cc optimizer bug

[Archie Lachner]

Several people have asked for copies of the program that exercises the cc
optimizer bug that I reported recently.  One suggested that I submit it
to this news group.  Though a fix for the bug has already been posted, I'm
happy to comply.

-------

#include <stdio.h>

main()

{
	union {
		int						one_word;			/* one-word form */
		struct {
			unsigned int		type:7;				/* type */
			unsigned int		flag_1:1;			/* flag no 1 */
			unsigned int		flag_2:1;			/* flag no 2 */
			unsigned int		count:7;			/* count of whatever */
			unsigned int		number:16;			/* number of "things" */
		}						split;				/* split form */
	}							field_union;

	int							type;
	int							flag_1;
	int							flag_2;
	int							count;
	int							number;

	field_union.one_word = 0x300;
	fprintf(stdout, "foobar:  field_union = %d (%x hex)\n",
		field_union.one_word, field_union.one_word);

	type = field_union.split.type;
	fprintf(stdout, "foobar:  type = %d\n", type);

	flag_1 = field_union.split.flag_1;
	fprintf(stdout, "foobar:  flag_1 = %d\n", flag_1);

	flag_2 = field_union.split.flag_2;
	fprintf(stdout, "foobar:  flag_2 = %d\n", flag_2);

	count = field_union.split.count;
	fprintf(stdout, "foobar:  count = %d\n", count);

	/*
	 *	when this is compiled with optimization, "number" will be 3
	 *
	 *	it should be 0
	 *
	 *	the error can be traced to line 54 of the assembler output
	 *	produced using "cc -O -S"
	 *
	 *	the source address in a "movzwl" instruction is incorrect
	 */

	number = field_union.split.number;
	fprintf(stdout, "foobar:  number = %d\n", number);

	exit(0);
}
-- 

				Archie Lachner
				Logic Design Systems Division
				Tektronix, Inc.

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