[Bug tree-optimization/101856] match_arith_overflow checks only mulv4_optab/umulv4_optab tables when smul_highpart_optab/umul_highpart_optab can produce decent code too

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101856

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:62d08a67c83b4a089866c6d19e82d70ee5b8aed1

commit r14-992-g62d08a67c83b4a089866c6d19e82d70ee5b8aed1
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri May 19 12:57:31 2023 +0200

    tree-ssa-math-opts: Pattern recognize hand written __builtin_mul_overflow_p
with same unsigned types even when target just has highpart umul [PR101856]

    As can be seen on the following testcase, we pattern recognize it on
    i?86/x86_64 as return __builtin_mul_overflow_p (x, y, 0UL) and avoid
    that way the extra division, but don't do it e.g. on aarch64 or ppc64le,
    even when return __builtin_mul_overflow_p (x, y, 0UL); actually produces
    there better code.  The reason for testing the presence of the optab
    handler is to make sure the generated code for it is short to ensure
    we don't actually pessimize code instead of optimizing it.
    But, we have one case that the internal-fn.cc .MUL_OVERFLOW expansion
    handles nicely, and that is when arguments/result is the same mode
    TYPE_UNSIGNED type, we only use IMAGPART_EXPR of it (i.e.
    __builtin_mul_overflow_p rather than __builtin_mul_overflow) and
    umul_highpart_optab supports the particular mode, in that case
    we emit comparison of the highpart umul result against zero.

    So, the following patch matches what we do in internal-fn.cc and
    also pattern matches __builtin_mul_overflow_p if
    1) we only need the flag whether it overflowed (i.e. !use_seen)
    2) it is unsigned (i.e. !cast_stmt)
    3) umul_highpart is supported for the mode

    2023-05-19  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/101856
            * tree-ssa-math-opts.cc (match_arith_overflow): Pattern detect
            unsigned __builtin_mul_overflow_p even when umulv4_optab doesn't
            support it but umul_highpart_optab does.

            * gcc.dg/tree-ssa/pr101856.c: New test.