[Bug tree-optimization/86723] not optimizing with bswap, that casts to int aftwards

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86723

--- Comment #7 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:b320edc0c29c838b0090c3c9be14187d132f73f2

commit r12-3072-gb320edc0c29c838b0090c3c9be14187d132f73f2
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Mon Aug 23 11:52:06 2021 +0200

    bswap: Recognize (int) __builtin_bswap64 (arg) idioms or __builtin_bswap??
(arg) & mask [PR86723]

    The following patch recognizes in the bswap pass (only there for now,
    haven't done it for store merging pass yet) code sequences that can
    be handled by (int32) __builtin_bswap64 (arg), i.e. where we have
    0x05060708 n->n with 64-bit non-memory argument (if it is memory, we
    can just load the 32-bit at 4 bytes into the address and n->n would
    be 0x01020304; and only 64 -> 32 bit, because 64 -> 16 bit or 32 -> 16 bit
    would mean only two bytes in the result and probably not worth it),
    and furthermore the case where we have in the 0x0102030405060708 etc.
    numbers some bytes 0 (i.e. known to contain zeros rather than source
bytes),
    as long as we have at least two original bytes in the right
    positions (and no unknown bytes).  This can be handled by
    __builtin_bswap64 (arg) & 0xff0000ffffff00ffULL etc.
    The latter change is the reason why counting the bswap messages doesn't
work
    too well in optimize-bswap* tests anymore, while the pass iterates from end
    of basic block towards start, it will often match both the bswap at the end
    and some of the earlier bswaps with some masks (not a problem generally,
    we'll just DCE it away whenever possible).  The pass right now doesn't
    handle __builtin_bswap* calls in the pattern matching (which is the reason
    why it operates backwards), but it uses FOR_EACH_BB_FN (bb, fun) order
    of handling blocks and matched sequences can span multiple blocks, so I was
    worried about cases like:
    void bar (unsigned long long);
    unsigned long long
    foo (unsigned long long value, int x)
    {
      unsigned long long tmp = (((value & 0x00000000000000ffull) << 56)
              | ((value & 0x000000000000ff00ull) << 40)
              | ((value & 0x00000000ff000000ull) << 8));
      if (x)
        bar (tmp);
      return (tmp
              | ((value & 0x000000ff00000000ull) >> 8)
              | ((value & 0x0000ff0000000000ull) >> 24)
              | ((value & 0x0000000000ff0000ull) << 24)
              | ((value & 0x00ff000000000000ull) >> 40)
              | ((value & 0xff00000000000000ull) >> 56));
    }
    but it seems we handle even that fine, while bb2 ending in GIMPLE_COND
    is processed first, we recognize there a __builtin_bswap64 (value) & mask1,
    in the last bb we recognize tmp | (__builtin_bswap64 (value) & mask2) and
    PRE optimizes that into t = __builtin_bswap64 (value); tmp = t & mask1;
    in the first bb and return t; in the last one.

    2021-08-23  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/86723
            * gimple-ssa-store-merging.c (find_bswap_or_nop_finalize): Add
            cast64_to_32 argument, set *cast64_to_32 to false, unless n is
            non-memory permutation of 64-bit src which only has bytes of
            0 or [5..8] and n->range is 4.
            (find_bswap_or_nop): Add cast64_to_32 and mask arguments, adjust
            find_bswap_or_nop_finalize caller, support bswap with some bytes
            zeroed, as long as at least two bytes are not zeroed.
            (bswap_replace): Add mask argument and handle masking of bswap
            result.
            (maybe_optimize_vector_constructor): Adjust find_bswap_or_nop
            caller, punt if cast64_to_32 or mask is not all ones.
            (pass_optimize_bswap::execute): Adjust find_bswap_or_nop_finalize
            caller, for now punt if cast64_to_32.

            * gcc.dg/pr86723.c: New test.
            * gcc.target/i386/pr86723.c: New test.
            * gcc.dg/optimize-bswapdi-1.c: Use -fdump-tree-optimized instead of
            -fdump-tree-bswap and scan for number of __builtin_bswap64 calls.
            * gcc.dg/optimize-bswapdi-2.c: Likewise.
            * gcc.dg/optimize-bswapsi-1.c: Use -fdump-tree-optimized instead of
            -fdump-tree-bswap and scan for number of __builtin_bswap32 calls.
            * gcc.dg/optimize-bswapsi-5.c: Likewise.
            * gcc.dg/optimize-bswapsi-3.c: Likewise.  Expect one
__builtin_bswap32
            call instead of zero.