I noticed this one while trying to install teTeX-1.0.  It compiles fine,
but the program does not work.  I isolated the problem, and the following 
program will show the error (it is available as

http://thales.memphis.edu/~tetex/try4.c)


#include <stdio.h>
#include <string.h>



int main(int argc, char *argv[])
{

  char *name;
  int loc;
  unsigned limit; 
  int i;
  
  name = argv[1];
  limit = 0;

  if (!name)
    {
      puts("name ?");
      return 0;
    }
  for (loc = strlen (name); (loc > limit) && (name[loc-1] != '/'); loc--)
    ;
  for (i = 0; i < loc - 1; i++)
    putchar(name[i]);
  putchar('\n');

  return 0;
}

This program should find dirname of argv[1].  But I get incorrect output if
I compile it with `-O2':

$ gcc -Wall -O2 try4.c
$ ./a.out /p/q/a-b-c
/p/q/a-

I get the correct output if I just use `-O' optimization:

$ gcc -Wall -O try4.c
$ ./a.out /p/q/a-b-c
/p/q

The problem somehow seems to be with declaring `limit' to be "unsigned". If
I change the declaration of limit to 

unsigned int limit;

all is well.

The problem is that the `for' loop terminates prematurely---even though the
value of 

(loc > limit) && (name[loc-1] != '/')

is one.  To test this, I made a test version of the program, and put teh
source at 

http://thales.memphis.edu/~tetex/try5.c

In try5.c, I put 

  test1 = (loc > limit);
  test2 = ( name[loc - 1] != '/' );
  test3 = (loc > limit) && ( name[loc - 1] != '/' );
  
  printf("test1: %d; test2: %d; test3: %d\n", test1, test2, test3);

after the for loop.  Here is what I get

$ gcc -Wall -O2 try5.c
$ ./a.out /p/q/a-b-c
test1: 1; test2: 1; test3: 1
/p/q/a-

Finally, let me point out that if I make any of the changes below in
try4.c, the program works correctly:


-- change (loc > limit)  to (limit < loc)

-- change (loc > limit) to (loc > 0)