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nir: Use writemasked store_vars in glsl_to_nir. 

Instead of performing the read-modify-write cycle in glsl->nir, we can
simply emit a partial writemask.  For locals, nir_lower_vars_to_ssa will
do the equivalent read-modify-write cycle for us, so we continue to get
the same SSA values we had before.

Because glsl_to_nir calls nir_lower_outputs_to_temporaries, all outputs
are shadowed with temporary values, and written out as whole vectors at
the end of the shader.  So, most consumers will still not see partial
writemasks.

However, nir_lower_outputs_to_temporaries bails for tessellation control
shader outputs.  So those remain actual variables, and stores to those
variables now get a writemask.  nir_lower_io passes that through.  This
means that TCS outputs should actually work now.

This is a functional change for tessellation control shaders.

v2: Relax the nir_validate assert to allow partial writemasks.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
This commit is contained in:
Kenneth Graunke 2015-11-29 23:23:44 -08:00
parent 7d539080c1
commit 0daf51e130
2 changed files with 10 additions and 32 deletions
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39
src/glsl/nir/glsl_to_nir.cpp
View File

@ -1129,44 +1129,23 @@ nir_visitor::visit(ir_assignment *ir)
nir_ssa_def *src = evaluate_rvalue(ir->rhs);
if (ir->write_mask != (1 << num_components) - 1 && ir->write_mask != 0) {
/*
* We have no good way to update only part of a variable, so just load
* the LHS and do a vec operation to combine the old with the new, and
* then store it
* back into the LHS. Copy propagation should get rid of the mess.
/* GLSL IR will give us the input to the write-masked assignment in a
* single packed vector. So, for example, if the writemask is xzw, then
* we have to swizzle x -> x, y -> z, and z -> w and get the y component
* from the load.
*/
nir_intrinsic_instr *load =
nir_intrinsic_instr_create(this->shader, nir_intrinsic_load_var);
load->num_components = ir->lhs->type->vector_elements;
nir_ssa_dest_init(&load->instr, &load->dest, num_components, NULL);
load->variables[0] = lhs_deref;
ralloc_steal(load, load->variables[0]);
nir_builder_instr_insert(&b, &load->instr);
nir_ssa_def *srcs[4];
unsigned swiz[4];
unsigned component = 0;
for (unsigned i = 0; i < ir->lhs->type->vector_elements; i++) {
if (ir->write_mask & (1 << i)) {
/* GLSL IR will give us the input to the write-masked assignment
* in a single packed vector. So, for example, if the
* writemask is xzw, then we have to swizzle x -> x, y -> z,
* and z -> w and get the y component from the load.
*/
srcs[i] = nir_channel(&b, src, component++);
} else {
srcs[i] = nir_channel(&b, &load->dest.ssa, i);
}
for (unsigned i = 0; i < 4; i++) {
swiz[i] = ir->write_mask & (1 << i) ? component++ : 0;
}
src = nir_vec(&b, srcs, ir->lhs->type->vector_elements);
src = nir_swizzle(&b, src, swiz, num_components, !supports_ints);
}
nir_intrinsic_instr *store =
nir_intrinsic_instr_create(this->shader, nir_intrinsic_store_var);
store->num_components = ir->lhs->type->vector_elements;
store->const_index[0] = (1 << store->num_components) - 1;
store->const_index[0] = ir->write_mask;
nir_deref *store_deref = nir_copy_deref(store, &lhs_deref->deref);
store->variables[0] = nir_deref_as_var(store_deref);
store->src[0] = nir_src_for_ssa(src);

3
src/glsl/nir/nir_validate.c
View File

@ -417,8 +417,7 @@ validate_intrinsic_instr(nir_intrinsic_instr *instr, validate_state *state)
assert(instr->variables[0]->var->data.mode != nir_var_shader_in &&
instr->variables[0]->var->data.mode != nir_var_uniform &&
instr->variables[0]->var->data.mode != nir_var_shader_storage);
/* Currently, writemasks must cover the entire value */
assert(instr->const_index[0] == (1 << instr->num_components) - 1);
assert((instr->const_index[0] & ~((1 << instr->num_components) - 1)) == 0);
break;
}
case nir_intrinsic_copy_var: