Valid types for a binary op in GENERIC?

[David Malcolm]

The ICE in PR analyzer/111441 is due to this assertion in
fold_binary_loc failing:

11722		      gcc_assert (TYPE_PRECISION (atype) == TYPE_PRECISION (type));

where code=MULT_EXPR, type=<integer_type 0x7fffea6645e8 int>, and:

(gdb) p type
$1 = <integer_type 0x7fffea6645e8 int>
(gdb) p atype
$2 = <integer_type 0x7fffea6647e0 long unsigned int>

due to the analyzer building a mult_expr node with those types for the
arguments.

I have a fix for this (by adding some missing casts within the
analyzer's svalue representation), but it got me wondering: is there a
way to check valid types for binary operations in GENERIC?

Looking at
https://gcc.gnu.org/onlinedocs/gccint/Unary-and-Binary-Expressions.html
I see that for PLUS_EXPR, MINUS_EXPR and MULT_EXPR their "operands may
have either integral or floating type, but there will never be [sic]
case in which one operand is of floating type and the other is of
integral type."

Is it the case that for PLUS_EXPR, MINUS_EXPR and MULT_EXPR, their
arguments *must* have the same precision?  Or that types_compatible_p
is true?  What about other binary operations?

FWIW I currently have this hacked-up assertion in my working copy:

const svalue *
region_model_manager::get_or_create_binop (tree type, enum tree_code op,
					   const svalue *arg0,
					   const svalue *arg1)
{
  if (arg0->get_type ()
      && arg1->get_type ()
      && op != POINTER_PLUS_EXPR)
    {
      // FIXME: what ops does this apply to?  MULT_EXPR?
      gcc_assert (types_compatible_p (arg0->get_type (), arg1->get_type ()));
    }


Is there a function to check type-compatibility of the args given a
particular enum tree_code?

Sorry if I'm missing something here
Dave