During a mainline bootstrap on alpha-dec-osf5.1b, the libstdc++ configure
failed:

checking for exception model to use... configure: error: unable to detect exception model
make[1]: *** [configure-target-libstdc++-v3] Error 1

config.log reveals:

configure:13794: checking for exception model to use
configure:13838:  /vol/gccsrc/obj/gcc-4.3.0-20070612/5.1b-gcc/./gcc/xgcc -shared-libgcc -B/vol/gccsrc/obj/gcc-4.3.0-20070612/5.1b-gcc/./gcc -nostdinc++ -L/vol/gccsrc/obj/gcc-4.3.0-20070612/5.1b-gcc/alpha-dec-osf5.1b/libstdc++-v3/src -L/vol/gccsrc/obj/gcc-4.3.0-20070612/5.1b-gcc/alpha-dec-osf5.1b/libstdc++-v3/src/.libs -B/vol/gcc/alpha-dec-osf5.1b/bin/ -B/vol/gcc/alpha-dec-osf5.1b/lib/ -isystem /vol/gcc/alpha-dec-osf5.1b/include -isystem /vol/gcc/alpha-dec-osf5.1b/sys-include -c -S  conftest.cc >&5
configure: In function 'void foo()':
configure:13836: error: end insn 27 for block 7 not found in the insn stream
configure:13836: error: head insn 24 for block 7 not found in the insn stream
configure:13836: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.
configure:13841: $? = 1
configure:13870: error: unable to detect exception model

This happens with the following conftest.cc:

struct S { ~S(); };
void bar();
void foo()
{
  S s;
  bar();
}

 % ./cc1plus conftest.cc
 void foo()
Analyzing compilation unit
Performing interprocedural optimizations
 <visibility> <early_local_cleanups> <inline>Assembling functions:
 void foo()
conftest.cc: In function 'void foo()':
conftest.cc:7: error: end insn 27 for block 7 not found in the insn stream
conftest.cc:7: error: head insn 24 for block 7 not found in the insn stream
conftest.cc:7: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.

Running gdb reveals

Program received signal SIGSEGV, Segmentation fault.
rtl_verify_flow_info () at /vol/gcc/src/gcc-dist/gcc/cfgrtl.c:2005
(gdb) where
#0  rtl_verify_flow_info () at /vol/gcc/src/gcc-dist/gcc/cfgrtl.c:2005
#1  0x0000000120516638 in verify_flow_info () at /vol/gcc/src/gcc-dist/gcc/cfghooks.c:245
#2  0x0000000120618934 in commit_edge_insertions () at /vol/gcc/src/gcc-dist/gcc/cfgrtl.c:1467
#3  0x0000000120415bcc in alpha_gp_save_rtx () at /vol/gcc/src/gcc-dist/gcc/config/alpha/alpha.c:4784
#4  0x00000001206406fc in gen_exception_receiver () at /vol/gcc/src/gcc-dist/gcc/config/alpha/alpha.md:7019
#5  0x0000000120314dc8 in finish_eh_generation () at /vol/gcc/src/gcc-dist/gcc/except.c:1633
#6  0x0000000120314f98 in rest_of_handle_eh () at /vol/gcc/src/gcc-dist/gcc/except.c:3985
#7  0x0000000120421978 in execute_one_pass (pass=0x0) at /vol/gcc/src/gcc-dist/gcc/passes.c:1124
#8  0x0000000120421c48 in execute_pass_list (pass=0x0) at /vol/gcc/src/gcc-dist/gcc/passes.c:1177
#9  0x0000000120421c5c in execute_pass_list (pass=0x0) at /vol/gcc/src/gcc-dist/gcc/passes.c:1178
#10 0x00000001204fef44 in tree_rest_of_compilation (fndecl=0x0) at /vol/gcc/src/gcc-dist/gcc/tree-optimize.c:406
#11 0x00000001202535c8 in c_expand_body (fndecl=0x140137d80) at /vol/gcc/src/gcc-dist/gcc/c-common.c:4331
#12 0x00000001201ea958 in expand_body (fn=0x18de60) at /vol/gcc/src/gcc-dist/gcc/cp/semantics.c:3136
#13 0x0000000120423f60 in cgraph_expand_function (node=0x18de60) at /vol/gcc/src/gcc-dist/gcc/cgraphunit.c:1073
#14 0x0000000120427400 in cgraph_optimize () at /vol/gcc/src/gcc-dist/gcc/cgraphunit.c:1142
#15 0x000000012015e054 in cp_write_global_declarations () at /vol/gcc/src/gcc-dist/gcc/cp/decl2.c:3305
#16 0x00000001204432e0 in toplev_main (argc=1, argv=0x0) at /vol/gcc/src/gcc-dist/gcc/toplev.c:1064
#17 0x000000012029fe98 in main (argc=1075019136, argv=0x11fffbb30) at /vol/gcc/src/gcc-dist/gcc/main.c:35
(gdb) p x
$1 = 0x0

I.e. rtl_verify_flow_info dereferences a NULL pointer.  This happens only
on alpha-dec-osf5.1b, alpha-dec-osf4.0f is unaffected.

Environment:
System: OSF1 bartok V5.1 2650 alpha
Machine: alpha
	
host: alpha-dec-osf5.1b
build: alpha-dec-osf5.1b
target: alpha-dec-osf5.1b
configured with: /vol/gcc/src/gcc-dist/configure --prefix=/vol/gcc --with-local-prefix=/vol/gcc --disable-nls --host alpha-dec-osf5.1b --build alpha-dec-osf5.1b --target alpha-dec-osf5.1b --with-gmp=/vol/gcc --with-mpfr=/vol/gcc --enable-languages=c,c++,fortran,java,objc,ada --disable-libmudflap

How-To-Repeat:
Bootstrap as described above.