[Bug tree-optimization/98464] [11 Regression] ICE: tree check: expected class 'type', have 'exceptional' (error_mark) in tree_nop_conversion_p, at tree.c:12825 by r11-4637

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98464

--- Comment #9 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 4 Jan 2021, linkw at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98464
> 
> --- Comment #8 from Kewen Lin <linkw at gcc dot gnu.org> ---
> (In reply to Richard Biener from comment #5)
> > But this
> > 
> >         sprime = eliminate_avail (gimple_bb (SSA_NAME_DEF_STMT (use)), use);
> > 
> > should make it more conservative (compared to the more desirable use of
> > gimple_bb (stmt) aka 'b').
> > 
> > The issue is really that dominated_by_p_w_unex is not "transitive" with
> > respect to an intermediate immediate dominator chain.
> > 
> > We can make that more consistent at least by doing sth like your patch but
> > only in vn_valueize_wrapper.  
> 
> OK, just noticed that wrapper is only for simplify_replace_tree. Thanks for
> fixing.  But I still don't get why it's buggy for rpo_vn_valueize.

Because rpo_vn_valueize argument can be a value handle SSA which does
not need to be a definition on the path to the stmt we are simplifying.
rpo_vn_valueize is called from (too) many contexts and I'm not 100%
convinced we're only feeding it names available at the location we are
processing.

Note I think we should use 'b' and not SSA_NAME_DEF_STMT of the use but
then this code is as-is since the rewrite and I don't feel tracking down
fallout of changing this back now (but I'll try to remember for stage1,
as well as somehow better dealing with dominated_by_w_unex)