On Tue, 8 Oct 2024, Jakub Jelinek wrote:
> On Mon, Oct 07, 2024 at 10:32:57AM +0200, Richard Biener wrote:
> > > They are implementation defined, -1, 0, 1, 2 is defined by libstdc++:
> > > using type = signed char;
> > > enum class _Ord : type { equivalent = 0, less = -1, greater = 1 };
> > > enum class _Ncmp : type { _Unordered = 2 };
> > > https://eel.is/c++draft/cmp#categories.pre-1 documents them as
> > > enum class ord { equal = 0, equivalent = equal, less = -1, greater = 1 };
> > > // exposition only
> > > enum class ncmp { unordered = -127 };
> > > // exposition only
> > > and now looking at it, LLVM's libc++ takes that literally and uses
> > > -1, 0, 1, -127. One can't use <=> operator without including <compare>
> > > which provides the enums, so I think if all we care about is libstdc++,
> > > then just hardcoding -1, 0, 1, 2 is fine, if we want to also optimize
> > > libc++ when used with gcc, we could support -1, 0, 1, -127 as another
> > > option.
> > > Supporting arbitrary 4 values doesn't make sense, at least on x86 the
> > > only reason to do the conversion to int in an optab is a good sequence
> > > to turn the flag comparisons to -1, 0, 1. So, either we do nothing
> > > more than the patch, or add handle both 2 and -127 for unordered,
> > > or add support for arbitrary value for the unordered case except
> > > -1, 0, 1 (then -1 could mean signed int, 1 unsigned int, 0 do the jumps
> > > and any other value what should be returned for unordered.
>
> Here is an incremental patch which adds support for (almost) arbitrary
> unordered constant value. It changes the .SPACESHIP and spaceship<mode>4
> optab conventions, so 0 means use branches, floating point, -1, 0, 1, 2
> results consumed by tree-ssa-math-opts.cc emitted comparisons, -1
> means signed int comparisons, -1, 0, 1 results, 1 means unsigned int
> comparisons, -1, 0, 1 results, and for constant other than -1, 0, 1
> which fit into [-128, 127] converted to the PHI type are otherwise
> specified as the last argument (then it is -1, 0, 1, C results).
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
LGTM, please give others some time to comment.
Thanks,
Richard.
> 2024-10-08 Jakub Jelinek <[email protected]>
>
> PR middle-end/116896
> * tree-ssa-math-opts.cc (optimize_spaceship): Handle unordered values
> other than 2, but they still need to be signed char range possibly
> converted to the PHI result and can't be in [-1, 1] range. Use
> last .SPACESHIP argument of 1 for unsigned int comparisons, -1 for
> signed int, 0 for floating point branches and any other for floating
> point with that value as unordered.
> * config/i386/i386-expand.cc (ix86_expand_fp_spaceship): Use op2 rather
> const2_rtx if op2 is not const0_rtx for unordered result.
> (ix86_expand_int_spaceship): Change INTVAL (op2) == 1 tests to
> INTVAL (op2) != -1.
> * doc/md.texi (spaceship@var{m}4): Document the above changes.
>
> * gcc.target/i386/pr116896.c: New test.
>
> --- gcc/tree-ssa-math-opts.cc.jj 2024-10-07 11:37:46.576977487 +0200
> +++ gcc/tree-ssa-math-opts.cc 2024-10-07 14:23:12.918608708 +0200
> @@ -6023,11 +6023,12 @@ optimize_spaceship (gcond *stmt)
>
> /* Check if there is a single bb into which all failed conditions
> jump to (perhaps through an empty block) and if it results in
> - a single integral PHI which just sets it to -1, 0, 1, 2
> + a single integral PHI which just sets it to -1, 0, 1, X
> (or -1, 0, 1 when NaNs can't happen). In that case use 1 rather
> than 0 as last .SPACESHIP argument to tell backends it might
> consider different code generation and just cast the result
> - of .SPACESHIP to the PHI result. */
> + of .SPACESHIP to the PHI result. X above is some value
> + other than -1, 0, 1, for libstdc++ 2, for libc++ -127. */
> tree arg3 = integer_zero_node;
> edge e = EDGE_SUCC (bb0, 0);
> if (e->dest == bb1)
> @@ -6054,6 +6055,7 @@ optimize_spaceship (gcond *stmt)
> && integer_zerop (gimple_phi_arg_def_from_edge (phi, e))
> && EDGE_COUNT (bbp->preds) == (HONOR_NANS (TREE_TYPE (arg1)) ? 4 : 3))
> {
> + HOST_WIDE_INT argval = SCALAR_FLOAT_TYPE_P (TREE_TYPE (arg1)) ? 2 : -1;
> for (unsigned i = 0; phi && i < EDGE_COUNT (bbp->preds) - 1; ++i)
> {
> edge e3 = i == 0 ? e1 : i == 1 ? em1 : e2;
> @@ -6071,16 +6073,29 @@ optimize_spaceship (gcond *stmt)
> tree a = gimple_phi_arg_def_from_edge (phi, e3);
> if (TREE_CODE (a) != INTEGER_CST
> || (i == 0 && !integer_onep (a))
> - || (i == 1 && !integer_all_onesp (a))
> - || (i == 2 && wi::to_widest (a) != 2))
> + || (i == 1 && !integer_all_onesp (a)))
> {
> phi = NULL;
> break;
> }
> + if (i == 2)
> + {
> + tree minv = TYPE_MIN_VALUE (signed_char_type_node);
> + tree maxv = TYPE_MAX_VALUE (signed_char_type_node);
> + widest_int w = widest_int::from (wi::to_wide (a), SIGNED);
> + if ((w >= -1 && w <= 1)
> + || w < wi::to_widest (minv)
> + || w > wi::to_widest (maxv))
> + {
> + phi = NULL;
> + break;
> + }
> + argval = w.to_shwi ();
> + }
> }
> if (phi)
> arg3 = build_int_cst (integer_type_node,
> - TYPE_UNSIGNED (TREE_TYPE (arg1)) ? 2 : 1);
> + TYPE_UNSIGNED (TREE_TYPE (arg1)) ? 1 : argval);
> }
>
> /* For integral <=> comparisons only use .SPACESHIP if it is turned
> @@ -6094,11 +6109,18 @@ optimize_spaceship (gcond *stmt)
> gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
> gsi_insert_before (&gsi, gc, GSI_SAME_STMT);
>
> - wide_int wm1 = wi::minus_one (TYPE_PRECISION (integer_type_node));
> - wide_int w2 = (HONOR_NANS (TREE_TYPE (arg1))
> - ? wi::two (TYPE_PRECISION (integer_type_node))
> - : wi::one (TYPE_PRECISION (integer_type_node)));
> - int_range<1> vr (TREE_TYPE (lhs), wm1, w2);
> + wide_int wmin = wi::minus_one (TYPE_PRECISION (integer_type_node));
> + wide_int wmax = wi::one (TYPE_PRECISION (integer_type_node));
> + if (HONOR_NANS (TREE_TYPE (arg1)))
> + {
> + if (arg3 == integer_zero_node)
> + wmax = wi::two (TYPE_PRECISION (integer_type_node));
> + else if (tree_int_cst_sgn (arg3) < 0)
> + wmin = wi::to_wide (arg3);
> + else
> + wmax = wi::to_wide (arg3);
> + }
> + int_range<1> vr (TREE_TYPE (lhs), wmin, wmax);
> set_range_info (lhs, vr);
>
> if (arg3 != integer_zero_node)
> --- gcc/config/i386/i386-expand.cc.jj 2024-10-07 11:37:46.286981563 +0200
> +++ gcc/config/i386/i386-expand.cc 2024-10-07 14:02:05.798392986 +0200
> @@ -3234,7 +3234,7 @@ ix86_expand_fp_spaceship (rtx dest, rtx
> if (l2)
> {
> emit_label (l2);
> - emit_move_insn (dest, const2_rtx);
> + emit_move_insn (dest, op2 == const0_rtx ? const2_rtx : op2);
> }
> emit_label (lend);
> }
> @@ -3250,11 +3250,11 @@ ix86_expand_int_spaceship (rtx dest, rtx
> operands nor optimize CC mode - we need a mode usable for both
> LT and GT resp. LTU and GTU comparisons with the same unswapped
> operands. */
> - rtx flags = gen_rtx_REG (INTVAL (op2) == 1 ? CCGCmode : CCmode, FLAGS_REG);
> + rtx flags = gen_rtx_REG (INTVAL (op2) != 1 ? CCGCmode : CCmode, FLAGS_REG);
> rtx tmp = gen_rtx_COMPARE (GET_MODE (flags), op0, op1);
> emit_insn (gen_rtx_SET (flags, tmp));
> rtx lt_tmp = gen_reg_rtx (QImode);
> - ix86_expand_setcc (lt_tmp, INTVAL (op2) == 1 ? LT : LTU, flags,
> + ix86_expand_setcc (lt_tmp, INTVAL (op2) != 1 ? LT : LTU, flags,
> const0_rtx);
> if (GET_MODE (dest) != QImode)
> {
> @@ -3264,7 +3264,7 @@ ix86_expand_int_spaceship (rtx dest, rtx
> lt_tmp = tmp;
> }
> rtx gt_tmp = gen_reg_rtx (QImode);
> - ix86_expand_setcc (gt_tmp, INTVAL (op2) == 1 ? GT : GTU, flags,
> + ix86_expand_setcc (gt_tmp, INTVAL (op2) != 1 ? GT : GTU, flags,
> const0_rtx);
> if (GET_MODE (dest) != QImode)
> {
> --- gcc/doc/md.texi.jj 2024-10-07 11:37:46.380980242 +0200
> +++ gcc/doc/md.texi 2024-10-07 14:10:39.037195535 +0200
> @@ -8575,8 +8575,11 @@ if operand 1 with mode @var{m} compares
> operand 2, greater than operand 2 or is unordered with operand 2.
> Operand 3 should be @code{const0_rtx} if the result is used in comparisons,
> @code{const1_rtx} if the result is used as integer value and the comparison
> -is signed, @code{const2_rtx} if the result is used as integer value and
> -the comparison is unsigned.
> +is integral unsigned, @code{constm1_rtx} if the result is used as integer
> +value and the comparison is integral signed and some other @code{CONST_INT}
> +if the result is used as integer value and the comparison is floating point.
> +In the last case, instead of setting output operand 0 to 2 for unordered,
> +set it to operand 3.
> @var{m} should be a scalar floating point mode.
>
> This pattern is not allowed to @code{FAIL}.
> --- gcc/testsuite/gcc.target/i386/pr116896.c.jj 2024-10-07
> 14:17:38.024311384 +0200
> +++ gcc/testsuite/gcc.target/i386/pr116896.c 2024-10-07 14:17:33.409376197
> +0200
> @@ -0,0 +1,59 @@
> +/* PR middle-end/116896 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -masm=att -fno-stack-protector" } */
> +/* { dg-final { scan-assembler-times "\tjp\t" 2 } } */
> +/* { dg-final { scan-assembler-not "\tj\[^mp\]\[a-z\]*\t" } } */
> +/* { dg-final { scan-assembler-times "\tsbb\[bl\]\t\\\$0, " 4 } } */
> +/* { dg-final { scan-assembler-times "\tseta\t" 4 } } */
> +
> +signed char
> +foo (float x, float y)
> +{
> + if (x == y)
> + return 0;
> + else if (x < y)
> + return -1;
> + else if (x > y)
> + return 1;
> + else
> + return 2;
> +}
> +
> +__attribute__((optimize ("fast-math"))) signed char
> +bar (float x, float y)
> +{
> + if (x == y)
> + return 0;
> + else if (x < y)
> + return -1;
> + else if (x > y)
> + return 1;
> + else
> + return 2;
> +}
> +
> +signed char
> +baz (float x, float y)
> +{
> + if (x == y)
> + return 0;
> + else if (x < y)
> + return -1;
> + else if (x > y)
> + return 1;
> + else
> + return -127;
> +}
> +
> +__attribute__((optimize ("fast-math"))) signed char
> +qux (float x, float y)
> +{
> + if (x == y)
> + return 0;
> + else if (x < y)
> + return -1;
> + else if (x > y)
> + return 1;
> + else
> + return -127;
> +}
>
>
> Jakub
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
