Improved Scalar-To-Vector (STV) support for TImode to V1TImode on x86_64.

Improved Scalar-To-Vector (STV) support for TImode to V1TImode on x86_64.

This patch upgrades x86_64's scalar-to-vector (STV) pass to more
aggressively transform 128-bit scalar TImode operations into vector
V1TImode operations performed on SSE registers.  TImode functionality
already exists in STV, but only for move operations.  This change
brings support for logical operations (AND, IOR, XOR, NOT and ANDN)
and comparisons.

The effect of these changes are conveniently demonstrated by the new
sse4_1-stv-5.c test case:

__int128 a[16];
__int128 b[16];
__int128 c[16];

void foo()
{
  for (unsigned int i=0; i<16; i++)
    a[i] = b[i] & ~c[i];
}

which when currently compiled on mainline wtih -O2 -msse4 produces:

foo:    xorl    %eax, %eax
.L2:    movq    c(%rax), %rsi
        movq    c+8(%rax), %rdi
        addq    $16, %rax
        notq    %rsi
        notq    %rdi
        andq    b-16(%rax), %rsi
        andq    b-8(%rax), %rdi
        movq    %rsi, a-16(%rax)
        movq    %rdi, a-8(%rax)
        cmpq    $256, %rax
        jne     .L2
        ret

but with this patch now produces:

foo:    xorl    %eax, %eax
.L2:    movdqa  c(%rax), %xmm0
        pandn   b(%rax), %xmm0
        addq    $16, %rax
        movaps  %xmm0, a-16(%rax)
        cmpq    $256, %rax
        jne     .L2
        ret

Technically, the STV pass is implemented by three C++ classes, a common
abstract base class "scalar_chain" that contains common functionality,
and two derived classes: general_scalar_chain (which handles SI and
DI modes) and timode_scalar_chain (which handles TI modes).  As
mentioned previously, because only TI mode moves were handled the
two worker classes behaved significantly differently.  These changes
bring the functionality of these two classes closer together, which
is reflected by refactoring more shared code from general_scalar_chain
to the parent scalar_chain and reusing it from timode_scalar_chain.
There still remain significant differences (and simplifications) so
the existing division of classes (as specializations) continues to
make sense.

2022-07-11  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386-features.h (scalar_chain): Add fields
	insns_conv, n_sse_to_integer and n_integer_to_sse to this
	parent class, moved from general_scalar_chain.
	(scalar_chain::convert_compare): Protected method moved
	from general_scalar_chain.
	(mark_dual_mode_def): Make protected, not private virtual.
	(scalar_chain:convert_op): New private virtual method.

	(general_scalar_chain::general_scalar_chain): Simplify constructor.
	(general_scalar_chain::~general_scalar_chain): Delete destructor.
	(general_scalar_chain): Move insns_conv, n_sse_to_integer and
	n_integer_to_sse fields to parent class, scalar_chain.
	(general_scalar_chain::mark_dual_mode_def): Delete prototype.
	(general_scalar_chain::convert_compare): Delete prototype.

	(timode_scalar_chain::compute_convert_gain): Remove simplistic
	implementation, convert to a method prototype.
	(timode_scalar_chain::mark_dual_mode_def): Delete prototype.
	(timode_scalar_chain::convert_op): Prototype new virtual method.

	* config/i386/i386-features.cc (scalar_chain::scalar_chain):
	Allocate insns_conv and initialize n_sse_to_integer and
	n_integer_to_sse fields in constructor.
	(scalar_chain::scalar_chain): Free insns_conv in destructor.

	(general_scalar_chain::general_scalar_chain): Delete
	constructor, now defined in the class declaration.
	(general_scalar_chain::~general_scalar_chain): Delete destructor.

	(scalar_chain::mark_dual_mode_def): Renamed from
	general_scalar_chain::mark_dual_mode_def.
	(timode_scalar_chain::mark_dual_mode_def): Delete.
	(scalar_chain::convert_compare): Renamed from
	general_scalar_chain::convert_compare.

	(timode_scalar_chain::compute_convert_gain): New method to
	determine the gain from converting a TImode chain to V1TImode.
	(timode_scalar_chain::convert_op): New method to convert an
	operand from TImode to V1TImode.

	(timode_scalar_chain::convert_insn) <case REG>: Only PUT_MODE
	on REG_EQUAL notes that were originally TImode (not CONST_INT).
	Handle AND, ANDN, XOR, IOR, NOT and COMPARE.
	(timode_mem_p): Helper predicate to check where operand is
	memory reference with sufficient alignment for TImode STV.
	(timode_scalar_to_vector_candidate_p): Use convertible_comparison_p
	to check whether COMPARE is convertible.  Handle SET_DESTs that
	that are REG_P or MEM_P and SET_SRCs that are REG, CONST_INT,
	CONST_WIDE_INT, MEM, AND, ANDN, IOR, XOR or NOT.

gcc/testsuite/ChangeLog
	* gcc.target/i386/sse4_1-stv-2.c: New test case, pand.
	* gcc.target/i386/sse4_1-stv-3.c: New test case, por.
	* gcc.target/i386/sse4_1-stv-4.c: New test case, pxor.
	* gcc.target/i386/sse4_1-stv-5.c: New test case, pandn.
	* gcc.target/i386/sse4_1-stv-6.c: New test case, ptest.