gimple, internal-fn: Add IFN_TRAP and use it for __builtin_unreachable [PR106099]

gimple, internal-fn: Add IFN_TRAP and use it for __builtin_unreachable [PR106099]

__builtin_unreachable and __ubsan_handle_builtin_unreachable don't
use vops, they are marked const/leaf/noreturn/nothrow/cold.
But __builtin_trap uses vops, isn't const, just leaf/noreturn/nothrow/cold.
This is I believe so that when users explicitly use __builtin_trap in their
sources they get stores visible at the trap side.
-fsanitize=unreachable -fsanitize-undefined-trap-on-error used to transform
__builtin_unreachable to __builtin_trap even in the past, but the sanopt pass
has TODO_update_ssa, so it worked fine.

Now that gimple_build_builtin_unreachable can build a __builtin_trap call
right away, we can run into problems that whenever we need it we would need
to either manually or through TODO_update* ensure the vops being updated.

Though, as it is originally __builtin_unreachable which is just implemented
as trap, I think for this case it is fine to avoid vops.  For this the
patch introduces IFN_TRAP, which has ECF_* flags like __builtin_unreachable
and is expanded as __builtin_trap.

2022-07-28  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/106099
	* internal-fn.def (TRAP): New internal fn.
	* internal-fn.h (expand_TRAP): Declare.
	* internal-fn.cc (expand_TRAP): Define.
	* gimple.cc (gimple_build_builtin_unreachable): For BUILT_IN_TRAP,
	use internal fn rather than builtin.

	* gcc.dg/ubsan/pr106099.c: New test.