On Thursday, January 29, 2015 01:40:18 PM Jason Ekstrand wrote: [snip] > diff --git a/src/glsl/nir/nir_lower_phis_to_scalar.c > b/src/glsl/nir/nir_lower_phis_to_scalar.c > new file mode 100644 > index 0000000..bf65f5a > --- /dev/null > +++ b/src/glsl/nir/nir_lower_phis_to_scalar.c > @@ -0,0 +1,278 @@ > +/* > + * Copyright © 2015 Intel Corporation > + * > + * Permission is hereby granted, free of charge, to any person obtaining a > + * copy of this software and associated documentation files (the "Software"), > + * to deal in the Software without restriction, including without limitation > + * the rights to use, copy, modify, merge, publish, distribute, sublicense, > + * and/or sell copies of the Software, and to permit persons to whom the > + * Software is furnished to do so, subject to the following conditions: > + * > + * The above copyright notice and this permission notice (including the next > + * paragraph) shall be included in all copies or substantial portions of the > + * Software. > + * > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL > + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER > + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING > + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER > DEALINGS > + * IN THE SOFTWARE. > + * > + * Authors: > + * Jason Ekstrand (ja...@jlekstrand.net) > + * > + */ > + > +#include "nir.h" > + > +/*
I believe proper doxygen would be:
/**
* \file nir_lower_phis_to_scalar.c
*
* Implements a pass that...
*/
(double star opening, \file line)
> + * Implements a pass that lowers vector phi nodes to scalar phi nodes when
> + * we don't think it will hurt anything.
> + */
> +
> +struct lower_phis_to_scalar_state {
> + void *mem_ctx;
> + void *dead_ctx;
> +
> + /* Hash table marking which phi nodes are scalarizable. The key is
> + * pointers to phi instructions and the entry is either NULL for not
> + * scalarizable or non-null for scalarizable.
> + */
> + struct hash_table *phi_table;
> +};
> +
> +static bool
> +should_lower_phi(nir_phi_instr *phi, struct lower_phis_to_scalar_state
> *state);
> +
> +static bool
> +is_phi_src_scalarizable(nir_phi_src *src,
> + struct lower_phis_to_scalar_state *state)
> +{
> + /* Don't know what to do with non-ssa sources */
> + if (!src->src.is_ssa)
Can phi nodes with non-SSA sources even exist? That sounds crazy.
Perhaps just assert(src->src.is_ssa)?
> + return false;
> +
> + nir_instr *src_instr = src->src.ssa->parent_instr;
> + switch (src_instr->type) {
> + case nir_instr_type_alu: {
> + nir_alu_instr *src_alu = nir_instr_as_alu(src_instr);
> +
> + /* ALU operations with output_size == 0 should be scalarized. We
> + * will also see a bunch of vecN operations from scalarizing ALU
> + * operations and, since they can easily be copy-propagated, they
> + * are ok too.
> + */
> + return nir_op_infos[src_alu->op].output_size == 0 ||
> + src_alu->op != nir_op_vec2 ||
> + src_alu->op != nir_op_vec3 ||
> + src_alu->op != nir_op_vec4;
> + }
> +
> + case nir_instr_type_phi:
> + /* A phi is scalarizable if we're going to lower it */
> + return should_lower_phi(nir_instr_as_phi(src_instr), state);
> +
> + case nir_instr_type_load_const:
> + /* These are trivially scalarizable */
> + return true;
> +
> + case nir_instr_type_intrinsic: {
> + nir_intrinsic_instr *src_intrin = nir_instr_as_intrinsic(src_instr);
> +
> + switch (src_intrin->intrinsic) {
> + case nir_intrinsic_load_var:
> + return src_intrin->variables[0]->var->data.mode ==
> nir_var_shader_in ||
> + src_intrin->variables[0]->var->data.mode == nir_var_uniform;
Perhaps add:
case nir_intrinsic_load_uniform:
case nir_intrinsic_load_const:
return true;
so that the pass could handle this same concept after nir_lower_io()?
It looks like patch 2 adds this to brw_fs_nir.cpp's nir_optimize() loop, which
is run after nir_lower_io(). It's possible that there will be no additional
work to do then, so it might be useless, but...might be worth adding anyway...
> + default:
> + break;
> + }
> + }
> +
> + default:
> + /* We can't scalarize this type of instruction */
> + return false;
> + }
> +}
> +
/**
* Determines ...
> +/* Determines if the given phi node should be lowered. The only phi nodes
> + * we will scalarize at the moment are those where all of the sources are
> + * scalarizable.
> + *
> + * The reason for this comes down to coalescing. Since phi sources can't
> + * swizzle, swizzles on phis have to be resolved by inserting a mov right
> + * before the phi. The choice then becomes between movs to pick off
> + * components for a scalar phi or potentially movs to recombine components
> + * for a vector phi. The problem is that the movs generated to pick off
> + * the components are almost uncoalescable. We can't coalesce them in NIR
> + * because we need them to pick off components and we can't coalesce them
> + * in the backend because the source register is a vector and the
> + * destination is a scalar that may be used at other places in the program.
> + * On the other hand, if we have a bunch of scalars going into a vector
> + * phi, the situation is much better. In this case, if the SSA def is
> + * generated in the predecessor block to the corresponding phi source, the
> + * backend code will be an ALU op into a temporary and then a mov into the
> + * given vector component; this move can almost certainly be coalesced
> + * away.
> + */
> +static bool
> +should_lower_phi(nir_phi_instr *phi, struct lower_phis_to_scalar_state
> *state)
> +{
> + /* Already scalar */
> + if (phi->dest.ssa.num_components == 1)
> + return false;
> +
> + struct hash_entry *entry = _mesa_hash_table_search(state->phi_table, phi);
> + if (entry)
> + return entry->data != NULL;
> +
> + /* Insert an entry and mark it as scalarizable for now. That way
> + * we don't recurse forever and a cycle in the depencence graph
dependence graph
> + * won't automatically make us fail to scalarize.
> + */
> + entry = _mesa_hash_table_insert(state->phi_table, phi, (void
> *)(intptr_t)1);
This is weird. Why are you using a hash table and not a set? It sounds
like you're trying to store a tri-state: unknown (no entry in hash
table), known-not-scalarizable (entry in hash table, value of 0), and
known-scalarizable (entry in hash table, value of 1).
However, I don't see any code that actually inserts or updates a value
to 0 - are you missing some code?
Otherwise, this looks good to me...
> +
> + bool scalarizable = true;
> +
> + nir_foreach_phi_src(phi, src) {
> + scalarizable = is_phi_src_scalarizable(src, state);
> + if (!scalarizable)
> + break;
> + }
> +
> + entry->data = (void *)(intptr_t)scalarizable;
> +
> + return scalarizable;
> +}
> +
> +static bool
> +lower_phis_to_scalar_block(nir_block *block, void *void_state)
> +{
> + struct lower_phis_to_scalar_state *state = void_state;
> +
> + /* Find the last phi node in the block */
> + nir_phi_instr *last_phi = NULL;
> + nir_foreach_instr(block, instr) {
> + if (instr->type != nir_instr_type_phi)
> + break;
> +
> + last_phi = nir_instr_as_phi(instr);
> + }
> +
> + /* We have to handle the phi nodes in their own pass due to the way
> + * we're modifying the linked list of instructions.
> + */
> + nir_foreach_instr_safe(block, instr) {
> + if (instr->type != nir_instr_type_phi)
> + break;
> +
> + nir_phi_instr *phi = nir_instr_as_phi(instr);
> +
> + if (!should_lower_phi(phi, state))
> + continue;
> +
> + /* Create a vecN operation to combine the results. Most of these
> + * will be redundant, but copy propagation should clean them up for
> + * us. No need to add the complexity here.
> + */
> + nir_op vec_op;
> + switch (phi->dest.ssa.num_components) {
> + case 2: vec_op = nir_op_vec2; break;
> + case 3: vec_op = nir_op_vec3; break;
> + case 4: vec_op = nir_op_vec4; break;
> + default: unreachable("Invalid number of components");
> + }
> +
> + nir_alu_instr *vec = nir_alu_instr_create(state->mem_ctx, vec_op);
> + nir_ssa_dest_init(&vec->instr, &vec->dest.dest,
> + phi->dest.ssa.num_components, NULL);
> + vec->dest.write_mask = (1 << phi->dest.ssa.num_components) - 1;
> +
> + for (unsigned i = 0; i < phi->dest.ssa.num_components; i++) {
> + nir_phi_instr *new_phi = nir_phi_instr_create(state->mem_ctx);
> + nir_ssa_dest_init(&new_phi->instr, &new_phi->dest, 1, NULL);
> +
> + vec->src[i].src = nir_src_for_ssa(&new_phi->dest.ssa);
> +
> + nir_foreach_phi_src(phi, src) {
> + /* We need to insert a mov to grab the i'th component of src */
> + nir_alu_instr *mov = nir_alu_instr_create(state->mem_ctx,
> + nir_op_imov);
> + nir_ssa_dest_init(&mov->instr, &mov->dest.dest, 1, NULL);
> + mov->dest.write_mask = 1;
> + nir_src_copy(&mov->src[0].src, &src->src, state->mem_ctx);
> + mov->src[0].swizzle[0] = i;
> +
> + /* Insert at the end of the predecessor but before the jump */
> + nir_instr *pred_last_instr = nir_block_last_instr(src->pred);
> + if (pred_last_instr && pred_last_instr->type ==
> nir_instr_type_jump)
> + nir_instr_insert_before(pred_last_instr, &mov->instr);
> + else
> + nir_instr_insert_after_block(src->pred, &mov->instr);
> +
> + nir_phi_src *new_src = ralloc(state->mem_ctx, nir_phi_src);
> + new_src->pred = src->pred;
> + new_src->src = nir_src_for_ssa(&mov->dest.dest.ssa);
> +
> + exec_list_push_tail(&new_phi->srcs, &new_src->node);
> + }
> +
> + nir_instr_insert_before(&phi->instr, &new_phi->instr);
> + }
> +
> + nir_instr_insert_after(&last_phi->instr, &vec->instr);
> +
> + nir_ssa_def_rewrite_uses(&phi->dest.ssa,
> + nir_src_for_ssa(&vec->dest.dest.ssa),
> + state->mem_ctx);
> +
> + ralloc_steal(state->dead_ctx, phi);
> + nir_instr_remove(&phi->instr);
> +
> + /* We're using the safe iterator and inserting all the newly
> + * scalarized phi nodes before their non-scalarized version so that's
> + * ok. However, we are also inserting vec operations after all of
> + * the last phi node so once we get here, we can't trust even the
> + * safe iterator to stop properly. We have to break manually.
> + */
> + if (instr == &last_phi->instr)
> + break;
> + }
> +
> + return true;
> +}
> +
> +static void
> +lower_phis_to_scalar_impl(nir_function_impl *impl)
> +{
> + struct lower_phis_to_scalar_state state;
> +
> + state.mem_ctx = ralloc_parent(impl);
> + state.dead_ctx = ralloc_context(NULL);
> + state.phi_table = _mesa_hash_table_create(state.dead_ctx,
> _mesa_hash_pointer,
> + _mesa_key_pointer_equal);
> +
> + nir_foreach_block(impl, lower_phis_to_scalar_block, &state);
> +
> + nir_metadata_preserve(impl, nir_metadata_block_index |
> + nir_metadata_dominance);
> +
> + ralloc_free(state.dead_ctx);
> +}
> +
> +/** A pass that lowers vector phi nodes to scalar
> + *
> + * This pass loops through the blocks and lowers looks for vector phi nodes
> + * it can lower to scalar phi nodes. Not all phi nodes are lowered. For
> + * instance, if one of the sources is a non-scalarizable vector, then we
> + * don't bother lowering because that would generate hard-to-coalesce movs.
> + */
> +void
> +nir_lower_phis_to_scalar(nir_shader *shader)
> +{
> + nir_foreach_overload(shader, overload) {
> + if (overload->impl)
> + lower_phis_to_scalar_impl(overload->impl);
> + }
> +}
>
signature.asc
Description: This is a digitally signed message part.
_______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
