Re: [PATCH] tree-optimization/106904 - bogus -Wstringopt-overflow with vectors

[Jeff Law <jeffreyalaw@gmail.com>]

On 12/7/22 06:54, Richard Biener via Gcc-patches wrote:
> The following avoids CSE of &ps->wp to &ps->wp.hwnd confusing
> -Wstringopt-overflow by making sure to produce addresses to the
> biggest container from vectorization.  For this I introduce
> strip_zero_offset_components which turns &ps->wp.hwnd into
> &(*ps) and use that to base the vector data references on.
> That will also work for addresses with variable components,
> alternatively emitting pointer arithmetic via calling
> get_inner_reference and gimplifying that would be possible
> but likely more intrusive.
> 
> This is by no means a complete fix for all of those issues
> (avoiding ADDR_EXPRs in favor of pointer arithmetic might be).
> Other passes will have similar issues.
> 
> In theory that might now cause false negatives.
> 
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
> 
> Any opinion?
> 
> Thanks,
> Richard.
> 
> 	PR tree-optimization/106904
> 	* tree.h (strip_zero_offset_components): Declare.
> 	* tree.cc (strip_zero_offset_components): Define.
> 	* tree-vect-data-refs.cc (vect_create_addr_base_for_vector_ref):
> 	Strip zero offset components before building the address.
> 
> 	* gcc.dg/Wstringop-overflow-pr106904.c: New testcase.
So you're just canonicalizing to the widest container for a zero offset 
access.  While it may not fix everything, that seems like a good thing 
in general when we can do so.  I wouldn't be surprised if other passes 
could do the same thing to fix some of the missed CSE opportunities.

jeff