[Mesa-dev] [PATCH 19/21] nir: Add return lowering pass
Jason Ekstrand
jason at jlekstrand.net
Sun Feb 14 02:14:36 UTC 2016
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.
---
src/compiler/Makefile.sources | 1 +
src/compiler/nir/Makefile.sources | 1 +
src/compiler/nir/nir.h | 3 +
src/compiler/nir/nir_lower_returns.c | 246 +++++++++++++++++++++++++++++++++++
4 files changed, 251 insertions(+)
create mode 100644 src/compiler/nir/nir_lower_returns.c
diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
index b594c8e..60a899b 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -192,6 +192,7 @@ 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 a7188bf..27c2a2e 100644
--- a/src/compiler/nir/Makefile.sources
+++ b/src/compiler/nir/Makefile.sources
@@ -36,6 +36,7 @@ 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 e28070b..00ba3a2 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2078,6 +2078,9 @@ 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 0000000..91bb2f7
--- /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;
+}
--
2.5.0.400.gff86faf
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