[Bug c/106381] New: DCE depends on used programming language (C vs C++)

[Bug c/106381] New: DCE depends on used programming language (C vs C++)

[tmayerl at student dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106381

            Bug ID: 106381
           Summary: DCE depends on used programming language (C vs C++)
           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
used language (C vs C++).

GCC detects that the if expression in the following code snippet evaluates to
false and thus removes the dead code. The code is compiled as C++ code:

#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_();
    }
}

However, if the same code is compiled as C code, GCC cannot eliminate the dead
code anymore.

This can also be seen via the following Compiler Explorer link:
https://godbolt.org/z/a9ned9Exb

(Might be related to 106379 and 106380)

[Bug tree-optimization/106381] DCE depends on used programming language (C vs C++)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106381

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

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

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually it is worse in GCC 13. Both the C and C++ front-ends produced IR does
not get optimized.

[Bug tree-optimization/106381] DCE depends on used programming language (C vs C++)

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106381

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xry111 at gcc dot gnu.org

--- Comment #2 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Even if we change "unsigned" to "bool", it still does not get optimized with
GCC 13.

So generally should we try to solve 2-SAT if a boolean expression is a 2-SAT
form?