diff options
Diffstat (limited to 'mesalib/src/glsl/lower_jumps.cpp')
| -rw-r--r-- | mesalib/src/glsl/lower_jumps.cpp | 570 |
1 files changed, 570 insertions, 0 deletions
diff --git a/mesalib/src/glsl/lower_jumps.cpp b/mesalib/src/glsl/lower_jumps.cpp new file mode 100644 index 000000000..7c3463e58 --- /dev/null +++ b/mesalib/src/glsl/lower_jumps.cpp @@ -0,0 +1,570 @@ +/*
+ * Copyright © 2010 Luca Barbieri
+ *
+ * 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_jumps.cpp
+ *
+ * This pass lowers jumps (break, continue, and return) to if/else structures.
+ *
+ * It can be asked to:
+ * 1. Pull jumps out of ifs where possible
+ * 2. Remove all "continue"s, replacing them with an "execute flag"
+ * 3. Replace all "break" with a single conditional one at the end of the loop
+ * 4. Replace all "return"s with a single return at the end of the function,
+ * for the main function and/or other functions
+ *
+ * Applying this pass gives several benefits:
+ * 1. All functions can be inlined.
+ * 2. nv40 and other pre-DX10 chips without "continue" can be supported
+ * 3. nv30 and other pre-DX10 chips with no control flow at all are better
+ * supported
+ *
+ * Continues are lowered by adding a per-loop "execute flag", initialized to
+ * true, that when cleared inhibits all execution until the end of the loop.
+ *
+ * Breaks are lowered to continues, plus setting a "break flag" that is checked
+ * at the end of the loop, and trigger the unique "break".
+ *
+ * Returns are lowered to breaks/continues, plus adding a "return flag" that
+ * causes loops to break again out of their enclosing loops until all the
+ * loops are exited: then the "execute flag" logic will ignore everything
+ * until the end of the function.
+ *
+ * Note that "continue" and "return" can also be implemented by adding
+ * a dummy loop and using break.
+ * However, this is bad for hardware with limited nesting depth, and
+ * prevents further optimization, and thus is not currently performed.
+ */
+
+#include "glsl_types.h"
+#include <string.h>
+#include "ir.h"
+
+enum jump_strength
+{
+ strength_none,
+ strength_always_clears_execute_flag,
+ strength_continue,
+ strength_break,
+ strength_return,
+};
+
+struct block_record
+{
+ /* minimum jump strength (of lowered IR, not pre-lowering IR)
+ *
+ * If the block ends with a jump, must be the strength of the jump.
+ * Otherwise, the jump would be dead and have been deleted before)
+ *
+ * If the block doesn't end with a jump, it can be different than strength_none if all paths before it lead to some jump
+ * (e.g. an if with a return in one branch, and a break in the other, while not lowering them)
+ * Note that identical jumps are usually unified though.
+ */
+ jump_strength min_strength;
+
+ /* can anything clear the execute flag? */
+ bool may_clear_execute_flag;
+
+ block_record()
+ {
+ this->min_strength = strength_none;
+ this->may_clear_execute_flag = false;
+ }
+};
+
+struct loop_record
+{
+ ir_function_signature* signature;
+ ir_loop* loop;
+
+ /* used to avoid lowering the break used to represent lowered breaks */
+ unsigned nesting_depth;
+ bool in_if_at_the_end_of_the_loop;
+
+ bool may_set_return_flag;
+
+ ir_variable* break_flag;
+ ir_variable* execute_flag; /* cleared to emulate continue */
+
+ loop_record(ir_function_signature* p_signature = 0, ir_loop* p_loop = 0)
+ {
+ this->signature = p_signature;
+ this->loop = p_loop;
+ this->nesting_depth = 0;
+ this->in_if_at_the_end_of_the_loop = false;
+ this->may_set_return_flag = false;
+ this->break_flag = 0;
+ this->execute_flag = 0;
+ }
+
+ ir_variable* get_execute_flag()
+ {
+ /* also supported for the "function loop" */
+ if(!this->execute_flag) {
+ exec_list& list = this->loop ? this->loop->body_instructions : signature->body;
+ this->execute_flag = new(this->signature) ir_variable(glsl_type::bool_type, "execute_flag", ir_var_temporary);
+ list.push_head(new(this->signature) ir_assignment(new(this->signature) ir_dereference_variable(execute_flag), new(this->signature) ir_constant(true), 0));
+ list.push_head(this->execute_flag);
+ }
+ return this->execute_flag;
+ }
+
+ ir_variable* get_break_flag()
+ {
+ assert(this->loop);
+ if(!this->break_flag) {
+ this->break_flag = new(this->signature) ir_variable(glsl_type::bool_type, "break_flag", ir_var_temporary);
+ this->loop->insert_before(this->break_flag);
+ this->loop->insert_before(new(this->signature) ir_assignment(new(this->signature) ir_dereference_variable(break_flag), new(this->signature) ir_constant(false), 0));
+ }
+ return this->break_flag;
+ }
+};
+
+struct function_record
+{
+ ir_function_signature* signature;
+ ir_variable* return_flag; /* used to break out of all loops and then jump to the return instruction */
+ ir_variable* return_value;
+ bool is_main;
+ unsigned nesting_depth;
+
+ function_record(ir_function_signature* p_signature = 0)
+ {
+ this->signature = p_signature;
+ this->return_flag = 0;
+ this->return_value = 0;
+ this->nesting_depth = 0;
+ this->is_main = this->signature && (strcmp(this->signature->function_name(), "main") == 0);
+ }
+
+ ir_variable* get_return_flag()
+ {
+ if(!this->return_flag) {
+ this->return_flag = new(this->signature) ir_variable(glsl_type::bool_type, "return_flag", ir_var_temporary);
+ this->signature->body.push_head(new(this->signature) ir_assignment(new(this->signature) ir_dereference_variable(return_flag), new(this->signature) ir_constant(false), 0));
+ this->signature->body.push_head(this->return_flag);
+ }
+ return this->return_flag;
+ }
+
+ ir_variable* get_return_value()
+ {
+ if(!this->return_value) {
+ assert(!this->signature->return_type->is_void());
+ return_value = new(this->signature) ir_variable(this->signature->return_type, "return_value", ir_var_temporary);
+ this->signature->body.push_head(this->return_value);
+ }
+ return this->return_value;
+ }
+};
+
+struct ir_lower_jumps_visitor : public ir_control_flow_visitor {
+ bool progress;
+
+ struct function_record function;
+ struct loop_record loop;
+ struct block_record block;
+
+ bool pull_out_jumps;
+ bool lower_continue;
+ bool lower_break;
+ bool lower_sub_return;
+ bool lower_main_return;
+
+ ir_lower_jumps_visitor()
+ {
+ this->progress = false;
+ }
+
+ void truncate_after_instruction(exec_node *ir)
+ {
+ if (!ir)
+ return;
+
+ while (!ir->get_next()->is_tail_sentinel()) {
+ ((ir_instruction *)ir->get_next())->remove();
+ this->progress = true;
+ }
+ }
+
+ void move_outer_block_inside(ir_instruction *ir, exec_list *inner_block)
+ {
+ while (!ir->get_next()->is_tail_sentinel()) {
+ ir_instruction *move_ir = (ir_instruction *)ir->get_next();
+
+ move_ir->remove();
+ inner_block->push_tail(move_ir);
+ }
+ }
+
+ virtual void visit(class ir_loop_jump * ir)
+ {
+ truncate_after_instruction(ir);
+ this->block.min_strength = ir->is_break() ? strength_break : strength_continue;
+ }
+
+ virtual void visit(class ir_return * ir)
+ {
+ truncate_after_instruction(ir);
+ this->block.min_strength = strength_return;
+ }
+
+ virtual void visit(class ir_discard * ir)
+ {
+ }
+
+ enum jump_strength get_jump_strength(ir_instruction* ir)
+ {
+ if(!ir)
+ return strength_none;
+ else if(ir->ir_type == ir_type_loop_jump) {
+ if(((ir_loop_jump*)ir)->is_break())
+ return strength_break;
+ else
+ return strength_continue;
+ } else if(ir->ir_type == ir_type_return)
+ return strength_return;
+ else
+ return strength_none;
+ }
+
+ bool should_lower_jump(ir_jump* ir)
+ {
+ unsigned strength = get_jump_strength(ir);
+ bool lower;
+ switch(strength)
+ {
+ case strength_none:
+ lower = false; /* don't change this, code relies on it */
+ break;
+ case strength_continue:
+ lower = lower_continue;
+ break;
+ case strength_break:
+ assert(this->loop.loop);
+ /* never lower "canonical break" */
+ if(ir->get_next()->is_tail_sentinel() && (this->loop.nesting_depth == 0
+ || (this->loop.nesting_depth == 1 && this->loop.in_if_at_the_end_of_the_loop)))
+ lower = false;
+ else
+ lower = lower_break;
+ break;
+ case strength_return:
+ /* never lower return at the end of a this->function */
+ if(this->function.nesting_depth == 0 && ir->get_next()->is_tail_sentinel())
+ lower = false;
+ else if (this->function.is_main)
+ lower = lower_main_return;
+ else
+ lower = lower_sub_return;
+ break;
+ }
+ return lower;
+ }
+
+ block_record visit_block(exec_list* list)
+ {
+ block_record saved_block = this->block;
+ this->block = block_record();
+ visit_exec_list(list, this);
+ block_record ret = this->block;
+ this->block = saved_block;
+ return ret;
+ }
+
+ virtual void visit(ir_if *ir)
+ {
+ if(this->loop.nesting_depth == 0 && ir->get_next()->is_tail_sentinel())
+ this->loop.in_if_at_the_end_of_the_loop = true;
+
+ ++this->function.nesting_depth;
+ ++this->loop.nesting_depth;
+
+ block_record block_records[2];
+ ir_jump* jumps[2];
+
+ block_records[0] = visit_block(&ir->then_instructions);
+ block_records[1] = visit_block(&ir->else_instructions);
+
+retry: /* we get here if we put code after the if inside a branch */
+ for(unsigned i = 0; i < 2; ++i) {
+ exec_list& list = i ? ir->else_instructions : ir->then_instructions;
+ jumps[i] = 0;
+ if(!list.is_empty() && get_jump_strength((ir_instruction*)list.get_tail()))
+ jumps[i] = (ir_jump*)list.get_tail();
+ }
+
+ for(;;) {
+ jump_strength jump_strengths[2];
+
+ for(unsigned i = 0; i < 2; ++i) {
+ if(jumps[i]) {
+ jump_strengths[i] = block_records[i].min_strength;
+ assert(jump_strengths[i] == get_jump_strength(jumps[i]));
+ } else
+ jump_strengths[i] = strength_none;
+ }
+
+ /* move both jumps out if possible */
+ if(pull_out_jumps && jump_strengths[0] == jump_strengths[1]) {
+ bool unify = true;
+ if(jump_strengths[0] == strength_continue)
+ ir->insert_after(new(ir) ir_loop_jump(ir_loop_jump::jump_continue));
+ else if(jump_strengths[0] == strength_break)
+ ir->insert_after(new(ir) ir_loop_jump(ir_loop_jump::jump_break));
+ /* FINISHME: unify returns with identical expressions */
+ else if(jump_strengths[0] == strength_return && this->function.signature->return_type->is_void())
+ ir->insert_after(new(ir) ir_return(NULL));
+ else
+ unify = false;
+
+ if(unify) {
+ jumps[0]->remove();
+ jumps[1]->remove();
+ this->progress = true;
+
+ jumps[0] = 0;
+ jumps[1] = 0;
+ block_records[0].min_strength = strength_none;
+ block_records[1].min_strength = strength_none;
+ break;
+ }
+ }
+
+ /* lower a jump: if both need to lowered, start with the strongest one, so that
+ * we might later unify the lowered version with the other one
+ */
+ bool should_lower[2];
+ for(unsigned i = 0; i < 2; ++i)
+ should_lower[i] = should_lower_jump(jumps[i]);
+
+ int lower;
+ if(should_lower[1] && should_lower[0])
+ lower = jump_strengths[1] > jump_strengths[0];
+ else if(should_lower[0])
+ lower = 0;
+ else if(should_lower[1])
+ lower = 1;
+ else
+ break;
+
+ if(jump_strengths[lower] == strength_return) {
+ ir_variable* return_flag = this->function.get_return_flag();
+ if(!this->function.signature->return_type->is_void()) {
+ ir_variable* return_value = this->function.get_return_value();
+ jumps[lower]->insert_before(new(ir) ir_assignment(new (ir) ir_dereference_variable(return_value), ((ir_return*)jumps[lower])->value, NULL));
+ }
+ jumps[lower]->insert_before(new(ir) ir_assignment(new (ir) ir_dereference_variable(return_flag), new (ir) ir_constant(true), NULL));
+ this->loop.may_set_return_flag = true;
+ if(this->loop.loop) {
+ ir_loop_jump* lowered = 0;
+ lowered = new(ir) ir_loop_jump(ir_loop_jump::jump_break);
+ block_records[lower].min_strength = strength_break;
+ jumps[lower]->replace_with(lowered);
+ jumps[lower] = lowered;
+ } else
+ goto lower_continue;
+ this->progress = true;
+ } else if(jump_strengths[lower] == strength_break) {
+ /* We can't lower to an actual continue because that would execute the increment.
+ *
+ * In the lowered code, we instead put the break check between the this->loop body and the increment,
+ * which is impossible with a real continue as defined by the GLSL IR currently.
+ *
+ * Smarter options (such as undoing the increment) are possible but it's not worth implementing them,
+ * because if break is lowered, continue is almost surely lowered too.
+ */
+ jumps[lower]->insert_before(new(ir) ir_assignment(new (ir) ir_dereference_variable(this->loop.get_break_flag()), new (ir) ir_constant(true), 0));
+ goto lower_continue;
+ } else if(jump_strengths[lower] == strength_continue) {
+lower_continue:
+ ir_variable* execute_flag = this->loop.get_execute_flag();
+ jumps[lower]->replace_with(new(ir) ir_assignment(new (ir) ir_dereference_variable(execute_flag), new (ir) ir_constant(false), 0));
+ jumps[lower] = 0;
+ block_records[lower].min_strength = strength_always_clears_execute_flag;
+ block_records[lower].may_clear_execute_flag = true;
+ this->progress = true;
+ break;
+ }
+ }
+
+ /* move out a jump out if possible */
+ if(pull_out_jumps) {
+ int move_out = -1;
+ if(jumps[0] && block_records[1].min_strength >= strength_continue)
+ move_out = 0;
+ else if(jumps[1] && block_records[0].min_strength >= strength_continue)
+ move_out = 1;
+
+ if(move_out >= 0)
+ {
+ jumps[move_out]->remove();
+ ir->insert_after(jumps[move_out]);
+ jumps[move_out] = 0;
+ block_records[move_out].min_strength = strength_none;
+ this->progress = true;
+ }
+ }
+
+ if(block_records[0].min_strength < block_records[1].min_strength)
+ this->block.min_strength = block_records[0].min_strength;
+ else
+ this->block.min_strength = block_records[1].min_strength;
+ this->block.may_clear_execute_flag = this->block.may_clear_execute_flag || block_records[0].may_clear_execute_flag || block_records[1].may_clear_execute_flag;
+
+ if(this->block.min_strength)
+ truncate_after_instruction(ir);
+ else if(this->block.may_clear_execute_flag)
+ {
+ int move_into = -1;
+ if(block_records[0].min_strength && !block_records[1].may_clear_execute_flag)
+ move_into = 1;
+ else if(block_records[1].min_strength && !block_records[0].may_clear_execute_flag)
+ move_into = 0;
+
+ if(move_into >= 0) {
+ assert(!block_records[move_into].min_strength && !block_records[move_into].may_clear_execute_flag); /* otherwise, we just truncated */
+
+ exec_list* list = move_into ? &ir->else_instructions : &ir->then_instructions;
+ exec_node* next = ir->get_next();
+ if(!next->is_tail_sentinel()) {
+ move_outer_block_inside(ir, list);
+
+ exec_list list;
+ list.head = next;
+ block_records[move_into] = visit_block(&list);
+
+ this->progress = true;
+ goto retry;
+ }
+ } else {
+ ir_instruction* ir_after;
+ for(ir_after = (ir_instruction*)ir->get_next(); !ir_after->is_tail_sentinel();)
+ {
+ ir_if* ir_if = ir_after->as_if();
+ if(ir_if && ir_if->else_instructions.is_empty()) {
+ ir_dereference_variable* ir_if_cond_deref = ir_if->condition->as_dereference_variable();
+ if(ir_if_cond_deref && ir_if_cond_deref->var == this->loop.execute_flag) {
+ ir_instruction* ir_next = (ir_instruction*)ir_after->get_next();
+ ir_after->insert_before(&ir_if->then_instructions);
+ ir_after->remove();
+ ir_after = ir_next;
+ continue;
+ }
+ }
+ ir_after = (ir_instruction*)ir_after->get_next();
+
+ /* only set this if we find any unprotected instruction */
+ this->progress = true;
+ }
+
+ if(!ir->get_next()->is_tail_sentinel()) {
+ assert(this->loop.execute_flag);
+ ir_if* if_execute = new(ir) ir_if(new(ir) ir_dereference_variable(this->loop.execute_flag));
+ move_outer_block_inside(ir, &if_execute->then_instructions);
+ ir->insert_after(if_execute);
+ }
+ }
+ }
+ --this->loop.nesting_depth;
+ --this->function.nesting_depth;
+ }
+
+ virtual void visit(ir_loop *ir)
+ {
+ ++this->function.nesting_depth;
+ loop_record saved_loop = this->loop;
+ this->loop = loop_record(this->function.signature, ir);
+
+ block_record body = visit_block(&ir->body_instructions);
+
+ if(body.min_strength >= strength_break) {
+ /* FINISHME: turn the this->loop into an if, or replace it with its body */
+ }
+
+ if(this->loop.break_flag) {
+ ir_if* break_if = new(ir) ir_if(new(ir) ir_dereference_variable(this->loop.break_flag));
+ break_if->then_instructions.push_tail(new(ir) ir_loop_jump(ir_loop_jump::jump_break));
+ ir->body_instructions.push_tail(break_if);
+ }
+
+ if(this->loop.may_set_return_flag) {
+ assert(this->function.return_flag);
+ ir_if* return_if = new(ir) ir_if(new(ir) ir_dereference_variable(this->function.return_flag));
+ saved_loop.may_set_return_flag = true;
+ if(saved_loop.loop)
+ return_if->then_instructions.push_tail(new(ir) ir_loop_jump(ir_loop_jump::jump_break));
+ else
+ move_outer_block_inside(ir, &return_if->else_instructions);
+ ir->insert_after(return_if);
+ }
+
+ this->loop = saved_loop;
+ --this->function.nesting_depth;
+ }
+
+ virtual void visit(ir_function_signature *ir)
+ {
+ /* these are not strictly necessary */
+ assert(!this->function.signature);
+ assert(!this->loop.loop);
+
+ function_record saved_function = this->function;
+ loop_record saved_loop = this->loop;
+ this->function = function_record(ir);
+ this->loop = loop_record(ir);
+
+ assert(!this->loop.loop);
+ visit_block(&ir->body);
+
+ if(this->function.return_value)
+ ir->body.push_tail(new(ir) ir_return(new (ir) ir_dereference_variable(this->function.return_value)));
+
+ this->loop = saved_loop;
+ this->function = saved_function;
+ }
+
+ virtual void visit(class ir_function * ir)
+ {
+ visit_block(&ir->signatures);
+ }
+};
+
+bool
+do_lower_jumps(exec_list *instructions, bool pull_out_jumps, bool lower_sub_return, bool lower_main_return, bool lower_continue, bool lower_break)
+{
+ ir_lower_jumps_visitor v;
+ v.pull_out_jumps = pull_out_jumps;
+ v.lower_continue = lower_continue;
+ v.lower_break = lower_break;
+ v.lower_sub_return = lower_sub_return;
+ v.lower_main_return = lower_main_return;
+
+ do {
+ v.progress = false;
+ visit_exec_list(instructions, &v);
+ } while (v.progress);
+
+ return v.progress;
+}
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