[Bug middle-end/111701] New: [11/12/13/14 Regression] wrong code for __builtin_signbit(x*x)

[Bug middle-end/111701] New: [11/12/13/14 Regression] wrong code for __builtin_signbit(x*x)

[amonakov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111701

            Bug ID: 111701
           Summary: [11/12/13/14 Regression] wrong code for
                    __builtin_signbit(x*x)
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amonakov at gcc dot gnu.org
                CC: amonakov at gcc dot gnu.org, eggert at cs dot ucla.edu,
                    rguenth at gcc dot gnu.org, unassigned at gcc dot gnu.org
        Depends on: 111655
  Target Milestone: ---
            Target: x86_64-linux-gnu

+++ This bug was initially created as a clone of Bug #111655 +++

See bug 111655 comment 11: we incorrectly deduce nonnegative_p for
floating-point 'x * x', and the following aborts:

__attribute__((noipa))
static int f(float *x)
{
    *x *= *x;
    return __builtin_signbit(*x);
}

int main()
{
    float x = -__builtin_nan("");
    int s = f(&x);
    if (s != __builtin_signbit(x))
        __builtin_abort();
}


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111655
[Bug 111655] [11/12/13/14 Regression] wrong code generated for
__builtin_signbit and 0./0. on x86-64 -O2

[Bug middle-end/111701] [11/12/13/14 Regression] wrong code for __builtin_signbit(x*x)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111701

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-10-06
           Priority|P3                          |P2
   Target Milestone|---                         |11.5
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

[Bug middle-end/111701] [11/12/13/14 Regression] wrong code for __builtin_signbit(x*x)

[roger at nextmovesoftware dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111701

Roger Sayle <roger at nextmovesoftware dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |roger at nextmovesoftware dot com

--- Comment #2 from Roger Sayle <roger at nextmovesoftware dot com> ---
A patch to provide a possible solution/workaround has been proposed at
https://gcc.gnu.org/pipermail/gcc-patches/2024-April/650054.html
With that change, compiling the code in the original description with the
-fsignaling-nans command line option, avoids the abort.