Dear all,

as found by the reporter, the result of the intrinsic IBITS
differed from other compilers (e.g. Intel, NAG) for the corner
case that the LEN argument was equal to BIT_SIZE(I), which is
explicitly allowed by the standard.

We actually had an inconsistency for this case between
code generated by the frontend and compile-time simplified
expressions.

The reporter noticed that this is related to a restriction in
gcc that requires that shift widths shall be smaller than the
bit sizes, and we already special case this for ISHFT.
It makes sense to use the same special casing for IBITS.

Attached patch fixes this and regtests on x86_64-pc-linux-gnu.

OK for mainline?

This issue has been there for ages.  Shall this be backported
or left in release branches as is?

Thanks,
Harald