#include "nir_control_flow.h"
#include "nir_loop_analyze.h"
+static nir_ssa_def *clone_alu_and_replace_src_defs(nir_builder *b,
+ const nir_alu_instr *alu,
+ nir_ssa_def **src_defs);
+
/**
* Gets the single block that jumps back to the loop header. Already assumes
* there is exactly one such block.
return true;
}
+static bool
+alu_instr_is_comparison(const nir_alu_instr *alu)
+{
+ switch (alu->op) {
+ case nir_op_flt32:
+ case nir_op_fge32:
+ case nir_op_feq32:
+ case nir_op_fne32:
+ case nir_op_ilt32:
+ case nir_op_ult32:
+ case nir_op_ige32:
+ case nir_op_uge32:
+ case nir_op_ieq32:
+ case nir_op_ine32:
+ return true;
+ default:
+ return nir_alu_instr_is_comparison(alu);
+ }
+}
+
+static bool
+alu_instr_is_type_conversion(const nir_alu_instr *alu)
+{
+ return nir_op_infos[alu->op].num_inputs == 1 &&
+ nir_alu_type_get_base_type(nir_op_infos[alu->op].output_type) !=
+ nir_alu_type_get_base_type(nir_op_infos[alu->op].input_types[0]);
+}
+
+/**
+ * Splits ALU instructions that have a source that is a phi node
+ *
+ * ALU instructions in the header block of a loop that meet the following
+ * criteria can be split.
+ *
+ * - The loop has no continue instructions other than the "natural" continue
+ * at the bottom of the loop.
+ *
+ * - At least one source of the instruction is a phi node from the header block.
+ *
+ * and either this rule
+ *
+ * - The phi node selects undef from the block before the loop and a value
+ * from the continue block of the loop.
+ *
+ * or these two rules
+ *
+ * - The phi node selects a constant from the block before the loop.
+ *
+ * - The non-phi source of the ALU instruction comes from a block that
+ * dominates the block before the loop. The most common failure mode for
+ * this check is sources that are generated in the loop header block.
+ *
+ * The split process moves the original ALU instruction to the bottom of the
+ * loop. The phi node source is replaced with the value from the phi node
+ * selected from the continue block (i.e., the non-undef value). A new phi
+ * node is added to the header block that selects either undef from the block
+ * before the loop or the result of the (moved) ALU instruction.
+ *
+ * The splitting transforms a loop like:
+ *
+ * vec1 32 ssa_7 = undefined
+ * vec1 32 ssa_8 = load_const (0x00000001)
+ * vec1 32 ssa_10 = load_const (0x00000000)
+ * // succs: block_1
+ * loop {
+ * block block_1:
+ * // preds: block_0 block_4
+ * vec1 32 ssa_11 = phi block_0: ssa_7, block_4: ssa_15
+ * vec1 32 ssa_12 = phi block_0: ssa_1, block_4: ssa_15
+ * vec1 32 ssa_13 = phi block_0: ssa_10, block_4: ssa_16
+ * vec1 32 ssa_14 = iadd ssa_11, ssa_8
+ * vec1 32 ssa_15 = b32csel ssa_13, ssa_14, ssa_12
+ * ...
+ * // succs: block_1
+ * }
+ *
+ * into:
+ *
+ * vec1 32 ssa_7 = undefined
+ * vec1 32 ssa_8 = load_const (0x00000001)
+ * vec1 32 ssa_10 = load_const (0x00000000)
+ * // succs: block_1
+ * loop {
+ * block block_1:
+ * // preds: block_0 block_4
+ * vec1 32 ssa_11 = phi block_0: ssa_7, block_4: ssa_15
+ * vec1 32 ssa_12 = phi block_0: ssa_1, block_4: ssa_15
+ * vec1 32 ssa_13 = phi block_0: ssa_10, block_4: ssa_16
+ * vec1 32 ssa_21 = phi block_0: sss_7, block_4: ssa_20
+ * vec1 32 ssa_15 = b32csel ssa_13, ssa_21, ssa_12
+ * ...
+ * vec1 32 ssa_20 = iadd ssa_15, ssa_8
+ * // succs: block_1
+ * }
+ *
+ * If the phi does not select an undef, the instruction is duplicated in the
+ * loop continue block (as in the undef case) and in the previous block. When
+ * the ALU instruction is duplicated in the previous block, the correct source
+ * must be selected from the phi node.
+ */
+static bool
+opt_split_alu_of_phi(nir_builder *b, nir_loop *loop)
+{
+ bool progress = false;
+ nir_block *header_block = nir_loop_first_block(loop);
+ nir_block *const prev_block =
+ nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
+
+ /* It would be insane if this were not true */
+ assert(_mesa_set_search(header_block->predecessors, prev_block));
+
+ /* The loop must have exactly one continue block which could be a block
+ * ending in a continue instruction or the "natural" continue from the
+ * last block in the loop back to the top.
+ */
+ if (header_block->predecessors->entries != 2)
+ return false;
+
+ nir_foreach_instr_safe(instr, header_block) {
+ if (instr->type != nir_instr_type_alu)
+ continue;
+
+ nir_alu_instr *const alu = nir_instr_as_alu(instr);
+
+ /* Most ALU ops produce an undefined result if any source is undef.
+ * However, operations like bcsel only produce undefined results of the
+ * first operand is undef. Even in the undefined case, the result
+ * should be one of the other two operands, so the result of the bcsel
+ * should never be replaced with undef.
+ *
+ * nir_op_vec{2,3,4}, nir_op_imov, and nir_op_fmov are excluded because
+ * they can easily lead to infinite optimization loops.
+ */
+ if (alu->op == nir_op_bcsel ||
+ alu->op == nir_op_b32csel ||
+ alu->op == nir_op_fcsel ||
+ alu->op == nir_op_vec2 ||
+ alu->op == nir_op_vec3 ||
+ alu->op == nir_op_vec4 ||
+ alu->op == nir_op_imov ||
+ alu->op == nir_op_fmov ||
+ alu_instr_is_comparison(alu) ||
+ alu_instr_is_type_conversion(alu))
+ continue;
+
+ bool has_phi_src_from_prev_block = false;
+ bool all_non_phi_exist_in_prev_block = true;
+ bool is_prev_result_undef = true;
+ bool is_prev_result_const = true;
+ nir_ssa_def *prev_srcs[8]; // FINISHME: Array size?
+ nir_ssa_def *continue_srcs[8]; // FINISHME: Array size?
+
+ for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
+ nir_instr *const src_instr = alu->src[i].src.ssa->parent_instr;
+
+ /* If the source is a phi in the loop header block, then the
+ * prev_srcs and continue_srcs will come from the different sources
+ * of the phi.
+ */
+ if (src_instr->type == nir_instr_type_phi &&
+ src_instr->block == header_block) {
+ nir_phi_instr *const phi = nir_instr_as_phi(src_instr);
+
+ /* Only strictly need to NULL out the pointers when the assertions
+ * (below) are compiled in. Debugging a NULL pointer deref in the
+ * wild is easier than debugging a random pointer deref, so set
+ * NULL unconditionally just to be safe.
+ */
+ prev_srcs[i] = NULL;
+ continue_srcs[i] = NULL;
+
+ nir_foreach_phi_src(src_of_phi, phi) {
+ if (src_of_phi->pred == prev_block) {
+ if (src_of_phi->src.ssa->parent_instr->type !=
+ nir_instr_type_ssa_undef) {
+ is_prev_result_undef = false;
+ }
+
+ if (src_of_phi->src.ssa->parent_instr->type !=
+ nir_instr_type_load_const) {
+ is_prev_result_const = false;
+ }
+
+ prev_srcs[i] = src_of_phi->src.ssa;
+ has_phi_src_from_prev_block = true;
+ } else
+ continue_srcs[i] = src_of_phi->src.ssa;
+ }
+
+ assert(prev_srcs[i] != NULL);
+ assert(continue_srcs[i] != NULL);
+ } else {
+ /* If the source is not a phi (or a phi in a block other than the
+ * loop header), then the value must exist in prev_block.
+ */
+ if (!nir_block_dominates(src_instr->block, prev_block)) {
+ all_non_phi_exist_in_prev_block = false;
+ break;
+ }
+
+ prev_srcs[i] = alu->src[i].src.ssa;
+ continue_srcs[i] = alu->src[i].src.ssa;
+ }
+ }
+
+ if (has_phi_src_from_prev_block && all_non_phi_exist_in_prev_block &&
+ (is_prev_result_undef || is_prev_result_const)) {
+ nir_block *const continue_block = find_continue_block(loop);
+ nir_ssa_def *prev_value;
+
+ if (!is_prev_result_undef) {
+ b->cursor = nir_after_block(prev_block);
+ prev_value = clone_alu_and_replace_src_defs(b, alu, prev_srcs);
+ } else {
+ /* Since the undef used as the source of the original ALU
+ * instruction may have different number of components or
+ * bit size than the result of that instruction, a new
+ * undef must be created.
+ */
+ nir_ssa_undef_instr *undef =
+ nir_ssa_undef_instr_create(b->shader,
+ alu->dest.dest.ssa.num_components,
+ alu->dest.dest.ssa.bit_size);
+
+ nir_instr_insert_after_block(prev_block, &undef->instr);
+
+ prev_value = &undef->def;
+ }
+
+ /* Make a copy of the original ALU instruction. Replace the sources
+ * of the new instruction that read a phi with an undef source from
+ * prev_block with the non-undef source of that phi.
+ *
+ * Insert the new instruction at the end of the continue block.
+ */
+ b->cursor = nir_after_block(continue_block);
+
+ nir_ssa_def *const alu_copy =
+ clone_alu_and_replace_src_defs(b, alu, continue_srcs);
+
+ /* Make a new phi node that selects a value from prev_block and the
+ * result of the new instruction from continue_block.
+ */
+ nir_phi_instr *const phi = nir_phi_instr_create(b->shader);
+ nir_phi_src *phi_src;
+
+ phi_src = ralloc(phi, nir_phi_src);
+ phi_src->pred = prev_block;
+ phi_src->src = nir_src_for_ssa(prev_value);
+ exec_list_push_tail(&phi->srcs, &phi_src->node);
+
+ phi_src = ralloc(phi, nir_phi_src);
+ phi_src->pred = continue_block;
+ phi_src->src = nir_src_for_ssa(alu_copy);
+ exec_list_push_tail(&phi->srcs, &phi_src->node);
+
+ nir_ssa_dest_init(&phi->instr, &phi->dest,
+ alu_copy->num_components, alu_copy->bit_size, NULL);
+
+ b->cursor = nir_after_phis(header_block);
+ nir_builder_instr_insert(b, &phi->instr);
+
+ /* Modify all readers of the original ALU instruction to read the
+ * result of the phi.
+ */
+ nir_foreach_use_safe(use_src, &alu->dest.dest.ssa) {
+ nir_instr_rewrite_src(use_src->parent_instr,
+ use_src,
+ nir_src_for_ssa(&phi->dest.ssa));
+ }
+
+ nir_foreach_if_use_safe(use_src, &alu->dest.dest.ssa) {
+ nir_if_rewrite_condition(use_src->parent_if,
+ nir_src_for_ssa(&phi->dest.ssa));
+ }
+
+ /* Since the original ALU instruction no longer has any readers, just
+ * remove it.
+ */
+ nir_instr_remove_v(&alu->instr);
+ ralloc_free(alu);
+
+ progress = true;
+ }
+ }
+
+ return progress;
+}
+
static bool
is_block_empty(nir_block *block)
{
case nir_cf_node_loop: {
nir_loop *loop = nir_cf_node_as_loop(cf_node);
progress |= opt_if_safe_cf_list(b, &loop->body);
+ progress |= opt_split_alu_of_phi(b, loop);
break;
}
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