Mesa (7.9): glsl: Add a lowering pass to move discards out of if-statements .
Ian Romanick
idr at kemper.freedesktop.org
Thu Dec 16 23:08:34 UTC 2010
Module: Mesa
Branch: 7.9
Commit: 927c752dd688f4293816d544b0d0302a4da32ade
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=927c752dd688f4293816d544b0d0302a4da32ade
Author: Ian Romanick <ian.d.romanick at intel.com>
Date: Wed Dec 15 15:29:21 2010 -0800
glsl: Add a lowering pass to move discards out of if-statements.
This should allow lower_if_to_cond_assign to work in the presence of
discards, fixing bug #31690 and likely #31983.
NOTE: This is a candidate for the 7.9 branch.
(cherry picked from commit 940df10100d740ef27fa39026fd51c3199ed3d62)
---
src/glsl/Makefile | 1 +
src/glsl/SConscript | 1 +
src/glsl/ir_optimization.h | 1 +
src/glsl/lower_discard.cpp | 198 +++++++++++++++++++++++++++++++++++++++
src/mesa/program/ir_to_mesa.cpp | 4 +-
5 files changed, 204 insertions(+), 1 deletions(-)
diff --git a/src/glsl/Makefile b/src/glsl/Makefile
index 2dff732..9a642d8 100644
--- a/src/glsl/Makefile
+++ b/src/glsl/Makefile
@@ -75,6 +75,7 @@ CXX_SOURCES = \
loop_analysis.cpp \
loop_controls.cpp \
loop_unroll.cpp \
+ lower_discard.cpp \
lower_noise.cpp \
lower_variable_index_to_cond_assign.cpp \
opt_discard_simplification.cpp \
diff --git a/src/glsl/SConscript b/src/glsl/SConscript
index f52f528..209b5f0 100644
--- a/src/glsl/SConscript
+++ b/src/glsl/SConscript
@@ -72,6 +72,7 @@ sources = [
'loop_analysis.cpp',
'loop_controls.cpp',
'loop_unroll.cpp',
+ 'lower_discard.cpp',
'lower_noise.cpp',
'lower_variable_index_to_cond_assign.cpp',
'opt_discard_simplification.cpp',
diff --git a/src/glsl/ir_optimization.h b/src/glsl/ir_optimization.h
index ae4f4a9..ce939b3 100644
--- a/src/glsl/ir_optimization.h
+++ b/src/glsl/ir_optimization.h
@@ -56,6 +56,7 @@ bool do_swizzle_swizzle(exec_list *instructions);
bool do_tree_grafting(exec_list *instructions);
bool do_vec_index_to_cond_assign(exec_list *instructions);
bool do_vec_index_to_swizzle(exec_list *instructions);
+bool lower_discard(exec_list *instructions);
bool lower_noise(exec_list *instructions);
bool lower_variable_index_to_cond_assign(exec_list *instructions,
bool lower_input, bool lower_output, bool lower_temp, bool lower_uniform);
diff --git a/src/glsl/lower_discard.cpp b/src/glsl/lower_discard.cpp
new file mode 100644
index 0000000..b95313d
--- /dev/null
+++ b/src/glsl/lower_discard.cpp
@@ -0,0 +1,198 @@
+/*
+ * Copyright © 2010 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.
+ */
+
+/**
+ * \file lower_discard.cpp
+ *
+ * This pass moves discards out of if-statements.
+ *
+ * Case 1: The "then" branch contains a conditional discard:
+ * ---------------------------------------------------------
+ *
+ * if (cond1) {
+ * s1;
+ * discard cond2;
+ * s2;
+ * } else {
+ * s3;
+ * }
+ *
+ * becomes:
+ *
+ * temp = false;
+ * if (cond1) {
+ * s1;
+ * temp = cond2;
+ * s2;
+ * } else {
+ * s3;
+ * }
+ * discard temp;
+ *
+ * Case 2: The "else" branch contains a conditional discard:
+ * ---------------------------------------------------------
+ *
+ * if (cond1) {
+ * s1;
+ * } else {
+ * s2;
+ * discard cond2;
+ * s3;
+ * }
+ *
+ * becomes:
+ *
+ * temp = false;
+ * if (cond1) {
+ * s1;
+ * } else {
+ * s2;
+ * temp = cond2;
+ * s3;
+ * }
+ * discard temp;
+ *
+ * Case 3: Both branches contain a conditional discard:
+ * ----------------------------------------------------
+ *
+ * if (cond1) {
+ * s1;
+ * discard cond2;
+ * s2;
+ * } else {
+ * s3;
+ * discard cond3;
+ * s4;
+ * }
+ *
+ * becomes:
+ *
+ * temp = false;
+ * if (cond1) {
+ * s1;
+ * temp = cond2;
+ * s2;
+ * } else {
+ * s3;
+ * temp = cond3;
+ * s4;
+ * }
+ * discard temp;
+ *
+ * If there are multiple conditional discards, we need only deal with one of
+ * them. Repeatedly applying this pass will take care of the others.
+ *
+ * Unconditional discards are treated as having a condition of "true".
+ */
+
+#include "glsl_types.h"
+#include "ir.h"
+
+class lower_discard_visitor : public ir_hierarchical_visitor {
+public:
+ lower_discard_visitor()
+ {
+ this->progress = false;
+ }
+
+ ir_visitor_status visit_leave(ir_if *);
+
+ bool progress;
+};
+
+
+bool
+lower_discard(exec_list *instructions)
+{
+ lower_discard_visitor v;
+
+ visit_list_elements(&v, instructions);
+
+ return v.progress;
+}
+
+
+static ir_discard *
+find_discard(exec_list &instructions)
+{
+ foreach_list(n, &instructions) {
+ ir_discard *ir = ((ir_instruction *) n)->as_discard();
+ if (ir != NULL)
+ return ir;
+ }
+ return NULL;
+}
+
+
+static void
+replace_discard(void *mem_ctx, ir_variable *var, ir_discard *ir)
+{
+ ir_rvalue *condition = ir->condition;
+
+ /* For unconditional discards, use "true" as the condition. */
+ if (condition == NULL)
+ condition = new(mem_ctx) ir_constant(true);
+
+ ir_assignment *assignment =
+ new(mem_ctx) ir_assignment(new(mem_ctx) ir_dereference_variable(var),
+ condition, NULL);
+
+ ir->replace_with(assignment);
+}
+
+
+ir_visitor_status
+lower_discard_visitor::visit_leave(ir_if *ir)
+{
+ ir_discard *then_discard = find_discard(ir->then_instructions);
+ ir_discard *else_discard = find_discard(ir->else_instructions);
+
+ if (then_discard == NULL && else_discard == NULL)
+ return visit_continue;
+
+ void *mem_ctx = talloc_parent(ir);
+
+ ir_variable *temp = new(mem_ctx) ir_variable(glsl_type::bool_type,
+ "discard_cond_temp",
+ ir_var_temporary);
+ ir_assignment *temp_initializer =
+ new(mem_ctx) ir_assignment(new(mem_ctx) ir_dereference_variable(temp),
+ new(mem_ctx) ir_constant(false), NULL);
+
+ ir->insert_before(temp);
+ ir->insert_before(temp_initializer);
+
+ if (then_discard != NULL)
+ replace_discard(mem_ctx, temp, then_discard);
+
+ if (else_discard != NULL)
+ replace_discard(mem_ctx, temp, else_discard);
+
+ ir_discard *discard = then_discard != NULL ? then_discard : else_discard;
+ discard->condition = new(mem_ctx) ir_dereference_variable(temp);
+ ir->insert_after(discard);
+
+ this->progress = true;
+
+ return visit_continue;
+}
diff --git a/src/mesa/program/ir_to_mesa.cpp b/src/mesa/program/ir_to_mesa.cpp
index 80cc8c7..4737c6d 100644
--- a/src/mesa/program/ir_to_mesa.cpp
+++ b/src/mesa/program/ir_to_mesa.cpp
@@ -2801,8 +2801,10 @@ _mesa_ir_link_shader(GLcontext *ctx, struct gl_shader_program *prog)
progress = do_common_optimization(ir, true, options->MaxUnrollIterations) || progress;
- if (options->EmitNoIfs)
+ if (options->EmitNoIfs) {
+ progress = lower_discard(ir) || progress;
progress = do_if_to_cond_assign(ir) || progress;
+ }
if (options->EmitNoNoise)
progress = lower_noise(ir) || progress;
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