analyzer: handle more casts of string literals [PR98797]
gcc/analyzer/ChangeLog:
PR analyzer/98797
* region-model-manager.cc
(region_model_manager::maybe_fold_sub_svalue): Generalize getting
individual chars of a STRING_CST from element_region to any
subregion which is a concrete access of a single byte from its
parent region.
* region.cc (region::get_relative_concrete_byte_range): New.
* region.h (region::get_relative_concrete_byte_range): New decl.
gcc/testsuite/ChangeLog:
PR analyzer/98797
* gcc.dg/analyzer/casts-1.c: Mark xfails as fixed; add further
test coverage for casts of string literals.
Signed-off-by: David Malcolm <dmalcolm@redhat.com>