Ian Romanick <i...@freedesktop.org> writes:
> On 02/08/2013 04:24 PM, Eric Anholt wrote:
>> Ian Romanick <i...@freedesktop.org> writes:
>>
>>> From: Ian Romanick <ian.d.roman...@intel.com>
>>> + * modes. In the first mode, when \c want_availability_mask is \c true,
>>> it is
>>> + * assumed that any field of the vector may be written. This is used when
>>> + * adding an assignment to the assignment list. In the second mode, when
>>> + * \c want_availability_mask is \c false, it is assumed that no fields of
>>> the
>>> + * vector are written. This is used when trying to remove earlier
>>> assignments
>>> + * from the list.
>>> + */
>>> +static int
>>> +may_set_mask(ir_assignment *ir, bool want_availability_mask)
>>> +{
>>> + int mask = ir->write_mask;
>>> +
>>> + /* If the LHS is an array derefernce of a vector, try to figure out what
>>> + * the real write mask is. If the index is not a constant, assume that
>>> any
>>> + * element may be written.
>>> + */
>>> + if (is_array_deref_of_vector(ir->lhs)) {
>>> + ir_dereference_array *const d = ir->lhs->as_dereference_array();
>>> + ir_constant *const c = d->array_index->as_constant();
>>> +
>>> + if (c != NULL) {
>>> + const int idx = (c != NULL) ? c->get_uint_component(0) : -1;
>>> +
>>> + if (idx >= 0 && idx <= 3)
>>> + mask = 1U << idx;
>>> + else
>>> + mask = 0;
>>> + } else {
>>> + /* Set the write-mask depending on the size of the vector.
>>> + */
>>> + if (want_availability_mask)
>>> + mask = (1U << d->array->type->vector_components()) - 1;
>>> + else
>>> + mask = 0;
>>> + }
>>> + }
>>> +
>>> + return mask;
>>> +}
>>
>>
>>> +
>>> class assignment_entry : public exec_node
>>> {
>>> public:
>>> @@ -51,7 +114,7 @@ public:
>>> assert(ir);
>>> this->lhs = lhs;
>>> this->ir = ir;
>>> - this->available = ir->write_mask;
>>> + this->available = may_set_mask(ir, true);
>>
>> I don't think the want_availability_mask makes sense. If you're noting
>> an array deref of a vector for later dead code elimination, a later
>> instruction that sets the vector's .x shouldn't go turn off .x of this
>> instruction.
>
> I did it like this so that we could still optimize things like:
>
> vec4 v = ...;
>
> v[i] = ...; // i is a uniform or similar
> ...
> v.x = ...;
> ...
> v.y = ...;
> ...
> v.z = ...;
> ...
> v.w = ...;
>
> Even though the initial assignment(s) set "any field", the later
> assignments wipe them all out.But for code that's just: > v[i] = ...; // i is a uniform or similar > ... > v.x = ...; you'll turn off the write_mask of the v[i] write, right? And now the read of v.yzw is broken.
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