From: Jason Ekstrand Date: Sun, 14 Feb 2016 01:08:57 +0000 (-0800) Subject: nir: Add return lowering pass X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=79dec93ead6e3b95b1240a9d843d617a88ee9179;p=mesa.git nir: Add return lowering pass This commit adds a NIR pass for lowering away returns in functions. If the return is in a loop, it is lowered to a break. If it is not in a loop, it's lowered away by moving/deleting code as needed. Reviewed-by: Jordan Justen --- diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources index 796d0044f46..74636b13e12 100644 --- a/src/compiler/Makefile.sources +++ b/src/compiler/Makefile.sources @@ -194,6 +194,7 @@ NIR_FILES = \ nir/nir_lower_io.c \ nir/nir_lower_outputs_to_temporaries.c \ nir/nir_lower_phis_to_scalar.c \ + nir/nir_lower_returns.c \ nir/nir_lower_samplers.c \ nir/nir_lower_system_values.c \ nir/nir_lower_tex.c \ diff --git a/src/compiler/nir/Makefile.sources b/src/compiler/nir/Makefile.sources index c1493551192..b9506e8a393 100644 --- a/src/compiler/nir/Makefile.sources +++ b/src/compiler/nir/Makefile.sources @@ -37,6 +37,7 @@ NIR_FILES = \ nir_lower_io.c \ nir_lower_outputs_to_temporaries.c \ nir_lower_phis_to_scalar.c \ + nir_lower_returns.c \ nir_lower_samplers.c \ nir_lower_system_values.c \ nir_lower_tex.c \ diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h index 51d2e79f570..78bbdc0b78c 100644 --- a/src/compiler/nir/nir.h +++ b/src/compiler/nir/nir.h @@ -2146,6 +2146,9 @@ int nir_gs_count_vertices(const nir_shader *shader); bool nir_split_var_copies(nir_shader *shader); +bool nir_lower_returns_impl(nir_function_impl *impl); +bool nir_lower_returns(nir_shader *shader); + void nir_lower_var_copy_instr(nir_intrinsic_instr *copy, void *mem_ctx); void nir_lower_var_copies(nir_shader *shader); diff --git a/src/compiler/nir/nir_lower_returns.c b/src/compiler/nir/nir_lower_returns.c new file mode 100644 index 00000000000..91bb2f7dfeb --- /dev/null +++ b/src/compiler/nir/nir_lower_returns.c @@ -0,0 +1,246 @@ +/* + * Copyright © 2015 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. + */ + +#include "nir.h" +#include "nir_builder.h" +#include "nir_control_flow.h" + +struct lower_returns_state { + nir_builder builder; + struct exec_list *cf_list; + nir_loop *loop; + nir_variable *return_flag; +}; + +static bool lower_returns_in_cf_list(struct exec_list *cf_list, + struct lower_returns_state *state); + +static void +predicate_following(nir_cf_node *node, struct lower_returns_state *state) +{ + nir_builder *b = &state->builder; + b->cursor = nir_after_cf_node_and_phis(node); + + if (nir_cursors_equal(b->cursor, nir_after_cf_list(state->cf_list))) + return; /* Nothing to predicate */ + + assert(state->return_flag); + + nir_if *if_stmt = nir_if_create(b->shader); + if_stmt->condition = nir_src_for_ssa(nir_load_var(b, state->return_flag)); + nir_cf_node_insert(b->cursor, &if_stmt->cf_node); + + if (state->loop) { + /* If we're inside of a loop, then all we need to do is insert a + * conditional break. + */ + nir_jump_instr *brk = + nir_jump_instr_create(state->builder.shader, nir_jump_break); + nir_instr_insert(nir_before_cf_list(&if_stmt->then_list), &brk->instr); + } else { + /* Otherwise, we need to actually move everything into the else case + * of the if statement. + */ + nir_cf_list list; + nir_cf_extract(&list, nir_after_cf_node(&if_stmt->cf_node), + nir_after_cf_list(state->cf_list)); + assert(!exec_list_is_empty(&list.list)); + nir_cf_reinsert(&list, nir_before_cf_list(&if_stmt->else_list)); + } +} + +static bool +lower_returns_in_loop(nir_loop *loop, struct lower_returns_state *state) +{ + nir_loop *parent = state->loop; + state->loop = loop; + bool progress = lower_returns_in_cf_list(&loop->body, state); + state->loop = parent; + + /* If the recursive call made progress, then there were returns inside + * of the loop. These would have been lowered to breaks with the return + * flag set to true. We need to predicate everything following the loop + * on the return flag. + */ + if (progress) + predicate_following(&loop->cf_node, state); + + return progress; +} + +static bool +lower_returns_in_if(nir_if *if_stmt, struct lower_returns_state *state) +{ + bool progress; + + progress = lower_returns_in_cf_list(&if_stmt->then_list, state); + progress = lower_returns_in_cf_list(&if_stmt->else_list, state) || progress; + + /* If either of the recursive calls made progress, then there were + * returns inside of the body of the if. If we're in a loop, then these + * were lowered to breaks which automatically skip to the end of the + * loop so we don't have to do anything. If we're not in a loop, then + * all we know is that the return flag is set appropreately and that the + * recursive calls ensured that nothing gets executed *inside* the if + * after a return. In order to ensure nothing outside gets executed + * after a return, we need to predicate everything following on the + * return flag. + */ + if (progress && !state->loop) + predicate_following(&if_stmt->cf_node, state); + + return progress; +} + +static bool +lower_returns_in_block(nir_block *block, struct lower_returns_state *state) +{ + if (block->predecessors->entries == 0 && + block != nir_start_block(state->builder.impl)) { + /* This block is unreachable. Delete it and everything after it. */ + nir_cf_list list; + nir_cf_extract(&list, nir_before_cf_node(&block->cf_node), + nir_after_cf_list(state->cf_list)); + + if (exec_list_is_empty(&list.list)) { + /* There's nothing here, which also means there's nothing in this + * block so we have nothing to do. + */ + return false; + } else { + nir_cf_delete(&list); + return true; + } + } + + nir_instr *last_instr = nir_block_last_instr(block); + if (last_instr == NULL) + return false; + + if (last_instr->type != nir_instr_type_jump) + return false; + + nir_jump_instr *jump = nir_instr_as_jump(last_instr); + if (jump->type != nir_jump_return) + return false; + + nir_instr_remove(&jump->instr); + + nir_builder *b = &state->builder; + b->cursor = nir_after_block(block); + + /* Set the return flag */ + if (state->return_flag == NULL) { + state->return_flag = + nir_local_variable_create(b->impl, glsl_bool_type(), "return"); + + /* Set a default value of false */ + state->return_flag->constant_initializer = + rzalloc(state->return_flag, nir_constant); + } + nir_store_var(b, state->return_flag, nir_imm_int(b, NIR_TRUE), 1); + + if (state->loop) { + /* We're in a loop; we need to break out of it. */ + nir_jump(b, nir_jump_break); + } else { + /* Not in a loop; we'll deal with predicating later*/ + assert(nir_cf_node_next(&block->cf_node) == NULL); + } + + return true; +} + +static bool +lower_returns_in_cf_list(struct exec_list *cf_list, + struct lower_returns_state *state) +{ + bool progress = false; + + struct exec_list *parent_list = state->cf_list; + state->cf_list = cf_list; + + /* We iterate over the list backwards because any given lower call may + * take everything following the given CF node and predicate it. In + * order to avoid recursion/iteration problems, we want everything after + * a given node to already be lowered before this happens. + */ + foreach_list_typed_reverse_safe(nir_cf_node, node, node, cf_list) { + switch (node->type) { + case nir_cf_node_block: + if (lower_returns_in_block(nir_cf_node_as_block(node), state)) + progress = true; + break; + + case nir_cf_node_if: + if (lower_returns_in_if(nir_cf_node_as_if(node), state)) + progress = true; + break; + + case nir_cf_node_loop: + if (lower_returns_in_loop(nir_cf_node_as_loop(node), state)) + progress = true; + break; + + default: + unreachable("Invalid inner CF node type"); + } + } + + state->cf_list = parent_list; + + return progress; +} + +bool +nir_lower_returns_impl(nir_function_impl *impl) +{ + struct lower_returns_state state; + + state.cf_list = &impl->body; + state.loop = NULL; + state.return_flag = NULL; + nir_builder_init(&state.builder, impl); + + bool progress = lower_returns_in_cf_list(&impl->body, &state); + + if (progress) { + nir_metadata_preserve(impl, nir_metadata_none); + nir_repair_ssa_impl(impl); + } + + return progress; +} + +bool +nir_lower_returns(nir_shader *shader) +{ + bool progress = false; + + nir_foreach_function(shader, function) { + if (function->impl) + progress = nir_lower_returns_impl(function->impl) || progress; + } + + return progress; +}