With more testing (building GDB, Glibc, Busybox, and the Linux
kernel) I found a few bugs and weaknesses in the initial patch.
Attached is version 2 that fixes the uncovered problems and makes
further enhancements to handle more cases.

Martin

On 07/16/2017 05:47 PM, Martin Sebor wrote:
> Being implemented in the front end, the -Wrestrict warning
> detects only trivial instances of violations.  The attached
> patch extends the implementation to the middle-end where
> data flow and alias analysis can be combined to detect even
> complex cases of overlap.  This work is independent of but
> follows on the patch below (waiting for review):
>
>   https://gcc.gnu.org/ml/gcc-patches/2017-07/msg00036.html
>
> The changes rely on extending the tree-ssa-{alias,structalias}
> machinery in a simple way to answer the "must-alias" kind of
> question in addition to the current "may-alias."
>
> The rest of the changes are in gimple-fold.c, tree-ssa-strlen.c,
> and builtins.c.
>
> Even though this change makes -Wrestrict a lot more useful, it's
> not a complete implementation.  Not all built-ins are handled yet
> (e.g., strncat), and support for user-defined functions is still
> subject to the limitations of the front end implementation.  To
> complete the support, handlers for the missing string built-ins
> will need to be added to tree-ssa-strlen.c, and the remaining
> bits should be moved from the front end to somewhere in
> the middle-end (e.g., calls.c).
>
> Martin