Hello,
As instructed in http://gcc.gnu.org/ml/gcc/2010-04/msg00505.html i'm filing
this.
I've noticed gcc 4.5 has more trouble than it used to to removed dead stores
when dealing with arrays, as exemplified by
$ cat huh.cc
struct foo_t {
float x, y, z;
foo_t() {}
foo_t(float a, float b, float c) : x(a),y(b),z(c) {}
friend foo_t operator*(foo_t lhs, float s) { return foo_t(lhs.x*s,
lhs.y*s, lhs.z*s); }
friend float dot(foo_t lhs, foo_t rhs) { return lhs.x*rhs.x +
lhs.y*rhs.y + lhs.z*rhs.z; }
};
struct bar_t {
float m[3];
bar_t() {}
bar_t(float a, float b, float c) { m[0]=a; m[1]=b; m[2]=c; }
friend bar_t operator*(bar_t lhs, float s) { return bar_t(lhs.m[0]*s,
lhs.m[1]*s, lhs.m[2]*s); }
friend float dot(bar_t lhs, bar_t rhs) { return lhs.m[0]*rhs.m[0] +
lhs.m[1]*rhs.m[1] + lhs.m[2]*rhs.m[2]; }
};
namespace {
template<typename T> float magsqr(T v) { return dot(v, v); }
template<typename T> T norm(T v) { return
v*(1/__builtin_sqrtf(magsqr(v))); }
}
void frob1(const foo_t &a, foo_t &b) { b = norm(a); }
void frob2(const bar_t &a, bar_t &b) { b = norm(a); }
int main() { return 0; }
$ /usr/local/gcc-4.5.0/bin/g++ -O2 -ffast-math -march=native huh.cc
Whereas frob1 and frob2 do not differ with, say, gcc 4.4.1, they now do.
$ /usr/local/gcc-4.5.0/bin/g++ -v
Using built-in specs.
COLLECT_GCC=/usr/local/gcc-4.5.0/bin/g++
COLLECT_LTO_WRAPPER=/usr/local/gcc-4.5.0/libexec/gcc/x86_64-unknown-linux-gnu/4.5.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --prefix=/usr/local/gcc-4.5.0
--enable-languages=c,c++ --enable-threads=posix --disable-checking
--disable-nls --with-system-zlib --disable-shared --enable-checking=none
--disable-bootstrap --enable-mpfr --enable-gold
Thread model: posix
gcc version 4.5.0 (GCC)
$ g++ -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.1-4ubuntu9'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --disable-werror
--with-arch-32=i486 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu9)
--
Summary: 4.5.0 regression, array vs members, dead code removal
issues
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: tbptbp at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43846
