| /* |
| * Copyright © 2012 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: |
| * Eric Anholt <eric@anholt.net> |
| * |
| */ |
| |
| #include "brw_cfg.h" |
| |
| /** @file brw_cfg.cpp |
| * |
| * Walks the shader instructions generated and creates a set of basic |
| * blocks with successor/predecessor edges connecting them. |
| */ |
| |
| static bblock_t * |
| pop_stack(exec_list *list) |
| { |
| bblock_link *link = (bblock_link *)list->get_tail(); |
| bblock_t *block = link->block; |
| link->link.remove(); |
| |
| return block; |
| } |
| |
| static exec_node * |
| link(void *mem_ctx, bblock_t *block, enum bblock_link_kind kind) |
| { |
| bblock_link *l = new(mem_ctx) bblock_link(block, kind); |
| return &l->link; |
| } |
| |
| void |
| push_stack(exec_list *list, void *mem_ctx, bblock_t *block) |
| { |
| /* The kind of the link is immaterial, but we need to provide one since |
| * this is (ab)using the edge data structure in order to implement a stack. |
| */ |
| list->push_tail(link(mem_ctx, block, bblock_link_logical)); |
| } |
| |
| bblock_t::bblock_t(cfg_t *cfg) : |
| cfg(cfg), idom(NULL), start_ip(0), end_ip(0), num(0), cycle_count(0) |
| { |
| instructions.make_empty(); |
| parents.make_empty(); |
| children.make_empty(); |
| } |
| |
| void |
| bblock_t::add_successor(void *mem_ctx, bblock_t *successor, |
| enum bblock_link_kind kind) |
| { |
| successor->parents.push_tail(::link(mem_ctx, this, kind)); |
| children.push_tail(::link(mem_ctx, successor, kind)); |
| } |
| |
| bool |
| bblock_t::is_predecessor_of(const bblock_t *block, |
| enum bblock_link_kind kind) const |
| { |
| foreach_list_typed_safe (bblock_link, parent, link, &block->parents) { |
| if (parent->block == this && parent->kind <= kind) { |
| return true; |
| } |
| } |
| |
| return false; |
| } |
| |
| bool |
| bblock_t::is_successor_of(const bblock_t *block, |
| enum bblock_link_kind kind) const |
| { |
| foreach_list_typed_safe (bblock_link, child, link, &block->children) { |
| if (child->block == this && child->kind <= kind) { |
| return true; |
| } |
| } |
| |
| return false; |
| } |
| |
| static bool |
| ends_block(const backend_instruction *inst) |
| { |
| enum opcode op = inst->opcode; |
| |
| return op == BRW_OPCODE_IF || |
| op == BRW_OPCODE_ELSE || |
| op == BRW_OPCODE_CONTINUE || |
| op == BRW_OPCODE_BREAK || |
| op == BRW_OPCODE_DO || |
| op == BRW_OPCODE_WHILE; |
| } |
| |
| static bool |
| starts_block(const backend_instruction *inst) |
| { |
| enum opcode op = inst->opcode; |
| |
| return op == BRW_OPCODE_DO || |
| op == BRW_OPCODE_ENDIF; |
| } |
| |
| bool |
| bblock_t::can_combine_with(const bblock_t *that) const |
| { |
| if ((const bblock_t *)this->link.next != that) |
| return false; |
| |
| if (ends_block(this->end()) || |
| starts_block(that->start())) |
| return false; |
| |
| return true; |
| } |
| |
| void |
| bblock_t::combine_with(bblock_t *that) |
| { |
| assert(this->can_combine_with(that)); |
| foreach_list_typed (bblock_link, link, link, &that->parents) { |
| assert(link->block == this); |
| } |
| |
| this->end_ip = that->end_ip; |
| this->instructions.append_list(&that->instructions); |
| |
| this->cfg->remove_block(that); |
| } |
| |
| void |
| bblock_t::dump(backend_shader *s) const |
| { |
| int ip = this->start_ip; |
| foreach_inst_in_block(backend_instruction, inst, this) { |
| fprintf(stderr, "%5d: ", ip); |
| s->dump_instruction(inst); |
| ip++; |
| } |
| } |
| |
| cfg_t::cfg_t(exec_list *instructions) |
| { |
| mem_ctx = ralloc_context(NULL); |
| block_list.make_empty(); |
| blocks = NULL; |
| num_blocks = 0; |
| idom_dirty = true; |
| cycle_count = 0; |
| |
| bblock_t *cur = NULL; |
| int ip = 0; |
| |
| bblock_t *entry = new_block(); |
| bblock_t *cur_if = NULL; /**< BB ending with IF. */ |
| bblock_t *cur_else = NULL; /**< BB ending with ELSE. */ |
| bblock_t *cur_endif = NULL; /**< BB starting with ENDIF. */ |
| bblock_t *cur_do = NULL; /**< BB starting with DO. */ |
| bblock_t *cur_while = NULL; /**< BB immediately following WHILE. */ |
| exec_list if_stack, else_stack, do_stack, while_stack; |
| bblock_t *next; |
| |
| set_next_block(&cur, entry, ip); |
| |
| foreach_in_list_safe(backend_instruction, inst, instructions) { |
| /* set_next_block wants the post-incremented ip */ |
| ip++; |
| |
| inst->exec_node::remove(); |
| |
| switch (inst->opcode) { |
| case BRW_OPCODE_IF: |
| cur->instructions.push_tail(inst); |
| |
| /* Push our information onto a stack so we can recover from |
| * nested ifs. |
| */ |
| push_stack(&if_stack, mem_ctx, cur_if); |
| push_stack(&else_stack, mem_ctx, cur_else); |
| |
| cur_if = cur; |
| cur_else = NULL; |
| cur_endif = NULL; |
| |
| /* Set up our immediately following block, full of "then" |
| * instructions. |
| */ |
| next = new_block(); |
| cur_if->add_successor(mem_ctx, next, bblock_link_logical); |
| |
| set_next_block(&cur, next, ip); |
| break; |
| |
| case BRW_OPCODE_ELSE: |
| cur->instructions.push_tail(inst); |
| |
| cur_else = cur; |
| |
| next = new_block(); |
| assert(cur_if != NULL); |
| cur_if->add_successor(mem_ctx, next, bblock_link_logical); |
| |
| set_next_block(&cur, next, ip); |
| break; |
| |
| case BRW_OPCODE_ENDIF: { |
| if (cur->instructions.is_empty()) { |
| /* New block was just created; use it. */ |
| cur_endif = cur; |
| } else { |
| cur_endif = new_block(); |
| |
| cur->add_successor(mem_ctx, cur_endif, bblock_link_logical); |
| |
| set_next_block(&cur, cur_endif, ip - 1); |
| } |
| |
| cur->instructions.push_tail(inst); |
| |
| if (cur_else) { |
| cur_else->add_successor(mem_ctx, cur_endif, bblock_link_logical); |
| } else { |
| assert(cur_if != NULL); |
| cur_if->add_successor(mem_ctx, cur_endif, bblock_link_logical); |
| } |
| |
| assert(cur_if->end()->opcode == BRW_OPCODE_IF); |
| assert(!cur_else || cur_else->end()->opcode == BRW_OPCODE_ELSE); |
| |
| /* Pop the stack so we're in the previous if/else/endif */ |
| cur_if = pop_stack(&if_stack); |
| cur_else = pop_stack(&else_stack); |
| break; |
| } |
| case BRW_OPCODE_DO: |
| /* Push our information onto a stack so we can recover from |
| * nested loops. |
| */ |
| push_stack(&do_stack, mem_ctx, cur_do); |
| push_stack(&while_stack, mem_ctx, cur_while); |
| |
| /* Set up the block just after the while. Don't know when exactly |
| * it will start, yet. |
| */ |
| cur_while = new_block(); |
| |
| if (cur->instructions.is_empty()) { |
| /* New block was just created; use it. */ |
| cur_do = cur; |
| } else { |
| cur_do = new_block(); |
| |
| cur->add_successor(mem_ctx, cur_do, bblock_link_logical); |
| |
| set_next_block(&cur, cur_do, ip - 1); |
| } |
| |
| cur->instructions.push_tail(inst); |
| |
| /* Represent divergent execution of the loop as a pair of alternative |
| * edges coming out of the DO instruction: For any physical iteration |
| * of the loop a given logical thread can either start off enabled |
| * (which is represented as the "next" successor), or disabled (if it |
| * has reached a non-uniform exit of the loop during a previous |
| * iteration, which is represented as the "cur_while" successor). |
| * |
| * The disabled edge will be taken by the logical thread anytime we |
| * arrive at the DO instruction through a back-edge coming from a |
| * conditional exit of the loop where divergent control flow started. |
| * |
| * This guarantees that there is a control-flow path from any |
| * divergence point of the loop into the convergence point |
| * (immediately past the WHILE instruction) such that it overlaps the |
| * whole IP region of divergent control flow (potentially the whole |
| * loop) *and* doesn't imply the execution of any instructions part |
| * of the loop (since the corresponding execution mask bit will be |
| * disabled for a diverging thread). |
| * |
| * This way we make sure that any variables that are live throughout |
| * the region of divergence for an inactive logical thread are also |
| * considered to interfere with any other variables assigned by |
| * active logical threads within the same physical region of the |
| * program, since otherwise we would risk cross-channel data |
| * corruption. |
| */ |
| next = new_block(); |
| cur->add_successor(mem_ctx, next, bblock_link_logical); |
| cur->add_successor(mem_ctx, cur_while, bblock_link_physical); |
| set_next_block(&cur, next, ip); |
| break; |
| |
| case BRW_OPCODE_CONTINUE: |
| cur->instructions.push_tail(inst); |
| |
| /* A conditional CONTINUE may start a region of divergent control |
| * flow until the start of the next loop iteration (*not* until the |
| * end of the loop which is why the successor is not the top-level |
| * divergence point at cur_do). The live interval of any variable |
| * extending through a CONTINUE edge is guaranteed to overlap the |
| * whole region of divergent execution, because any variable live-out |
| * at the CONTINUE instruction will also be live-in at the top of the |
| * loop, and therefore also live-out at the bottom-most point of the |
| * loop which is reachable from the top (since a control flow path |
| * exists from a definition of the variable through this CONTINUE |
| * instruction, the top of the loop, the (reachable) bottom of the |
| * loop, the top of the loop again, into a use of the variable). |
| */ |
| assert(cur_do != NULL); |
| cur->add_successor(mem_ctx, cur_do->next(), bblock_link_logical); |
| |
| next = new_block(); |
| if (inst->predicate) |
| cur->add_successor(mem_ctx, next, bblock_link_logical); |
| |
| set_next_block(&cur, next, ip); |
| break; |
| |
| case BRW_OPCODE_BREAK: |
| cur->instructions.push_tail(inst); |
| |
| /* A conditional BREAK instruction may start a region of divergent |
| * control flow until the end of the loop if the condition is |
| * non-uniform, in which case the loop will execute additional |
| * iterations with the present channel disabled. We model this as a |
| * control flow path from the divergence point to the convergence |
| * point that overlaps the whole IP range of the loop and skips over |
| * the execution of any other instructions part of the loop. |
| * |
| * See the DO case for additional explanation. |
| */ |
| assert(cur_do != NULL); |
| cur->add_successor(mem_ctx, cur_do, bblock_link_physical); |
| cur->add_successor(mem_ctx, cur_while, bblock_link_logical); |
| |
| next = new_block(); |
| if (inst->predicate) |
| cur->add_successor(mem_ctx, next, bblock_link_logical); |
| |
| set_next_block(&cur, next, ip); |
| break; |
| |
| case BRW_OPCODE_WHILE: |
| cur->instructions.push_tail(inst); |
| |
| assert(cur_do != NULL && cur_while != NULL); |
| |
| /* A conditional WHILE instruction may start a region of divergent |
| * control flow until the end of the loop, just like the BREAK |
| * instruction. See the BREAK case for more details. OTOH an |
| * unconditional WHILE instruction is non-divergent (just like an |
| * unconditional CONTINUE), and will necessarily lead to the |
| * execution of an additional iteration of the loop for all enabled |
| * channels, so we may skip over the divergence point at the top of |
| * the loop to keep the CFG as unambiguous as possible. |
| */ |
| if (inst->predicate) { |
| cur->add_successor(mem_ctx, cur_do, bblock_link_logical); |
| } else { |
| cur->add_successor(mem_ctx, cur_do->next(), bblock_link_logical); |
| } |
| |
| set_next_block(&cur, cur_while, ip); |
| |
| /* Pop the stack so we're in the previous loop */ |
| cur_do = pop_stack(&do_stack); |
| cur_while = pop_stack(&while_stack); |
| break; |
| |
| default: |
| cur->instructions.push_tail(inst); |
| break; |
| } |
| } |
| |
| cur->end_ip = ip - 1; |
| |
| make_block_array(); |
| } |
| |
| cfg_t::~cfg_t() |
| { |
| ralloc_free(mem_ctx); |
| } |
| |
| void |
| cfg_t::remove_block(bblock_t *block) |
| { |
| foreach_list_typed_safe (bblock_link, predecessor, link, &block->parents) { |
| /* Remove block from all of its predecessors' successor lists. */ |
| foreach_list_typed_safe (bblock_link, successor, link, |
| &predecessor->block->children) { |
| if (block == successor->block) { |
| successor->link.remove(); |
| ralloc_free(successor); |
| } |
| } |
| |
| /* Add removed-block's successors to its predecessors' successor lists. */ |
| foreach_list_typed (bblock_link, successor, link, &block->children) { |
| if (!successor->block->is_successor_of(predecessor->block, |
| successor->kind)) { |
| predecessor->block->children.push_tail(link(mem_ctx, |
| successor->block, |
| successor->kind)); |
| } |
| } |
| } |
| |
| foreach_list_typed_safe (bblock_link, successor, link, &block->children) { |
| /* Remove block from all of its childrens' parents lists. */ |
| foreach_list_typed_safe (bblock_link, predecessor, link, |
| &successor->block->parents) { |
| if (block == predecessor->block) { |
| predecessor->link.remove(); |
| ralloc_free(predecessor); |
| } |
| } |
| |
| /* Add removed-block's predecessors to its successors' predecessor lists. */ |
| foreach_list_typed (bblock_link, predecessor, link, &block->parents) { |
| if (!predecessor->block->is_predecessor_of(successor->block, |
| predecessor->kind)) { |
| successor->block->parents.push_tail(link(mem_ctx, |
| predecessor->block, |
| predecessor->kind)); |
| } |
| } |
| } |
| |
| block->link.remove(); |
| |
| for (int b = block->num; b < this->num_blocks - 1; b++) { |
| this->blocks[b] = this->blocks[b + 1]; |
| this->blocks[b]->num = b; |
| } |
| |
| this->blocks[this->num_blocks - 1]->num = this->num_blocks - 2; |
| this->num_blocks--; |
| idom_dirty = true; |
| } |
| |
| bblock_t * |
| cfg_t::new_block() |
| { |
| bblock_t *block = new(mem_ctx) bblock_t(this); |
| |
| return block; |
| } |
| |
| void |
| cfg_t::set_next_block(bblock_t **cur, bblock_t *block, int ip) |
| { |
| if (*cur) { |
| (*cur)->end_ip = ip - 1; |
| } |
| |
| block->start_ip = ip; |
| block->num = num_blocks++; |
| block_list.push_tail(&block->link); |
| *cur = block; |
| } |
| |
| void |
| cfg_t::make_block_array() |
| { |
| blocks = ralloc_array(mem_ctx, bblock_t *, num_blocks); |
| |
| int i = 0; |
| foreach_block (block, this) { |
| blocks[i++] = block; |
| } |
| assert(i == num_blocks); |
| } |
| |
| void |
| cfg_t::dump(backend_shader *s) |
| { |
| if (idom_dirty) |
| calculate_idom(); |
| |
| foreach_block (block, this) { |
| if (block->idom) |
| fprintf(stderr, "START B%d IDOM(B%d)", block->num, block->idom->num); |
| else |
| fprintf(stderr, "START B%d IDOM(none)", block->num); |
| |
| foreach_list_typed(bblock_link, link, link, &block->parents) { |
| fprintf(stderr, " <%cB%d", |
| link->kind == bblock_link_logical ? '-' : '~', |
| link->block->num); |
| } |
| fprintf(stderr, "\n"); |
| if (s != NULL) |
| block->dump(s); |
| fprintf(stderr, "END B%d", block->num); |
| foreach_list_typed(bblock_link, link, link, &block->children) { |
| fprintf(stderr, " %c>B%d", |
| link->kind == bblock_link_logical ? '-' : '~', |
| link->block->num); |
| } |
| fprintf(stderr, "\n"); |
| } |
| } |
| |
| /* Calculates the immediate dominator of each block, according to "A Simple, |
| * Fast Dominance Algorithm" by Keith D. Cooper, Timothy J. Harvey, and Ken |
| * Kennedy. |
| * |
| * The authors claim that for control flow graphs of sizes normally encountered |
| * (less than 1000 nodes) that this algorithm is significantly faster than |
| * others like Lengauer-Tarjan. |
| */ |
| void |
| cfg_t::calculate_idom() |
| { |
| foreach_block(block, this) { |
| block->idom = NULL; |
| } |
| blocks[0]->idom = blocks[0]; |
| |
| bool changed; |
| do { |
| changed = false; |
| |
| foreach_block(block, this) { |
| if (block->num == 0) |
| continue; |
| |
| bblock_t *new_idom = NULL; |
| foreach_list_typed(bblock_link, parent, link, &block->parents) { |
| if (parent->block->idom) { |
| if (new_idom == NULL) { |
| new_idom = parent->block; |
| } else if (parent->block->idom != NULL) { |
| new_idom = intersect(parent->block, new_idom); |
| } |
| } |
| } |
| |
| if (block->idom != new_idom) { |
| block->idom = new_idom; |
| changed = true; |
| } |
| } |
| } while (changed); |
| |
| idom_dirty = false; |
| } |
| |
| bblock_t * |
| cfg_t::intersect(bblock_t *b1, bblock_t *b2) |
| { |
| /* Note, the comparisons here are the opposite of what the paper says |
| * because we index blocks from beginning -> end (i.e. reverse post-order) |
| * instead of post-order like they assume. |
| */ |
| while (b1->num != b2->num) { |
| while (b1->num > b2->num) |
| b1 = b1->idom; |
| while (b2->num > b1->num) |
| b2 = b2->idom; |
| } |
| assert(b1); |
| return b1; |
| } |
| |
| void |
| cfg_t::dump_cfg() |
| { |
| printf("digraph CFG {\n"); |
| for (int b = 0; b < num_blocks; b++) { |
| bblock_t *block = this->blocks[b]; |
| |
| foreach_list_typed_safe (bblock_link, child, link, &block->children) { |
| printf("\t%d -> %d\n", b, child->block->num); |
| } |
| } |
| printf("}\n"); |
| } |
| |
| void |
| cfg_t::dump_domtree() |
| { |
| printf("digraph DominanceTree {\n"); |
| foreach_block(block, this) { |
| if (block->idom) { |
| printf("\t%d -> %d\n", block->idom->num, block->num); |
| } |
| } |
| printf("}\n"); |
| } |