[Bug tree-optimization/86265] New: Wrong code on an invalid code starting with r255790

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86265

            Bug ID: 86265
           Summary: Wrong code on an invalid code starting with r255790
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: msebor at gcc dot gnu.org
  Target Milestone: ---

Starting from the mentioned revision we do:

$ cat tester.c
#include <stdio.h>
#include <string.h>

#define min(a, b) (((a) < (b)) ? (a) : (b))

struct S {
  char data[4];
  char fallout[100];
};

int main(int argc, char **argv) {
  struct S s;
  strncpy(s.data, argv[1], 4 + 100);
  int length = min(strlen(s.data), 4);
  printf("length: %d\n", length);
  return 0;
}

$ gcc tester.c -O3 && ./a.out 123456
length: 6

before the mentioned revision we did:
length: 4.

optimized dumps:
after revision:


;; Function main (main, funcdef_no=11, decl_uid=2580, cgraph_uid=11,
symbol_order=11) (executed once)

main (int argc, char * * argv)
{
  struct S s;
  char * _1;
  long unsigned int _2;
  int iftmp.0_3;

  <bb 2> [local count: 1073741825]:
  _1 = MEM[(char * *)argv_4(D) + 8B];
  strncpy (&s.data, _1, 104);
  _2 = strlen (&s.data);
  iftmp.0_3 = (int) _2;
  printf ("length: %d\n", iftmp.0_3);
  s ={v} {CLOBBER};
  return 0;

}

before:


;; Function main (main, funcdef_no=11, decl_uid=2580, cgraph_uid=11,
symbol_order=11) (executed once)

main (int argc, char * * argv)
{
  struct S s;
  char * _1;
  long unsigned int _2;
  int iftmp.0_3;
  long unsigned int _10;

  <bb 2> [local count: 1073741825]:
  _1 = MEM[(char * *)argv_4(D) + 8B];
  strncpy (&s.data, _1, 104);
  _2 = strlen (&s.data);
  if (_2 <= 3)
    goto <bb 4>; [50.00%]
  else
    goto <bb 3>; [50.00%]

  <bb 3> [local count: 536870913]:

  <bb 4> [local count: 1073741825]:
  # _10 = PHI <_2(2), 4(3)>
  iftmp.0_3 = (int) _10;
  printf ("length: %d\n", iftmp.0_3);
  s ={v} {CLOBBER};
  return 0;

}