Sign extension of type with precision of 0 causes fault in force_fit_type

[John David Anglin]

The following error occured in my latest build under vax ultrix:

/xxx/gnu/gcc-3.0/objdir/gcc/xgcc -B/xxx/gnu/gcc-3.0/objdir/gcc/ -nostdinc++ -L/xxx/gnu/gcc-3.0/objdir/vax-dec-ultrix4.3/libstdc++-v3/src -L/xxx/gnu/gcc-3.0/objdir/vax-dec-ultrix4.3/libstdc++-v3/src/.libs -B/usr/local/vax-dec-ultrix4.3/bin/ -B/usr/local/vax-dec-ultrix4.3/lib/ -isystem /usr/local/vax-dec-ultrix4.3/include -nostdinc++ -I../../../../libstdc++-v3/include -I../../../../libstdc++-v3/include/std -I../../../../libstdc++-v3/include/c_std -I../include -I../../../../libstdc++-v3/libsupc++ -I../libio -I../../../../libstdc++-v3/libio -I../../../../libstdc++-v3/libmath -g -O2 -fno-implicit-templates -Wall -Wno-format -W -Wwrite-strings -Winline -fdiagnostics-show-location=once -g -c limitsMEMBERS.cc -o limitsMEMBERS.o
In file included from limitsMEMBERS.cc:37:
../include/bits/std_limits.h:56: Internal error: Illegal instruction

The following simplified program will generate the illegal instruction
fault:

namespace std {

    enum float_round_style {
	round_indeterminate = -1,
	round_toward_zero = 0,
	round_to_nearest = 1,
	round_toward_infinity = 2,
	round_toward_neg_infinity = 3
    };

}

The fault occurs in force_fit_type in fold-const.c.  This code causes
the problem when prec has the value 0:

  /* If the value's sign bit is set, extend the sign.  */
  if (prec != 2 * HOST_BITS_PER_WIDE_INT
      && (prec > HOST_BITS_PER_WIDE_INT
	  ? 0 != (TREE_INT_CST_HIGH (t)
		  & ((HOST_WIDE_INT) 1
		     << (prec - HOST_BITS_PER_WIDE_INT - 1)))
	  : 0 != (TREE_INT_CST_LOW (t)
		  & ((unsigned HOST_WIDE_INT) 1 << (prec - 1)))))
    {

Is a precision of 0 illegal or should the above be fixed to handle
this situation?

Dave
-- 
J. David Anglin                                  dave.anglin@nrc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6605)