http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58478
Bug ID: 58478
Summary: very slow compilation at -O1 and above on a nested
loop
Product: gcc
Version: 4.7.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: su at cs dot ucdavis.edu
The following testcase takes much longer to compile at -O1 and above using GCC
4.7.3 on x86_64-linux (in both 32-bit and 64-bit modes).
It does not seem to affect 4.8 and the current trunk.
$ gcc-4.7 -v
Using built-in specs.
COLLECT_GCC=gcc-4.7
COLLECT_LTO_WRAPPER=/usr/local/gcc-4.7/libexec/gcc/x86_64-unknown-linux-gnu/4.7.3/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-4.7.3/configure
--enable-languages=c,c++,objc,obj-c++,fortran,lto --disable-checking
--with-gmp=/usr/local/gcc-4.7 --with-mpfr=/usr/local/gcc-4.7
--with-mpc=/usr/local/gcc-4.7 --with-ppl=/usr/local/gcc-4.7
--with-cloog=/usr/local/gcc-4.7 --prefix=/usr/local/gcc-4.7
Thread model: posix
gcc version 4.7.3 (GCC)
$ time gcc-4.7 -O0 small.c
0.02user 0.02system 0:00.05elapsed 86%CPU (0avgtext+0avgdata 38336maxresident)k
0inputs+32outputs (0major+6471minor)pagefaults 0swaps
$ time gcc-4.7 -O1 small.c
33.43user 0.12system 0:33.64elapsed 99%CPU (0avgtext+0avgdata
660976maxresident)k
0inputs+32outputs (0major+53023minor)pagefaults 0swaps
$ time gcc-4.8 -O1 small.c
0.02user 0.02system 0:00.05elapsed 85%CPU (0avgtext+0avgdata 36704maxresident)k
0inputs+32outputs (0major+6364minor)pagefaults 0swaps
$ time gcc-trunk -O1 small.c
0.04user 0.01system 0:00.07elapsed 82%CPU (0avgtext+0avgdata 42656maxresident)k
0inputs+32outputs (0major+6700minor)pagefaults 0swaps
$
-----------------------------
int a, b, c, d, e;
int main ()
{
for (a = 0; a < 10; a++)
for (b = 0; b < 10; b++)
for (c = 0; c < 10; c++)
for (d = 0; d < 10; d++)
for (e = 0; e < 10; e++)
;
return 0;
}
