[Bug middle-end/96397] New: GCC Fails to exploit ranges from overflow tests

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96397

            Bug ID: 96397
           Summary: GCC Fails to exploit ranges from overflow tests
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: law at redhat dot com
  Target Milestone: ---

Compile with -O2.  We should be able to eliminate the x > p1 test if we were
smart about back propagating equivalences to generate a range from the
__builtin_add_overflow.

This was derived from a bogus warning in tpm2-pkcs11's testsuite.

#include <stddef.h>
#include <stdlib.h>
extern void frob (void);

void
foo(size_t p1)
{
  size_t x = p1 - 4;
  size_t y;
  if (__builtin_add_overflow (x, 8, &y))
    {
      frob ();
    }
  else
    {
      if (x > p1)
        abort ();
    }
}