[Bug c++/39425] New: gcc loops after reporting template instantiation errors

["mm at mezzarobba dot net" <gcc-bugzilla at gcc dot gnu dot org>]

On the following example, gcc seems to loop and starts filling the ram after
reporting the errors. Same issue on x86_64-linux-gnu or with older 4.x
versions.

~/tmp$ cat test2.cpp
class a {

  template<unsigned int s>
    struct _rec {
      static const char size = _rec< (s >> 1) >::size;
    };

  template<>
  struct _rec <0> {
    static const char size = 0;
  };

  static const unsigned int value = _rec < 1 >::size;

}
~/tmp$ g++-4.3 -v -ftemplate-depth-4 test2.cpp
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.3.3-5'
--with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.3
--program-suffix=-4.3 --enable-clocale=gnu --enable-libstdcxx-debug
--enable-objc-gc --enable-mpfr --enable-targets=all --with-tune=generic
--enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
--target=i486-linux-gnu
Thread model: posix
gcc version 4.3.3 (Debian 4.3.3-5) 
COLLECT_GCC_OPTIONS='-v' '-ftemplate-depth-4' '-shared-libgcc' '-mtune=generic'
 /usr/lib/gcc/i486-linux-gnu/4.3.3/cc1plus -quiet -v -D_GNU_SOURCE test2.cpp
-quiet -dumpbase test2.cpp -mtune=generic -auxbase test2 -version
-ftemplate-depth-4 -o /tmp/ccZ7Hrtb.s
ignoring nonexistent directory "/usr/local/include/i486-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/i486-linux-gnu/4.3.3/../../../../i486-linux-gnu/include"
ignoring nonexistent directory "/usr/include/i486-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/4.3
 /usr/include/c++/4.3/i486-linux-gnu
 /usr/include/c++/4.3/backward
 /usr/local/include
 /usr/lib/gcc/i486-linux-gnu/4.3.3/include
 /usr/lib/gcc/i486-linux-gnu/4.3.3/include-fixed
 /usr/include
End of search list.
GNU C++ (Debian 4.3.3-5) version 4.3.3 (i486-linux-gnu)
        compiled by GNU C version 4.3.3, GMP version 4.2.4, MPFR version
2.4.0-p2.
GGC heuristics: --param ggc-min-expand=64 --param ggc-min-heapsize=64543
Compiler executable checksum: 6dda33bccb1e3fda2076fc047c4bfa75
test2.cpp:8: error: explicit specialization in non-namespace scope &#8216;class
a&#8217;
test2.cpp:5: error: template instantiation depth exceeds maximum of 4 (use
-ftemplate-depth-NN to increase the maximum) instantiating
&#8216;a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<1u>::size&#8217;
test2.cpp:13:   instantiated from here

test2.cpp:5: error: template instantiation depth exceeds maximum of 4 (use
-ftemplate-depth-NN to increase the maximum) instantiating
&#8216;a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<1u>::size&#8217;
test2.cpp:13:   instantiated from here

test2.cpp:5: error: template instantiation depth exceeds maximum of 4 (use
-ftemplate-depth-NN to increase the maximum) instantiating
&#8216;a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<1u>::size&#8217;
test2.cpp:13:   instantiated from here

test2.cpp:5: error: &#8216;a::_rec<0u>::size&#8217; cannot be initialized by a
non-constant expression when being declared
test2.cpp:5: error: template instantiation depth exceeds maximum of 4 (use
-ftemplate-depth-NN to increase the maximum) instantiating
&#8216;a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<1u>::size&#8217;
test2.cpp:13:   instantiated from here

test2.cpp:5: error: template instantiation depth exceeds maximum of 4 (use
-ftemplate-depth-NN to increase the maximum) instantiating
&#8216;a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<0u>::size&#8217;
test2.cpp:5:   instantiated from &#8216;const char a::_rec<1u>::size&#8217;
test2.cpp:13:   instantiated from here

^C
(exit 130)


-- 
           Summary: gcc loops after reporting template instantiation errors
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mm at mezzarobba dot net
 GCC build triplet: i486-linux-gnu
  GCC host triplet: i486-linux-gnu
GCC target triplet: i486-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39425