[Bug c/106380] New: DCE depends on datatype used (bool vs unsigned)

[Bug c/106380] New: DCE depends on datatype used (bool vs unsigned)

[tmayerl at student dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106380

            Bug ID: 106380
           Summary: DCE depends on datatype used (bool vs unsigned)
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tmayerl at student dot ethz.ch
  Target Milestone: ---

In some cases, the compiler's ability to eliminate dead code depends on the
datatype used (bool vs unsigned).

GCC detects that the if expression in the following code snippet evaluates to
false and thus removes the dead code:

#include <stdio.h>
#include <stdbool.h>

static void __attribute__ ((noinline)) DCEMarker0_() {printf("DCE2.0");}

void f(bool s, bool c) {
    if (((!s == !c) && c && !(s))) {
        DCEMarker0_();
    }
}

In the following snippet the datatype is switched to unsigned (the semantics
stay the same). However, GCC cannot eliminate the dead code anymore:

#include <stdio.h>
#include <stdbool.h>

static void __attribute__ ((noinline)) DCEMarker0_() {printf("DCE2.0");}

void f(unsigned s, unsigned c) {
    if (((!s == !c) && c && !(s))) {
        DCEMarker0_();
    }
}


This can also be seen via the following Compiler Explorer link: 
https://godbolt.org/z/aMcEvEaYa

(Might be related to 106379)

[Bug tree-optimization/106380] DCE depends on datatype used (bool vs unsigned)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106380

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu.org
           Severity|normal                      |enhancement

[Bug tree-optimization/106380] DCE depends on datatype used (bool vs unsigned)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106380

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-05-18
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Mine.

In this case if we fold:
  _1 = ~s_4(D);
  _2 = _1 & c_5(D);

to
s < c

Then the rest will be optimized by normally.

[Bug tree-optimization/106380] DCE depends on datatype used (bool vs unsigned)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106380

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot gnu.org