glsl: Combine many instruction lowering passes into one.

This should save on the overhead of tree-walking and provide a
convenient place to add more instruction lowering in the future.

Signed-off-by: Ian Romanick <[email protected]>

1 files changed, 262 insertions, 0 deletions

diff --git a/src/glsl/lower_instructions.cpp b/src/glsl/lower_instructions.cpp
new file mode 100644
index 00000000000..d460ba1a97a
--- /dev/null
+++ b/src/glsl/lower_instructions.cpp
@@ -0,0 +1,262 @@
+/*
+ * 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_instructions.cpp
+ *
+ * Many GPUs lack native instructions for certain expression operations, and
+ * must replace them with some other expression tree.  This pass lowers some
+ * of the most common cases, allowing the lowering code to be implemented once
+ * rather than in each driver backend.
+ *
+ * Currently supported transformations:
+ * - SUB_TO_ADD_NEG
+ * - DIV_TO_MUL_RCP
+ * - EXP_TO_EXP2
+ * - LOG_TO_LOG2
+ * - MOD_TO_FRACT
+ *
+ * SUB_TO_ADD_NEG:
+ * ---------------
+ * Breaks an ir_binop_sub expression down to add(op0, neg(op1))
+ *
+ * This simplifies expression reassociation, and for many backends
+ * there is no subtract operation separate from adding the negation.
+ * For backends with native subtract operations, they will probably
+ * want to recognize add(op0, neg(op1)) or the other way around to
+ * produce a subtract anyway.
+ *
+ * DIV_TO_MUL_RCP:
+ * ---------------
+ * Breaks an ir_unop_div expression down to op0 * (rcp(op1)).
+ *
+ * Many GPUs don't have a divide instruction (945 and 965 included),
+ * but they do have an RCP instruction to compute an approximate
+ * reciprocal.  By breaking the operation down, constant reciprocals
+ * can get constant folded.
+ *
+ * EXP_TO_EXP2 and LOG_TO_LOG2:
+ * ----------------------------
+ * Many GPUs don't have a base e log or exponent instruction, but they
+ * do have base 2 versions, so this pass converts exp and log to exp2
+ * and log2 operations.
+ *
+ * MOD_TO_FRACT:
+ * -------------
+ * Breaks an ir_unop_mod expression down to (op1 * fract(op0 / op1))
+ *
+ * Many GPUs don't have a MOD instruction (945 and 965 included), and
+ * if we have to break it down like this anyway, it gives an
+ * opportunity to do things like constant fold the (1.0 / op1) easily.
+ */
+
+#include "main/core.h" /* for M_E */
+#include "glsl_types.h"
+#include "ir.h"
+#include "ir_optimization.h"
+
+class lower_instructions_visitor : public ir_hierarchical_visitor {
+public:
+   lower_instructions_visitor(unsigned lower)
+      : progress(false), lower(lower) { }
+
+   ir_visitor_status visit_leave(ir_expression *);
+
+   bool progress;
+
+private:
+   unsigned lower; /** Bitfield of which operations to lower */
+
+   void sub_to_add_neg(ir_expression *);
+   void div_to_mul_rcp(ir_expression *);
+   void mod_to_fract(ir_expression *);
+   void exp_to_exp2(ir_expression *);
+   void log_to_log2(ir_expression *);
+};
+
+/**
+ * Determine if a particular type of lowering should occur
+ */
+#define lowering(x) (this->lower & x)
+
+bool
+lower_instructions(exec_list *instructions, unsigned what_to_lower)
+{
+   lower_instructions_visitor v(what_to_lower);
+
+   visit_list_elements(&v, instructions);
+   return v.progress;
+}
+
+void
+lower_instructions_visitor::sub_to_add_neg(ir_expression *ir)
+{
+   ir->operation = ir_binop_add;
+   ir->operands[1] = new(ir) ir_expression(ir_unop_neg, ir->operands[1]->type,
+					   ir->operands[1], NULL);
+   this->progress = true;
+}
+
+void
+lower_instructions_visitor::div_to_mul_rcp(ir_expression *ir)
+{
+   if (!ir->operands[1]->type->is_integer()) {
+      /* New expression for the 1.0 / op1 */
+      ir_rvalue *expr;
+      expr = new(ir) ir_expression(ir_unop_rcp,
+				   ir->operands[1]->type,
+				   ir->operands[1],
+				   NULL);
+
+      /* op0 / op1 -> op0 * (1.0 / op1) */
+      ir->operation = ir_binop_mul;
+      ir->operands[1] = expr;
+   } else {
+      /* Be careful with integer division -- we need to do it as a
+       * float and re-truncate, since rcp(n > 1) of an integer would
+       * just be 0.
+       */
+      ir_rvalue *op0, *op1;
+      const struct glsl_type *vec_type;
+
+      vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
+					 ir->operands[1]->type->vector_elements,
+					 ir->operands[1]->type->matrix_columns);
+
+      if (ir->operands[1]->type->base_type == GLSL_TYPE_INT)
+	 op1 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[1], NULL);
+      else
+	 op1 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[1], NULL);
+
+      op1 = new(ir) ir_expression(ir_unop_rcp, op1->type, op1, NULL);
+
+      vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
+					 ir->operands[0]->type->vector_elements,
+					 ir->operands[0]->type->matrix_columns);
+
+      if (ir->operands[0]->type->base_type == GLSL_TYPE_INT)
+	 op0 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[0], NULL);
+      else
+	 op0 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[0], NULL);
+
+      op0 = new(ir) ir_expression(ir_binop_mul, vec_type, op0, op1);
+
+      ir->operation = ir_unop_f2i;
+      ir->operands[0] = op0;
+      ir->operands[1] = NULL;
+   }
+
+   this->progress = true;
+}
+
+void
+lower_instructions_visitor::exp_to_exp2(ir_expression *ir)
+{
+   ir_constant *log2_e = new(ir) ir_constant(log2f(M_E));
+
+   ir->operation = ir_unop_exp2;
+   ir->operands[0] = new(ir) ir_expression(ir_binop_mul, ir->operands[0]->type,
+					   ir->operands[0], log2_e);
+   this->progress = true;
+}
+
+void
+lower_instructions_visitor::log_to_log2(ir_expression *ir)
+{
+   ir->operation = ir_binop_mul;
+   ir->operands[0] = new(ir) ir_expression(ir_unop_log2, ir->operands[0]->type,
+					   ir->operands[0], NULL);
+   ir->operands[1] = new(ir) ir_constant(1.0f / log2f(M_E));
+   this->progress = true;
+}
+
+void
+lower_instructions_visitor::mod_to_fract(ir_expression *ir)
+{
+   ir_variable *temp = new(ir) ir_variable(ir->operands[1]->type, "mod_b",
+					   ir_var_temporary);
+   this->base_ir->insert_before(temp);
+
+   ir_assignment *const assign =
+      new(ir) ir_assignment(new(ir) ir_dereference_variable(temp),
+			    ir->operands[1], NULL);
+
+   this->base_ir->insert_before(assign);
+
+   ir_expression *const div_expr =
+      new(ir) ir_expression(ir_binop_div, ir->operands[0]->type,
+			    ir->operands[0],
+			    new(ir) ir_dereference_variable(temp));
+
+   /* Don't generate new IR that would need to be lowered in an additional
+    * pass.
+    */
+   if (lowering(DIV_TO_MUL_RCP))
+      div_to_mul_rcp(div_expr);
+
+   ir_rvalue *expr = new(ir) ir_expression(ir_unop_fract,
+					   ir->operands[0]->type,
+					   div_expr,
+					   NULL);
+
+   ir->operation = ir_binop_mul;
+   ir->operands[0] = new(ir) ir_dereference_variable(temp);
+   ir->operands[1] = expr;
+   this->progress = true;
+}
+
+ir_visitor_status
+lower_instructions_visitor::visit_leave(ir_expression *ir)
+{
+   switch (ir->operation) {
+   case ir_binop_sub:
+      if (lowering(SUB_TO_ADD_NEG))
+	 sub_to_add_neg(ir);
+      break;
+
+   case ir_binop_div:
+      if (lowering(DIV_TO_MUL_RCP))
+	 div_to_mul_rcp(ir);
+      break;
+
+   case ir_unop_exp:
+      if (lowering(EXP_TO_EXP2))
+	 exp_to_exp2(ir);
+      break;
+
+   case ir_unop_log:
+      if (lowering(LOG_TO_LOG2))
+	 log_to_log2(ir);
+      break;
+
+   case ir_binop_mod:
+      if (lowering(MOD_TO_FRACT))
+	 mod_to_fract(ir);
+      break;
+
+   default:
+      return visit_continue;
+   }
+
+   return visit_continue;
+}