with clang 8.0.7 and other versions there is an error on compilation. With gcc all works without issue.
Could you fix this bug?
It's an incompatibility, but it's unclear that it's a bug. Clang
intentionally range-checks these intrinsics because they map to
instructions that only have a valid form with the permitted (positive)
shift amounts.
If we relaxed that requirement then -O0 compilation would still be
broken but with a significantly worse error message, which I don't
think many Clang devs would consider acceptable (both because of the
different behaviour depending on -O* and the message) -- I certainly
wouldn't. GCC appears to do some kind of basic optimization that
eliminates the invalid instructions even at -O0, but that's not how
Clang works and is also unlikely to change in the short-medium term.
I have seen someone propose that intrinsics taking immediates should
also accept variables and lower to multiple-instruction equivalents if
necessary, but I wasn't terribly keen on that either personally. It
would add a reciprocal incompatibility with GCC in at least the short
term (possiblty forever if they nope out), and I tend to think most
people writing these would prefer to know if their call was
inefficient anyway.
Someone keen *might* be able to get a patch through cfe-commits that
allows the user to demote these errors to a warning as a compromise,
but I'm afraid otherwise the only suggestion is to rewrite code so
that invalid intrinsics are never called statically.