C++ instance copy bug on powerpc

[Jan Nieuwenhuizen <janneke at gnu dot org>]

Hi egcs gurus,

We've been experiencing weird bugs with LilyPond (1.1.35-1.1.51)
on the Linux-powerpc platform, that seemed guile-related.  However,
yesterday, I got the latest glibc-2.1 based LinuxPPC release 
(ftp.linuxppc.org/linuxppc/R5), including an upgrade from egcs 1.1b 
to 1.1.2.

Now it seems that an egcs bug can be pinned down:

    template<class T>
    T*dest, T*src

      *dest++ = *src++;

produces erroneous code, if class T is fat enough.  See the file below.

Greetings,

Jan.


/*

  egcs.cc -- powerpc bug
  
  19:58:39 appel ~/usr/src/c++$ make 
  g++  egcs.cc -o egcs
  19:59:03 appel ~/usr/src/c++$ ./egcs 
  Foo: 0 (0)
  Foo: 1 (0)
  Foo: 2 (0)
  Foo: 3 (0)
  19:59:22 appel ~/usr/src/c++$ rm egcs
  19:59:28 appel ~/usr/src/c++$ make CFLAGS=-Dweird_powerpc_bug
  g++ -Dweird_powerpc_bug egcs.cc -o egcs
  19:59:30 appel ~/usr/src/c++$ ./egcs 
  Foo: 1 (0)
  Foo: 2 (0)
  Foo: 3 (0)
  Foo: 1 (0)


  vanilla LinuxPPC Release5 (1999)
  19:59:32 appel ~/usr/src/c++$ uname -a
  Linux appel.flower 2.2.6-15apmac #1 Fri Apr 30 12:52:03 EDT 1999 ppc unknown


  20:01:26 appel ~/usr/src/c++$ egcs -v
  Reading specs from /usr/lib/gcc-lib/ppc-redhat-linux/egcs-2.91.66/specs
  gcc version egcs-2.91.66 19990314 (egcs-1.1.2 release)

  egcs-1.1.2-12c.src.rpm
  glibc-2.1.1-6c.src.rpm
 */
  

#include <stdio.h>

#define INLINE

template<class T> INLINE void 
arrcpy (T*dest, T*src, int count)
{
  for (int i_shadows_local=0; i_shadows_local < count ; i_shadows_local++)
#ifdef weird_powerpc_bug
    *dest++ = *src++;
#else
    {
      // urg: wierd egcs-1.1.2 bug on ppc
      *dest = *src;
      dest++, src++;
    }
#endif
}

/*
  Modelled after LilyPond's Stem_info
 */
class Foo
{
private:
  int bar_;
  int copied_;

  /*
    Must be big enough to trigger the memcpy implementation
   */
  int int3;
  double d1, d2, d3, d4, d5;
  char* p1;
public:
  Foo ()
    {
      bar_ = -1;
      copied_ = 0;
    }
  Foo (int i)
    {
      bar_ = i;
      copied_ = 0;
    }
  Foo (Foo const& src)
    {
      bar_ = src.bar_;
      copied_ = 1;
    }
#if 0 // this will fix it too: no memcpy
  Foo& operator = (Foo const& src)
    {
      bar_ = src.bar_;
      copied_ = 1;
      return *this;
    }
#endif
  void print ()
    {
      printf ("Foo: %d (%d)\n", bar_, copied_);
    }
};

int
main ()
{
  Foo a[4];
  Foo b[4];

  for (int i = 0; i < 4; i++)
    a[i] = Foo (i);
  
  arrcpy (b, a, 4);

  for (int i = 0; i < 4; i++)
    b[i].print ();

  return 0;
}


Jan Nieuwenhuizen <janneke@gnu.org> | GNU LilyPond - The music typesetter
http://www.xs4all.nl/~jantien/      | http://www.lilypond.org/