Bootstrap failure with --enable-checking in flow.c

[Jeffrey A Law]

  In message < u8wvl8rnrg.fsf@gromit.rhein-neckar.de >you write:
  > I get a segmentation fault in cc1 when compiling function.c:
  > stage1/xgcc -Bstage1/ -B/opt/gcc-2.96/i686-pc-linux-gnu/bin/ -c  -DIN_GCC  
  >   -W -Wall -Wtraditional -pedantic -Wno-long-long -O2 -g -O2  -DHAVE_CONFIG
  > _H    -I. -I/cvs/gcc/gcc -I/cvs/gcc/gcc/config -I/cvs/gcc/gcc/../include /c
  > vs/gcc/gcc/function.c
  > 
  > Here's some output from gdb:
  > 0x82ce7ac in make_edge (edge_cache=0x0, src=0x88e6228, dst=0x0, flags=0) at
  >  /cvs/gcc/gcc/flow.c:1121
  > 1121      e->pred_next = dst->pred;
  > (gdb) up
  > #1  0x82ceacb in make_label_edge (edge_cache=0x0, src=0x88e6228, label=0x40
  > 6c92c0, flags=0) at /cvs/gcc/gcc/flow.c:1153
  > 1153      make_edge (edge_cache, src, BLOCK_FOR_INSN (label), flags);
  > (gdb) p label
  > $1 = 0x406c92c0
  > (gdb) pr label
  > (code_label 3751 0 0 1167 "" "" [5 uses])
This label is not threaded onto the insn chain, thus BLOCK_FOR_INSN is
NULL.

The first step is to find out if that label is used by an insn that is
in the chain.  If so, then something incorrectly deleted that label.

jeff