The following code compiled with just -O0 generates bad assembler with
undefined label:

int x(int a, int b)
{
  __label__ xlab;
  __label__ xlab2;

  void y(int b)
    {
       switch (b)
        {
          case 1: goto xlab;
          case 2: goto xlab;
        }
    }

  a = a + 2;

  y (b);

 xlab:;
  return a;

 xlab2:;
      a++;
  return a;

}

main (int ac)
{
  int i;
  if ((i=x (1, ac), printf("%d\n",i), i) != 2 + ac)
    abort ();

  exit (0);
}

The assembler failure looks like:
Undefined                       first referenced
 symbol                             in file
.LL9                                /var/tmp//ccLPhTcj.o
ld: fatal: Symbol referencing errors. No output written to a.out

The t04.nested tree already looks bad:
----------------------------------
y (b)
{
  voidD.28 *[3] * D.1136;
  voidD.28 *[3] * D.1138;

  switch (bD.1124)
    {
      case 1: goto <D1127>;
      case 2: goto <D1128>;
      default : goto <D1131>;
    }
  <D1127>:;
  D.1136 = &CHAIN.1D.1135->__nl_goto_bufD.1133;
  __builtin_nonlocal_goto (&<D1132>, D.1136);
  <D1128>:;
  D.1138 = &CHAIN.1D.1135->__nl_goto_bufD.1133;
  __builtin_nonlocal_goto (&<D1137>, D.1138);
  <D1131>:;
}

x (a, b)
{ 
  struct FRAME.x FRAME.0D.1134;
  intD.0 D.1129;
  voidD.28 xlabD.1122 = <<< error >>>;
  voidD.28 xlab2D.1123 = <<< error >>>;
  static voidD.28 yD.1125 (intD.0);
  
  aD.1118 = aD.1118 + 2;
  y (bD.1119) [static-chain: &FRAME.0D.1134];
  goto xlabD.1122;
  <D1137>: [non-local];
  xlabD.1122:;
  D.1129 = aD.1118;
  return D.1129;
  xlab2D.1123:;
  aD.1118 = aD.1118 + 1;
  D.1129 = aD.1118;
  return D.1129;
}
----------------------------------

The line with problems:  __builtin_nonlocal_goto (&<D1132>, D.1136);

The reference to &<D1132> is a reference to non-existent label.
This problem can be reproduced on all 4.0.* versions and 4.1-20050924 as well.
The versions 3.x are ok.

I think all hardware platforms may be affected.

Alex.