+++ /dev/null
-/*
- * 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 (jason@jlekstrand.net)
- *
- */
-
-#include "nir.h"
-
-/*
- * 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)
- 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:
- case nir_instr_type_ssa_undef:
- /* 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;
-
- case nir_intrinsic_interp_var_at_centroid:
- case nir_intrinsic_interp_var_at_sample:
- case nir_intrinsic_interp_var_at_offset:
- case nir_intrinsic_load_uniform:
- case nir_intrinsic_load_ubo:
- case nir_intrinsic_load_ssbo:
- case nir_intrinsic_load_input:
- return true;
- default:
- break;
- }
- }
-
- default:
- /* We can't scalarize this type of instruction */
- return false;
- }
-}
-
-/**
- * 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 dependence graph
- * won't automatically make us fail to scalarize.
- */
- entry = _mesa_hash_table_insert(state->phi_table, phi, (void *)(intptr_t)1);
-
- bool scalarizable = true;
-
- nir_foreach_phi_src(phi, src) {
- scalarizable = is_phi_src_scalarizable(src, state);
- if (!scalarizable)
- break;
- }
-
- /* The hash table entry for 'phi' may have changed while recursing the
- * dependence graph, so we need to reset it */
- entry = _mesa_hash_table_search(state->phi_table, phi);
- assert(entry);
-
- 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(new_phi, 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));
-
- 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_function(shader, function) {
- if (function->impl)
- lower_phis_to_scalar_impl(function->impl);
- }
-}
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