Subject: B19: gcc optimizer generates bad code
From: [email-masked] (Tom Uban)

22 Mar 1998 06:05:19 -0800
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To: [email-masked]

/*
 * When this simple code sample is compiled with the Cygnus B19.1 gcc
 * compiler using either -O2 or -O3, bad code is generated.
 *	gcc -O2 test.c
 *  or
 *	gcc -O3 test.c
 *
 * This program should always print the number 4. When compiled
 * with -O2 or -O3 the number 1 is printed. The dissassembled output
 * seems to indicate that the loop code generation is broken.
 *
 * The result of gcc -v is:
 *	Reading specs from
C:\CYGNUS\B19\H-I386~1\lib\gcc-lib\i386-cygwin32\2.7-B19\specs
 *	gcc driver version 2.7-B19 executing gcc version 2.7-97r2aBeta
 *
 * The Cygnus B18 (gcc version cygnus-2.7.2-970404) release did not
 * exhibit this behavior.
 *
 * Tom Uban - 17 March 1998
 * [email-masked]
 */
unsigned short foobar = 1;

main()
{
	unsigned short *sptr = &foobar;
	unsigned long cksum;
	int i;

	cksum = 0;

	for (i = 0; i < 4; i++)
		cksum += *sptr;

	printf("%d\n", cksum);
}

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