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From: "a dot simon at kent dot ac dot uk" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug optimization/13816] New: access to local array in while loop is optimized away Date: Thu, 22 Jan 2004 17:37:00 -0000 [thread overview] Message-ID: <20040122173740.13816.a.simon@kent.ac.uk> (raw) The body of a while loop that operates on a stack-allocated array is optimized away. Turning optimizations off gives correct bahviour. I observed this bug with gcc 3.2.2 on FreeBSD, other people have confirmed this for gcc 3.3.3 20031229 on Debian. This program: #include<stdio.h> void runBug(int lastElem) { int localArray[lastElem]; int j; for(j=0; j<lastElem; j++) localArray[j]=j; int temp=localArray[0]; size_t current=0; while (current<lastElem) localArray[current]=localArray[++current]; localArray[lastElem-1]=temp; for(j=0; j<lastElem; j++) printf("%i, ",localArray[j]); }; int main() { runBug(4); return 0; }; compiled with: gcc -O0 bug.c gives ./a.out 1, 2, 3, 0, (the while loop shuffles the list around, which is what I want). However with optimizations the loop reduces to incrementing the loop counter and nothing else: gcc -O2 bug.c gives: ./a.out 0, 1, 2, 0, Thanks, Axel. -- Summary: access to local array in while loop is optimized away Product: gcc Version: 3.3.3 Status: UNCONFIRMED Severity: critical Priority: P2 Component: optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: a dot simon at kent dot ac dot uk CC: gcc-bugs at gcc dot gnu dot org GCC build triplet: i386-unknown-freebsd5.1 GCC host triplet: i386-unknown-freebsd5.1 GCC target triplet: i386-unknown-freebsd5.1 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13816
next reply other threads:[~2004-01-22 17:37 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2004-01-22 17:37 a dot simon at kent dot ac dot uk [this message] 2004-01-22 18:14 ` [Bug optimization/13816] " pinskia at gcc dot gnu dot org
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