-bit version, enabling the register allocator to perform this
operation using SSE registers, which is implemented/split after reload
using vec_concatv2di.

To demonstrate the improvement, the test case from PR88873:

typedef struct { double x, y; } s_t;

s_t foo (s_t a, s_t b, s_t c)
{
  return (s_t){ __builtin_fma(a.x, b.x, c.x), __builtin_fma (a.y, b.y, c.y) };
}

when compiled with -O2 -march=cascadelake, currently generates:

foo:	vmovq   %xmm2, -56(%rsp)
        movq    -56(%rsp), %rax
        vmovq   %xmm3, -48(%rsp)
        vmovq   %xmm4, -40(%rsp)
        movq    -48(%rsp), %rcx
        vmovq   %xmm5, -32(%rsp)
        vmovq   %rax, %xmm6
        movq    -40(%rsp), %rax
        movq    -32(%rsp), %rsi
        vpinsrq $1, %rcx, %xmm6, %xmm6
        vmovq   %xmm0, -24(%rsp)
        vmovq   %rax, %xmm7
        vmovq   %xmm1, -16(%rsp)
        vmovapd %xmm6, %xmm2
        vpinsrq $1, %rsi, %xmm7, %xmm7
        vfmadd132pd     -24(%rsp), %xmm7, %xmm2
        vmovapd %xmm2, -56(%rsp)
        vmovsd  -48(%rsp), %xmm1
        vmovsd  -56(%rsp), %xmm0
        ret

with this change, we avoid many of the reloads via memory,

foo:    vpunpcklqdq     %xmm3, %xmm2, %xmm7
        vpunpcklqdq     %xmm1, %xmm0, %xmm6
        vpunpcklqdq     %xmm5, %xmm4, %xmm2
        vmovdqa %xmm7, -24(%rsp)
        vmovdqa %xmm6, %xmm1
        movq    -16(%rsp), %rax
        vpinsrq $1, %rax, %xmm7, %xmm4
        vmovapd %xmm4, %xmm6
        vfmadd132pd     %xmm1, %xmm2, %xmm6
        vmovapd %xmm6, -24(%rsp)
        vmovsd  -16(%rsp), %xmm1
        vmovsd  -24(%rsp), %xmm0
        ret

2023-07-20  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386-expand.cc (ix86_expand_move): Don't call
	force_reg, to use SUBREG rather than create a new pseudo when
	inserting DFmode fields into TImode with insvti_{high,low}part.
	* config/i386/i386.md (*concat<mode><dwi>3_3): Split into two
	define_insn_and_split...
	(*concatditi3_3): 64-bit implementation.  Provide alternative
	that allows register allocation to use SSE registers that is
	split into vec_concatv2di after reload.
	(*concatsidi3_3): 32-bit implementation.

gcc/testsuite/ChangeLog
	* gcc.target/i386/pr88873.c: New test case.