/* * Copyright © 2014 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: * Connor Abbott (cwabbott0@gmail.com) * */ #include "nir_control_flow_private.h" /** * \name Control flow modification * * These functions modify the control flow tree while keeping the control flow * graph up-to-date. The invariants respected are: * 1. Each then statement, else statement, or loop body must have at least one * control flow node. * 2. Each if-statement and loop must have one basic block before it and one * after. * 3. Two basic blocks cannot be directly next to each other. * 4. If a basic block has a jump instruction, there must be only one and it * must be at the end of the block. * 5. The CFG must always be connected - this means that we must insert a fake * CFG edge for loops with no break statement. * * The purpose of the second one is so that we have places to insert code during * GCM, as well as eliminating the possibility of critical edges. */ /*@{*/ static bool block_ends_in_jump(nir_block *block) { return !exec_list_is_empty(&block->instr_list) && nir_block_last_instr(block)->type == nir_instr_type_jump; } static inline void block_add_pred(nir_block *block, nir_block *pred) { _mesa_set_add(block->predecessors, pred); } static inline void block_remove_pred(nir_block *block, nir_block *pred) { struct set_entry *entry = _mesa_set_search(block->predecessors, pred); assert(entry); _mesa_set_remove(block->predecessors, entry); } static void link_blocks(nir_block *pred, nir_block *succ1, nir_block *succ2) { pred->successors[0] = succ1; if (succ1 != NULL) block_add_pred(succ1, pred); pred->successors[1] = succ2; if (succ2 != NULL) block_add_pred(succ2, pred); } static void unlink_blocks(nir_block *pred, nir_block *succ) { if (pred->successors[0] == succ) { pred->successors[0] = pred->successors[1]; pred->successors[1] = NULL; } else { assert(pred->successors[1] == succ); pred->successors[1] = NULL; } block_remove_pred(succ, pred); } static void unlink_block_successors(nir_block *block) { if (block->successors[1] != NULL) unlink_blocks(block, block->successors[1]); if (block->successors[0] != NULL) unlink_blocks(block, block->successors[0]); } static void link_non_block_to_block(nir_cf_node *node, nir_block *block) { if (node->type == nir_cf_node_if) { /* * We're trying to link an if to a block after it; this just means linking * the last block of the then and else branches. */ nir_if *if_stmt = nir_cf_node_as_if(node); nir_cf_node *last_then = nir_if_last_then_node(if_stmt); assert(last_then->type == nir_cf_node_block); nir_block *last_then_block = nir_cf_node_as_block(last_then); nir_cf_node *last_else = nir_if_last_else_node(if_stmt); assert(last_else->type == nir_cf_node_block); nir_block *last_else_block = nir_cf_node_as_block(last_else); if (!block_ends_in_jump(last_then_block)) { unlink_block_successors(last_then_block); link_blocks(last_then_block, block, NULL); } if (!block_ends_in_jump(last_else_block)) { unlink_block_successors(last_else_block); link_blocks(last_else_block, block, NULL); } } else { assert(node->type == nir_cf_node_loop); /* * We can only get to this codepath if we're inserting a new loop, or * at least a loop with no break statements; we can't insert break * statements into a loop when we haven't inserted it into the CFG * because we wouldn't know which block comes after the loop * and therefore, which block should be the successor of the block with * the break). Therefore, we need to insert a fake edge (see invariant * #5). */ nir_loop *loop = nir_cf_node_as_loop(node); nir_cf_node *last = nir_loop_last_cf_node(loop); assert(last->type == nir_cf_node_block); nir_block *last_block = nir_cf_node_as_block(last); last_block->successors[1] = block; block_add_pred(block, last_block); } } static void link_block_to_non_block(nir_block *block, nir_cf_node *node) { if (node->type == nir_cf_node_if) { /* * We're trying to link a block to an if after it; this just means linking * the block to the first block of the then and else branches. */ nir_if *if_stmt = nir_cf_node_as_if(node); nir_cf_node *first_then = nir_if_first_then_node(if_stmt); assert(first_then->type == nir_cf_node_block); nir_block *first_then_block = nir_cf_node_as_block(first_then); nir_cf_node *first_else = nir_if_first_else_node(if_stmt); assert(first_else->type == nir_cf_node_block); nir_block *first_else_block = nir_cf_node_as_block(first_else); unlink_block_successors(block); link_blocks(block, first_then_block, first_else_block); } else { /* * For similar reasons as the corresponding case in * link_non_block_to_block(), don't worry about if the loop header has * any predecessors that need to be unlinked. */ assert(node->type == nir_cf_node_loop); nir_loop *loop = nir_cf_node_as_loop(node); nir_cf_node *loop_header = nir_loop_first_cf_node(loop); assert(loop_header->type == nir_cf_node_block); nir_block *loop_header_block = nir_cf_node_as_block(loop_header); unlink_block_successors(block); link_blocks(block, loop_header_block, NULL); } } /** * Replace a block's successor with a different one. */ static void replace_successor(nir_block *block, nir_block *old_succ, nir_block *new_succ) { if (block->successors[0] == old_succ) { block->successors[0] = new_succ; } else { assert(block->successors[1] == old_succ); block->successors[1] = new_succ; } block_remove_pred(old_succ, block); block_add_pred(new_succ, block); } /** * Takes a basic block and inserts a new empty basic block before it, making its * predecessors point to the new block. This essentially splits the block into * an empty header and a body so that another non-block CF node can be inserted * between the two. Note that this does *not* link the two basic blocks, so * some kind of cleanup *must* be performed after this call. */ static nir_block * split_block_beginning(nir_block *block) { nir_block *new_block = nir_block_create(ralloc_parent(block)); new_block->cf_node.parent = block->cf_node.parent; exec_node_insert_node_before(&block->cf_node.node, &new_block->cf_node.node); struct set_entry *entry; set_foreach(block->predecessors, entry) { nir_block *pred = (nir_block *) entry->key; replace_successor(pred, block, new_block); } /* Any phi nodes must stay part of the new block, or else their * sourcse will be messed up. This will reverse the order of the phi's, but * order shouldn't matter. */ nir_foreach_instr_safe(block, instr) { if (instr->type != nir_instr_type_phi) break; exec_node_remove(&instr->node); instr->block = new_block; exec_list_push_head(&new_block->instr_list, &instr->node); } return new_block; } static void rewrite_phi_preds(nir_block *block, nir_block *old_pred, nir_block *new_pred) { nir_foreach_instr_safe(block, instr) { if (instr->type != nir_instr_type_phi) break; nir_phi_instr *phi = nir_instr_as_phi(instr); nir_foreach_phi_src(phi, src) { if (src->pred == old_pred) { src->pred = new_pred; break; } } } } static void insert_phi_undef(nir_block *block, nir_block *pred) { nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node); nir_foreach_instr(block, instr) { if (instr->type != nir_instr_type_phi) break; nir_phi_instr *phi = nir_instr_as_phi(instr); nir_ssa_undef_instr *undef = nir_ssa_undef_instr_create(ralloc_parent(phi), phi->dest.ssa.num_components, phi->dest.ssa.bit_size); nir_instr_insert_before_cf_list(&impl->body, &undef->instr); nir_phi_src *src = ralloc(phi, nir_phi_src); src->pred = pred; src->src.parent_instr = &phi->instr; src->src.is_ssa = true; src->src.ssa = &undef->def; list_addtail(&src->src.use_link, &undef->def.uses); exec_list_push_tail(&phi->srcs, &src->node); } } /** * Moves the successors of source to the successors of dest, leaving both * successors of source NULL. */ static void move_successors(nir_block *source, nir_block *dest) { nir_block *succ1 = source->successors[0]; nir_block *succ2 = source->successors[1]; if (succ1) { unlink_blocks(source, succ1); rewrite_phi_preds(succ1, source, dest); } if (succ2) { unlink_blocks(source, succ2); rewrite_phi_preds(succ2, source, dest); } unlink_block_successors(dest); link_blocks(dest, succ1, succ2); } /* Given a basic block with no successors that has been inserted into the * control flow tree, gives it the successors it would normally have assuming * it doesn't end in a jump instruction. Also inserts phi sources with undefs * if necessary. */ static void block_add_normal_succs(nir_block *block) { if (exec_node_is_tail_sentinel(block->cf_node.node.next)) { nir_cf_node *parent = block->cf_node.parent; if (parent->type == nir_cf_node_if) { nir_cf_node *next = nir_cf_node_next(parent); assert(next->type == nir_cf_node_block); nir_block *next_block = nir_cf_node_as_block(next); link_blocks(block, next_block, NULL); } else if (parent->type == nir_cf_node_loop) { nir_loop *loop = nir_cf_node_as_loop(parent); nir_cf_node *head = nir_loop_first_cf_node(loop); assert(head->type == nir_cf_node_block); nir_block *head_block = nir_cf_node_as_block(head); link_blocks(block, head_block, NULL); insert_phi_undef(head_block, block); } else { assert(parent->type == nir_cf_node_function); nir_function_impl *impl = nir_cf_node_as_function(parent); link_blocks(block, impl->end_block, NULL); } } else { nir_cf_node *next = nir_cf_node_next(&block->cf_node); if (next->type == nir_cf_node_if) { nir_if *next_if = nir_cf_node_as_if(next); nir_cf_node *first_then = nir_if_first_then_node(next_if); assert(first_then->type == nir_cf_node_block); nir_block *first_then_block = nir_cf_node_as_block(first_then); nir_cf_node *first_else = nir_if_first_else_node(next_if); assert(first_else->type == nir_cf_node_block); nir_block *first_else_block = nir_cf_node_as_block(first_else); link_blocks(block, first_then_block, first_else_block); } else { assert(next->type == nir_cf_node_loop); nir_loop *next_loop = nir_cf_node_as_loop(next); nir_cf_node *first = nir_loop_first_cf_node(next_loop); assert(first->type == nir_cf_node_block); nir_block *first_block = nir_cf_node_as_block(first); link_blocks(block, first_block, NULL); insert_phi_undef(first_block, block); } } } static nir_block * split_block_end(nir_block *block) { nir_block *new_block = nir_block_create(ralloc_parent(block)); new_block->cf_node.parent = block->cf_node.parent; exec_node_insert_after(&block->cf_node.node, &new_block->cf_node.node); if (block_ends_in_jump(block)) { /* Figure out what successor block would've had if it didn't have a jump * instruction, and make new_block have that successor. */ block_add_normal_succs(new_block); } else { move_successors(block, new_block); } return new_block; } static nir_block * split_block_before_instr(nir_instr *instr) { assert(instr->type != nir_instr_type_phi); nir_block *new_block = split_block_beginning(instr->block); nir_foreach_instr_safe(instr->block, cur_instr) { if (cur_instr == instr) break; exec_node_remove(&cur_instr->node); cur_instr->block = new_block; exec_list_push_tail(&new_block->instr_list, &cur_instr->node); } return new_block; } /* Splits a basic block at the point specified by the cursor. The "before" and * "after" arguments are filled out with the blocks resulting from the split * if non-NULL. Note that the "beginning" of the block is actually interpreted * as before the first non-phi instruction, and it's illegal to split a block * before a phi instruction. */ static void split_block_cursor(nir_cursor cursor, nir_block **_before, nir_block **_after) { nir_block *before, *after; switch (cursor.option) { case nir_cursor_before_block: after = cursor.block; before = split_block_beginning(cursor.block); break; case nir_cursor_after_block: before = cursor.block; after = split_block_end(cursor.block); break; case nir_cursor_before_instr: after = cursor.instr->block; before = split_block_before_instr(cursor.instr); break; case nir_cursor_after_instr: /* We lower this to split_block_before_instr() so that we can keep the * after-a-jump-instr case contained to split_block_end(). */ if (nir_instr_is_last(cursor.instr)) { before = cursor.instr->block; after = split_block_end(cursor.instr->block); } else { after = cursor.instr->block; before = split_block_before_instr(nir_instr_next(cursor.instr)); } break; default: unreachable("not reached"); } if (_before) *_before = before; if (_after) *_after = after; } /** * Inserts a non-basic block between two basic blocks and links them together. */ static void insert_non_block(nir_block *before, nir_cf_node *node, nir_block *after) { node->parent = before->cf_node.parent; exec_node_insert_after(&before->cf_node.node, &node->node); link_block_to_non_block(before, node); link_non_block_to_block(node, after); } /* walk up the control flow tree to find the innermost enclosed loop */ static nir_loop * nearest_loop(nir_cf_node *node) { while (node->type != nir_cf_node_loop) { node = node->parent; } return nir_cf_node_as_loop(node); } /* * update the CFG after a jump instruction has been added to the end of a block */ void nir_handle_add_jump(nir_block *block) { nir_instr *instr = nir_block_last_instr(block); nir_jump_instr *jump_instr = nir_instr_as_jump(instr); unlink_block_successors(block); nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node); nir_metadata_preserve(impl, nir_metadata_none); if (jump_instr->type == nir_jump_break || jump_instr->type == nir_jump_continue) { nir_loop *loop = nearest_loop(&block->cf_node); if (jump_instr->type == nir_jump_continue) { nir_cf_node *first_node = nir_loop_first_cf_node(loop); assert(first_node->type == nir_cf_node_block); nir_block *first_block = nir_cf_node_as_block(first_node); link_blocks(block, first_block, NULL); } else { nir_cf_node *after = nir_cf_node_next(&loop->cf_node); assert(after->type == nir_cf_node_block); nir_block *after_block = nir_cf_node_as_block(after); link_blocks(block, after_block, NULL); /* If we inserted a fake link, remove it */ nir_cf_node *last = nir_loop_last_cf_node(loop); assert(last->type == nir_cf_node_block); nir_block *last_block = nir_cf_node_as_block(last); if (last_block->successors[1] != NULL) unlink_blocks(last_block, after_block); } } else { assert(jump_instr->type == nir_jump_return); link_blocks(block, impl->end_block, NULL); } } static void remove_phi_src(nir_block *block, nir_block *pred) { nir_foreach_instr(block, instr) { if (instr->type != nir_instr_type_phi) break; nir_phi_instr *phi = nir_instr_as_phi(instr); nir_foreach_phi_src_safe(phi, src) { if (src->pred == pred) { list_del(&src->src.use_link); exec_node_remove(&src->node); } } } } /* Removes the successor of a block with a jump, and inserts a fake edge for * infinite loops. Note that the jump to be eliminated may be free-floating. */ static void unlink_jump(nir_block *block, nir_jump_type type, bool add_normal_successors) { nir_block *next = block->successors[0]; if (block->successors[0]) remove_phi_src(block->successors[0], block); if (block->successors[1]) remove_phi_src(block->successors[1], block); unlink_block_successors(block); if (add_normal_successors) block_add_normal_succs(block); /* If we've just removed a break, and the block we were jumping to (after * the loop) now has zero predecessors, we've created a new infinite loop. * * NIR doesn't allow blocks (other than the start block) to have zero * predecessors. In particular, dominance assumes all blocks are reachable. * So, we insert a "fake link" by making successors[1] point after the loop. * * Note that we have to do this after unlinking/recreating the block's * successors. If we removed a "break" at the end of the loop, then * block == last_block, so block->successors[0] would already be "next", * and adding a fake link would create two identical successors. Doing * this afterward works, as we'll have changed block->successors[0] to * be the top of the loop. */ if (type == nir_jump_break && next->predecessors->entries == 0) { nir_loop *loop = nir_cf_node_as_loop(nir_cf_node_prev(&next->cf_node)); /* insert fake link */ nir_cf_node *last = nir_loop_last_cf_node(loop); assert(last->type == nir_cf_node_block); nir_block *last_block = nir_cf_node_as_block(last); last_block->successors[1] = next; block_add_pred(next, last_block); } } void nir_handle_remove_jump(nir_block *block, nir_jump_type type) { unlink_jump(block, type, true); nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node); nir_metadata_preserve(impl, nir_metadata_none); } static void update_if_uses(nir_cf_node *node) { if (node->type != nir_cf_node_if) return; nir_if *if_stmt = nir_cf_node_as_if(node); if_stmt->condition.parent_if = if_stmt; if (if_stmt->condition.is_ssa) { list_addtail(&if_stmt->condition.use_link, &if_stmt->condition.ssa->if_uses); } else { list_addtail(&if_stmt->condition.use_link, &if_stmt->condition.reg.reg->if_uses); } } /** * Stitch two basic blocks together into one. The aggregate must have the same * predecessors as the first and the same successors as the second. */ static void stitch_blocks(nir_block *before, nir_block *after) { /* * We move after into before, so we have to deal with up to 2 successors vs. * possibly a large number of predecessors. * * TODO: special case when before is empty and after isn't? */ if (block_ends_in_jump(before)) { assert(exec_list_is_empty(&after->instr_list)); if (after->successors[0]) remove_phi_src(after->successors[0], after); if (after->successors[1]) remove_phi_src(after->successors[1], after); unlink_block_successors(after); exec_node_remove(&after->cf_node.node); } else { move_successors(after, before); foreach_list_typed(nir_instr, instr, node, &after->instr_list) { instr->block = before; } exec_list_append(&before->instr_list, &after->instr_list); exec_node_remove(&after->cf_node.node); } } void nir_cf_node_insert(nir_cursor cursor, nir_cf_node *node) { nir_block *before, *after; split_block_cursor(cursor, &before, &after); if (node->type == nir_cf_node_block) { nir_block *block = nir_cf_node_as_block(node); exec_node_insert_after(&before->cf_node.node, &block->cf_node.node); block->cf_node.parent = before->cf_node.parent; /* stitch_blocks() assumes that any block that ends with a jump has * already been setup with the correct successors, so we need to set * up jumps here as the block is being inserted. */ if (block_ends_in_jump(block)) nir_handle_add_jump(block); stitch_blocks(block, after); stitch_blocks(before, block); } else { update_if_uses(node); insert_non_block(before, node, after); } } static bool replace_ssa_def_uses(nir_ssa_def *def, void *void_impl) { nir_function_impl *impl = void_impl; void *mem_ctx = ralloc_parent(impl); nir_ssa_undef_instr *undef = nir_ssa_undef_instr_create(mem_ctx, def->num_components, def->bit_size); nir_instr_insert_before_cf_list(&impl->body, &undef->instr); nir_ssa_def_rewrite_uses(def, nir_src_for_ssa(&undef->def)); return true; } static void cleanup_cf_node(nir_cf_node *node, nir_function_impl *impl) { switch (node->type) { case nir_cf_node_block: { nir_block *block = nir_cf_node_as_block(node); /* We need to walk the instructions and clean up defs/uses */ nir_foreach_instr_safe(block, instr) { if (instr->type == nir_instr_type_jump) { nir_jump_type jump_type = nir_instr_as_jump(instr)->type; unlink_jump(block, jump_type, false); } else { nir_foreach_ssa_def(instr, replace_ssa_def_uses, impl); nir_instr_remove(instr); } } break; } case nir_cf_node_if: { nir_if *if_stmt = nir_cf_node_as_if(node); foreach_list_typed(nir_cf_node, child, node, &if_stmt->then_list) cleanup_cf_node(child, impl); foreach_list_typed(nir_cf_node, child, node, &if_stmt->else_list) cleanup_cf_node(child, impl); list_del(&if_stmt->condition.use_link); break; } case nir_cf_node_loop: { nir_loop *loop = nir_cf_node_as_loop(node); foreach_list_typed(nir_cf_node, child, node, &loop->body) cleanup_cf_node(child, impl); break; } case nir_cf_node_function: { nir_function_impl *impl = nir_cf_node_as_function(node); foreach_list_typed(nir_cf_node, child, node, &impl->body) cleanup_cf_node(child, impl); break; } default: unreachable("Invalid CF node type"); } } void nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end) { nir_block *block_begin, *block_end, *block_before, *block_after; if (nir_cursors_equal(begin, end)) { exec_list_make_empty(&extracted->list); extracted->impl = NULL; /* we shouldn't need this */ return; } /* In the case where begin points to an instruction in some basic block and * end points to the end of the same basic block, we rely on the fact that * splitting on an instruction moves earlier instructions into a new basic * block. If the later instructions were moved instead, then the end cursor * would be pointing to the same place that begin used to point to, which * is obviously not what we want. */ split_block_cursor(begin, &block_before, &block_begin); split_block_cursor(end, &block_end, &block_after); extracted->impl = nir_cf_node_get_function(&block_begin->cf_node); exec_list_make_empty(&extracted->list); /* Dominance and other block-related information is toast. */ nir_metadata_preserve(extracted->impl, nir_metadata_none); nir_cf_node *cf_node = &block_begin->cf_node; nir_cf_node *cf_node_end = &block_end->cf_node; while (true) { nir_cf_node *next = nir_cf_node_next(cf_node); exec_node_remove(&cf_node->node); cf_node->parent = NULL; exec_list_push_tail(&extracted->list, &cf_node->node); if (cf_node == cf_node_end) break; cf_node = next; } stitch_blocks(block_before, block_after); } void nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor) { nir_block *before, *after; if (exec_list_is_empty(&cf_list->list)) return; split_block_cursor(cursor, &before, &after); foreach_list_typed_safe(nir_cf_node, node, node, &cf_list->list) { exec_node_remove(&node->node); node->parent = before->cf_node.parent; exec_node_insert_node_before(&after->cf_node.node, &node->node); } stitch_blocks(before, nir_cf_node_as_block(nir_cf_node_next(&before->cf_node))); stitch_blocks(nir_cf_node_as_block(nir_cf_node_prev(&after->cf_node)), after); } void nir_cf_delete(nir_cf_list *cf_list) { foreach_list_typed(nir_cf_node, node, node, &cf_list->list) { cleanup_cf_node(node, cf_list->impl); } }