[Bug middle-end/112600] Failed to optimize saturating addition using __builtin_add_overflow

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112600

--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Pan Li <panli@gcc.gnu.org>:

https://gcc.gnu.org/g:abe6d39365476e6be724815d09d072e305018755

commit r15-1030-gabe6d39365476e6be724815d09d072e305018755
Author: Pan Li <pan2.li@intel.com>
Date:   Tue May 28 15:37:44 2024 +0800

    Internal-fn: Support new IFN SAT_SUB for unsigned scalar int

    This patch would like to add the middle-end presentation for the
    saturation sub.  Aka set the result of add to the min when downflow.
    It will take the pattern similar as below.

    SAT_SUB (x, y) => (x - y) & (-(TYPE)(x >= y));

    For example for uint8_t, we have

    * SAT_SUB (255, 0)   => 255
    * SAT_SUB (1, 2)     => 0
    * SAT_SUB (254, 255) => 0
    * SAT_SUB (0, 255)   => 0

    Given below SAT_SUB for uint64

    uint64_t sat_sub_u64 (uint64_t x, uint64_t y)
    {
      return (x - y) & (-(TYPE)(x >= y));
    }

    Before this patch:
    uint64_t sat_sub_u_0_uint64_t (uint64_t x, uint64_t y)
    {
      _Bool _1;
      long unsigned int _3;
      uint64_t _6;

    ;;   basic block 2, loop depth 0
    ;;    pred:       ENTRY
      _1 = x_4(D) >= y_5(D);
      _3 = x_4(D) - y_5(D);
      _6 = _1 ? _3 : 0;
      return _6;
    ;;    succ:       EXIT
    }

    After this patch:
    uint64_t sat_sub_u_0_uint64_t (uint64_t x, uint64_t y)
    {
      uint64_t _6;

    ;;   basic block 2, loop depth 0
    ;;    pred:       ENTRY
      _6 = .SAT_SUB (x_4(D), y_5(D)); [tail call]
      return _6;
    ;;    succ:       EXIT
    }

    The below tests are running for this patch:
    *. The riscv fully regression tests.
    *. The x86 bootstrap tests.
    *. The x86 fully regression tests.

            PR target/51492
            PR target/112600

    gcc/ChangeLog:

            * internal-fn.def (SAT_SUB): Add new IFN define for SAT_SUB.
            * match.pd: Add new match for SAT_SUB.
            * optabs.def (OPTAB_NL): Remove fixed-point for ussub/ssub.
            * tree-ssa-math-opts.cc (gimple_unsigned_integer_sat_sub): Add
            new decl for generated in match.pd.
            (build_saturation_binary_arith_call): Add new helper function
            to build the gimple call to binary SAT alu.
            (match_saturation_arith): Rename from.
            (match_unsigned_saturation_add): Rename to.
            (match_unsigned_saturation_sub): Add new func to match the
            unsigned sat sub.
            (math_opts_dom_walker::after_dom_children): Add SAT_SUB matching
            try when COND_EXPR.

    Signed-off-by: Pan Li <pan2.li@intel.com>