Dear all,

error recovery on arithmetic errors during simplification has bugged
me for a long time, especially since the occurence of ICEs depended
on whether -frange-check is specified or not, whether array ctors
were involved, etc.

I've now come up with the attached patch that classifies the arithmetic
result codes into "hard" and "soft" errors.

A "soft" error means that it is an overflow or other exception (e.g. NaN)
that is ignored with -fno-range-check.  After the patch, a soft error
will not stop simplification (a hard one will), and error status will be
passed along.

I took this opportunity to change the emitted error for division by zero
for real and complex division dependent on whether the numerator is
regular or not.  This makes e.g. (0.)/0 a NaN and now says so, in
accordance with some other brands.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

Other comments?

Thanks,
Harald