[Bug tree-optimization/65391] missed store motion for conditionally updated pointer in loop

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65391

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
                 CC|                            |rguenth at gcc dot gnu.org
          Component|middle-end                  |tree-optimization
            Summary|unnecessary load of         |missed store motion for
                   |conditionally updated       |conditionally updated
                   |pointer in loop             |pointer in loop

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
The issue is that invariant/store motion doesn't see the unconditional store
to *o_ptr before the loop and thus thinks that the conditional one may trap.

LIM doesn't consider stores/loads in blocks that are post-dominated by
the loop header to alter that loops "effectively accessed" set of references.
I think considering only the loop preheader is good enough - but we also do not
analyze memory references in non-loop areas (loop preheaders would need to be
added here as well).