[Mesa-dev] [PATCH 2/2] glsl: Implement a lowering pass for gl_ClipDistance.
Paul Berry
stereotype441 at gmail.com
Thu Sep 15 16:40:12 PDT 2011
In i965 GEN6+ (and I suspect most other hardware), gl_ClipDistance
needs to be laid out as a pair of vec4's (the first containing clip
distances 0-3, and the second containing clip distances 4-7).
However, it is declared in GLSL as an array of 8 floats.
This lowering pass acts at the GLSL level, modifying the declaration
of gl_ClipDistance so that it is an array of vec4's rather than an
array of floats, and renaming it to gl_ClipDistanceMESA. In addition,
it modifies all accesses to the array so that they access the
appropiate component of one of the vec4's.
Since some hardware may not internally represent gl_ClipDistance as a
pair of vec4's, this lowering pass is optional. To enable it, set the
LowerClipDistance flag in gl_shader_compiler_options to true.
---
src/glsl/Makefile | 1 +
src/glsl/SConscript | 1 +
src/glsl/ir_optimization.h | 1 +
src/glsl/linker.cpp | 3 +
src/glsl/lower_clip_distance.cpp | 347 ++++++++++++++++++++++++++++++++++++++
src/mesa/main/mtypes.h | 1 +
6 files changed, 354 insertions(+), 0 deletions(-)
create mode 100644 src/glsl/lower_clip_distance.cpp
diff --git a/src/glsl/Makefile b/src/glsl/Makefile
index c20a6c9..bee21c2 100644
--- a/src/glsl/Makefile
+++ b/src/glsl/Makefile
@@ -56,6 +56,7 @@ CXX_SOURCES = \
loop_analysis.cpp \
loop_controls.cpp \
loop_unroll.cpp \
+ lower_clip_distance.cpp \
lower_discard.cpp \
lower_if_to_cond_assign.cpp \
lower_instructions.cpp \
diff --git a/src/glsl/SConscript b/src/glsl/SConscript
index 1da58a9..b4786c5 100644
--- a/src/glsl/SConscript
+++ b/src/glsl/SConscript
@@ -67,6 +67,7 @@ glsl_sources = [
'loop_analysis.cpp',
'loop_controls.cpp',
'loop_unroll.cpp',
+ 'lower_clip_distance.cpp',
'lower_discard.cpp',
'lower_if_to_cond_assign.cpp',
'lower_instructions.cpp',
diff --git a/src/glsl/ir_optimization.h b/src/glsl/ir_optimization.h
index 48448d4..af80e26 100644
--- a/src/glsl/ir_optimization.h
+++ b/src/glsl/ir_optimization.h
@@ -69,6 +69,7 @@ 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);
bool lower_quadop_vector(exec_list *instructions, bool dont_lower_swz);
+bool lower_clip_distance(exec_list *instructions);
bool optimize_redundant_jumps(exec_list *instructions);
ir_rvalue *
diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 195f58f..ceb49fd 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -1743,6 +1743,9 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
if (!prog->LinkStatus)
goto done;
+ if (ctx->ShaderCompilerOptions[i].LowerClipDistance)
+ lower_clip_distance(prog->_LinkedShaders[i]->ir);
+
while (do_common_optimization(prog->_LinkedShaders[i]->ir, true, 32))
;
}
diff --git a/src/glsl/lower_clip_distance.cpp b/src/glsl/lower_clip_distance.cpp
new file mode 100644
index 0000000..55a9e9d
--- /dev/null
+++ b/src/glsl/lower_clip_distance.cpp
@@ -0,0 +1,347 @@
+/*
+ * Copyright © 2011 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_clip_distance.cpp
+ *
+ * This pass accounts for the difference between the way
+ * gl_ClipDistance is declared in standard GLSL (as an array of
+ * floats), and the way it is frequently implemented in hardware (as
+ * a pair of vec4s, with four clip distances packed into each).
+ *
+ * The declaration of gl_ClipDistance is replaced with a declaration
+ * of gl_ClipDistanceMESA, and any references to gl_ClipDistance are
+ * translated to refer to gl_ClipDistanceMESA with the appropriate
+ * swizzling of array indices. For instance:
+ *
+ * gl_ClipDistance[i]
+ *
+ * is translated into:
+ *
+ * gl_ClipDistanceMESA[i>>2][i&3]
+ *
+ * Since some hardware may not internally represent gl_ClipDistance as a pair
+ * of vec4's, this lowering pass is optional. To enable it, set the
+ * LowerClipDistance flag in gl_shader_compiler_options to true.
+ */
+
+#include "ir_hierarchical_visitor.h"
+#include "ir.h"
+
+class lower_clip_distance_visitor : public ir_hierarchical_visitor {
+public:
+ lower_clip_distance_visitor()
+ : progress(false), old_clip_distance_var(NULL),
+ new_clip_distance_var(NULL)
+ {
+ }
+
+ virtual ir_visitor_status visit(ir_variable *);
+ void create_indices(ir_rvalue*, ir_rvalue *&, ir_rvalue *&);
+ virtual ir_visitor_status visit_leave(ir_dereference_array *);
+ virtual ir_visitor_status visit_leave(ir_assignment *);
+ void visit_new_assignment(ir_assignment *ir);
+ virtual ir_visitor_status visit_leave(ir_call *);
+
+ bool progress;
+
+ /**
+ * Pointer to the declaration of gl_ClipDistance, if found.
+ */
+ ir_variable *old_clip_distance_var;
+
+ /**
+ * Pointer to the newly-created gl_ClipDistanceMESA variable.
+ */
+ ir_variable *new_clip_distance_var;
+};
+
+
+/**
+ * Replace any declaration of gl_ClipDistance as an array of floats with a
+ * declaration of gl_ClipDistanceMESA as an array of vec4's.
+ */
+ir_visitor_status
+lower_clip_distance_visitor::visit(ir_variable *ir)
+{
+ /* No point in looking for the declaration of gl_ClipDistance if
+ * we've already found it.
+ */
+ if (this->old_clip_distance_var)
+ return visit_continue;
+
+ if (ir->name && strcmp(ir->name, "gl_ClipDistance") == 0) {
+ this->progress = true;
+ this->old_clip_distance_var = ir;
+ assert (ir->type->is_array());
+ assert (ir->type->element_type() == glsl_type::float_type);
+ unsigned new_size = (ir->type->array_size() + 3) / 4;
+
+ /* Clone the old var so that we inherit all of its properties */
+ this->new_clip_distance_var = ir->clone(ralloc_parent(ir), NULL);
+
+ /* And change the properties that we need to change */
+ this->new_clip_distance_var->name
+ = ralloc_strdup(this->new_clip_distance_var, "gl_ClipDistanceMESA");
+ this->new_clip_distance_var->type
+ = glsl_type::get_array_instance(glsl_type::vec4_type, new_size);
+ this->new_clip_distance_var->max_array_access = ir->max_array_access / 4;
+
+ ir->replace_with(this->new_clip_distance_var);
+ }
+ return visit_continue;
+}
+
+
+/**
+ * Create the necessary GLSL rvalues to index into gl_ClipDistanceMESA based
+ * on the rvalue previously used to index into gl_ClipDistance. The first,
+ * "outer" index, selects one of the vec4's in gl_ClipDistanceMESA, and the
+ * second, "inner" index, selects a component within that vec4.
+ */
+void
+lower_clip_distance_visitor::create_indices(ir_rvalue *old_index,
+ ir_rvalue *&outer_index,
+ ir_rvalue *&inner_index)
+{
+ void *ctx = ralloc_parent(old_index);
+
+ /* Make sure old_index is a signed int so that the bitwise "shift" and
+ * "and" operations below type check properly.
+ */
+ if (old_index->type != glsl_type::int_type) {
+ assert (old_index->type == glsl_type::uint_type);
+ old_index = new(ctx) ir_expression(ir_unop_u2i, old_index);
+ }
+
+ ir_constant *old_index_constant = old_index->constant_expression_value();
+ if (old_index_constant) {
+ /* gl_ClipDistance is being accessed via a constant index. Don't bother
+ * creating expressions to calculate the lowered indices. Just create
+ * constants.
+ */
+ int const_val = old_index_constant->get_int_component(0);
+ outer_index = new(ctx) ir_constant(const_val / 4);
+ inner_index = new(ctx) ir_constant(const_val % 4);
+ } else {
+ /* Create a variable to hold the value of old_index (so that we
+ * don't compute it twice).
+ */
+ ir_variable *old_index_var = new(ctx) ir_variable(
+ glsl_type::int_type, "clip_distance_index", ir_var_temporary);
+ this->base_ir->insert_before(old_index_var);
+ this->base_ir->insert_before(new(ctx) ir_assignment(
+ new(ctx) ir_dereference_variable(old_index_var), old_index));
+
+ /* Create the expression clip_distance_index / 4. Do this as a bit
+ * shift because that's likely to be more efficient.
+ */
+ outer_index = new(ctx) ir_expression(
+ ir_binop_rshift, new(ctx) ir_dereference_variable(old_index_var),
+ new(ctx) ir_constant(2));
+
+ /* Create the expression clip_distance_index % 4. Do this as a bitwise
+ * AND because that's likely to be more efficient.
+ */
+ inner_index = new(ctx) ir_expression(
+ ir_binop_bit_and, new(ctx) ir_dereference_variable(old_index_var),
+ new(ctx) ir_constant(3));
+ }
+}
+
+
+/**
+ * Replace any expression that indexes into the gl_ClipDistance array with an
+ * expression that indexes into one of the vec4's in gl_ClipDistanceMESA and
+ * accesses the appropriate component.
+ */
+ir_visitor_status
+lower_clip_distance_visitor::visit_leave(ir_dereference_array *ir)
+{
+ /* If the gl_ClipDistance var hasn't been declared yet, then
+ * there's no way this deref can refer to it.
+ */
+ if (!this->old_clip_distance_var)
+ return visit_continue;
+
+ ir_dereference_variable *old_var_ref = ir->array->as_dereference_variable();
+ if (old_var_ref && old_var_ref->variable_referenced()
+ == this->old_clip_distance_var) {
+ this->progress = true;
+ ir_rvalue *outer_index;
+ ir_rvalue *inner_index;
+ this->create_indices(ir->array_index, outer_index, inner_index);
+ void *mem_ctx = ralloc_parent(ir);
+ ir->array = new(mem_ctx) ir_dereference_array(
+ this->new_clip_distance_var, outer_index);
+ ir->array_index = inner_index;
+ }
+
+ return visit_continue;
+}
+
+
+/**
+ * Replace any assignment having gl_ClipDistance (undereferenced) as its LHS
+ * or RHS with a sequence of assignments, one for each component of the array.
+ * Each of these assignments is lowered to refer to gl_ClipDistanceMESA as
+ * appropriate.
+ */
+ir_visitor_status
+lower_clip_distance_visitor::visit_leave(ir_assignment *ir)
+{
+ ir_dereference_variable *lhs_var = ir->lhs->as_dereference_variable();
+ ir_dereference_variable *rhs_var = ir->rhs->as_dereference_variable();
+ if ((lhs_var && lhs_var->variable_referenced()
+ == this->old_clip_distance_var)
+ || (rhs_var && rhs_var->variable_referenced()
+ == this->old_clip_distance_var)) {
+ /* LHS or RHS of the assignment is the entire gl_ClipDistance array.
+ * Since we are reshaping gl_ClipDistance from an array of floats to an
+ * array of vec4's, this isn't going to work as a bulk assignment
+ * anymore, so unroll it to element-by-element assignments and lower
+ * each of them.
+ *
+ * Note: to unroll into element-by-element assignments, we need to make
+ * clones of the LHS and RHS. This is only safe if the LHS and RHS are
+ * side-effect free. Fortunately, we know that they are, because the
+ * only kind of rvalue that can have side effects is an ir_call, and
+ * ir_calls only appear (a) as a statement on their own, or (b) as the
+ * RHS of an assignment that stores the result of the call in a
+ * temporary variable.
+ */
+ void *ctx = ralloc_parent(ir);
+ int array_size = this->old_clip_distance_var->type->array_size();
+ for (int i = 0; i < array_size; ++i) {
+ ir_dereference_array *new_lhs = new(ctx) ir_dereference_array(
+ ir->lhs->clone(ctx, NULL), new(ctx) ir_constant(i));
+ this->visit_leave(new_lhs);
+ ir_dereference_array *new_rhs = new(ctx) ir_dereference_array(
+ ir->rhs->clone(ctx, NULL), new(ctx) ir_constant(i));
+ this->visit_leave(new_rhs);
+ this->base_ir->insert_before(
+ new(ctx) ir_assignment(new_lhs, new_rhs));
+ }
+ ir->remove();
+ }
+
+ return visit_continue;
+}
+
+
+/**
+ * Set up base_ir properly and call visit_leave() on a newly created
+ * ir_assignment node. This is used in cases where we have to insert an
+ * ir_assignment in a place where we know the hierarchical visitor won't see
+ * it.
+ */
+void
+lower_clip_distance_visitor::visit_new_assignment(ir_assignment *ir)
+{
+ ir_instruction *old_base_ir = this->base_ir;
+ this->base_ir = ir;
+ this->visit_leave(ir);
+ this->base_ir = old_base_ir;
+}
+
+
+/**
+ * If gl_ClipDistance appears as an argument in an ir_call expression, replace
+ * it with a temporary variable, and make sure the ir_call is preceded and/or
+ * followed by assignments that copy the contents of the temporary variable to
+ * and/or from gl_ClipDistance. Each of these assignments is then lowered to
+ * refer to gl_ClipDistanceMESA.
+ */
+ir_visitor_status
+lower_clip_distance_visitor::visit_leave(ir_call *ir)
+{
+ void *ctx = ralloc_parent(ir);
+
+ const exec_node *formal_param_node = ir->get_callee()->parameters.head;
+ const exec_node *actual_param_node = ir->actual_parameters.head;
+ while (!actual_param_node->is_tail_sentinel()) {
+ ir_variable *formal_param = (ir_variable *) formal_param_node;
+ ir_rvalue *actual_param = (ir_rvalue *) actual_param_node;
+
+ /* Advance formal_param_node and actual_param_node now so that we can
+ * safely replace actual_param with another node, if necessary, below.
+ */
+ formal_param_node = formal_param_node->next;
+ actual_param_node = actual_param_node->next;
+
+ ir_dereference_variable *deref = actual_param->as_dereference_variable();
+ if (deref && deref->variable_referenced()
+ == this->old_clip_distance_var) {
+ /* User is trying to pass gl_ClipDistance as an in, out, or inout
+ * parameter to a function call. Since we are reshaping
+ * gl_ClipDistance from an array of floats to an array of vec4's,
+ * this isn't going to work anymore, so use a temporary array
+ * instead.
+ */
+ ir_variable *temp_clip_distance = new(ctx) ir_variable(
+ actual_param->type, "temp_clip_distance", ir_var_temporary);
+ this->base_ir->insert_before(temp_clip_distance);
+ actual_param->replace_with(
+ new(ctx) ir_dereference_variable(temp_clip_distance));
+ if (formal_param->mode == ir_var_in
+ || formal_param->mode == ir_var_inout) {
+ /* Copy from gl_ClipDistance to the temporary before the call.
+ * Since we are going to insert this copy before the current
+ * instruction, we need to visit it afterwards to make sure it
+ * gets lowered.
+ */
+ ir_assignment *new_assignment = new(ctx) ir_assignment(
+ new(ctx) ir_dereference_variable(temp_clip_distance),
+ actual_param->clone(ctx, NULL));
+ this->base_ir->insert_before(new_assignment);
+ this->visit_new_assignment(new_assignment);
+ }
+ if (formal_param->mode == ir_var_out
+ || formal_param->mode == ir_var_inout) {
+ /* Copy from the temporary to gl_ClipDistance after the call.
+ * Since visit_list_elements() has already decided which
+ * instruction it's going to visit next, we need to visit
+ * afterwards to make sure it gets lowered.
+ */
+ ir_assignment *new_assignment = new(ctx) ir_assignment(
+ actual_param->clone(ctx, NULL),
+ new(ctx) ir_dereference_variable(temp_clip_distance));
+ this->base_ir->insert_after(new_assignment);
+ this->visit_new_assignment(new_assignment);
+ }
+ }
+ }
+
+ return visit_continue;
+}
+
+
+bool
+lower_clip_distance(exec_list *instructions)
+{
+ lower_clip_distance_visitor v;
+
+ visit_list_elements(&v, instructions);
+
+ return v.progress;
+}
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 8671ecd..ef04749 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -2297,6 +2297,7 @@ struct gl_shader_compiler_options
GLboolean EmitNoMainReturn; /**< Emit CONT/RET opcodes? */
GLboolean EmitNoNoise; /**< Emit NOISE opcodes? */
GLboolean EmitNoPow; /**< Emit POW opcodes? */
+ GLboolean LowerClipDistance; /**< Lower gl_ClipDistance from float[8] to vec4[2]? */
/**
* \name Forms of indirect addressing the driver cannot do.
--
1.7.6
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