+++ /dev/null
-/*
- * Copyright © 2014 Intel Corporation
- * Copyright © 2015 Red Hat
- *
- * 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)
- * Rob Clark (robclark@freedesktop.org)
- *
- */
-
-#include "ir3_nir.h"
-#include "compiler/nir/nir_builder.h"
-#include "compiler/nir/nir_control_flow.h"
-
-/* Based on nir_opt_peephole_select, and hacked up to more aggressively
- * flatten anything that can be flattened
- *
- * This *might* be something that other drivers could use. On the other
- * hand, I think most other hw has predicated instructions or similar
- * to select which side of if/else writes back result (and therefore
- * not having to assign unique registers to both sides of the if/else.
- * (And hopefully those drivers don't also have crazy scheduling reqs
- * and can more easily do this in their backend.)
- *
- * TODO eventually when we have proper flow control in the backend:
- *
- * + Probably weight differently normal ALUs vs SFUs (cos/rcp/exp)
- * since executing extra SFUs for the branch-not-taken path will
- * generally be much more expensive.
- *
- * Possibly what constitutes an ALU vs SFU differs between hw
- * backends.. but that seems doubtful.
- *
- * + Account for texture fetch and memory accesses (incl UBOs)
- * since these will be more expensive..
- *
- * + When if-condition is const (or uniform) or we have some way
- * to know that all threads in the warp take the same branch
- * then we should prefer to not flatten the if/else..
- */
-
-static bool
-valid_dest(nir_block *block, nir_dest *dest)
-{
- /* It must be SSA */
- if (!dest->is_ssa)
- return false;
-
- /* We only lower blocks that do not contain other blocks
- * (so this is run iteratively in a loop). Therefore if
- * we get this far, it should not have any if_uses:
- */
- assert(list_empty(&dest->ssa.if_uses));
-
- /* The only uses of this definition must be phi's in the
- * successor or in the current block
- */
- nir_foreach_use(use, &dest->ssa) {
- nir_instr *dest_instr = use->parent_instr;
- if (dest_instr->block == block)
- continue;
- if ((dest_instr->type == nir_instr_type_phi) &&
- (dest_instr->block == block->successors[0]))
- continue;
- return false;
- }
-
- return true;
-}
-
-static bool
-block_check_for_allowed_instrs(nir_block *block)
-{
- nir_foreach_instr(instr, block) {
- switch (instr->type) {
- case nir_instr_type_intrinsic: {
- nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
- const nir_intrinsic_info *info =
- &nir_intrinsic_infos[intr->intrinsic];
-
- switch (intr->intrinsic) {
- case nir_intrinsic_discard_if:
- /* to simplify things, we want discard_if src in ssa: */
- if (!intr->src[0].is_ssa)
- return false;
- /* fallthrough */
- case nir_intrinsic_discard:
- /* discard/discard_if can be reordered, but only
- * with some special care
- */
- break;
- case nir_intrinsic_store_output:
- /* TODO technically, if both if and else store
- * the same output, we can hoist that out to
- * the end of the block w/ a phi..
- * In practice, the tgsi shaders we already get
- * do this for us, so I think we don't need to
- */
- default:
- if (!(info->flags & NIR_INTRINSIC_CAN_REORDER))
- return false;
- }
-
- break;
- }
-
- case nir_instr_type_tex: {
- nir_tex_instr *tex = nir_instr_as_tex(instr);
- if (!valid_dest(block, &tex->dest))
- return false;
- break;
- }
- case nir_instr_type_phi: {
- nir_phi_instr *phi = nir_instr_as_phi(instr);
- if (!valid_dest(block, &phi->dest))
- return false;
- break;
- }
- case nir_instr_type_alu: {
- nir_alu_instr *alu = nir_instr_as_alu(instr);
- if (!valid_dest(block, &alu->dest.dest))
- return false;
- break;
- }
-
- case nir_instr_type_load_const:
- case nir_instr_type_ssa_undef:
- break; /* always ssa dest */
-
- default:
- return false;
- }
- }
-
- return true;
-}
-
-/* flatten an then or else block: */
-static void
-flatten_block(nir_builder *bld, nir_block *if_block, nir_block *prev_block,
- nir_ssa_def *condition, bool invert)
-{
- nir_foreach_instr_safe(instr, if_block) {
- if (instr->type == nir_instr_type_intrinsic) {
- nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
- if ((intr->intrinsic == nir_intrinsic_discard) ||
- (intr->intrinsic == nir_intrinsic_discard_if)) {
- nir_ssa_def *discard_cond;
-
- bld->cursor = nir_after_instr(
- nir_block_last_instr(prev_block));
-
- if (invert) {
- condition = nir_inot(bld, condition);
- invert = false;
- }
-
- if (intr->intrinsic == nir_intrinsic_discard) {
- discard_cond = condition;
- } else {
- assert(intr->src[0].is_ssa);
- /* discard_if gets re-written w/ src and'd: */
- discard_cond = nir_iand(bld, condition, intr->src[0].ssa);
- }
-
- nir_intrinsic_instr *discard_if =
- nir_intrinsic_instr_create(bld->shader,
- nir_intrinsic_discard_if);
- discard_if->src[0] = nir_src_for_ssa(discard_cond);
-
- nir_instr_insert_after(nir_block_last_instr(prev_block),
- &discard_if->instr);
- nir_instr_remove(instr);
- instr = NULL;
- }
- }
- /* if not an handled specially, just move to prev block: */
- if (instr) {
- /* NOTE: exec_node_remove() is safe here (vs nir_instr_remove()
- * since we are re-adding the instructin back in to the prev
- * block (so no dangling SSA uses)
- */
- exec_node_remove(&instr->node);
- instr->block = prev_block;
- exec_list_push_tail(&prev_block->instr_list, &instr->node);
- }
- }
-}
-
-static bool
-lower_if_else_block(nir_block *block, nir_builder *b, void *mem_ctx)
-{
- /* If the block is empty, then it certainly doesn't have any phi nodes,
- * so we can skip it. This also ensures that we do an early skip on the
- * end block of the function which isn't actually attached to the CFG.
- */
- if (exec_list_is_empty(&block->instr_list))
- return false;
-
- if (nir_cf_node_is_first(&block->cf_node))
- return false;
-
- nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
- if (prev_node->type != nir_cf_node_if)
- return false;
-
- nir_if *if_stmt = nir_cf_node_as_if(prev_node);
- nir_block *then_block = nir_if_first_then_block(if_stmt);
- nir_block *else_block = nir_if_first_else_block(if_stmt);
-
- /* We can only have one block in each side ... */
- if (nir_if_last_then_block(if_stmt) != then_block ||
- nir_if_last_else_block(if_stmt) != else_block)
- return false;
-
- /* ... and those blocks must only contain "allowed" instructions. */
- if (!block_check_for_allowed_instrs(then_block) ||
- !block_check_for_allowed_instrs(else_block))
- return false;
-
- /* condition should be ssa too, which simplifies flatten_block: */
- if (!if_stmt->condition.is_ssa)
- return false;
-
- /* At this point, we know that the previous CFG node is an if-then
- * statement containing only moves to phi nodes in this block. We can
- * just remove that entire CF node and replace all of the phi nodes with
- * selects.
- */
-
- nir_block *prev_block = nir_cf_node_as_block(nir_cf_node_prev(prev_node));
- assert(prev_block->cf_node.type == nir_cf_node_block);
-
- /* First, we move the remaining instructions from the blocks to the
- * block before. There are a few things that need handling specially
- * like discard/discard_if.
- */
- flatten_block(b, then_block, prev_block,
- if_stmt->condition.ssa, false);
- flatten_block(b, else_block, prev_block,
- if_stmt->condition.ssa, true);
-
- nir_foreach_instr_safe(instr, block) {
- if (instr->type != nir_instr_type_phi)
- break;
-
- nir_phi_instr *phi = nir_instr_as_phi(instr);
- nir_alu_instr *sel = nir_alu_instr_create(mem_ctx, nir_op_bcsel);
- nir_src_copy(&sel->src[0].src, &if_stmt->condition, mem_ctx);
- /* Splat the condition to all channels */
- memset(sel->src[0].swizzle, 0, sizeof sel->src[0].swizzle);
-
- assert(exec_list_length(&phi->srcs) == 2);
- nir_foreach_phi_src(src, phi) {
- assert(src->pred == then_block || src->pred == else_block);
- assert(src->src.is_ssa);
-
- unsigned idx = src->pred == then_block ? 1 : 2;
- nir_src_copy(&sel->src[idx].src, &src->src, mem_ctx);
- }
-
- nir_ssa_dest_init(&sel->instr, &sel->dest.dest,
- phi->dest.ssa.num_components, 32, phi->dest.ssa.name);
- sel->dest.write_mask = (1 << phi->dest.ssa.num_components) - 1;
-
- nir_ssa_def_rewrite_uses(&phi->dest.ssa,
- nir_src_for_ssa(&sel->dest.dest.ssa));
-
- nir_instr_insert_before(&phi->instr, &sel->instr);
- nir_instr_remove(&phi->instr);
- }
-
- nir_cf_node_remove(&if_stmt->cf_node);
- return true;
-}
-
-static bool
-lower_if_else_impl(nir_function_impl *impl)
-{
- void *mem_ctx = ralloc_parent(impl);
- nir_builder b;
- nir_builder_init(&b, impl);
-
- bool progress = false;
- nir_foreach_block_safe(block, impl) {
- progress |= lower_if_else_block(block, &b, mem_ctx);
- }
-
- if (progress)
- nir_metadata_preserve(impl, nir_metadata_none);
-
- return progress;
-}
-
-bool
-ir3_nir_lower_if_else(nir_shader *shader)
-{
- bool progress = false;
-
- nir_foreach_function(function, shader) {
- if (function->impl)
- progress |= lower_if_else_impl(function->impl);
- }
-
- return progress;
-}
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