[Bug c/52283] "error: case label does not reduce to an integer constant" for constant folded cast expr

["joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52283

--- Comment #5 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2012-02-16 17:54:03 UTC ---
On Thu, 16 Feb 2012, manu at gcc dot gnu.org wrote:

> What is the problem with stripping the nops *before giving the error* and if it
> still fails, give an error?

NOPs are used to represent an intermediate expression that folded to an 
integer constant but is not an integer constant expression and cannot 
appear in one, as well as to carry TREE_NO_WARNING.  So you need to be 
careful about where you strip them to avoid making something into an 
integer constant expression that should not be one; don't strip them too 
early.

I think it would be OK to have a c_fully_fold_no_nop (which removes any 
TREE_NO_WARNING nop from the return from c_fully_fold) that is used in the 
relevant places (set_init_index, do_case, check_bitfield_type_and_width, 
build_enumerator at least) which have the pedwarn-if-pedantic logic for 
things folding to an integer constant where an integer constant expression 
is required.