[Bug middle-end/112639] New: Incorrect handling of __builtin_c[lt]zg argument side-effects

[Bug middle-end/112639] New: Incorrect handling of __builtin_c[lt]zg argument side-effects

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112639

            Bug ID: 112639
           Summary: Incorrect handling of __builtin_c[lt]zg argument
                    side-effects
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

unsigned long long b = 0;

int
foo (void)
{
  return __builtin_clzg (b++, __SIZEOF_LONG__ * __CHAR_BIT__);
}

int
bar (void)
{
  return __builtin_ctzg (b++, __SIZEOF_LONG__ * __CHAR_BIT__);
}

int
main ()
{
  if (foo () != __SIZEOF_LONG__ * __CHAR_BIT__ || b != 1)
    __builtin_abort ();
  if (foo () != __SIZEOF_LONG__ * __CHAR_BIT__ - 1 || b != 2)
    __builtin_abort ();
  if (foo () != __SIZEOF_LONG__ * __CHAR_BIT__ - 2 || b != 3)
    __builtin_abort ();
  b = 0;
  if (bar () != __SIZEOF_LONG__ * __CHAR_BIT__ || b != 1)
    __builtin_abort ();
  if (bar () != 0 || b != 2)
    __builtin_abort ();
  if (bar () != 1 || b != 3)
    __builtin_abort ();
}

is miscompiled.

[Bug middle-end/112639] Incorrect handling of __builtin_c[lt]zg argument side-effects

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112639

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2023-11-20
     Ever confirmed|0                           |1
   Target Milestone|---                         |14.0
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

[Bug middle-end/112639] Incorrect handling of __builtin_c[lt]zg argument side-effects

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112639

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 56650
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56650&action=edit
gcc14-pr112639.patch

Untested fix.

[Bug middle-end/112639] Incorrect handling of __builtin_c[lt]zg argument side-effects

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112639

--- 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:8a8a6d60c670c5153c5109df5fe68deb6fcf466d

commit r14-5638-g8a8a6d60c670c5153c5109df5fe68deb6fcf466d
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Nov 21 09:32:37 2023 +0100

    builtins: Fix fold_builtin_query clzg/ctzg side-effects handling [PR112639]

    As the testcase shows, I've missed one spot where initially the code thinks
    it could use 2 argument IFN_CLZ/IFN_CTZ form, but then verifies it can't
    because it doesn't have the right target value and turns it into the
    arg0 ? arg1 : .C[LT]Z (arg0)
    form.  That form evaluates the argument twice though and so needs
save_expr,
    which I've missed to call in that case.  In other cases where it is known
    from the beginning that it will be needed (e.g. the __builtin_clzg case
    on types smaller than unsigned int where we'll need to add an addend
    to the clz value) or the unsigned __int128 expansion called save_expr
    before.

    2023-11-21  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/112639
            * builtins.cc (fold_builtin_bit_query): If arg0 has side-effects,
arg1
            is specified but cleared, call save_expr on arg0.

            * gcc.dg/torture/pr112639.c: New test.

[Bug middle-end/112639] Incorrect handling of __builtin_c[lt]zg argument side-effects

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112639

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed.