--- /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 "glsl/nir/nir_builder.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..
+ */
+
+struct lower_state {
+ nir_builder b;
+ void *mem_ctx;
+ bool progress;
+};
+
+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(dest->ssa.if_uses->entries == 0);
+
+ /* The only uses of this definition must be phi's in the
+ * successor or in the current block
+ */
+ struct set_entry *entry;
+ set_foreach(dest->ssa.uses, entry) {
+ const nir_instr *dest_instr = entry->key;
+ 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(block, instr) {
+ 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(if_block, instr) {
+ 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;
+
+ nir_builder_insert_after_instr(bld,
+ 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, void *void_state)
+{
+ struct lower_state *state = void_state;
+
+ /* 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 true;
+
+ if (nir_cf_node_is_first(&block->cf_node))
+ return true;
+
+ nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
+ if (prev_node->type != nir_cf_node_if)
+ return true;
+
+ nir_if *if_stmt = nir_cf_node_as_if(prev_node);
+ nir_cf_node *then_node = nir_if_first_then_node(if_stmt);
+ nir_cf_node *else_node = nir_if_first_else_node(if_stmt);
+
+ /* We can only have one block in each side ... */
+ if (nir_if_last_then_node(if_stmt) != then_node ||
+ nir_if_last_else_node(if_stmt) != else_node)
+ return true;
+
+ nir_block *then_block = nir_cf_node_as_block(then_node);
+ nir_block *else_block = nir_cf_node_as_block(else_node);
+
+ /* ... and those blocks must only contain "allowed" instructions. */
+ if (!block_check_for_allowed_instrs(then_block) ||
+ !block_check_for_allowed_instrs(else_block))
+ return true;
+
+ /* condition should be ssa too, which simplifies flatten_block: */
+ if (!if_stmt->condition.is_ssa)
+ return true;
+
+ /* 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(&state->b, then_block, prev_block,
+ if_stmt->condition.ssa, false);
+ flatten_block(&state->b, else_block, prev_block,
+ if_stmt->condition.ssa, true);
+
+ nir_foreach_instr_safe(block, instr) {
+ 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(state->mem_ctx, nir_op_bcsel);
+ nir_src_copy(&sel->src[0].src, &if_stmt->condition, state->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(phi, src) {
+ 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, state->mem_ctx);
+ }
+
+ nir_ssa_dest_init(&sel->instr, &sel->dest.dest,
+ phi->dest.ssa.num_components, 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),
+ state->mem_ctx);
+
+ nir_instr_insert_before(&phi->instr, &sel->instr);
+ nir_instr_remove(&phi->instr);
+ }
+
+ nir_cf_node_remove(&if_stmt->cf_node);
+ state->progress = true;
+
+ return true;
+}
+
+static bool
+lower_if_else_impl(nir_function_impl *impl)
+{
+ struct lower_state state;
+
+ state.mem_ctx = ralloc_parent(impl);
+ state.progress = false;
+ nir_builder_init(&state.b, impl);
+
+ nir_foreach_block(impl, lower_if_else_block, &state);
+
+ if (state.progress)
+ nir_metadata_preserve(impl, nir_metadata_none);
+
+ return state.progress;
+}
+
+bool
+ir3_nir_lower_if_else(nir_shader *shader)
+{
+ bool progress = false;
+
+ nir_foreach_overload(shader, overload) {
+ if (overload->impl)
+ progress |= lower_if_else_impl(overload->impl);
+ }
+
+ return progress;
+}
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