[Bug tree-optimization/82060] [7/8 Regression] ICE in refs_may_alias_p_1 with devirtualization enabled

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82060

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2017-09-01
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
#1  0x0000000001329897 in refs_may_alias_p_1 (ref1=0x7fffffffd4b0, 
    ref2=0x7fffffffd2a0, tbaa_p=true) at /tmp/trunk2/gcc/tree-ssa-alias.c:1538
1538      gcc_unreachable ();
(gdb) p ref2->ref
$3 = <mem_ref 0x7ffff69e67d0>
(gdb) p ref2->base
$4 = <component_ref 0x7ffff6a0e690>

because

(gdb) p debug_gimple_stmt (stmt)
# .MEM_10 = VDEF <.MEM_4>
MEM[(struct B *)&c].ma = OBJ_TYPE_REF(_2;(struct D)d_6(D)->0) (d_6(D));
$11 = void

has an unfolded LHS:

 <mem_ref 0x7ffff69e67d0
    type <record_type 0x7ffff69e89d8 A sizes-gimplified type_5 type_6 QI
        size <integer_cst 0x7ffff6891fc0 constant 8>
...
    arg:0 <addr_expr 0x7ffff6a09d40
        type <pointer_type 0x7ffff69e83f0 type <record_type 0x7ffff69e89d8 A>
            public unsigned DI
            size <integer_cst 0x7ffff6891ed0 constant 64>
            unit-size <integer_cst 0x7ffff6891ee8 constant 8>
            align:64 warn_if_not_align:0 symtab:0 alias-set 1 canonical-type
0x7ffff69e83f0>

        arg:0 <component_ref 0x7ffff6a0e690 type <record_type 0x7ffff69e89d8 A>

            arg:0 <mem_ref 0x7ffff6a128c0 type <record_type 0x7ffff69e8c78 B>

                arg:0 <addr_expr 0x7ffff6a09d60 type <pointer_type
0x7ffff69e87e0>
                    arg:0 <var_decl 0x7ffff69fe870 c>>

propagated by PRE.  So this ends up running into


      /* Visit indirect calls and turn them into direct calls if
         possible using the devirtualization machinery.  */
      if (gcall *call_stmt = dyn_cast <gcall *> (stmt))
        {

before we fold (and thus canonicalize) the stmt:

      if (gimple_modified_p (stmt))
        {
...