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[Bug tree-optimization/30493] New: [4.1 Regression] Unexpected compilation results: -O versus no optimization
- From: "sam at sambromley dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 17 Jan 2007 17:29:35 -0000
- Subject: [Bug tree-optimization/30493] New: [4.1 Regression] Unexpected compilation results: -O versus no optimization
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
The following C code demonstrates incorrect results when any optimization
is used:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <complex.h>
#include <math.h>
struct fs {
int order;
int numpoles;
unsigned int polemask;
complex data[100];
};
void choosepole(complex z, struct fs *flt)
{
static int i=0;
if (creal(z) < 0.0)
{
if (flt->polemask & 1)
flt->numpoles++;
flt->polemask >>= 1;
}
flt->data[i++]=z;
}
int main(int argc, char *argv[])
{
struct fs flt;
int i;
flt.order=3;
flt.numpoles=0;
flt.polemask=(~0);
memset(flt.data,0,100*sizeof(complex));
for (i=0;i<2*flt.order;i++)
{
/* Following line is optimized incorrectly!!! */
double theta = (flt.order&1) ?
(i*M_PI)/flt.order :
((i+0.5)*M_PI)/flt.order;
choosepole(cexp(I*theta),&flt);
}
for (i=0;i<2*flt.order;i++)
{
fprintf(stderr,"flt.data[%d]=%lg + I * %lg\n",
i,
creal(flt.data[i]),
cimag(flt.data[i]));
}
return EXIT_SUCCESS;
}
+++ This bug was initially created as a clone of Bug #30088 +++
The following C++ program (preprocessed source attached) produces unexpected
results when compiled with -O1 -fstrict-aliasing (as opposed to -O1 only) or
with any higher level of optimization (-O2 or -O3). No compilation warnings
are emitted in any of the cases.
#include <cassert>
#include <string>
struct A
{
A() : _x(0.0), _y(0.0) { }
float& f(const int& i) { return (i == 0 ? _x : _y); }
float _x, _y;
};
struct B
{
B(const char* s) : _s(s) { }
std::string g() { return std::string(_s); }
const char* _s;
};
A h(const char* s)
{
if (s == 0)
return A();
A a;
B b(s);
if (b.g().compare(std::string("")) == 0)
a.f(0) = a.f(1) = 1.0;
else if (b.g().compare(std::string("")))
b.g().compare(std::string(""));
return a;
}
int main()
{
A a(h(""));
assert(a._x > 0.0 && a._y > 0.0);
return 0;
}
Compilation results:
$ g++ -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../src/configure --prefix=/opt/gcc-4.1.1
Thread model: posix
gcc version 4.1.1
$ g++ -W -Wall -O1 testcase.cc
$ ./a.out
$ g++ -W -Wall -O1 -fstrict-aliasing testcase.cc
$ ./a.out
a.out: testcase.cc:34: int main(): Assertion `a._x > 0.0 && a._y > 0.0' failed.
Aborted
The assertion ceases to fail (with -O1 -fstrict-aliasing) when adding any
(single one) of the options -fno-tree-copy-prop, -fno-tree-dce,
-fno-tree-salias or -fno-inline to the compiler command line.
--
Summary: [4.1 Regression] Unexpected compilation results: -O
versus no optimization
Product: gcc
Version: 4.2.1
Status: UNCONFIRMED
Severity: critical
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: sam at sambromley dot com
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30493