glsl: Implement a lowering pass for gl_ClipDistance.

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.

Reviewed-by: Kenneth Graunke <[email protected]>

6 files changed, 351 insertions, 0 deletions

diff --git a/src/glsl/Makefile b/src/glsl/Makefile
index 00b7b91643c..b2efb2abc51 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 1da58a91f91..b4786c5e539 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 48448d4a16a..af80e26b9ff 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 195f58f29c6..ceb49fd5b20 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 00000000000..143e378f97b
--- /dev/null
+++ b/src/glsl/lower_clip_distance.cpp
@@ -0,0 +1,344 @@
+/*
+ * 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.
+ *
+ * \param array_index Selects one of the vec4's in gl_ClipDistanceMESA
+ * \param swizzle_index Selects a component within the vec4 selected by
+ *        array_index.
+ */
+void
+lower_clip_distance_visitor::create_indices(ir_rvalue *old_index,
+                                            ir_rvalue *&array_index,
+                                            ir_rvalue *&swizzle_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);
+      array_index = new(ctx) ir_constant(const_val / 4);
+      swizzle_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.
+       */
+      array_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.
+       */
+      swizzle_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->var == this->old_clip_distance_var) {
+      this->progress = true;
+      ir_rvalue *array_index;
+      ir_rvalue *swizzle_index;
+      this->create_indices(ir->array_index, array_index, swizzle_index);
+      void *mem_ctx = ralloc_parent(ir);
+      ir->array = new(mem_ctx) ir_dereference_array(
+         this->new_clip_distance_var, array_index);
+      ir->array_index = swizzle_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->var == this->old_clip_distance_var)
+       || (rhs_var && rhs_var->var == 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));
+         new_lhs->accept(this);
+         ir_dereference_array *new_rhs = new(ctx) ir_dereference_array(
+            ir->rhs->clone(ctx, NULL), new(ctx) ir_constant(i));
+         new_rhs->accept(this);
+         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;
+   ir->accept(this);
+   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->var == this->old_clip_distance_var) {
+         /* User is trying to pass the whole gl_ClipDistance array 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),
+               new(ctx) ir_dereference_variable(old_clip_distance_var));
+            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(
+               new(ctx) ir_dereference_variable(old_clip_distance_var),
+               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 6efd9559651..74e7e2adf68 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -2235,6 +2235,7 @@ 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.