[Bug tree-optimization/67953] New: [6 Regression] match.pd: X - (X / Y) * Y wrong on change of sign

["glisse at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67953

            Bug ID: 67953
           Summary: [6 Regression] match.pd: X - (X / Y) * Y wrong on
                    change of sign
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org
                CC: mpolacek at gcc dot gnu.org
  Target Milestone: ---

$ cat z.c
#include <stdio.h>
unsigned f(signed a){
  return (unsigned)a-((a/3)*3);
}
unsigned g(signed a){
  return a-((a/3)*3);
}
int main(){
  printf("%d %d\n", f(-5), g(-5));
}
$ gcc-5 z.c && ./a.out
-2 -2
$ clang z.c && ./a.out       
-2 -2
$ gcc-snapshot z.c && ./a.out 
2 -2