[Bug tree-optimization/96801] New: Refactoring of LIM introduced possible bug

[stefansf at linux dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96801

            Bug ID: 96801
           Summary: Refactoring of LIM introduced possible bug
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: stefansf at linux dot ibm.com
  Target Milestone: ---

Consider the following example:

int a = 0, f = 0, g = 0, h = 0, i = 0;                                          
int b = 0;                                                                      
static int c[1][1];                                                             
static int *const d = &c[0][0];                                                 
int *e = 0;                                                                     
int main() {                                                                    
  for (; i < 1; i++) { // LOOP-A                                                
    for (; b != 0; b++) // LOOP-B                                               
      if (f != 0) {                                                             
        *e = (*d)--;                                                            
        break;                                                                  
      }                                                                         
  }                                                                             
  for (g = 0; g < 1; g++) { // LOOP-C                                           
    for (h = 0; h < 1; h++) // LOOP-D                                           
      a = a ^ c[g][h];                                                          
  }                                                                             
  printf("checksum = %X\n", a);                                                 
  return a;                                                                     
}

Basically LOOP-A does nothing since the condition of inner LOOP-B never
evaluates to true. Thus we are left with LOOP-C which runs exactly one time as
does LOOP-D. Expression a ^ c[g][h] should evaluate to 0 since a as well as
c[0][0] are 0. In total we would expect to see "checksum = 0" being printed.
This is the case for me prior commit 6aec53ee4f7. With this commit "random"
numbers are printed.

Can someone confirm this?