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Diffstat (limited to 'src/compiler/glsl/opt_constant_propagation.cpp')
| -rw-r--r-- | src/compiler/glsl/opt_constant_propagation.cpp | 524 |
1 files changed, 524 insertions, 0 deletions
diff --git a/src/compiler/glsl/opt_constant_propagation.cpp b/src/compiler/glsl/opt_constant_propagation.cpp new file mode 100644 index 0000000000..416ba16a3c --- /dev/null +++ b/src/compiler/glsl/opt_constant_propagation.cpp @@ -0,0 +1,524 @@ +/* + * Copyright © 2010 Intel Corporation + * + * Permission is hereby granted, free of charge, to any person obtaining a + * constant of this software and associated documentation files (the "Software"), + * to deal in the Software without restriction, including without limitation + * the rights to use, constant, 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 constantright 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 CONSTANTRIGHT 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 opt_constant_propagation.cpp + * + * Tracks assignments of constants to channels of variables, and + * usage of those constant channels with direct usage of the constants. + * + * This can lead to constant folding and algebraic optimizations in + * those later expressions, while causing no increase in instruction + * count (due to constants being generally free to load from a + * constant push buffer or as instruction immediate values) and + * possibly reducing register pressure. + */ + +#include "ir.h" +#include "ir_visitor.h" +#include "ir_rvalue_visitor.h" +#include "ir_basic_block.h" +#include "ir_optimization.h" +#include "compiler/glsl_types.h" +#include "util/hash_table.h" + +namespace { + +class acp_entry : public exec_node +{ +public: + acp_entry(ir_variable *var, unsigned write_mask, ir_constant *constant) + { + assert(var); + assert(constant); + this->var = var; + this->write_mask = write_mask; + this->constant = constant; + this->initial_values = write_mask; + } + + acp_entry(const acp_entry *src) + { + this->var = src->var; + this->write_mask = src->write_mask; + this->constant = src->constant; + this->initial_values = src->initial_values; + } + + ir_variable *var; + ir_constant *constant; + unsigned write_mask; + + /** Mask of values initially available in the constant. */ + unsigned initial_values; +}; + + +class kill_entry : public exec_node +{ +public: + kill_entry(ir_variable *var, unsigned write_mask) + { + assert(var); + this->var = var; + this->write_mask = write_mask; + } + + ir_variable *var; + unsigned write_mask; +}; + +class ir_constant_propagation_visitor : public ir_rvalue_visitor { +public: + ir_constant_propagation_visitor() + { + progress = false; + killed_all = false; + mem_ctx = ralloc_context(0); + this->acp = new(mem_ctx) exec_list; + this->kills = _mesa_hash_table_create(mem_ctx, _mesa_hash_pointer, + _mesa_key_pointer_equal); + } + ~ir_constant_propagation_visitor() + { + ralloc_free(mem_ctx); + } + + virtual ir_visitor_status visit_enter(class ir_loop *); + virtual ir_visitor_status visit_enter(class ir_function_signature *); + virtual ir_visitor_status visit_enter(class ir_function *); + virtual ir_visitor_status visit_leave(class ir_assignment *); + virtual ir_visitor_status visit_enter(class ir_call *); + virtual ir_visitor_status visit_enter(class ir_if *); + + void add_constant(ir_assignment *ir); + void constant_folding(ir_rvalue **rvalue); + void constant_propagation(ir_rvalue **rvalue); + void kill(ir_variable *ir, unsigned write_mask); + void handle_if_block(exec_list *instructions); + void handle_rvalue(ir_rvalue **rvalue); + + /** List of acp_entry: The available constants to propagate */ + exec_list *acp; + + /** + * List of kill_entry: The masks of variables whose values were + * killed in this block. + */ + hash_table *kills; + + bool progress; + + bool killed_all; + + void *mem_ctx; +}; + + +void +ir_constant_propagation_visitor::constant_folding(ir_rvalue **rvalue) { + + if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant) + return; + + /* Note that we visit rvalues one leaving. So if an expression has a + * non-constant operand, no need to go looking down it to find if it's + * constant. This cuts the time of this pass down drastically. + */ + ir_expression *expr = (*rvalue)->as_expression(); + if (expr) { + for (unsigned int i = 0; i < expr->get_num_operands(); i++) { + if (!expr->operands[i]->as_constant()) + return; + } + } + + /* Ditto for swizzles. */ + ir_swizzle *swiz = (*rvalue)->as_swizzle(); + if (swiz && !swiz->val->as_constant()) + return; + + ir_constant *constant = (*rvalue)->constant_expression_value(); + if (constant) { + *rvalue = constant; + this->progress = true; + } +} + +void +ir_constant_propagation_visitor::constant_propagation(ir_rvalue **rvalue) { + + if (this->in_assignee || !*rvalue) + return; + + const glsl_type *type = (*rvalue)->type; + if (!type->is_scalar() && !type->is_vector()) + return; + + ir_swizzle *swiz = NULL; + ir_dereference_variable *deref = (*rvalue)->as_dereference_variable(); + if (!deref) { + swiz = (*rvalue)->as_swizzle(); + if (!swiz) + return; + + deref = swiz->val->as_dereference_variable(); + if (!deref) + return; + } + + ir_constant_data data; + memset(&data, 0, sizeof(data)); + + for (unsigned int i = 0; i < type->components(); i++) { + int channel; + acp_entry *found = NULL; + + if (swiz) { + switch (i) { + case 0: channel = swiz->mask.x; break; + case 1: channel = swiz->mask.y; break; + case 2: channel = swiz->mask.z; break; + case 3: channel = swiz->mask.w; break; + default: assert(!"shouldn't be reached"); channel = 0; break; + } + } else { + channel = i; + } + + foreach_in_list(acp_entry, entry, this->acp) { + if (entry->var == deref->var && entry->write_mask & (1 << channel)) { + found = entry; + break; + } + } + + if (!found) + return; + + int rhs_channel = 0; + for (int j = 0; j < 4; j++) { + if (j == channel) + break; + if (found->initial_values & (1 << j)) + rhs_channel++; + } + + switch (type->base_type) { + case GLSL_TYPE_FLOAT: + data.f[i] = found->constant->value.f[rhs_channel]; + break; + case GLSL_TYPE_DOUBLE: + data.d[i] = found->constant->value.d[rhs_channel]; + break; + case GLSL_TYPE_INT: + data.i[i] = found->constant->value.i[rhs_channel]; + break; + case GLSL_TYPE_UINT: + data.u[i] = found->constant->value.u[rhs_channel]; + break; + case GLSL_TYPE_BOOL: + data.b[i] = found->constant->value.b[rhs_channel]; + break; + default: + assert(!"not reached"); + break; + } + } + + *rvalue = new(ralloc_parent(deref)) ir_constant(type, &data); + this->progress = true; +} + +void +ir_constant_propagation_visitor::handle_rvalue(ir_rvalue **rvalue) +{ + constant_propagation(rvalue); + constant_folding(rvalue); +} + +ir_visitor_status +ir_constant_propagation_visitor::visit_enter(ir_function_signature *ir) +{ + /* Treat entry into a function signature as a completely separate + * block. Any instructions at global scope will be shuffled into + * main() at link time, so they're irrelevant to us. + */ + exec_list *orig_acp = this->acp; + hash_table *orig_kills = this->kills; + bool orig_killed_all = this->killed_all; + + this->acp = new(mem_ctx) exec_list; + this->kills = _mesa_hash_table_create(mem_ctx, _mesa_hash_pointer, + _mesa_key_pointer_equal); + this->killed_all = false; + + visit_list_elements(this, &ir->body); + + this->kills = orig_kills; + this->acp = orig_acp; + this->killed_all = orig_killed_all; + + return visit_continue_with_parent; +} + +ir_visitor_status +ir_constant_propagation_visitor::visit_leave(ir_assignment *ir) +{ + constant_folding(&ir->rhs); + + if (this->in_assignee) + return visit_continue; + + unsigned kill_mask = ir->write_mask; + if (ir->lhs->as_dereference_array()) { + /* The LHS of the assignment uses an array indexing operator (e.g. v[i] + * = ...;). Since we only try to constant propagate vectors and + * scalars, this means that either (a) array indexing is being used to + * select a vector component, or (b) the variable in question is neither + * a scalar or a vector, so we don't care about it. In the former case, + * we want to kill the whole vector, since in general we can't predict + * which vector component will be selected by array indexing. In the + * latter case, it doesn't matter what we do, so go ahead and kill the + * whole variable anyway. + * + * Note that if the array index is constant (e.g. v[2] = ...;), we could + * in principle be smarter, but we don't need to, because a future + * optimization pass will convert it to a simple assignment with the + * correct mask. + */ + kill_mask = ~0; + } + kill(ir->lhs->variable_referenced(), kill_mask); + + add_constant(ir); + + return visit_continue; +} + +ir_visitor_status +ir_constant_propagation_visitor::visit_enter(ir_function *ir) +{ + (void) ir; + return visit_continue; +} + +ir_visitor_status +ir_constant_propagation_visitor::visit_enter(ir_call *ir) +{ + /* Do constant propagation on call parameters, but skip any out params */ + foreach_two_lists(formal_node, &ir->callee->parameters, + actual_node, &ir->actual_parameters) { + ir_variable *sig_param = (ir_variable *) formal_node; + ir_rvalue *param = (ir_rvalue *) actual_node; + if (sig_param->data.mode != ir_var_function_out + && sig_param->data.mode != ir_var_function_inout) { + ir_rvalue *new_param = param; + handle_rvalue(&new_param); + if (new_param != param) + param->replace_with(new_param); + else + param->accept(this); + } + } + + /* Since we're unlinked, we don't (necssarily) know the side effects of + * this call. So kill all copies. + */ + acp->make_empty(); + this->killed_all = true; + + return visit_continue_with_parent; +} + +void +ir_constant_propagation_visitor::handle_if_block(exec_list *instructions) +{ + exec_list *orig_acp = this->acp; + hash_table *orig_kills = this->kills; + bool orig_killed_all = this->killed_all; + + this->acp = new(mem_ctx) exec_list; + this->kills = _mesa_hash_table_create(mem_ctx, _mesa_hash_pointer, + _mesa_key_pointer_equal); + this->killed_all = false; + + /* Populate the initial acp with a constant of the original */ + foreach_in_list(acp_entry, a, orig_acp) { + this->acp->push_tail(new(this->mem_ctx) acp_entry(a)); + } + + visit_list_elements(this, instructions); + + if (this->killed_all) { + orig_acp->make_empty(); + } + + hash_table *new_kills = this->kills; + this->kills = orig_kills; + this->acp = orig_acp; + this->killed_all = this->killed_all || orig_killed_all; + + hash_entry *htk; + hash_table_foreach(new_kills, htk) { + kill_entry *k = (kill_entry *) htk->data; + kill(k->var, k->write_mask); + } +} + +ir_visitor_status +ir_constant_propagation_visitor::visit_enter(ir_if *ir) +{ + ir->condition->accept(this); + handle_rvalue(&ir->condition); + + handle_if_block(&ir->then_instructions); + handle_if_block(&ir->else_instructions); + + /* handle_if_block() already descended into the children. */ + return visit_continue_with_parent; +} + +ir_visitor_status +ir_constant_propagation_visitor::visit_enter(ir_loop *ir) +{ + exec_list *orig_acp = this->acp; + hash_table *orig_kills = this->kills; + bool orig_killed_all = this->killed_all; + + /* FINISHME: For now, the initial acp for loops is totally empty. + * We could go through once, then go through again with the acp + * cloned minus the killed entries after the first run through. + */ + this->acp = new(mem_ctx) exec_list; + this->kills = _mesa_hash_table_create(mem_ctx, _mesa_hash_pointer, + _mesa_key_pointer_equal); + this->killed_all = false; + + visit_list_elements(this, &ir->body_instructions); + + if (this->killed_all) { + orig_acp->make_empty(); + } + + hash_table *new_kills = this->kills; + this->kills = orig_kills; + this->acp = orig_acp; + this->killed_all = this->killed_all || orig_killed_all; + + hash_entry *htk; + hash_table_foreach(new_kills, htk) { + kill_entry *k = (kill_entry *) htk->data; + kill(k->var, k->write_mask); + } + + /* already descended into the children. */ + return visit_continue_with_parent; +} + +void +ir_constant_propagation_visitor::kill(ir_variable *var, unsigned write_mask) +{ + assert(var != NULL); + + /* We don't track non-vectors. */ + if (!var->type->is_vector() && !var->type->is_scalar()) + return; + + /* Remove any entries currently in the ACP for this kill. */ + foreach_in_list_safe(acp_entry, entry, this->acp) { + if (entry->var == var) { + entry->write_mask &= ~write_mask; + if (entry->write_mask == 0) + entry->remove(); + } + } + + /* Add this writemask of the variable to the list of killed + * variables in this block. + */ + hash_entry *kill_hash_entry = _mesa_hash_table_search(this->kills, var); + if (kill_hash_entry) { + kill_entry *entry = (kill_entry *) kill_hash_entry->data; + entry->write_mask |= write_mask; + return; + } + /* Not already in the list. Make new entry. */ + _mesa_hash_table_insert(this->kills, var, + new(this->mem_ctx) kill_entry(var, write_mask)); +} + +/** + * Adds an entry to the available constant list if it's a plain assignment + * of a variable to a variable. + */ +void +ir_constant_propagation_visitor::add_constant(ir_assignment *ir) +{ + acp_entry *entry; + + if (ir->condition) + return; + + if (!ir->write_mask) + return; + + ir_dereference_variable *deref = ir->lhs->as_dereference_variable(); + ir_constant *constant = ir->rhs->as_constant(); + + if (!deref || !constant) + return; + + /* Only do constant propagation on vectors. Constant matrices, + * arrays, or structures would require more work elsewhere. + */ + if (!deref->var->type->is_vector() && !deref->var->type->is_scalar()) + return; + + /* We can't do copy propagation on buffer variables, since the underlying + * memory storage is shared across multiple threads we can't be sure that + * the variable value isn't modified between this assignment and the next + * instruction where its value is read. + */ + if (deref->var->data.mode == ir_var_shader_storage || + deref->var->data.mode == ir_var_shader_shared) + return; + + entry = new(this->mem_ctx) acp_entry(deref->var, ir->write_mask, constant); + this->acp->push_tail(entry); +} + +} /* unnamed namespace */ + +/** + * Does a constant propagation pass on the code present in the instruction stream. + */ +bool +do_constant_propagation(exec_list *instructions) +{ + ir_constant_propagation_visitor v; + + visit_list_elements(&v, instructions); + + return v.progress; +} |