I hope you will find this information usefull.
I am not in the linux-kernel list so, if posible, I would like to be
personally CC'ed the answers/comments sent to the list in response to
this posting.
I think I heve found a bug in gcc. I have tried both egcs 1.1.2 (gcc
2.91.66) and gcc 2.95.2 versions.
I am attaching you a simplified test program ('bug.c', a really simple
program).
To generate the faulty program from correct code compile as:
gcc -O2 -o bug bug.c
You can generate good code in two ways:
1. Compiling with:
gcc -fno-strength-reduce -O2 -o bug bug.c
So the problem is with the option -fstrength-reduce which is
active with the common '-O2' optimization option.
2. Uncomment the printf at line 34. Bugs are surprising.
I have also sent the bug report to the gcc maintainers.
Is it really a bug?
Thank you,
David Llorens.
/*
#include <stdio.h>
*/
#define SMALL_N 2
#define NUM_ELEM 4
int main(void)
{
int listElem[NUM_ELEM]={30,2,10,5};
int listSmall[SMALL_N];
int i, j;
int posGreatest=-1, greatest=-1;
for (i=0; i<SMALL_N; i++) {
listSmall[i] = listElem[i];
if (listElem[i] > greatest) {
posGreatest = i;
greatest = listElem[i];
}
}
for (i=SMALL_N; i<NUM_ELEM; i++) {
if (listElem[i] < greatest) {
listSmall[posGreatest] = listElem[i];
posGreatest = 0;
greatest = listSmall[0];
for (j=1; j<SMALL_N; j++)
if (listSmall[j] > greatest) {
posGreatest = j;
greatest = listSmall[j];
}
/*
printf("%d\n", posGreatest);
*/
}
}
printf("Correct output: 5 2\n");
printf("GCC output: ");
for (i=0; i<SMALL_N; i++) printf(" %.1d", listSmall[i]);
printf("\n");
return (1);
}
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This archive was generated by hypermail 2b29 : Wed Feb 28 2001 - 21:00:11 EST