http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48418
--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-04-03 11:21:27 UTC --- It's deliberate that folding of references to const variables is now delayed - and ideally it would move out of the front end altogether. While decl_constant_value_for_optimization still exists it would be easy enough to have a second check for this warning in c_fully_fold_internal, but in general the alternatives (which are not mutually exclusive) are predictable warnings in the front end that may not catch all cases and may sometimes warn in unreachable code, and less-predictable middle-end warnings if the problem operation is reachable (here, if a shift by an out-of-range constant is found after optimization, which could include where the variable with the shift amount isn't marked const).
