On Thu, 18 Aug 2011, Artem Shinkarov wrote:
> >> + /* Avoid C_MAYBE_CONST in VEC_COND_EXPR. */
> >> + sc = c_fully_fold (ifexp, false, &maybe_const);
> >> + sc = save_expr (sc);
> >> + if (!maybe_const)
> >> + ifexp = c_wrap_maybe_const (sc, true);
> >> + else
> >> + ifexp = sc;
> >
> > This looks like it's duplicating c_save_expr; that is, like "ifexp =
> > c_save_expr (ifexp);" would suffice.
> >
> > But, it's not clear that it actually achieves the effect described in the
> > comment; have you actually tried with function calls, assignments etc. in
> > the operands?
>
> I tested it with gcc.dg/vector-compare-2.c:
> typedef int vec __attribute__((vector_size(16)));
>
> vec i,j;
> extern vec a, b, c;
>
> vec
> foo (int x)
> {
> return (x ? i : j) ? a : b;
> }
>
> vec
> bar (int x)
> {
> return a ? (x ? i : j) : b;
> }
>
> vec
> baz (int x)
> {
> return a ? b : (x ? i : j);
> }
>
> Is it good enough?
No, because none of the operands there involve assignment, increment,
decrement, function call or comma operators (which are the main cases that
would trigger the creation of C_MAYBE_CONST_EXPR).
> > The code in build_binary_op uses save_expr rather than
> > c_save_expr because it does some intermediate operations before calling
> > c_wrap_maybe_const, and if you really want to avoid C_MAYBE_CONST in
> > VEC_COND_EXPR then you'll need to continue calling save_expr, as here, but
> > delay the call to c_wrap_maybe_const so that the whole VEC_COND_EXPR is
> > wrapped if required.
>
> Ok, but I need to wrap it at some point, where do you think it would
> be appropriate to do?
After the creation of the VEC_COND_EXPR. I.e. don't just return the
results of build3 or convert, wrap them as needed before returning them.
--
Joseph S. Myers
jos...@codesourcery.com
