On 10/10/17 09:31, Timothy Arceri wrote:
On 10/10/17 09:06, Eric Anholt wrote:
Timothy Arceri <tarc...@itsqueeze.com> writes:
This is intended to be called before nir_lower_io() so that we
can do some linking optimisations with the results. It can also
be used with drivers that don't use nir_lower_io() at all such
as RADV.
+static void
+lower_load_to_scalar_early(nir_builder *b, nir_intrinsic_instr *intr,
+ nir_variable *var, struct hash_table
*split_inputs,
+ struct hash_table *split_outputs)
+{
+ b->cursor = nir_before_instr(&intr->instr);
+
+ assert(intr->dest.is_ssa);
+
+ nir_ssa_def *loads[4];
+
+ nir_variable **chan_vars;
+ if (var->data.mode == nir_var_shader_in) {
+ chan_vars = get_channel_variables(split_inputs, var);
+ } else {
+ chan_vars = get_channel_variables(split_outputs, var);
+ }
+
+ for (unsigned i = 0; i < intr->num_components; i++) {
+ nir_variable *chan_var = chan_vars[var->data.location_frac + i];
+ if (!chan_vars[var->data.location_frac + i]) {
+ chan_var = nir_variable_clone(var, b->shader);
+ chan_var->data.location_frac = var->data.location_frac + i;
+ chan_var->type = glsl_channel_type(chan_var->type);
+
+ chan_vars[var->data.location_frac + i] = chan_var;
+
+ nir_shader_add_variable(b->shader, chan_var);
+ }
+
+ nir_intrinsic_instr *chan_intr =
+ nir_intrinsic_instr_create(b->shader, intr->intrinsic);
+ nir_ssa_dest_init(&chan_intr->instr, &chan_intr->dest,
+ 1, intr->dest.ssa.bit_size, NULL);
+ chan_intr->num_components = 1;
+ chan_intr->variables[0] = nir_deref_var_create(chan_intr,
chan_var);
+
+ if (intr->variables[0]->deref.child) {
+ chan_intr->variables[0]->deref.child =
+
&clone_deref_array(nir_deref_as_array(intr->variables[0]->deref.child),
+ &chan_intr->variables[0]->deref)->deref;
+ }
Weird. I would have expected that we would turn arrays into separate
vectors (if possible) before this pass, so there wouldn't be any deref
chains. Has scalarizing arryas, specifically, been useful?
I don't have any shader-db numbers for this specifically (I guess I
could check it out) but I was definitely ending up here via the test
suites.
Seems I've looked at it before but forgot. The GLSL IR array splitting
pass has a comment:
" * This skips uniform/varying arrays, which would need careful
* handling due to their ir->location fields tying them to the GL API
* and other shader stages."
So we don't split varying arrays at all there, and there is nothing in
nir that does it either. I seem to have created a file to do the
splitting in nir but its empty, I think I wanted to get this pass done
first.
To answer your question I've spotted shaders in shader-db where removing
components of an array helps, and also where splitting the array so we
can remove dead elements would help.
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