cc -O producing faulty code

[Craig Macbride]

drake at drake.almaden.ibm.com writes:

>How about posting an example, and the level of AIX you're running?

Release 1, Version 3. An example follows, with test script and result. You
will notice that I've put the optimised program's output through "cat -v" to
make it at least keep to ASCII characters. :-)

It seems very strange that code which occurs after the fprintf() statement
seems to be causing the result of it to change. The full-sized program was,
of course, using the variable new_usual_dom in output as well, but like all
code which didn't affect the problem, I've removed it.

-------------------------------program-------------------------------------
#include <stdio.h>
#include <string.h>
#include <memory.h>

char lga_name[100];
char usual_dom[100];

char line[1000];

char new_lga_name[100];
char new_usual_dom[100];

main(argc,argv)
int argc;
char **argv;
{
while (fgets(line,1000,stdin) != NULL)
{
	memcpy(usual_dom,line+31,20);
	usual_dom[20] = '\0';
	memcpy(lga_name,line+51,10);
	lga_name[10] = '\0';

	if (strcmp(lga_name,"ELTHAM    ")==0) strcpy(new_lga_name,"2640");
	else if (strcmp(lga_name,"PRESTON   ")==0) strcpy(new_lga_name,"6000");
	else if (strcmp(lga_name,"WHIT/SEA  ")==0) strcpy(new_lga_name,"8040");
	else if (strcmp(lga_name,"D/VALLEY  ")==0) strcpy(new_lga_name,"2280");
	else if (strcmp(lga_name,"UNKNOWN   ")==0) strcpy(new_lga_name,"9999");
	else strcpy(new_lga_name,"0000");

	fprintf(stdout, "'%s'\n", new_lga_name);

#ifndef KILL3
if (strcmp(usual_dom,"it doesn't seem to  ")==0) strcpy(new_usual_dom,"1");
else if (strcmp(usual_dom,"matter what this    ")==0) strcpy(new_usual_dom,"2");
else if (strcmp(usual_dom,"text is exactly, nor")==0) strcpy(new_usual_dom,"3");
else if (strcmp(usual_dom,"matter that it is   ")==0) strcpy(new_usual_dom,"4");
else if (strcmp(usual_dom,"_after_ the fprintf ")==0) strcpy(new_usual_dom,"5");
else if (strcmp(usual_dom,"... it still causes ")==0) strcpy(new_usual_dom,"6");
else if (strcmp(usual_dom,"the optimised output")==0) strcpy(new_usual_dom,"7");
else if (strcmp(usual_dom,"to be wrong...      ")==0) strcpy(new_usual_dom,"7");
else if (strcmp(usual_dom,"                    ")==0) strcpy(new_usual_dom,"7");
else if (strcmp(usual_dom,"xxxxxxxxxxxxxxx     ")==0) strcpy(new_usual_dom,"7");
else if (strcmp(usual_dom,"OTHER               ")==0) strcpy(new_usual_dom,"7");
else if (strcmp(usual_dom,"UNKNOWN             ")==0) strcpy(new_usual_dom,"0");
else strcpy(new_usual_dom,"X");
#endif
}
exit(0);
}

-------------------------------script to test it---------------------------
echo Normal
cc -o x x.c
x < in

echo Optimised
cc -O -o xopt x.c
xopt < in | cat -v

echo Optimised with what should be irrelevant code removed
cc -O -DKILL3 -o xopt2 x.c
xopt2 < in
-------------------------------output of test------------------------------
Normal
'8040'
'6000'
Optimised
' ^ClD'
' ^Cl0'
Optimised with what should be irrelevant code removed
'8040'
'6000'
-- 
 _--_|\		Craig Macbride	<s900387 at minyos.xx.rmit.oz.au>
/      \
\_.--.*/	The above are simply my comments, not necessarily
      v		the views of any other being or organisation.