[Bug middle-end/101950] __builtin_clrsb is never inlined

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101950

--- Comment #2 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:301dc6011cbceb7ea9debd86aaec7cadb37213c8

commit r12-3017-g301dc6011cbceb7ea9debd86aaec7cadb37213c8
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Aug 19 11:00:27 2021 +0200

    expand: Add new clrsb fallback expansion [PR101950]

    As suggested in the PR, the following patch adds two new clrsb
    expansion possibilities if target doesn't have clrsb_optab for the
    requested nor wider modes, but does have clz_optab for the requested
    mode.
    One expansion is
    clrsb (op0)
    expands as
    clz (op0 ^ (((stype)op0) >> (prec-1))) - 1
    which is usable if CLZ_DEFINED_VALUE_AT_ZERO is 2 with value
    of prec, because the clz argument can be 0 and clrsb should give
    prec-1 in that case.
    The other expansion is
    clz (((op0 << 1) ^ (((stype)op0) >> (prec-1))) | 1)
    where the clz argument is never 0, but it is one operation longer.
    E.g. on x86_64-linux with -O2 -mno-lzcnt, this results for
    int foo (int x) { return __builtin_clrsb (x); }
    in
    -       subq    $8, %rsp
    -       movslq  %edi, %rdi
    -       call    __clrsbdi2
    -       addq    $8, %rsp
    -       subl    $32, %eax
    +       leal    (%rdi,%rdi), %eax
    +       sarl    $31, %edi
    +       xorl    %edi, %eax
    +       orl     $1, %eax
    +       bsrl    %eax, %eax
    +       xorl    $31, %eax
    and with -O2 -mlzcnt:
    +       movl    %edi, %eax
    +       sarl    $31, %eax
    +       xorl    %edi, %eax
    +       lzcntl  %eax, %eax
    +       subl    $1, %eax
    On armv7hl-linux-gnueabi with -O2:
    -       push    {r4, lr}
    -       bl      __clrsbsi2
    -       pop     {r4, pc}
    +       @ link register save eliminated.
    +       eor     r0, r0, r0, asr #31
    +       clz     r0, r0
    +       sub     r0, r0, #1
    +       bx      lr
    As it (at least usually) will make code larger, it is
    disabled for -Os or cold instructions.

    2021-08-19  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/101950
            * optabs.c (expand_clrsb_using_clz): New function.
            (expand_unop): Use it as another clrsb expansion fallback.

            * gcc.target/i386/pr101950-1.c: New test.
            * gcc.target/i386/pr101950-2.c: New test.