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

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

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

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Pan Li <pa...@gcc.gnu.org>:

https://gcc.gnu.org/g:52b0536710ff3f3ace72ab00ce9ef6c630cd1183

commit r15-576-g52b0536710ff3f3ace72ab00ce9ef6c630cd1183
Author: Pan Li <pan2...@intel.com>
Date:   Wed May 15 10:14:05 2024 +0800

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

    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
    }

    The below tests are passed for this patch:
    1. The riscv 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(es).
            * 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 when IOR expr.

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