Implicit assumptions (was: Re: Some fun with -O2)

[Walter von Entferndt]

Dear Sirs,
the behaviour on signed overflow is /explicitely undefined/ in C...
I'd like to kindly suggest to fix the bug instead of fiddling around with 
compiler switches to compile a buggy program:
--- check_mktime.c.patch ---
--- check_mktime.c.orig 2021-01-15 03:19:33.962253000 +0100
+++ check_mktime.c      2021-01-15 04:04:22.291014000 +0100
@@ -1,13 +1,16 @@
 /* Test program from Paul Eggert (eggert at twinsun.com)
    and Tony Leneis (tony at plaza.ds.adp.com).  */
 # include <sys/time.h>
+# include <sys/param.h>                /* NBBY: #bits of a byte */
 # include <time.h>
 # include <unistd.h>
+# include <stdlib.h>

 /* Work around redefinition to rpl_putenv by other config tests.  */
 #undef putenv

-static time_t time_t_max;
+const time_t t0 = (time_t) 1 << (NBBY*sizeof t0 - 2); /* unused elsewhere */
+static const time_t time_t_max = t0|(t0 - 1);

 /* Values we'll use to set the TZ environment variable.  */
 static const char *const tz_strings[] = {
@@ -106,9 +109,6 @@
   time_t t, delta;
   int i, j;

-  for (time_t_max = 1; 0 < time_t_max; time_t_max *= 2)
-    continue;
-  time_t_max--;
   delta = time_t_max / 997; /* a suitable prime number */
   for (i = 0; i < N_STRINGS; i++)
     {
-- 
=|o)	"Stell' Dir vor es geht und keiner kriegt's hin." (Wolfgang Neuss)
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