The following very simple testcase causes a hang when compiled with certain
flags:
int main (int argc, char **argv) {
char v = !**argv;
if (**argv != v)
**argv = argc;
if (**argv)
**argv = argc;
return 0;
}
The following command lines cause gcc to hang:
$ gcc -O2 -ftracer foo.c
$ gcc -O -fcse-follow-jumps -frerun-cse-after-loop -ftracer foo.c
I could not find a command line that causes a hang without -O (I tried the docs
and the "options enabled" output of -v -Q; I haven't tried going through the gcc
sources).
When run with -dy, the last few lines of output are:
Next token is 125 ('}' [}])
Shifting token 125 ('}'), Entering state 540
Reducing via rule 447 (line 1970), -> poplevel
state stack now 0 2 40 144 223 314 423 502 593 559 278 379 463 540
Entering state 625
Reducing via rule 459 (line 2046), pushlevel maybe_label_decls
compstmt_contents_nonempty '}' poplevel -> compstmt_nostart
state stack now 0 2 40 144 223 314 423 502 593 559
Entering state 650
Reducing via rule 463 (line 2076), compstmt_start compstmt_nostart -> compstmt
state stack now 0 2 40 144 223 314 423 502 593
Entering state 586
Reducing via rule 455 (line 2034), compstmt -> compstmt_or_error
state stack now 0 2 40 144 223 314 423 502 593
Entering state 695
Reducing via rule 21 (line 375), declspecs_ts setspecs declarator @3
old_style_parm_decls save_location @4 compstmt_or_error -> fndef
When run with -da, foo.c.15.tracer is written and foo.c.18.cse2 is zero-length.
I assume this means it is hanging during the second CSE pass or subsequent jump
optimization.
This is my gcc -v:
Reading specs from /usr/lib/gcc/i686-pc-linux-gnu/3.4.3/specs
Configured with: /var/tmp/portage/gcc-3.4.3.20050110/work/gcc-3.4.3/configure
--enable-version-specific-runtime-libs --prefix=/usr
--bindir=/usr/i686-pc-linux-gnu/gcc-bin/3.4.3
--includedir=/usr/lib/gcc/i686-pc-linux-gnu/3.4.3/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/3.4.3
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/3.4.3/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/3.4.3/info
--with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/3.4.3/include/g++-v3
--host=i686-pc-linux-gnu --disable-altivec --enable-nls
--without-included-gettext --enable-__cxa_atexit --enable-clocale=gnu
--with-system-zlib --disable-checking --disable-werror
--disable-libunwind-exceptions --enable-shared --enable-threads=posix
--disable-multilib --disable-libgcj --enable-languages=c,c++,f77
Thread model: posix
gcc version 3.4.3 20050110 (Gentoo Linux 3.4.3.20050110, ssp-3.4.3.20050110-0,
pie-8.7.7)
System type is Gentoo Linux 2005.0, glibc 2.3.4.20041102, kernel 2.6.10-nitro4,
Athlon XP.
The source file produces no warnings with -Wall.
The preprocessed output of the source file is the same as the original (with #
lines at the start and tabs converted to spaces).
--
Summary: CSE hang on very simple code with -O2 -ftracer
Product: gcc
Version: 3.4.3
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: rtl-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ed at catmur dot co dot uk
CC: gcc-bugs at gcc dot gnu dot org
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=19767
