[Bug tree-optimization/94216] [10 Regression] ICE in maybe_canonicalize_mem_ref_addr, at gimple-fold.c:4899 since r10-7237-g4e3d3e40726e1b68bf52fa205c68495124ea60b8

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94216

--- Comment #10 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 19 Mar 2020, Richard Biener wrote:

> On Thu, 19 Mar 2020, jakub at gcc dot gnu.org wrote:
> 
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94216
> > 
> > --- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
> > (In reply to Richard Biener from comment #5)
> > > (In reply to Jakub Jelinek from comment #1)
> > > > I wonder if we shouldn't do:
> > > > --- gcc/fold-const.c.jj	2020-03-18 12:47:36.000000000 +0100
> > > > +++ gcc/fold-const.c	2020-03-18 17:34:14.586455801 +0100
> > > > @@ -82,6 +82,7 @@ along with GCC; see the file COPYING3.
> > > >  #include "attribs.h"
> > > >  #include "tree-vector-builder.h"
> > > >  #include "vec-perm-indices.h"
> > > > +#include "tree-ssa.h"
> > > >  
> > > >  /* Nonzero if we are folding constants inside an initializer; zero
> > > >     otherwise.  */
> > > > @@ -10262,6 +10263,10 @@ fold_binary_loc (location_t loc, enum tr
> > > >    switch (code)
> > > >      {
> > > >      case MEM_REF:
> > > > +      STRIP_USELESS_TYPE_CONVERSION (arg0);
> > > 
> > > We already applied STRIP_NOPS to arg0
> > 
> > Though, if we don't want to strip non-useless conversions, that is wrong even
> > for the two special cases we have afterwards.
> > So, shouldn't case MEM_REF: start then with
> >       arg0 = op0;
> >       STRIP_USELESS_TYPE_CONVERSION (arg0);
> >       arg1 = op1;
> > ?
> 
> While we "abuse" fold_binary (MEM_REF,...) to make MEM_REFs valid
> we still expect some basic hygiene there..
> 
> > Or fold_convert to the type of op0 if the type conversion isn't useless?
> > Also, isn't the arg1 handling incorrect or at least dangerous?
> > I mean, if it does int_const_binop (PLUS_EXPR, arg1, ...) in both cases
> > then it will have the type of arg1 which is op1 after STRIP_NOPS, so could have
> > completely different type.  One needs to hope that the last argument to
> > fold_binary_loc of MEM_REF will always be an INTEGER_CST from which nothing can
> > be stripped...
> 
> ..for example INTEGER_CST 2nd argument (implicit in the use of
> int_const_binop).  For the 2nd arg we could be more explicit and
> instead of arg1 use op1.  Likewise we should probably use
> 
>       if (TREE_CODE (op0) == ADDR_EXPR
>           && TREE_CODE (TREE_OPERAND (op0, 0)) == MEM_REF)
> 
> that is, we don't even expect to need to strip nops here.  I'll try
> to bootstrap/test such changes to see where other possible issues
> in fold_build_addr_expr callers lie...

That worked well without any further visible fallout.