FYI: Latest gcc-8 snapshot gives ICE with later isl's

[Donald Parsons <dparsons at brightdsl dot net>]

I am getting ICE bootstrapping gcc-8-20180304.tar.xz when using either
isl-0.18 or isl-0.19.   I had never had a problem using latest isl over
the past couple of years, so a change in gcc last week introduced the
problem.

Normally I disable-bootstrap and use last weeks gcc-8 to build this
weeks gcc-8 and avoid the extra long bootstrap time.  This actually
worked, at least with isl-0.18 but the resulting gcc-8 gave ICE errors
building latest "pari-gp" and the latest-rc4 Linux kernel.  So went
back to bootstrapping with (Redhat gcc-7.3.1-2) and discovered the
above.

Here is failure (using isl-0.18; 0.19 looks same):
...
libtool: compile:  /home/don/src/gcc-8-20180304-obj/./prev-gcc/xgcc
-B/home/don/src/gcc-8-20180304-obj/./prev-gcc/ -B/opt/gcc/gcc-8-
0304/x86_64-redhat-linux/bin/ -B/opt/gcc/gcc-8-0304/x86_64-redhat-
linux/bin/ -B/opt/gcc/gcc-8-0304/x86_64-redhat-linux/lib/ -isystem
/opt/gcc/gcc-8-0304/x86_64-redhat-linux/include -isystem /opt/gcc/gcc-
8-0304/x86_64-redhat-linux/sys-include -DHAVE_CONFIG_H -I. -I../../gcc-
8-20180304/isl -I../../gcc-8-20180304/isl/include -Iinclude/ -g -O2
-gtoggle -MT isl_factorization.lo -MD -MP -MF
.deps/isl_factorization.Tpo -c ../../gcc-8-
20180304/isl/isl_factorization.c -o isl_factorization.o
during GIMPLE pass: pre
../../gcc-8-20180304/isl/isl_factorization.c: In function
'isl_basic_set_factorizer':
../../gcc-8-20180304/isl/isl_factorization.c:256:28: internal compiler
error: in compute_antic_aux, at tree-ssa-pre.c:2148
 __isl_give isl_factorizer *isl_basic_set_factorizer(
                            ^~~~~~~~~~~~~~~~~~~~~~~~
0x11e6790 compute_antic_aux
	../../gcc-8-20180304/gcc/tree-ssa-pre.c:2148
0x11e713b compute_antic
	../../gcc-8-20180304/gcc/tree-ssa-pre.c:2364
0x11ec1b1 execute
	../../gcc-8-20180304/gcc/tree-ssa-pre.c:4131
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
make[5]: *** [Makefile:1463: isl_factorization.lo] Error 1
make[5]: Leaving directory '/home/don/src/gcc-8-20180304-obj/isl'
make[4]: *** [Makefile:1571: all-recursive] Error 1
make[4]: Leaving directory '/home/don/src/gcc-8-20180304-obj/isl'
make[3]: *** [Makefile:1167: all] Error 2
make[3]: Leaving directory '/home/don/src/gcc-8-20180304-obj/isl'
make[2]: *** [Makefile:6155: all-stage2-isl] Error 2
make[2]: Leaving directory '/home/don/src/gcc-8-20180304-obj'
make[1]: *** [Makefile:25157: stage2-bubble] Error 2
make[1]: Leaving directory '/home/don/src/gcc-8-20180304-obj'
make: *** [Makefile:947: all] Error 2

Thanks,
Don