On Mon, Aug 22, 2011 at 12:53 AM, Artem Shinkarov
<artyom.shinkar...@gmail.com> wrote:
> Richard
>
> I formalized an approach a little-bit, now it works without target
> hooks, but some polishing is still required. I want you to comment on
> the several important approaches that I use in the patch.
>
> So how does it work.
> 1) All the vector comparisons at the level of type-checker are
> introduced using VEC_COND_EXPR with constant selection operands being
> {-1} and {0}. For example v0 > v1 is transformed into VEC_COND_EXPR<v0
>> v1, {-1}, {0}>.
>
> 2) When optabs expand VEC_COND_EXPR, two cases are considered:
> 2.a) first operand of VEC_COND_EXPR is comparison, in that case nothing
> changes.
> 2.b) first operand is something else, in that case, we specially mark
> this case, recognize it in the backend, and do not create a
> comparison, but use the mask as it was a result of some comparison.
>
> 3) In order to make sure that mask in VEC_COND_EXPR<mask, v0, v1> is a
> vector comparison we use is_vector_comparison function, if it returns
> false, then we replace mask with mask != {0}.
>
> So we end-up with the following functionality:
> VEC_COND_EXPR<mask, v0,v1> -- if we know that mask is a result of
> comparison of two vectors, we leave it as it is, otherwise change with
> mask != {0}.
>
> Plain vector comparison a <op> b is represented with VEC_COND_EXPR,
> which correctly expands, without creating useless masking.
>
>
> Basically for me there are two questions:
> 1) Can we perform information passing in optabs in a nicer way?
> 2) How is_vector_comparison could be improved? I have several ideas,
> like checking if constant vector all consists of 0 and -1, and so on.
> But first is it conceptually fine.
>
> P.S. I tired to put the functionality of is_vector_comparison in
> tree-ssa-forwprop, but the thing is that it is called only with -On,
> which I find inappropriate, and the functionality gets more
> complicated.
Why is it inappropriate to not optimize it at -O0? If the user
separates comparison and ?: expression it's his own fault.
Btw, the new hook is still in the patch.
I would simply always create != 0 if it isn't and let optimizers
(tree-ssa-forwprop.c) optimize this. You still have to deal with
non-comparison operands during expansion though, but if
you always forced a != 0 from the start you can then simply
interpret it as a proper comparison result (in which case I'd
modify the backends to have an alternate pattern or directly
expand to masking operations - using the fake comparison
RTX is too much of a hack).
tree
constant_boolean_node (int value, tree type)
{
- if (type == integer_type_node)
+ if (TREE_CODE (type) == VECTOR_TYPE)
+ {
+ tree tval;
+
+ gcc_assert (TREE_CODE (TREE_TYPE (type)) == INTEGER_TYPE);
+ tval = build_int_cst (TREE_TYPE (type), value);
+ return build_vector_from_val (type, tval);
as value is either 0 or 1 that won't work. Oh, I see you pass -1
for true in the callers. But I think we should simply decide that true (1)
means -1 for a vector boolean node (and the value parameter should
be a bool instead). Thus,
+ if (TREE_CODE (type) == VECTOR_TYPE)
+ {
+ tree tval;
+
+ gcc_assert (TREE_CODE (TREE_TYPE (type)) == INTEGER_TYPE);
+ tval = build_int_cst (TREE_TYPE (type), value ? -1 : 0);
+ return build_vector_from_val (type, tval);
instead.
@@ -9073,26 +9082,29 @@ fold_comparison (location_t loc, enum tr
floating-point, we can only do some of these simplifications.) */
if (operand_equal_p (arg0, arg1, 0))
{
+ int true_val = TREE_CODE (type) == VECTOR_TYPE ? -1 : 0;
+ tree arg0_type = TREE_TYPE (arg0);
+
as I said this is not necessary - the FLOAT_TYPE_P and HONOR_NANS
macros work perfectly fine on vector types.
Richard.
>
> Thanks,
> Artem.
>
