i386: More use of m{32,64}bcst addressing modes with ternlog.

i386: More use of m{32,64}bcst addressing modes with ternlog.

This patch makes more use of m32bcst and m64bcst addressing modes in
ix86_expand_ternlog.  Previously, the i386 backend would only consider
using a m32bcst if the inner mode of the vector was 32-bits, or using
m64bcst if the inner mode was 64-bits.  For ternlog (and other logic
operations) this is a strange restriction, as how the same constant
is materialized is dependent upon the mode it is used/operated on.
Hence, the V16QI constant {2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2} wouldn't
use m??bcst, but (V4SI){0x02020202,0x02020202,0x02020202,0x02020202}
which has the same bit pattern would.  This can optimized by (re)checking
whether a CONST_VECTOR can be broadcast from memory after casting it
to VxSI (or for m64bst to VxDI) where x has the appropriate vector size.

Taking the test case from pr115407:

__attribute__((__vector_size__(64))) char v;
void foo() {
  v = v | v << 7;
}

Compiled with -O2 -mcmodel=large -mavx512bw
GCC 14 generates a 64-byte (512-bit) load from the constant pool:

foo:	movabsq $v, %rax				// 10
        movabsq $.LC0, %rdx				// 10
        vpsllw  $7, (%rax), %zmm1			// 7
        vmovdqa64       (%rax), %zmm0			// 6
        vpternlogd      $248, (%rdx), %zmm1, %zmm0	// 7
        vmovdqa64       %zmm0, (%rax)			// 6
        vzeroupper					// 3
        ret						// 1
.LC0:	.byte   -12					// 64 = 114 bytes
	.byte	-128
	;; repeated another 62 times

mainline currently generates two instructions, using interunit broadcast:

foo:	movabsq $v, %rdx				// 10
        movl    $-2139062144, %eax			// 5
        vmovdqa64       (%rdx), %zmm2			// 6
        vpbroadcastd    %eax, %zmm0			// 6
        vpsllw  $7, %zmm2, %zmm1			// 7
        vpternlogd      $236, %zmm0, %zmm2, %zmm1	// 7
        vmovdqa64       %zmm1, (%rdx)			// 6
        vzeroupper					// 3
        ret						// 1 = 51 bytes

With this patch, we now generate a broadcast addressing mode:

foo:	movabsq $v, %rax				   // 10
        movabsq $.LC1, %rdx				   // 10
        vmovdqa64       (%rax), %zmm1			   // 6
        vpsllw  $7, %zmm1, %zmm0			   // 7
        vpternlogd      $236, (%rdx){1to16}, %zmm1, %zmm0  // 7
        vmovdqa64       %zmm0, (%rax)			   // 6
        vzeroupper					   // 3
        ret						   // 1 = 50 total

Without -mcmodel=large, the benefit is two instructions:

foo:	vmovdqa64       v(%rip), %zmm1			       // 10
        vpsllw  $7, %zmm1, %zmm0			       // 7
        vpternlogd      $236, .LC2(%rip){1to16}, %zmm1, %zmm0  // 11
        vmovdqa64       %zmm0, v(%rip)			       // 10
        vzeroupper					       // 3
        ret						       // 1 = 42 total

2024-06-14  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386-expand.cc (ix86_expand_ternlog): Try performing
	logic operation in a different vector mode if that enables use of
	a 32-bit or 64-bit broadcast addressing mode.

gcc/testsuite/ChangeLog
	* gcc.target/i386/pr115407.c: New test case.