Mesa (master): glsl2: Add module to analyze variables used in loops
Ian Romanick
idr at kemper.freedesktop.org
Fri Sep 3 19:01:04 UTC 2010
Module: Mesa
Branch: master
Commit: 9434a0749f26c640305f68ef85d17a31063a5705
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=9434a0749f26c640305f68ef85d17a31063a5705
Author: Ian Romanick <ian.d.romanick at intel.com>
Date: Thu Aug 26 15:58:33 2010 -0700
glsl2: Add module to analyze variables used in loops
This is the first step eventually leading to loop unrolling.
---
src/glsl/Makefile | 1 +
src/glsl/Makefile.am | 3 +-
src/glsl/loop_analysis.cpp | 479 ++++++++++++++++++++++++++++++++++++++++++++
src/glsl/loop_analysis.h | 190 ++++++++++++++++++
4 files changed, 672 insertions(+), 1 deletions(-)
diff --git a/src/glsl/Makefile b/src/glsl/Makefile
index aedca0f..e5375ef 100644
--- a/src/glsl/Makefile
+++ b/src/glsl/Makefile
@@ -72,6 +72,7 @@ CXX_SOURCES = \
ir_vec_index_to_swizzle.cpp \
linker.cpp \
link_functions.cpp \
+ loop_analysis.cpp \
s_expression.cpp
LIBS = \
diff --git a/src/glsl/Makefile.am b/src/glsl/Makefile.am
index 5728a8b..55e4332 100644
--- a/src/glsl/Makefile.am
+++ b/src/glsl/Makefile.am
@@ -62,7 +62,8 @@ glsl_SOURCES = \
ir_to_mesa.h \
ir_validate.cpp \
ir_vec_index_to_swizzle.cpp \
- linker.cpp
+ linker.cpp \
+ loop_analysis.cpp
BUILT_SOURCES = glsl_parser.h glsl_parser.cpp glsl_lexer.cpp
CLEANFILES = $(BUILT_SOURCES)
diff --git a/src/glsl/loop_analysis.cpp b/src/glsl/loop_analysis.cpp
new file mode 100644
index 0000000..2ea2f3d
--- /dev/null
+++ b/src/glsl/loop_analysis.cpp
@@ -0,0 +1,479 @@
+/*
+ * 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.
+ */
+
+#include "glsl_types.h"
+#include "loop_analysis.h"
+#include "ir_hierarchical_visitor.h"
+
+static bool is_loop_terminator(ir_if *ir);
+
+static bool all_expression_operands_are_loop_constant(ir_rvalue *,
+ hash_table *);
+
+static ir_rvalue *get_basic_induction_increment(ir_assignment *, hash_table *);
+
+
+loop_state::loop_state()
+{
+ this->ht = hash_table_ctor(0, hash_table_pointer_hash,
+ hash_table_pointer_compare);
+ this->mem_ctx = talloc_init("loop state");
+}
+
+
+loop_state::~loop_state()
+{
+ hash_table_dtor(this->ht);
+}
+
+
+loop_variable_state *
+loop_state::insert(ir_loop *ir)
+{
+ loop_variable_state *ls = new(this->mem_ctx) loop_variable_state;
+ hash_table_insert(this->ht, ls, ir);
+
+ return ls;
+}
+
+
+loop_variable_state *
+loop_state::get(const ir_loop *ir)
+{
+ return (loop_variable_state *) hash_table_find(this->ht, ir);
+}
+
+
+loop_variable *
+loop_variable_state::get(const ir_variable *ir)
+{
+ return (loop_variable *) hash_table_find(this->var_hash, ir);
+}
+
+
+loop_variable *
+loop_variable_state::insert(ir_variable *var)
+{
+ void *mem_ctx = talloc_parent(this);
+ loop_variable *lv = talloc_zero(mem_ctx, loop_variable);
+
+ lv->var = var;
+
+ hash_table_insert(this->var_hash, lv, lv->var);
+ this->variables.push_tail(lv);
+
+ return lv;
+}
+
+
+loop_terminator *
+loop_variable_state::insert(ir_if *if_stmt)
+{
+ void *mem_ctx = talloc_parent(this);
+ loop_terminator *t = talloc_zero(mem_ctx, loop_terminator);
+
+ t->ir = if_stmt;
+ this->terminators.push_tail(t);
+
+ return t;
+}
+
+
+class loop_analysis : public ir_hierarchical_visitor {
+public:
+ loop_analysis();
+
+ virtual ir_visitor_status visit(ir_dereference_variable *);
+
+ virtual ir_visitor_status visit_enter(ir_loop *);
+ virtual ir_visitor_status visit_leave(ir_loop *);
+ virtual ir_visitor_status visit_enter(ir_assignment *);
+ virtual ir_visitor_status visit_leave(ir_assignment *);
+ virtual ir_visitor_status visit_enter(ir_if *);
+ virtual ir_visitor_status visit_leave(ir_if *);
+
+ loop_state *loops;
+
+ int if_statement_depth;
+
+ ir_assignment *current_assignment;
+
+ exec_list state;
+};
+
+
+loop_analysis::loop_analysis()
+{
+ this->loops = new loop_state;
+
+ this->if_statement_depth = 0;
+ this->current_assignment = NULL;
+}
+
+
+ir_visitor_status
+loop_analysis::visit(ir_dereference_variable *ir)
+{
+ /* If we're not somewhere inside a loop, there's nothing to do.
+ */
+ if (this->state.is_empty())
+ return visit_continue_with_parent;
+
+ loop_variable_state *const ls =
+ (loop_variable_state *) this->state.get_head();
+
+ ir_variable *var = ir->variable_referenced();
+ loop_variable *lv = ls->get(var);
+
+ if (lv == NULL) {
+ lv = ls->insert(var);
+ lv->read_before_write = !this->in_assignee;
+ }
+
+ if (this->in_assignee) {
+ assert(this->current_assignment != NULL);
+
+ lv->conditional_assignment = (this->if_statement_depth > 0)
+ || (this->current_assignment->condition != NULL);
+
+ if (lv->first_assignment == NULL) {
+ assert(lv->num_assignments == 0);
+
+ lv->first_assignment = this->current_assignment;
+ }
+
+ lv->num_assignments++;
+ } else if (lv->first_assignment == this->current_assignment) {
+ /* This catches the case where the variable is used in the RHS of an
+ * assignment where it is also in the LHS.
+ */
+ lv->read_before_write = true;
+ }
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_enter(ir_loop *ir)
+{
+ loop_variable_state *ls = this->loops->insert(ir);
+ this->state.push_head(ls);
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_leave(ir_loop *ir)
+{
+ loop_variable_state *const ls =
+ (loop_variable_state *) this->state.pop_head();
+
+
+ foreach_list(node, &ir->body_instructions) {
+ /* Skip over declarations at the start of a loop.
+ */
+ if (((ir_instruction *) node)->as_variable())
+ continue;
+
+ ir_if *if_stmt = ((ir_instruction *) node)->as_if();
+
+ if ((if_stmt != NULL) && is_loop_terminator(if_stmt))
+ ls->insert(if_stmt);
+ else
+ break;
+ }
+
+
+ foreach_list_safe(node, &ls->variables) {
+ loop_variable *lv = (loop_variable *) node;
+
+ /* Move variables that are already marked as being loop constant to
+ * a separate list. These trivially don't need to be tested.
+ */
+ if (lv->is_loop_constant()) {
+ lv->remove();
+ ls->constants.push_tail(lv);
+ }
+ }
+
+ /* Each variable assigned in the loop that isn't already marked as being loop
+ * constant might still be loop constant. The requirements at this point
+ * are:
+ *
+ * - Variable is written before it is read.
+ *
+ * - Only one assignment to the variable.
+ *
+ * - All operands on the RHS of the assignment are also loop constants.
+ *
+ * The last requirement is the reason for the progress loop. A variable
+ * marked as a loop constant on one pass may allow other variables to be
+ * marked as loop constant on following passes.
+ */
+ bool progress;
+ do {
+ progress = false;
+
+ foreach_list_safe(node, &ls->variables) {
+ loop_variable *lv = (loop_variable *) node;
+
+ if (lv->conditional_assignment || (lv->num_assignments > 1))
+ continue;
+
+ /* Process the RHS of the assignment. If all of the variables
+ * accessed there are loop constants, then add this
+ */
+ ir_rvalue *const rhs = lv->first_assignment->rhs;
+ if (all_expression_operands_are_loop_constant(rhs, ls->var_hash)) {
+ lv->rhs_clean = true;
+
+ if (lv->is_loop_constant()) {
+ progress = true;
+
+ lv->remove();
+ ls->constants.push_tail(lv);
+ }
+ }
+ }
+ } while (progress);
+
+ /* The remaining variables that are not loop invariant might be loop
+ * induction variables.
+ */
+ foreach_list_safe(node, &ls->variables) {
+ loop_variable *lv = (loop_variable *) node;
+
+ /* If there is more than one assignment to a variable, it cannot be a
+ * loop induction variable. This isn't strictly true, but this is a
+ * very simple induction variable detector, and it can't handle more
+ * complex cases.
+ */
+ if (lv->num_assignments > 1)
+ continue;
+
+ /* All of the variables with zero assignments in the loop are loop
+ * invariant, and they should have already been filtered out.
+ */
+ assert(lv->num_assignments == 1);
+ assert(lv->first_assignment != NULL);
+
+ /* The assignmnet to the variable in the loop must be unconditional.
+ */
+ if (lv->conditional_assignment)
+ continue;
+
+ /* Basic loop induction variables have a single assignment in the loop
+ * that has the form 'VAR = VAR + i' or 'VAR = VAR - i' where i is a
+ * loop invariant.
+ */
+ ir_rvalue *const inc =
+ get_basic_induction_increment(lv->first_assignment, ls->var_hash);
+ if (inc != NULL) {
+ lv->iv_scale = NULL;
+ lv->biv = lv->var;
+ lv->increment = inc;
+
+ lv->remove();
+ ls->induction_variables.push_tail(lv);
+ }
+ }
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_enter(ir_if *ir)
+{
+ (void) ir;
+
+ if (!this->state.is_empty())
+ this->if_statement_depth++;
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_leave(ir_if *ir)
+{
+ (void) ir;
+
+ if (!this->state.is_empty())
+ this->if_statement_depth--;
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_enter(ir_assignment *ir)
+{
+ /* If we're not somewhere inside a loop, there's nothing to do.
+ */
+ if (this->state.is_empty())
+ return visit_continue_with_parent;
+
+ this->current_assignment = ir;
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_leave(ir_assignment *ir)
+{
+ /* Since the visit_enter exits with visit_continue_with_parent for this
+ * case, the loop state stack should never be empty here.
+ */
+ assert(!this->state.is_empty());
+
+ assert(this->current_assignment == ir);
+ this->current_assignment = NULL;
+
+ return visit_continue;
+}
+
+
+class examine_rhs : public ir_hierarchical_visitor {
+public:
+ examine_rhs(hash_table *loop_variables)
+ {
+ this->only_uses_loop_constants = true;
+ this->loop_variables = loop_variables;
+ }
+
+ virtual ir_visitor_status visit(ir_dereference_variable *ir)
+ {
+ loop_variable *lv =
+ (loop_variable *) hash_table_find(this->loop_variables, ir->var);
+
+ assert(lv != NULL);
+
+ if (lv->is_loop_constant()) {
+ return visit_continue;
+ } else {
+ this->only_uses_loop_constants = false;
+ return visit_stop;
+ }
+ }
+
+ hash_table *loop_variables;
+ bool only_uses_loop_constants;
+};
+
+
+bool
+all_expression_operands_are_loop_constant(ir_rvalue *ir, hash_table *variables)
+{
+ examine_rhs v(variables);
+
+ ir->accept(&v);
+
+ return v.only_uses_loop_constants;
+}
+
+
+ir_rvalue *
+get_basic_induction_increment(ir_assignment *ir, hash_table *var_hash)
+{
+ /* The RHS must be a binary expression.
+ */
+ ir_expression *const rhs = ir->rhs->as_expression();
+ if ((rhs == NULL)
+ || ((rhs->operation != ir_binop_add)
+ && (rhs->operation != ir_binop_sub)))
+ return NULL;
+
+ /* One of the of operands of the expression must be the variable assigned.
+ * If the operation is subtraction, the variable in question must be the
+ * "left" operand.
+ */
+ ir_variable *const var = ir->lhs->variable_referenced();
+
+ ir_variable *const op0 = rhs->operands[0]->variable_referenced();
+ ir_variable *const op1 = rhs->operands[1]->variable_referenced();
+
+ if (((op0 != var) && (op1 != var))
+ || ((op1 == var) && (rhs->operation == ir_binop_sub)))
+ return NULL;
+
+ ir_rvalue *inc = (op0 == var) ? rhs->operands[1] : rhs->operands[0];
+
+ if (inc->constant_expression_value() == NULL) {
+ ir_variable *const inc_var = inc->variable_referenced();
+ if (inc_var != NULL) {
+ loop_variable *lv =
+ (loop_variable *) hash_table_find(var_hash, inc_var);
+
+ if (!lv->is_loop_constant())
+ inc = NULL;
+ } else
+ inc = NULL;
+ }
+
+ if ((inc != NULL) && (rhs->operation == ir_binop_sub)) {
+ void *mem_ctx = talloc_parent(ir);
+
+ inc = new(mem_ctx) ir_expression(ir_unop_neg,
+ inc->type,
+ inc->clone(mem_ctx, NULL),
+ NULL);
+ }
+
+ return inc;
+}
+
+
+/**
+ * Detect whether an if-statement is a loop terminating condition
+ *
+ * Detects if-statements of the form
+ *
+ * (if (expression bool ...) (break))
+ */
+bool
+is_loop_terminator(ir_if *ir)
+{
+ if (!ir->else_instructions.is_empty())
+ return false;
+
+ ir_instruction *const inst =
+ (ir_instruction *) ir->then_instructions.get_head();
+ assert(inst != NULL);
+
+ if (inst->ir_type != ir_type_loop_jump)
+ return false;
+
+ ir_loop_jump *const jump = (ir_loop_jump *) inst;
+ if (jump->mode != ir_loop_jump::jump_break)
+ return false;
+
+ return true;
+}
+
+
+loop_state *
+analyze_loop_variables(exec_list *instructions)
+{
+ loop_analysis v;
+
+ v.run(instructions);
+ return v.loops;
+}
diff --git a/src/glsl/loop_analysis.h b/src/glsl/loop_analysis.h
new file mode 100644
index 0000000..50c512f
--- /dev/null
+++ b/src/glsl/loop_analysis.h
@@ -0,0 +1,190 @@
+/* -*- c++ -*- */
+/*
+ * 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.
+ */
+
+#pragma once
+#ifndef LOOP_ANALYSIS_H
+#define LOOP_ANALYSIS_H
+
+#include "ir.h"
+#include "program/hash_table.h"
+
+/**
+ * Analyze and classify all variables used in all loops in the instruction list
+ */
+extern class loop_state *
+analyze_loop_variables(exec_list *instructions);
+
+
+/**
+ * Tracking for all variables used in a loop
+ */
+class loop_variable_state : public exec_node {
+public:
+ class loop_variable *get(const ir_variable *);
+ class loop_variable *insert(ir_variable *);
+ class loop_terminator *insert(ir_if *);
+
+
+ /**
+ * Loop whose variable state is being tracked by this structure
+ */
+ ir_loop *loop;
+
+ /**
+ * Variables that have not yet been classified
+ */
+ exec_list variables;
+
+ /**
+ * Variables whose values are constant within the body of the loop
+ *
+ * This list contains \c loop_variable objects.
+ */
+ exec_list constants;
+
+ /**
+ * Induction variables for this loop
+ *
+ * This list contains \c loop_variable objects.
+ */
+ exec_list induction_variables;
+
+ /**
+ * Simple if-statements that lead to the termination of the loop
+ *
+ * This list contains \c loop_terminator objects.
+ *
+ * \sa is_loop_terminator
+ */
+ exec_list terminators;
+
+ /**
+ * Hash table containing all variables accessed in this loop
+ */
+ hash_table *var_hash;
+
+ loop_variable_state()
+ {
+ this->var_hash = hash_table_ctor(0, hash_table_pointer_hash,
+ hash_table_pointer_compare);
+ }
+
+ ~loop_variable_state()
+ {
+ hash_table_dtor(this->var_hash);
+ }
+};
+
+
+class loop_variable : public exec_node {
+public:
+ /** The variable in question. */
+ ir_variable *var;
+
+ /** Is the variable read in the loop before it is written? */
+ bool read_before_write;
+
+ /** Are all variables in the RHS of the assignment loop constants? */
+ bool rhs_clean;
+
+ /** Is there an assignment to the variable that is conditional? */
+ bool conditional_assignment;
+
+ /** Reference to the first assignment to the variable in the loop body. */
+ ir_assignment *first_assignment;
+
+ /** Number of assignments to the variable in the loop body. */
+ unsigned num_assignments;
+
+ /**
+ * Increment values for loop induction variables
+ *
+ * Loop induction variables have a single increment of the form
+ * \c b * \c biv + \c c, where \c b and \c c are loop constants and \c i
+ * is a basic loop induction variable.
+ *
+ * If \c iv_scale is \c NULL, 1 is used. If \c biv is the same as \c var,
+ * then \c var is a basic loop induction variable.
+ */
+ /*@{*/
+ ir_rvalue *iv_scale;
+ ir_variable *biv;
+ ir_rvalue *increment;
+ /*@}*/
+
+
+ inline bool is_loop_constant() const
+ {
+ const bool is_const = (this->num_assignments == 0)
+ || ((this->num_assignments == 1)
+ && !this->conditional_assignment
+ && !this->read_before_write
+ && this->rhs_clean);
+
+ /* If the RHS of *the* assignment is clean, then there must be exactly
+ * one assignment of the variable.
+ */
+ assert((this->rhs_clean && (this->num_assignments == 1))
+ || !this->rhs_clean);
+
+ /* Variables that are marked read-only *MUST* be loop constant.
+ */
+ assert(!this->var->read_only || (this->var->read_only && is_const));
+
+ return is_const;
+ }
+};
+
+
+class loop_terminator : public exec_node {
+public:
+ ir_if *ir;
+};
+
+
+class loop_state {
+public:
+ ~loop_state();
+
+ /**
+ * Get the loop variable state data for a particular loop
+ */
+ loop_variable_state *get(const ir_loop *);
+
+ loop_variable_state *insert(ir_loop *ir);
+
+private:
+ loop_state();
+
+ /**
+ * Hash table containing all loops that have been analyzed.
+ */
+ hash_table *ht;
+
+ void *mem_ctx;
+
+ friend class loop_analysis;
+};
+
+#endif /* LOOP_ANALYSIS_H */
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