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[Bug c/24004] New: gcc 4.0.1 gives bogus 'may be unused warnings' at -O3
- From: "SLTxLQEc4vuR5kMzK at anime dot net" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 21 Sep 2005 22:11:59 -0000
- Subject: [Bug c/24004] New: gcc 4.0.1 gives bogus 'may be unused warnings' at -O3
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
$ cat /etc/fedora-release
Fedora Core release 4 (Stentz)
$ uname -a
Linux host 2.6.13.1 #4 Sat Sep 17 10:57:37 PDT 2005 x86_64 x86_64 x86_64 GNU/Linux
$ gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-libgcj-multifile
--enable-languages=c,c++,objc,java,f95,ada --enable-java-awt=gtk
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --host=x86_64-redhat-linux
Thread model: posix
gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
testcase.c:
===========
#include <math.h>
typedef float vec_t;
typedef vec_t vec3_t[3];
void VectorSubtract( const vec3_t veca, const vec3_t vecb, vec3_t out ) {
out[0] = veca[0] - vecb[0];
out[1] = veca[1] - vecb[1];
out[2] = veca[2] - vecb[2];
}
void VectorCopy( const vec3_t in, vec3_t out ) {
out[0] = in[0];
out[1] = in[1];
out[2] = in[2];
}
vec_t VectorLength( const vec3_t v ) {
return sqrt (v[0]*v[0] + v[1]*v[1] + v[2]*v[2]);
}
float BG_SplineLength( void ) {
float i;
float granularity = 0.01f;
float dist = 0;
vec3_t vec[2];
vec3_t lastPoint;
vec3_t result;
for(i = 0; i <= 1.f; i += granularity ) {
VectorSubtract( vec[1], vec[0], result );
if( i != 0 ) {
VectorSubtract( result, lastPoint, vec[0] );
dist += VectorLength( vec[0] );
}
VectorCopy( result, lastPoint );
}
return dist;
}
int main( void ) {
BG_SplineLength();
return 0;
}
$ gcc -O2 -Wall -o testcase testcase.c
$ gcc -O3 -Wall -o testcase testcase.c
testcase.c: In function ?BG_SplineLength?:
testcase.c:26: warning: ?lastPoint[0]? may be used uninitialized in this function
testcase.c:26: warning: ?lastPoint[1]? may be used uninitialized in this function
testcase.c:26: warning: ?lastPoint[2]? may be used uninitialized in this function
testcase.c: In function ?main?:
testcase.c:26: warning: ?lastPoint[0]? may be used uninitialized in this function
testcase.c:26: warning: ?lastPoint[1]? may be used uninitialized in this function
testcase.c:26: warning: ?lastPoint[2]? may be used uninitialized in this function
gcc3.2 and 3.3 don't produce these bogus warnings.
--
Summary: gcc 4.0.1 gives bogus 'may be unused warnings' at -O3
Product: gcc
Version: 4.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: SLTxLQEc4vuR5kMzK at anime dot net
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24004