[Bug c++/40230] New: it takes too much time to compile using -O2

["gcc-bugzilla at m dot nya3 dot jp" <gcc-bugzilla at gcc dot gnu dot org>]

With -O2, the source code below takes too much time (about 20s) to compile.
If I change the typedef as follows, compile finishes instantly.
- typedef BigTerm<30> term_t;
+ typedef BigTerm<29> term_t;
I tried to shorten the code as short as possible, so changing almost any part
of it will cause the problem to disappear.

Thanks,
Shuhei


$ cat g++-stall.cpp

template<int N>
struct BigTerm {
    int lo;
    BigTerm<N-1> hi;

    BigTerm() {}
    BigTerm(int lo, const BigTerm<N-1>& hi) : lo(lo), hi(hi) {}

    bool any() {
        return (lo || hi.any());
    }

    BigTerm zero()  {
        return BigTerm(0, BigTerm<N-1>());
    }
};

template<>
struct BigTerm<1> {
    int u;

    BigTerm() {}
    BigTerm(const BigTerm& rhs) : u(rhs.u) {}

    bool any() {
        return 0;
    }
};

typedef BigTerm<30> term_t;

struct TermBase {
    term_t obj;
    term_t get() {
        return obj;
    }
};

struct virtual_reference {
    TermBase base;
    virtual void filter() {
        for(int i = 0; i < 10; i++) {
            base.get().any();
        }
    }
};

void f() {
    term_t a;
    a.zero();
    new virtual_reference();
}

$ time g++ -O2 -c -v g++-stall.cpp
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.3.2-1.1'
--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-cld --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.3.2 (Debian 4.3.2-1.1)
COLLECT_GCC_OPTIONS='-O2' '-c' '-v' '-shared-libgcc' '-mtune=generic'
 /usr/lib/gcc/x86_64-linux-gnu/4.3.2/cc1plus -quiet -v -D_GNU_SOURCE
g++-stall.cpp -quiet -dumpbase g++-stall.cpp -mtune=generic -auxbase g++-stall
-O2 -version -o /tmp/ccqqIC5b.s
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/4.3.2/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/usr/include/x86_64-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/4.3
 /usr/include/c++/4.3/x86_64-linux-gnu
 /usr/include/c++/4.3/backward
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/4.3.2/include
 /usr/lib/gcc/x86_64-linux-gnu/4.3.2/include-fixed
 /usr/include
End of search list.
GNU C++ (Debian 4.3.2-1.1) version 4.3.2 (x86_64-linux-gnu)
        compiled by GNU C version 4.3.2, GMP version 4.2.2, MPFR version 2.3.2.
warning: MPFR header version 2.3.2 differs from library version 2.3.1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 836c9d30f580c422b521aa9b7a9bf559
COLLECT_GCC_OPTIONS='-O2' '-c' '-v' '-shared-libgcc' '-mtune=generic'
 as -V -Qy -o g++-stall.o /tmp/ccqqIC5b.s
GNU assembler version 2.18.0 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Debian) 2.18.0.20080103
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.3.2/:/usr/lib/gcc/x86_64-linux-gnu/4.3.2/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.3.2/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.3.2/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.3.2/:/usr/lib/gcc/x86_64-linux-gnu/4.3.2/:/usr/lib/gcc/x86_64-linux-gnu/4.3.2/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.3.2/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-O2' '-c' '-v' '-shared-libgcc' '-mtune=generic'
g++ -O2 -c -v g++-stall.cpp  20.30s user 0.01s system 99% cpu 20.328 total


-- 
           Summary: it takes too much time to compile using -O2
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: gcc-bugzilla at m dot nya3 dot jp
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40230