X-Git-Url: https://git.libre-soc.org/?a=blobdiff_plain;f=src%2Fcompiler%2Fnir%2Fnir_opt_dead_cf.c;h=e796e6e85e344be7f0a1b05024ec1451792127e2;hb=08bfd710a25c14df5f690cce9604617536d7c560;hp=ca73e50061b8fc9b477a58e9502613e5a7499eeb;hpb=707e72f13bb78869ee95d3286980bf1709cba6cf;p=mesa.git diff --git a/src/compiler/nir/nir_opt_dead_cf.c b/src/compiler/nir/nir_opt_dead_cf.c index ca73e50061b..e796e6e85e3 100644 --- a/src/compiler/nir/nir_opt_dead_cf.c +++ b/src/compiler/nir/nir_opt_dead_cf.c @@ -30,7 +30,7 @@ /* * This file implements an optimization that deletes statically - * unreachable/dead code. In NIR, one way this can happen if if an if + * unreachable/dead code. In NIR, one way this can happen is when an if * statement has a constant condition: * * if (true) { @@ -60,12 +60,12 @@ * } * ... * - * Finally, we also handle removing useless loops, i.e. loops with no side - * effects and without any definitions that are used elsewhere. This case is a - * little different from the first two in that the code is actually run (it - * just never does anything), but there are similar issues with needing to - * be careful with restarting after deleting the cf_node (see dead_cf_list()) - * so this is a convenient place to remove them. + * Finally, we also handle removing useless loops and ifs, i.e. loops and ifs + * with no side effects and without any definitions that are used + * elsewhere. This case is a little different from the first two in that the + * code is actually run (it just never does anything), but there are similar + * issues with needing to be careful with restarting after deleting the + * cf_node (see dead_cf_list()) so this is a convenient place to remove them. */ static void @@ -87,9 +87,8 @@ opt_constant_if(nir_if *if_stmt, bool condition) * point to the correct source. */ nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&if_stmt->cf_node)); - nir_block *last_block = - nir_cf_node_as_block(condition ? nir_if_last_then_node(if_stmt) - : nir_if_last_else_node(if_stmt)); + nir_block *last_block = condition ? nir_if_last_then_block(if_stmt) + : nir_if_last_else_block(if_stmt); nir_foreach_instr_safe(instr, after) { if (instr->type != nir_instr_type_phi) @@ -97,7 +96,7 @@ opt_constant_if(nir_if *if_stmt, bool condition) nir_phi_instr *phi = nir_instr_as_phi(instr); nir_ssa_def *def = NULL; - nir_foreach_phi_src(phi, phi_src) { + nir_foreach_phi_src(phi_src, phi) { if (phi_src->pred != last_block) continue; @@ -128,87 +127,106 @@ opt_constant_if(nir_if *if_stmt, bool condition) : &if_stmt->else_list; nir_cf_list list; - nir_cf_extract(&list, nir_before_cf_list(cf_list), - nir_after_cf_list(cf_list)); + nir_cf_list_extract(&list, cf_list); nir_cf_reinsert(&list, nir_after_cf_node(&if_stmt->cf_node)); nir_cf_node_remove(&if_stmt->cf_node); } static bool -cf_node_has_side_effects(nir_cf_node *node) +def_only_used_in_cf_node(nir_ssa_def *def, void *_node) { - nir_foreach_block_in_cf_node(block, node) { - nir_foreach_instr(instr, block) { - if (instr->type == nir_instr_type_call) - return true; - - /* Return instructions can cause us to skip over other side-effecting - * instructions after the loop, so consider them to have side effects - * here. - */ - - if (instr->type == nir_instr_type_jump && - nir_instr_as_jump(instr)->type == nir_jump_return) - return true; - - if (instr->type != nir_instr_type_intrinsic) - continue; - - nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr); - if (!nir_intrinsic_infos[intrin->intrinsic].flags & - NIR_INTRINSIC_CAN_ELIMINATE) - return true; - } + nir_cf_node *node = _node; + assert(node->type == nir_cf_node_loop || node->type == nir_cf_node_if); + + nir_block *before = nir_cf_node_as_block(nir_cf_node_prev(node)); + nir_block *after = nir_cf_node_as_block(nir_cf_node_next(node)); + + nir_foreach_use(use, def) { + /* Because NIR is structured, we can easily determine whether or not a + * value escapes a CF node by looking at the block indices of its uses + * to see if they lie outside the bounds of the CF node. + * + * Note: Normally, the uses of a phi instruction are considered to be + * used in the block that is the predecessor of the phi corresponding to + * that use. If we were computing liveness or something similar, that + * would mean a special case here for phis. However, we're trying here + * to determine if the SSA def ever escapes the loop. If it's used by a + * phi that lives outside the loop then it doesn't matter if the + * corresponding predecessor is inside the loop or not because the value + * can go through the phi into the outside world and escape the loop. + */ + if (use->parent_instr->block->index <= before->index || + use->parent_instr->block->index >= after->index) + return false; } - return false; -} - -static bool -def_not_live_out(nir_ssa_def *def, void *state) -{ - nir_block *after = state; - - return !BITSET_TEST(after->live_in, def->live_index); + return true; } /* - * Test if a loop is dead. A loop is dead if: + * Test if a loop node or if node is dead. Such nodes are dead if: * * 1) It has no side effects (i.e. intrinsics which could possibly affect the * state of the program aside from producing an SSA value, indicated by a lack * of NIR_INTRINSIC_CAN_ELIMINATE). * - * 2) It has no phi nodes after it, since those indicate values inside the - * loop being used after the loop. + * 2) It has no phi instructions after it, since those indicate values inside + * the node being used after the node. + * + * 3) None of the values defined inside the node is used outside the node, + * i.e. none of the definitions that dominate the node exit are used outside. * - * 3) If there are no phi nodes after the loop, then the only way a value - * defined inside the loop can be used outside the loop is if its definition - * dominates the block after the loop. If none of the definitions that - * dominate the loop exit are used outside the loop, then the loop is dead - * and it can be deleted. + * If those conditions hold, then the node is dead and can be deleted. */ static bool -loop_is_dead(nir_loop *loop) +node_is_dead(nir_cf_node *node) { - nir_block *before = nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node)); - nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node)); + assert(node->type == nir_cf_node_loop || node->type == nir_cf_node_if); + + nir_block *after = nir_cf_node_as_block(nir_cf_node_next(node)); + /* Quick check if there are any phis that follow this CF node. If there + * are, then we automatically know it isn't dead. + */ if (!exec_list_is_empty(&after->instr_list) && nir_block_first_instr(after)->type == nir_instr_type_phi) return false; - if (cf_node_has_side_effects(&loop->cf_node)) - return false; + nir_function_impl *impl = nir_cf_node_get_function(node); + nir_metadata_require(impl, nir_metadata_block_index); + + nir_foreach_block_in_cf_node(block, node) { + bool inside_loop = node->type == nir_cf_node_loop; + for (nir_cf_node *n = &block->cf_node; + !inside_loop && n != node; n = n->parent) { + if (n->type == nir_cf_node_loop) + inside_loop = true; + } + + nir_foreach_instr(instr, block) { + if (instr->type == nir_instr_type_call) + return true; + + /* Return instructions can cause us to skip over other side-effecting + * instructions after the loop, so consider them to have side effects + * here. + * + * When the block is not inside a loop, break and continue might also + * cause a skip. + */ + if (instr->type == nir_instr_type_jump && + (!inside_loop || nir_instr_as_jump(instr)->type == nir_jump_return)) + return false; - nir_function_impl *impl = nir_cf_node_get_function(&loop->cf_node); - nir_metadata_require(impl, nir_metadata_live_ssa_defs | - nir_metadata_dominance); + if (instr->type == nir_instr_type_intrinsic) { + nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr); + if (!(nir_intrinsic_infos[intrin->intrinsic].flags & + NIR_INTRINSIC_CAN_ELIMINATE)) + return false; + } - for (nir_block *cur = after->imm_dom; cur != before; cur = cur->imm_dom) { - nir_foreach_instr(instr, cur) { - if (!nir_foreach_ssa_def(instr, def_not_live_out, after)) + if (!nir_foreach_ssa_def(instr, def_only_used_in_cf_node, node)) return false; } } @@ -221,13 +239,15 @@ dead_cf_block(nir_block *block) { nir_if *following_if = nir_block_get_following_if(block); if (following_if) { - nir_const_value *const_value = - nir_src_as_const_value(following_if->condition); + if (node_is_dead(&following_if->cf_node)) { + nir_cf_node_remove(&following_if->cf_node); + return true; + } - if (!const_value) - return false; + if (!nir_src_is_const(following_if->condition)) + return false; - opt_constant_if(following_if, const_value->u32[0] != 0); + opt_constant_if(following_if, nir_src_as_bool(following_if->condition)); return true; } @@ -235,23 +255,13 @@ dead_cf_block(nir_block *block) if (!following_loop) return false; - if (!loop_is_dead(following_loop)) + if (!node_is_dead(&following_loop->cf_node)) return false; nir_cf_node_remove(&following_loop->cf_node); return true; } -static bool -ends_in_jump(nir_block *block) -{ - if (exec_list_is_empty(&block->instr_list)) - return false; - - nir_instr *instr = nir_block_last_instr(block); - return instr->type == nir_instr_type_jump; -} - static bool dead_cf_list(struct exec_list *list, bool *list_ends_in_jump) { @@ -283,7 +293,7 @@ dead_cf_list(struct exec_list *list, bool *list_ends_in_jump) progress = true; } - if (ends_in_jump(block)) { + if (nir_block_ends_in_jump(block)) { *list_ends_in_jump = true; if (!exec_node_is_tail_sentinel(cur->node.next)) { @@ -338,8 +348,13 @@ opt_dead_cf_impl(nir_function_impl *impl) bool dummy; bool progress = dead_cf_list(&impl->body, &dummy); - if (progress) + if (progress) { nir_metadata_preserve(impl, nir_metadata_none); + } else { +#ifndef NDEBUG + impl->valid_metadata &= ~nir_metadata_not_properly_reset; +#endif + } return progress; } @@ -349,7 +364,7 @@ nir_opt_dead_cf(nir_shader *shader) { bool progress = false; - nir_foreach_function(shader, function) + nir_foreach_function(function, shader) if (function->impl) progress |= opt_dead_cf_impl(function->impl);