http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50067
Bug #: 50067
Summary: Wrong code with -fpredictive-commoning
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: [email protected]
ReportedBy: [email protected]
Created attachment 24994
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24994
Output of "ajo-gcc -std=c99 -O -fpredictive-commoning test.c -v"
This failure reproduces for me with svn revision 177688 (2011-08-11). I'm on
Ubuntu 10.10, x86-64.
cat >test.c <<EOF
#include <stdio.h>
int a[6] = {0, 0, 0, 0, 7, 0};
static int *p = &a[4];
int main (int argc, char* argv[]) {
for (int i=0; i < 4; ++i) {
a[i+1] = (a[i+2] > i);
*p &= ~1;
}
printf("%d\n", a[4]);
}
EOF
gcc -std=c99 -O test.c ; ./a.out
gcc -std=c99 -O -fpredictive-commoning test.c ; ./a.out
The first command line above correctly produces "0".
The second command line, with -fpredictive-commoning, produces "6".
Note that -fpredictive-commoning is enabled as part of -O3.
This test case is reduced from the output of Csmith 2.1.0 (git hash 01aa8b04,
https://github.com/Quuxplusone/csmith/), using the following command line:
csmith --paranoid --no-longlong --pointers --arrays --jumps --no-consts
--volatiles --checksum --no-divs --muls --no-bitfields --no-packed-struct -s
278348999
