[Bug tree-optimization/113411] New: ABS<a>*ABS<b> can be simplified to ABS<a*b>

[Bug tree-optimization/113411] New: ABS<a>*ABS<b> can be simplified to ABS<a*b>

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113411

            Bug ID: 113411
           Summary: ABS<a>*ABS<b> can be simplified to ABS<a*b>
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```

static inline int abs(int a)
{
  signed b = a;
  if (a < 0)
    b = -b;
  return b;
}

int foo1(int a, int b)
{
   return abs(a) * abs(b);
}
```

foo1 can be simplified down to `abs(a*b)`.  Note I think this is only valid for
signed overflowable types and not valid with -fwrapv (but I could be wrong).
Maybe ok for real types with -ffast-math.

[Bug tree-optimization/113411] ABS<a>*ABS<b> can be simplified to ABS<a*b>

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113411

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-01-16
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think it's OK for reals with -fno-rounding-math.

It's valid for integers with or without undefined overflow, the corner
case to consider is

  abs(-INT_MAX - 1) * abs (b)

where with undefined overflow the abs() is already invoking undefined
behavior.  The problematical multiplication is (-INT_MAX-1) * -1 but
we cannot arrive at this from a defined input.  For

  abs(a*b)

the problematical input is -INT_MAX - 1 but we can't arrive at that
either (b == 1 with a == -INT_MAX-1 is undefined, b == -1 the same).

[Bug tree-optimization/113411] ABS<a>*ABS<b> can be simplified to ABS<a*b>

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113411

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |56355

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
PR 56355 is the same but for floating point already ...


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56355
[Bug 56355] abs and multiplication