RE: [PATCH v4 1/3] Internal-fn: Support new IFN SAT_ADD for unsigned scalar int

["Li, Pan2" <pan2.li@intel.com>]

Thanks Richard for comments.

> If you require a gassign please statically type your function
> argument as gassign * instead and remove this assert.

Sure

> As addition to Tamars good comments why do you set *cfg_changed_p to
> true?  You are
> not changing the CFG afer all?

Yes, we can add it back in future if we really changed cfg, will update in v5 (include vect patch 2/3) after all test passed.

Pan


-----Original Message-----
From: Richard Biener <richard.guenther@gmail.com> 
Sent: Tuesday, May 14, 2024 9:18 PM
To: Li, Pan2 <pan2.li@intel.com>
Cc: gcc-patches@gcc.gnu.org; juzhe.zhong@rivai.ai; kito.cheng@gmail.com; tamar.christina@arm.com; Liu, Hongtao <hongtao.liu@intel.com>
Subject: Re: [PATCH v4 1/3] Internal-fn: Support new IFN SAT_ADD for unsigned scalar int

On Mon, May 6, 2024 at 4:48 PM <pan2.li@intel.com> wrote:
>
> From: Pan Li <pan2.li@intel.com>
>
> This patch would like to add the middle-end presentation for the
> saturation add.  Aka set the result of add to the max when overflow.
> It will take the pattern similar as below.
>
> SAT_ADD (x, y) => (x + y) | (-(TYPE)((TYPE)(x + y) < x))
>
> Take uint8_t as example, we will have:
>
> * SAT_ADD (1, 254)   => 255.
> * SAT_ADD (1, 255)   => 255.
> * SAT_ADD (2, 255)   => 255.
> * SAT_ADD (255, 255) => 255.
>
> Given below example for the unsigned scalar integer uint64_t:
>
> uint64_t sat_add_u64 (uint64_t x, uint64_t y)
> {
>   return (x + y) | (- (uint64_t)((uint64_t)(x + y) < x));
> }
>
> Before this patch:
> uint64_t sat_add_uint64_t (uint64_t x, uint64_t y)
> {
>   long unsigned int _1;
>   _Bool _2;
>   long unsigned int _3;
>   long unsigned int _4;
>   uint64_t _7;
>   long unsigned int _10;
>   __complex__ long unsigned int _11;
>
> ;;   basic block 2, loop depth 0
> ;;    pred:       ENTRY
>   _11 = .ADD_OVERFLOW (x_5(D), y_6(D));
>   _1 = REALPART_EXPR <_11>;
>   _10 = IMAGPART_EXPR <_11>;
>   _2 = _10 != 0;
>   _3 = (long unsigned int) _2;
>   _4 = -_3;
>   _7 = _1 | _4;
>   return _7;
> ;;    succ:       EXIT
>
> }
>
> After this patch:
> uint64_t sat_add_uint64_t (uint64_t x, uint64_t y)
> {
>   uint64_t _7;
>
> ;;   basic block 2, loop depth 0
> ;;    pred:       ENTRY
>   _7 = .SAT_ADD (x_5(D), y_6(D)); [tail call]
>   return _7;
> ;;    succ:       EXIT
> }
>
> We perform the tranform during widen_mult because that the sub-expr of
> SAT_ADD will be optimized to .ADD_OVERFLOW.  We need to try the .SAT_ADD
> pattern first and then .ADD_OVERFLOW,  or we may never catch the pattern
> .SAT_ADD.  Meanwhile, the isel pass is after widen_mult and then we
> cannot perform the .SAT_ADD pattern match as the sub-expr will be
> optmized to .ADD_OVERFLOW first.
>
> The below tests are passed for this patch:
> 1. The riscv fully regression tests.
> 2. The aarch64 fully regression tests.
> 3. The x86 bootstrap tests.
> 4. The x86 fully regression tests.
>
>         PR target/51492
>         PR target/112600
>
> gcc/ChangeLog:
>
>         * internal-fn.cc (commutative_binary_fn_p): Add type IFN_SAT_ADD
>         to the return true switch case(s).
>         * internal-fn.def (SAT_ADD):  Add new signed optab SAT_ADD.
>         * match.pd: Add unsigned SAT_ADD match.
>         * optabs.def (OPTAB_NL): Remove fixed-point limitation for us/ssadd.
>         * tree-ssa-math-opts.cc (gimple_unsigned_integer_sat_add): New extern
>         func decl generated in match.pd match.
>         (match_saturation_arith): New func impl to match the saturation arith.
>         (math_opts_dom_walker::after_dom_children): Try match saturation
>         arith.
>
> Signed-off-by: Pan Li <pan2.li@intel.com>
> ---
>  gcc/internal-fn.cc        |  1 +
>  gcc/internal-fn.def       |  2 ++
>  gcc/match.pd              | 28 ++++++++++++++++++++++++
>  gcc/optabs.def            |  4 ++--
>  gcc/tree-ssa-math-opts.cc | 46 +++++++++++++++++++++++++++++++++++++++
>  5 files changed, 79 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc
> index 0a7053c2286..73045ca8c8c 100644
> --- a/gcc/internal-fn.cc
> +++ b/gcc/internal-fn.cc
> @@ -4202,6 +4202,7 @@ commutative_binary_fn_p (internal_fn fn)
>      case IFN_UBSAN_CHECK_MUL:
>      case IFN_ADD_OVERFLOW:
>      case IFN_MUL_OVERFLOW:
> +    case IFN_SAT_ADD:
>      case IFN_VEC_WIDEN_PLUS:
>      case IFN_VEC_WIDEN_PLUS_LO:
>      case IFN_VEC_WIDEN_PLUS_HI:
> diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
> index 848bb9dbff3..25badbb86e5 100644
> --- a/gcc/internal-fn.def
> +++ b/gcc/internal-fn.def
> @@ -275,6 +275,8 @@ DEF_INTERNAL_SIGNED_OPTAB_FN (MULHS, ECF_CONST | ECF_NOTHROW, first,
>  DEF_INTERNAL_SIGNED_OPTAB_FN (MULHRS, ECF_CONST | ECF_NOTHROW, first,
>                               smulhrs, umulhrs, binary)
>
> +DEF_INTERNAL_SIGNED_OPTAB_FN (SAT_ADD, ECF_CONST, first, ssadd, usadd, binary)
> +
>  DEF_INTERNAL_COND_FN (ADD, ECF_CONST, add, binary)
>  DEF_INTERNAL_COND_FN (SUB, ECF_CONST, sub, binary)
>  DEF_INTERNAL_COND_FN (MUL, ECF_CONST, smul, binary)
> diff --git a/gcc/match.pd b/gcc/match.pd
> index d401e7503e6..7058e4cbe29 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -3043,6 +3043,34 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>         || POINTER_TYPE_P (itype))
>        && wi::eq_p (wi::to_wide (int_cst), wi::max_value (itype))))))
>
> +/* Unsigned Saturation Add */
> +(match (usadd_left_part @0 @1)
> + (plus:c @0 @1)
> + (if (INTEGRAL_TYPE_P (type)
> +      && TYPE_UNSIGNED (TREE_TYPE (@0))
> +      && types_match (type, TREE_TYPE (@0))
> +      && types_match (type, TREE_TYPE (@1)))))
> +
> +(match (usadd_right_part @0 @1)
> + (negate (convert (lt (plus:c @0 @1) @0)))
> + (if (INTEGRAL_TYPE_P (type)
> +      && TYPE_UNSIGNED (TREE_TYPE (@0))
> +      && types_match (type, TREE_TYPE (@0))
> +      && types_match (type, TREE_TYPE (@1)))))
> +
> +(match (usadd_right_part @0 @1)
> + (negate (convert (gt @0 (plus:c @0 @1))))
> + (if (INTEGRAL_TYPE_P (type)
> +      && TYPE_UNSIGNED (TREE_TYPE (@0))
> +      && types_match (type, TREE_TYPE (@0))
> +      && types_match (type, TREE_TYPE (@1)))))
> +
> +/* Unsigned saturation add, case 1 (branchless):
> +   SAT_U_ADD = (X + Y) | - ((X + Y) < X) or
> +   SAT_U_ADD = (X + Y) | - (X > (X + Y)).  */
> +(match (unsigned_integer_sat_add @0 @1)
> + (bit_ior:c (usadd_left_part @0 @1) (usadd_right_part @0 @1)))
> +
>  /* x >  y  &&  x != XXX_MIN  -->  x > y
>     x >  y  &&  x == XXX_MIN  -->  false . */
>  (for eqne (eq ne)
> diff --git a/gcc/optabs.def b/gcc/optabs.def
> index ad14f9328b9..3f2cb46aff8 100644
> --- a/gcc/optabs.def
> +++ b/gcc/optabs.def
> @@ -111,8 +111,8 @@ OPTAB_NX(add_optab, "add$F$a3")
>  OPTAB_NX(add_optab, "add$Q$a3")
>  OPTAB_VL(addv_optab, "addv$I$a3", PLUS, "add", '3', gen_intv_fp_libfunc)
>  OPTAB_VX(addv_optab, "add$F$a3")
> -OPTAB_NL(ssadd_optab, "ssadd$Q$a3", SS_PLUS, "ssadd", '3', gen_signed_fixed_libfunc)
> -OPTAB_NL(usadd_optab, "usadd$Q$a3", US_PLUS, "usadd", '3', gen_unsigned_fixed_libfunc)
> +OPTAB_NL(ssadd_optab, "ssadd$a3", SS_PLUS, "ssadd", '3', gen_signed_fixed_libfunc)
> +OPTAB_NL(usadd_optab, "usadd$a3", US_PLUS, "usadd", '3', gen_unsigned_fixed_libfunc)
>  OPTAB_NL(sub_optab, "sub$P$a3", MINUS, "sub", '3', gen_int_fp_fixed_libfunc)
>  OPTAB_NX(sub_optab, "sub$F$a3")
>  OPTAB_NX(sub_optab, "sub$Q$a3")
> diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
> index 705f4a4695a..35a46edc9f6 100644
> --- a/gcc/tree-ssa-math-opts.cc
> +++ b/gcc/tree-ssa-math-opts.cc
> @@ -4026,6 +4026,44 @@ arith_overflow_check_p (gimple *stmt, gimple *cast_stmt, gimple *&use_stmt,
>    return 0;
>  }
>
> +extern bool gimple_unsigned_integer_sat_add (tree, tree*, tree (*)(tree));
> +
> +/*
> + * Try to match saturation arith pattern(s).
> + *   1. SAT_ADD (unsigned)
> + *      _7 = _4 + _6;
> + *      _8 = _4 > _7;
> + *      _9 = (long unsigned int) _8;
> + *      _10 = -_9;
> + *      _12 = _7 | _10;
> + *      =>
> + *      _12 = .SAT_ADD (_4, _6);  */
> +static bool
> +match_saturation_arith (gimple_stmt_iterator *gsi, gimple *stmt,
> +                       bool *cfg_changed_p)
> +{
> +  gcall *call = NULL;
> +  bool changed_p = false;
> +
> +  gcc_assert (is_gimple_assign (stmt));

If you require a gassign please statically type your function
argument as gassign * instead and remove this assert.

> +
> +  tree ops[2];
> +  tree lhs = gimple_assign_lhs (stmt);
> +
> +  if (gimple_unsigned_integer_sat_add (lhs, ops, NULL)
> +      && direct_internal_fn_supported_p (IFN_SAT_ADD, TREE_TYPE (lhs),
> +                                       OPTIMIZE_FOR_SPEED))
> +    {
> +      call = gimple_build_call_internal (IFN_SAT_ADD, 2, ops[0], ops[1]);
> +      gimple_call_set_lhs (call, lhs);
> +      gsi_replace (gsi, call, true);
> +      changed_p = true;
> +      *cfg_changed_p = changed_p;

As addition to Tamars good comments why do you set *cfg_changed_p to
true?  You are
not changing the CFG afer all?

> +    }
> +
> +  return changed_p;
> +}
> +
>  /* Recognize for unsigned x
>     x = y - z;
>     if (x > y)
> @@ -5886,6 +5924,14 @@ math_opts_dom_walker::after_dom_children (basic_block bb)
>
>    fma_deferring_state fma_state (param_avoid_fma_max_bits > 0);
>
> +  for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); gsi_next (&gsi))
> +    {
> +      gimple *stmt = gsi_stmt (gsi);
> +
> +      if (is_gimple_assign (stmt))
> +       match_saturation_arith (&gsi, stmt, m_cfg_changed_p);
> +    }
> +
>    for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi);)
>      {
>        gimple *stmt = gsi_stmt (gsi);
> --
> 2.34.1
>