[Bug tree-optimization/105295] New: missed optimization with -ftrapv for conditional constants

[Bug tree-optimization/105295] New: missed optimization with -ftrapv for conditional constants

[roland.illig at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105295

            Bug ID: 105295
           Summary: missed optimization with -ftrapv for conditional
                    constants
           Product: gcc
           Version: 12.0
               URL: https://godbolt.org/z/4rojo77a7
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: roland.illig at gmx dot de
  Target Milestone: ---

~~~c
int sum_const(_Bool a, _Bool b)
{
        return (a ? 1 : 0 ) + (b ? 1 : 0);
}

int sum_unknown(int a, int b)
{
        return a + b;
}
~~~

For both functions, GCC calls __addvsi3, even though in sum_const, it is easy
to see that no overflow can ever happen since the sum is always in the range [0
... 2].

Clang optimizes this code reasonably.

ICC apparently does not care about -ftrapv at all.

[Bug tree-optimization/105295] missed optimization with -ftrapv for conditional constants

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105295

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
                URL|https://godbolt.org/z/4rojo |
                   |77a7                        |

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://godbolt.org/z/4rojo77a7

[Bug tree-optimization/105295] missed optimization with -ftrapv for conditional constants

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105295

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Yes trapv is implemented during expansion (from gimple to RTL) and not really
optimized.

[Bug tree-optimization/105295] missed optimization with -ftrapv for conditional constants

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105295

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |101521

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
PR 101521 records on how it should be implemented differently. Maybe for GCC
13, it will change.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101521
[Bug 101521] -ftrapv should become something like -fsanitize=undefined
-fsanitize-undefined-trap-on-error