[Bug tree-optimization/103121] [12 Regression] Warnings in cp/optimize.c causing build failure

["amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103121

--- Comment #11 from Andrew Macleod <amacleod at redhat dot com> ---
(In reply to Martin Sebor from comment #10)
> Sorry, I've been having trouble with GDB and so I'm running two GDB sessions
> and I have been mixing output from both of them.  I see the warning for the
> store to *_23 in BB 13, not for BB 12.  Here's a fresh session as a sanity
> check:
> 
> 
> Breakpoint 1, strlen_pass::maybe_warn_overflow (this=0x7fffffffd880,
> stmt=0x7ffff4c2eb40, call_lhs=true, len=1, si=0x0, plus_one=false,
> rawmem=false) at /src/gcc/master/gcc/tree-ssa-strlen.c:2181
> 2181	  tree tlen = build_int_cst (size_type_node, len);
> (gdb) p debug(gimple_bb(stmt))
> <bb 13> [local count: 105119324]:
> _23 = grp_name_37 + idx_47;
> *_23 = 0;
> if (diff_seen_24 != 0)
>   goto <bb 15>; [100.00%]
> else
>   goto <bb 14>; [0.00%]
> 
> $3 = void
> (gdb) c
> Continuing.
> ../../gcc/gcc/cp/optimize.c: In function 'tree_node*
> cdtor_comdat_group(tree, tree)':
> ../../gcc/gcc/cp/optimize.c:208:17: warning: writing 1 byte into a region of
> size 0 [-Wstringop-overflow=]
> ../../gcc/gcc/cp/optimize.c:191:40: note: at offset 1 into destination
> object of size 1 allocated by '__builtin_alloca'
> [Inferior 1 (process 11409) exited normally]

Im still not sure what you are asking, or think is wrong.  I don't see any
ranges here.  Presumably the range of _4 is [0,0][2,+INF] at this point since
we've take the other branch.

If you haven't switched to multi-ranges and are still using value_range, then
presumably you would see ~[1,1]

Which means its possible that _4 was 0 on this branch, which also means the
warning would trigger?

The way the IL reads, if _1 is MAX_INT, then _4 is 0, and that gets through on
the 4->16 edge...

Am I missing something?