| /* |
| * 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 recording the result of analyzing how control flow might exit |
| * an IR node. |
| * |
| * Each possible value of jump_strength indicates a strictly stronger |
| * guarantee on control flow than the previous value. |
| * |
| * The ordering of strengths roughly reflects the way jumps are |
| * lowered: jumps with higher strength tend to be lowered to jumps of |
| * lower strength. Accordingly, strength is used as a heuristic to |
| * determine which lowering to perform first. |
| * |
| * This enum is also used by get_jump_strength() to categorize |
| * instructions as either break, continue, return, or other. When |
| * used in this fashion, strength_always_clears_execute_flag is not |
| * used. |
| * |
| * The control flow analysis made by this optimization pass makes two |
| * simplifying assumptions: |
| * |
| * - It ignores discard instructions, since they are lowered by a |
| * separate pass (lower_discard.cpp). |
| * |
| * - It assumes it is always possible for control to flow from a loop |
| * to the instruction immediately following it. Technically, this |
| * is not true (since all execution paths through the loop might |
| * jump back to the top, or return from the function). |
| * |
| * Both of these simplifying assumtions are safe, since they can never |
| * cause reachable code to be incorrectly classified as unreachable; |
| * they can only do the opposite. |
| */ |
| enum jump_strength |
| { |
| /** |
| * Analysis has produced no guarantee on how control flow might |
| * exit this IR node. It might fall out the bottom (with or |
| * without clearing the execute flag, if present), or it might |
| * continue to the top of the innermost enclosing loop, break out |
| * of it, or return from the function. |
| */ |
| strength_none, |
| |
| /** |
| * The only way control can fall out the bottom of this node is |
| * through a code path that clears the execute flag. It might also |
| * continue to the top of the innermost enclosing loop, break out |
| * of it, or return from the function. |
| */ |
| strength_always_clears_execute_flag, |
| |
| /** |
| * Control cannot fall out the bottom of this node. It might |
| * continue to the top of the innermost enclosing loop, break out |
| * of it, or return from the function. |
| */ |
| strength_continue, |
| |
| /** |
| * Control cannot fall out the bottom of this node, or continue the |
| * top of the innermost enclosing loop. It can only break out of |
| * it or return from the function. |
| */ |
| strength_break, |
| |
| /** |
| * Control cannot fall out the bottom of this node, continue to the |
| * top of the innermost enclosing loop, or break out of it. It can |
| * only return from the function. |
| */ |
| 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 lower_return; |
| unsigned nesting_depth; |
| |
| function_record(ir_function_signature* p_signature = 0, |
| bool lower_return = false) |
| { |
| this->signature = p_signature; |
| this->return_flag = 0; |
| this->return_value = 0; |
| this->nesting_depth = 0; |
| this->lower_return = lower_return; |
| } |
| |
| 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 { |
| /* Postconditions: on exit of any visit() function: |
| * |
| * ANALYSIS: this->block.min_strength, |
| * this->block.may_clear_execute_flag, and |
| * this->loop.may_set_return_flag are updated to reflect the |
| * characteristics of the visited statement. |
| * |
| * DEAD_CODE_ELIMINATION: If this->block.min_strength is not |
| * strength_none, the visited node is at the end of its exec_list. |
| * In other words, any unreachable statements that follow the |
| * visited statement in its exec_list have been removed. |
| * |
| * CONTAINED_JUMPS_LOWERED: If the visited statement contains other |
| * statements, then should_lower_jump() is false for all of the |
| * return, break, or continue statements it contains. |
| * |
| * Note that visiting a jump does not lower it. That is the |
| * responsibility of the statement (or function signature) that |
| * contains the jump. |
| */ |
| |
| 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); |
| } |
| } |
| |
| /** |
| * Insert the instructions necessary to lower a return statement, |
| * before the given return instruction. |
| */ |
| void insert_lowered_return(ir_return *ir) |
| { |
| 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(); |
| ir->insert_before( |
| new(ir) ir_assignment( |
| new (ir) ir_dereference_variable(return_value), |
| ir->value)); |
| } |
| ir->insert_before( |
| new(ir) ir_assignment( |
| new (ir) ir_dereference_variable(return_flag), |
| new (ir) ir_constant(true))); |
| this->loop.may_set_return_flag = true; |
| } |
| |
| /** |
| * If the given instruction is a return, lower it to instructions |
| * that store the return value (if there is one), set the return |
| * flag, and then break. |
| * |
| * It is safe to pass NULL to this function. |
| */ |
| void lower_return_unconditionally(ir_instruction *ir) |
| { |
| if (get_jump_strength(ir) != strength_return) { |
| return; |
| } |
| insert_lowered_return((ir_return*)ir); |
| ir->replace_with(new(ir) ir_loop_jump(ir_loop_jump::jump_break)); |
| } |
| |
| /** |
| * Create the necessary instruction to replace a break instruction. |
| */ |
| ir_instruction *create_lowered_break() |
| { |
| void *ctx = this->function.signature; |
| return new(ctx) ir_assignment( |
| new(ctx) ir_dereference_variable(this->loop.get_break_flag()), |
| new(ctx) ir_constant(true), |
| 0); |
| } |
| |
| /** |
| * If the given instruction is a break, lower it to an instruction |
| * that sets the break flag, without consulting |
| * should_lower_jump(). |
| * |
| * It is safe to pass NULL to this function. |
| */ |
| void lower_break_unconditionally(ir_instruction *ir) |
| { |
| if (get_jump_strength(ir) != strength_break) { |
| return; |
| } |
| ir->replace_with(create_lowered_break()); |
| } |
| |
| /** |
| * If the block ends in a conditional or unconditional break, lower |
| * it, even though should_lower_jump() says it needn't be lowered. |
| */ |
| void lower_final_breaks(exec_list *block) |
| { |
| ir_instruction *ir = (ir_instruction *) block->get_tail(); |
| lower_break_unconditionally(ir); |
| ir_if *ir_if = ir->as_if(); |
| if (ir_if) { |
| lower_break_unconditionally( |
| (ir_instruction *) ir_if->then_instructions.get_tail()); |
| lower_break_unconditionally( |
| (ir_instruction *) ir_if->else_instructions.get_tail()); |
| } |
| } |
| |
| virtual void visit(class ir_loop_jump * ir) |
| { |
| /* Eliminate all instructions after each one, since they are |
| * unreachable. This satisfies the DEAD_CODE_ELIMINATION |
| * postcondition. |
| */ |
| truncate_after_instruction(ir); |
| |
| /* Set this->block.min_strength based on this instruction. This |
| * satisfies the ANALYSIS postcondition. It is not necessary to |
| * update this->block.may_clear_execute_flag or |
| * this->loop.may_set_return_flag, because an unlowered jump |
| * instruction can't change any flags. |
| */ |
| this->block.min_strength = ir->is_break() ? strength_break : strength_continue; |
| |
| /* The CONTAINED_JUMPS_LOWERED postcondition is already |
| * satisfied, because jump statements can't contain other |
| * statements. |
| */ |
| } |
| |
| virtual void visit(class ir_return * ir) |
| { |
| /* Eliminate all instructions after each one, since they are |
| * unreachable. This satisfies the DEAD_CODE_ELIMINATION |
| * postcondition. |
| */ |
| truncate_after_instruction(ir); |
| |
| /* Set this->block.min_strength based on this instruction. This |
| * satisfies the ANALYSIS postcondition. It is not necessary to |
| * update this->block.may_clear_execute_flag or |
| * this->loop.may_set_return_flag, because an unlowered return |
| * instruction can't change any flags. |
| */ |
| this->block.min_strength = strength_return; |
| |
| /* The CONTAINED_JUMPS_LOWERED postcondition is already |
| * satisfied, because jump statements can't contain other |
| * statements. |
| */ |
| } |
| |
| virtual void visit(class ir_discard * ir) |
| { |
| /* Nothing needs to be done. The ANALYSIS and |
| * DEAD_CODE_ELIMINATION postconditions are already satisfied, |
| * because discard statements are ignored by this optimization |
| * pass. The CONTAINED_JUMPS_LOWERED postcondition is already |
| * satisfied, because discard statements can't contain other |
| * statements. |
| */ |
| (void) 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 |
| lower = this->function.lower_return; |
| break; |
| } |
| return lower; |
| } |
| |
| block_record visit_block(exec_list* list) |
| { |
| /* Note: since visiting a node may change that node's next |
| * pointer, we can't use visit_exec_list(), because |
| * visit_exec_list() caches the node's next pointer before |
| * visiting it. So we use foreach_list() instead. |
| * |
| * foreach_list() isn't safe if the node being visited gets |
| * removed, but fortunately this visitor doesn't do that. |
| */ |
| |
| block_record saved_block = this->block; |
| this->block = block_record(); |
| foreach_list(node, list) { |
| ((ir_instruction *) node)->accept(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]; |
| |
| /* Recursively lower nested jumps. This satisfies the |
| * CONTAINED_JUMPS_LOWERED postcondition, except in the case of |
| * unconditional jumps at the end of ir->then_instructions and |
| * ir->else_instructions, which are handled below. |
| */ |
| 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 */ |
| |
| /* Determine which of ir->then_instructions and |
| * ir->else_instructions end with an unconditional jump. |
| */ |
| 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(); |
| } |
| |
| /* Loop until we have satisfied the CONTAINED_JUMPS_LOWERED |
| * postcondition by lowering jumps in both then_instructions and |
| * else_instructions. |
| */ |
| for(;;) { |
| /* Determine the types of the jumps that terminate |
| * ir->then_instructions and ir->else_instructions. |
| */ |
| 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; |
| } |
| |
| /* If both code paths end in a jump, and the jumps are the |
| * same, and we are pulling out jumps, replace them with a |
| * single jump that comes after the if instruction. The new |
| * jump will be visited next, and it will be lowered if |
| * necessary by the loop or conditional that encloses it. |
| */ |
| 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; |
| |
| /* Update jumps[] to reflect the fact that the jumps |
| * are gone, and update block_records[] to reflect the |
| * fact that control can now flow to the next |
| * instruction. |
| */ |
| jumps[0] = 0; |
| jumps[1] = 0; |
| block_records[0].min_strength = strength_none; |
| block_records[1].min_strength = strength_none; |
| |
| /* The CONTAINED_JUMPS_LOWERED postcondition is now |
| * satisfied, so we can break out of the loop. |
| */ |
| 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 |
| /* Neither code path ends in a jump that needs to be |
| * lowered, so the CONTAINED_JUMPS_LOWERED postcondition |
| * is satisfied and we can break out of the loop. |
| */ |
| break; |
| |
| if(jump_strengths[lower] == strength_return) { |
| /* To lower a return, we create a return flag (if the |
| * function doesn't have one already) and add instructions |
| * that: 1. store the return value (if this function has a |
| * non-void return) and 2. set the return flag |
| */ |
| insert_lowered_return((ir_return*)jumps[lower]); |
| if(this->loop.loop) { |
| /* If we are in a loop, replace the return instruction |
| * with a break instruction, and then loop so that the |
| * break instruction can be lowered if necessary. |
| */ |
| ir_loop_jump* lowered = 0; |
| lowered = new(ir) ir_loop_jump(ir_loop_jump::jump_break); |
| /* Note: we must update block_records and jumps to |
| * reflect the fact that the control path has been |
| * altered from a return to a break. |
| */ |
| block_records[lower].min_strength = strength_break; |
| jumps[lower]->replace_with(lowered); |
| jumps[lower] = lowered; |
| } else { |
| /* If we are not in a loop, we then proceed as we would |
| * for a continue statement (set the execute flag to |
| * false to prevent the rest of the function from |
| * executing). |
| */ |
| goto lower_continue; |
| } |
| this->progress = true; |
| } else if(jump_strengths[lower] == strength_break) { |
| /* To lower a break, we create a break flag (if the loop |
| * doesn't have one already) and add an instruction that |
| * sets it. |
| * |
| * Then we proceed as we would for a continue statement |
| * (set the execute flag to false to prevent the rest of |
| * the loop body from executing). |
| * |
| * The visit() function for the loop will ensure that the |
| * break flag is checked after executing the loop body. |
| */ |
| jumps[lower]->insert_before(create_lowered_break()); |
| goto lower_continue; |
| } else if(jump_strengths[lower] == strength_continue) { |
| lower_continue: |
| /* To lower a continue, we create an execute flag (if the |
| * loop doesn't have one already) and replace the continue |
| * with an instruction that clears it. |
| * |
| * Note that this code path gets exercised when lowering |
| * return statements that are not inside a loop, so |
| * this->loop must be initialized even outside of loops. |
| */ |
| 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)); |
| /* Note: we must update block_records and jumps to reflect |
| * the fact that the control path has been altered to an |
| * instruction that clears the execute flag. |
| */ |
| jumps[lower] = 0; |
| block_records[lower].min_strength = strength_always_clears_execute_flag; |
| block_records[lower].may_clear_execute_flag = true; |
| this->progress = true; |
| |
| /* Let the loop run again, in case the other branch of the |
| * if needs to be lowered too. |
| */ |
| } |
| } |
| |
| /* move out a jump out if possible */ |
| if(pull_out_jumps) { |
| /* If one of the branches ends in a jump, and control cannot |
| * fall out the bottom of the other branch, then we can move |
| * the jump after the if. |
| * |
| * Set move_out to the branch we are moving a jump out of. |
| */ |
| 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]); |
| /* Note: we must update block_records and jumps to reflect |
| * the fact that the jump has been moved out of the if. |
| */ |
| jumps[move_out] = 0; |
| block_records[move_out].min_strength = strength_none; |
| this->progress = true; |
| } |
| } |
| |
| /* Now satisfy the ANALYSIS postcondition by setting |
| * this->block.min_strength and |
| * this->block.may_clear_execute_flag based on the |
| * characteristics of the two branches. |
| */ |
| 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; |
| |
| /* Now we need to clean up the instructions that follow the |
| * if. |
| * |
| * If those instructions are unreachable, then satisfy the |
| * DEAD_CODE_ELIMINATION postcondition by eliminating them. |
| * Otherwise that postcondition is already satisfied. |
| */ |
| if(this->block.min_strength) |
| truncate_after_instruction(ir); |
| else if(this->block.may_clear_execute_flag) |
| { |
| /* If the "if" instruction might clear the execute flag, then |
| * we need to guard any instructions that follow so that they |
| * are only executed if the execute flag is set. |
| * |
| * If one of the branches of the "if" always clears the |
| * execute flag, and the other branch never clears it, then |
| * this is easy: just move all the instructions following the |
| * "if" into the branch that never clears it. |
| */ |
| 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); |
| |
| /* If any instructions moved, then we need to visit |
| * them (since they are now inside the "if"). Since |
| * block_records[move_into] is in its default state |
| * (see assertion above), we can safely replace |
| * block_records[move_into] with the result of this |
| * analysis. |
| */ |
| exec_list list; |
| list.head = next; |
| block_records[move_into] = visit_block(&list); |
| |
| /* |
| * Then we need to re-start our jump lowering, since one |
| * of the instructions we moved might be a jump that |
| * needs to be lowered. |
| */ |
| this->progress = true; |
| goto retry; |
| } |
| } else { |
| /* If we get here, then the simple case didn't apply; we |
| * need to actually guard the instructions that follow. |
| * |
| * To avoid creating unnecessarily-deep nesting, first |
| * look through the instructions that follow and unwrap |
| * any instructions that that are already wrapped in the |
| * appropriate guard. |
| */ |
| 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; |
| } |
| |
| /* Then, wrap all the instructions that follow in a single |
| * guard. |
| */ |
| 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) |
| { |
| /* Visit the body of the loop, with a fresh data structure in |
| * this->loop so that the analysis we do here won't bleed into |
| * enclosing loops. |
| * |
| * We assume that all code after a loop is reachable from the |
| * loop (see comments on enum jump_strength), so the |
| * DEAD_CODE_ELIMINATION postcondition is automatically |
| * satisfied, as is the block.min_strength portion of the |
| * ANALYSIS postcondition. |
| * |
| * The block.may_clear_execute_flag portion of the ANALYSIS |
| * postcondition is automatically satisfied because execute |
| * flags do not propagate outside of loops. |
| * |
| * The loop.may_set_return_flag portion of the ANALYSIS |
| * postcondition is handled below. |
| */ |
| ++this->function.nesting_depth; |
| loop_record saved_loop = this->loop; |
| this->loop = loop_record(this->function.signature, ir); |
| |
| /* Recursively lower nested jumps. This satisfies the |
| * CONTAINED_JUMPS_LOWERED postcondition, except in the case of |
| * an unconditional continue or return at the bottom of the |
| * loop, which are handled below. |
| */ |
| block_record body = visit_block(&ir->body_instructions); |
| |
| /* If the loop ends in an unconditional continue, eliminate it |
| * because it is redundant. |
| */ |
| ir_instruction *ir_last |
| = (ir_instruction *) ir->body_instructions.get_tail(); |
| if (get_jump_strength(ir_last) == strength_continue) { |
| ir_last->remove(); |
| } |
| |
| /* If the loop ends in an unconditional return, and we are |
| * lowering returns, lower it. |
| */ |
| if (this->function.lower_return) |
| lower_return_unconditionally(ir_last); |
| |
| if(body.min_strength >= strength_break) { |
| /* FINISHME: If the min_strength of the loop body is |
| * strength_break or strength_return, that means that it |
| * isn't a loop at all, since control flow always leaves the |
| * body of the loop via break or return. In principle the |
| * loop could be eliminated in this case. This optimization |
| * is not implemented yet. |
| */ |
| } |
| |
| if(this->loop.break_flag) { |
| /* We only get here if we are lowering breaks */ |
| assert (lower_break); |
| |
| /* If a break flag was generated while visiting the body of |
| * the loop, then at least one break was lowered, so we need |
| * to generate an if statement at the end of the loop that |
| * does a "break" if the break flag is set. The break we |
| * generate won't violate the CONTAINED_JUMPS_LOWERED |
| * postcondition, because should_lower_jump() always returns |
| * false for a break that happens at the end of a loop. |
| * |
| * However, if the loop already ends in a conditional or |
| * unconditional break, then we need to lower that break, |
| * because it won't be at the end of the loop anymore. |
| */ |
| lower_final_breaks(&ir->body_instructions); |
| |
| 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 the body of the loop may set the return flag, then at |
| * least one return was lowered to a break, so we need to ensure |
| * that the return flag is checked after the body of the loop is |
| * executed. |
| */ |
| if(this->loop.may_set_return_flag) { |
| assert(this->function.return_flag); |
| /* Generate the if statement to check the return flag */ |
| ir_if* return_if = new(ir) ir_if(new(ir) ir_dereference_variable(this->function.return_flag)); |
| /* Note: we also need to propagate the knowledge that the |
| * return flag may get set to the outer context. This |
| * satisfies the loop.may_set_return_flag part of the |
| * ANALYSIS postcondition. |
| */ |
| saved_loop.may_set_return_flag = true; |
| if(saved_loop.loop) |
| /* If this loop is nested inside another one, then the if |
| * statement that we generated should break out of that |
| * loop if the return flag is set. Caller will lower that |
| * break statement if necessary. |
| */ |
| return_if->then_instructions.push_tail(new(ir) ir_loop_jump(ir_loop_jump::jump_break)); |
| else |
| /* Otherwise, all we need to do is ensure that the |
| * instructions that follow are only executed if the |
| * return flag is clear. We can do that by moving those |
| * instructions into the else clause of the generated if |
| * statement. |
| */ |
| 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); |
| |
| bool lower_return; |
| if (strcmp(ir->function_name(), "main") == 0) |
| lower_return = lower_main_return; |
| else |
| lower_return = lower_sub_return; |
| |
| function_record saved_function = this->function; |
| loop_record saved_loop = this->loop; |
| this->function = function_record(ir, lower_return); |
| this->loop = loop_record(ir); |
| |
| assert(!this->loop.loop); |
| |
| /* Visit the body of the function to lower any jumps that occur |
| * in it, except possibly an unconditional return statement at |
| * the end of it. |
| */ |
| visit_block(&ir->body); |
| |
| /* If the body ended in an unconditional return of non-void, |
| * then we don't need to lower it because it's the one canonical |
| * return. |
| * |
| * If the body ended in a return of void, eliminate it because |
| * it is redundant. |
| */ |
| if (ir->return_type->is_void() && |
| get_jump_strength((ir_instruction *) ir->body.get_tail())) { |
| ir_jump *jump = (ir_jump *) ir->body.get_tail(); |
| assert (jump->ir_type == ir_type_return); |
| jump->remove(); |
| } |
| |
| 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; |
| } |
