Mesa (master): glsl2: Add module to suss out loop control variables from loop analysis data
Ian Romanick
idr at kemper.freedesktop.org
Fri Sep 3 19:01:04 UTC 2010
Module: Mesa
Branch: master
Commit: bfe3fbb38e0a3ae7c1efb74282628c2cc5abc3e0
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=bfe3fbb38e0a3ae7c1efb74282628c2cc5abc3e0
Author: Ian Romanick <ian.d.romanick at intel.com>
Date: Thu Aug 26 16:43:57 2010 -0700
glsl2: Add module to suss out loop control variables from loop analysis data
This is the next step on the road to loop unrolling
---
src/glsl/Makefile | 1 +
src/glsl/Makefile.am | 3 +-
src/glsl/loop_analysis.h | 20 +++
src/glsl/loop_controls.cpp | 282 ++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 305 insertions(+), 1 deletions(-)
diff --git a/src/glsl/Makefile b/src/glsl/Makefile
index e5375ef..ed1453b 100644
--- a/src/glsl/Makefile
+++ b/src/glsl/Makefile
@@ -73,6 +73,7 @@ CXX_SOURCES = \
linker.cpp \
link_functions.cpp \
loop_analysis.cpp \
+ loop_controls.cpp \
s_expression.cpp
LIBS = \
diff --git a/src/glsl/Makefile.am b/src/glsl/Makefile.am
index 55e4332..0811ffb 100644
--- a/src/glsl/Makefile.am
+++ b/src/glsl/Makefile.am
@@ -63,7 +63,8 @@ glsl_SOURCES = \
ir_validate.cpp \
ir_vec_index_to_swizzle.cpp \
linker.cpp \
- loop_analysis.cpp
+ loop_analysis.cpp \
+ loop_controls.cpp
BUILT_SOURCES = glsl_parser.h glsl_parser.cpp glsl_lexer.cpp
CLEANFILES = $(BUILT_SOURCES)
diff --git a/src/glsl/loop_analysis.h b/src/glsl/loop_analysis.h
index 50c512f..b7c0514 100644
--- a/src/glsl/loop_analysis.h
+++ b/src/glsl/loop_analysis.h
@@ -37,6 +37,26 @@ analyze_loop_variables(exec_list *instructions);
/**
+ * Fill in loop control fields
+ *
+ * Based on analysis of loop variables, this function tries to remove sequences
+ * in the loop of the form
+ *
+ * (if (expression bool ...) (break))
+ *
+ * and fill in the \c ir_loop::from, \c ir_loop::to, and \c ir_loop::counter
+ * fields of the \c ir_loop.
+ *
+ * In this process, some conditional break-statements may be eliminated
+ * altogether. For example, if it is provable that one loop exit condition will
+ * always be satisfied before another, the unnecessary exit condition will be
+ * removed.
+ */
+extern bool
+set_loop_controls(exec_list *instructions, loop_state *ls);
+
+
+/**
* Tracking for all variables used in a loop
*/
class loop_variable_state : public exec_node {
diff --git a/src/glsl/loop_controls.cpp b/src/glsl/loop_controls.cpp
new file mode 100644
index 0000000..2eddb91
--- /dev/null
+++ b/src/glsl/loop_controls.cpp
@@ -0,0 +1,282 @@
+/*
+ * 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 <climits>
+#include "main/compiler.h"
+#include "glsl_types.h"
+#include "loop_analysis.h"
+#include "ir_hierarchical_visitor.h"
+
+/**
+ * Find an initializer of a variable outside a loop
+ *
+ * Works backwards from the loop to find the pre-loop value of the variable.
+ * This is used, for example, to find the initial value of loop induction
+ * variables.
+ *
+ * \param loop Loop where \c var is an induction variable
+ * \param var Variable whose initializer is to be found
+ *
+ * \return
+ * The \c ir_rvalue assigned to the variable outside the loop. May return
+ * \c NULL if no initializer can be found.
+ */
+ir_rvalue *
+find_initial_value(ir_loop *loop, ir_variable *var)
+{
+ for (exec_node *node = loop->prev;
+ !node->is_head_sentinel();
+ node = node->prev) {
+ ir_instruction *ir = (ir_instruction *) node;
+
+ switch (ir->ir_type) {
+ case ir_type_call:
+ case ir_type_loop:
+ case ir_type_loop_jump:
+ case ir_type_return:
+ case ir_type_if:
+ return NULL;
+
+ case ir_type_function:
+ case ir_type_function_signature:
+ assert(!"Should not get here.");
+ return NULL;
+
+ case ir_type_assignment: {
+ ir_assignment *assign = ir->as_assignment();
+ ir_variable *assignee = assign->lhs->whole_variable_referenced();
+
+ if (assignee == var)
+ return (assign->condition != NULL) ? NULL : assign->rhs;
+
+ break;
+ }
+
+ default:
+ break;
+ }
+ }
+
+ return NULL;
+}
+
+
+int
+calculate_iterations(ir_rvalue *from, ir_rvalue *to, ir_rvalue *increment,
+ enum ir_expression_operation op)
+{
+ void *mem_ctx = talloc_init(__func__);
+
+ ir_expression *const sub =
+ new(mem_ctx) ir_expression(ir_binop_sub, from->type, to, from);
+
+ ir_expression *const div =
+ new(mem_ctx) ir_expression(ir_binop_div, sub->type, sub, increment);
+
+ ir_constant *iter = div->constant_expression_value();
+
+ if (iter == NULL)
+ return -1;
+
+ if (!iter->type->is_integer()) {
+ ir_rvalue *cast =
+ new(mem_ctx) ir_expression(ir_unop_f2i, glsl_type::int_type, iter,
+ NULL);
+
+ iter = cast->constant_expression_value();
+ }
+
+ int iter_value = iter->get_int_component(0);
+
+ /* Make sure that the calculated number of iterations satisfies the exit
+ * condition. This is needed to catch off-by-one errors and some types of
+ * ill-formed loops. For example, we need to detect that the following
+ * loop does not have a maximum iteration count.
+ *
+ * for (float x = 0.0; x != 0.9; x += 0.2)
+ * ;
+ */
+ const int bias[] = { -1, 0, 1 };
+ bool valid_loop = false;
+
+ for (unsigned i = 0; i < Elements(bias); i++) {
+ iter = (increment->type->is_integer())
+ ? new(mem_ctx) ir_constant(iter_value + bias[i])
+ : new(mem_ctx) ir_constant(float(iter_value + bias[i]));
+
+ ir_expression *const mul =
+ new(mem_ctx) ir_expression(ir_binop_mul, increment->type, iter,
+ increment);
+
+ ir_expression *const add =
+ new(mem_ctx) ir_expression(ir_binop_add, mul->type, mul, from);
+
+ ir_expression *const cmp =
+ new(mem_ctx) ir_expression(op, glsl_type::bool_type, add, to);
+
+ ir_constant *const cmp_result = cmp->constant_expression_value();
+
+ assert(cmp_result != NULL);
+ if (cmp_result->get_bool_component(0)) {
+ iter_value += bias[i];
+ valid_loop = true;
+ break;
+ }
+ }
+
+ talloc_free(mem_ctx);
+ return (valid_loop) ? iter_value : -1;
+}
+
+
+class loop_control_visitor : public ir_hierarchical_visitor {
+public:
+ loop_control_visitor(loop_state *state)
+ {
+ this->state = state;
+ this->progress = false;
+ }
+
+ virtual ir_visitor_status visit_leave(ir_loop *ir);
+
+ loop_state *state;
+
+ bool progress;
+};
+
+
+ir_visitor_status
+loop_control_visitor::visit_leave(ir_loop *ir)
+{
+ loop_variable_state *const ls = this->state->get(ir);
+
+ /* If we've entered a loop that hasn't been analyzed, something really,
+ * really bad has happened.
+ */
+ if (ls == NULL) {
+ assert(ls != NULL);
+ return visit_continue;
+ }
+
+ /* Search the loop terminating conditions for one of the form 'i < c' where
+ * i is a loop induction variable, c is a constant, and < is any relative
+ * operator.
+ */
+ int max_iterations = INT_MAX;
+ foreach_list(node, &ls->terminators) {
+ loop_terminator *t = (loop_terminator *) node;
+ ir_if *if_stmt = t->ir;
+
+ /* If-statements can be either 'if (expr)' or 'if (deref)'. We only care
+ * about the former here.
+ */
+ ir_expression *cond = if_stmt->condition->as_expression();
+ if (cond == NULL)
+ continue;
+
+ switch (cond->operation) {
+ case ir_binop_less:
+ case ir_binop_greater:
+ case ir_binop_lequal:
+ case ir_binop_gequal: {
+ /* The expressions that we care about will either be of the form
+ * 'counter < limit' or 'limit < counter'. Figure out which is
+ * which.
+ */
+ ir_rvalue *counter = cond->operands[0]->as_dereference_variable();
+ ir_constant *limit = cond->operands[1]->constant_expression_value();
+ enum ir_expression_operation cmp = cond->operation;
+
+ if (limit == NULL) {
+ counter = cond->operands[1]->as_dereference_variable();
+ limit = cond->operands[0]->constant_expression_value();
+
+ switch (cmp) {
+ case ir_binop_less: cmp = ir_binop_gequal; break;
+ case ir_binop_greater: cmp = ir_binop_lequal; break;
+ case ir_binop_lequal: cmp = ir_binop_greater; break;
+ case ir_binop_gequal: cmp = ir_binop_less; break;
+ default: assert(!"Should not get here.");
+ }
+ }
+
+ if ((counter == NULL) || (limit == NULL))
+ break;
+
+ ir_variable *var = counter->variable_referenced();
+
+ ir_rvalue *init = find_initial_value(ir, var);
+
+ foreach_list(iv_node, &ls->induction_variables) {
+ loop_variable *lv = (loop_variable *) iv_node;
+
+ if (lv->var == var) {
+ const int iterations = calculate_iterations(init, limit,
+ lv->increment,
+ cmp);
+ if (iterations > 0) {
+ /* If the new iteration count is lower than the previously
+ * believed iteration count, update the loop control values.
+ */
+ if (iterations < max_iterations) {
+ ir->from = init->clone(ir, NULL);
+ ir->to = limit->clone(ir, NULL);
+ ir->increment = lv->increment->clone(ir, NULL);
+ ir->counter = lv->var;
+ ir->cmp = cmp;
+
+ max_iterations = iterations;
+ }
+
+ /* Remove the conditional break statement. The loop
+ * controls are now set such that the exit condition will be
+ * satisfied.
+ */
+ if_stmt->remove();
+ this->progress = true;
+ }
+
+ break;
+ }
+ }
+ break;
+ }
+
+ default:
+ break;
+ }
+ }
+
+ return visit_continue;
+}
+
+
+bool
+set_loop_controls(exec_list *instructions, loop_state *ls)
+{
+ loop_control_visitor v(ls);
+
+ v.run(instructions);
+
+ return v.progress;
+}
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