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use crate::{
item_id::ItemId,
llir_nodes::{
BinaryOperation, Branch, Call, Condition, ExecuteRaw, ExecuteRawComponent, FastStore,
FastStoreFromResult, Node, VariableAccess,
},
minecraft_utils::{ScoreboardComparison, ScoreboardOperation, ScoreboardValue},
opt::{
global_opt::{Commands, GlobalOptimizer, Optimizer},
optimize_commands::{ExecuteRawUpdate, OptimizeCommand, OptimizeCommandKind},
NodeId,
},
};
/// Removes useless nodes
///
/// # Optimizations:
/// - Removes assignments to variables that are never read
/// - If a value a is copied to value b and value a is assigned directly before, remove assign directly to b
/// - If a value is copied but the original value could be used, the copy gets removed
/// - If a branch's condition in-directs to another condition, inline that other condition (right now only checks the previous node)
/// - If both branches of a branch end up at the same next node, add one goto after the branch
/// - Removes function calls to functions which are empty
#[derive(Default)]
pub struct RedundancyOptimizer {
pub aggressive_function_inlining: bool,
}
impl Optimizer for RedundancyOptimizer {
fn optimize(&mut self, commands: &mut Commands) {
use OptimizeCommandKind::*;
for (node_id, node) in commands.optimizer.iter_nodes() {
match node {
Node::Nop => commands
.commands
.push(OptimizeCommand::new(node_id, Delete)),
// Copies to itself (`a = a`) are useless and can be removed.
Node::FastStore(FastStore {
id: target,
value: ScoreboardValue::Scoreboard(rhs_value),
}) if target == rhs_value => {
commands
.commands
.push(OptimizeCommand::new(node_id, Delete));
}
// Matches a write that is never read
Node::FastStore(FastStore { id, .. }) if commands.is_id_unused(*id, node_id) => {
commands
.commands
.push(OptimizeCommand::new(node_id, Delete));
}
Node::FastStoreFromResult(FastStoreFromResult { id, command, .. })
if commands.is_id_unused(*id, node_id) =>
{
if command.is_effect_free(&commands.optimizer.functions) {
commands
.commands
.push(OptimizeCommand::new(node_id, Delete));
} else {
commands
.commands
.push(OptimizeCommand::new(node_id, DiscardResult));
}
}
Node::BinaryOperation(BinaryOperation {
id,
lhs: _,
rhs: _,
operation: _,
}) if commands.is_id_unused(*id, node_id) => {
commands
.commands
.push(OptimizeCommand::new(node_id, Delete));
}
// Checks if a variable is written to and then being overwritten in the same function,
// without being read first
Node::FastStore(FastStore { id, value: _ })
if write_after_write(commands.optimizer, *id, node_id) =>
{
commands
.commands
.push(OptimizeCommand::new(node_id, Delete));
}
Node::FastStoreFromResult(FastStoreFromResult { id, command })
if write_after_write(commands.optimizer, *id, node_id) =>
{
if command.is_effect_free(&commands.optimizer.functions) {
commands
.commands
.push(OptimizeCommand::new(node_id, Delete));
} else {
commands
.commands
.push(OptimizeCommand::new(node_id, DiscardResult));
}
}
// Checks if a variable y gets copied to variable x and changes all writes to y to write to x instead if
// y is only read here
Node::FastStore(FastStore {
id,
value: ScoreboardValue::Scoreboard(copy_from),
}) if commands.get_info(*copy_from).reads == 1 => {
// Now delete this assignment and update all writes to `copy_from`
commands
.commands
.push(OptimizeCommand::new(node_id, Delete));
for (other_node_id, other_node) in commands.optimizer.iter_nodes() {
if other_node.writes_to(*copy_from) {
commands
.commands
.push(OptimizeCommand::new(other_node_id, ChangeWrite(*id)));
}
}
// This optimization modifies commands other than the current one,
// So to avoid inconsistency, return here
return;
}
Node::FastStoreFromResult(FastStoreFromResult { id, command }) => {
if let Node::Condition(condition) = &**command {
if let Some(simplified_condition) = simplify_condition(condition) {
let id = *id;
match simplified_condition {
SimplifiedCondition::False | SimplifiedCondition::True => {
let value = i32::from(matches!(
simplified_condition,
SimplifiedCondition::True
));
commands.commands.push(OptimizeCommand::new(
node_id,
Replace(Node::FastStore(FastStore {
id,
value: ScoreboardValue::Static(value),
})),
));
}
SimplifiedCondition::NewCondition(condition) => {
commands.commands.push(OptimizeCommand::new(
node_id,
Replace(Node::FastStoreFromResult(FastStoreFromResult {
command: Box::new(Node::Condition(condition)),
id,
})),
));
}
}
} else if let Some((_, prev_node)) =
commands.optimizer.previous_node(&node_id)
{
if let Some((index, updated_condition)) =
merge_condition(prev_node, condition)
{
commands.commands.push(OptimizeCommand::new(
node_id,
SetCondition(updated_condition, index),
));
}
}
}
}
// If the operation is commutative, move the static value to the right side.
// This makes better consistency and is easier to implement in minecraft.
Node::BinaryOperation(BinaryOperation {
id,
lhs: ScoreboardValue::Static(value),
rhs: ScoreboardValue::Scoreboard(rhs_id),
operation: operation @ (ScoreboardOperation::Plus | ScoreboardOperation::Times),
}) => {
commands.commands.push(OptimizeCommand::new(
node_id,
Replace(Node::BinaryOperation(BinaryOperation {
id: *id,
lhs: ScoreboardValue::Scoreboard(*rhs_id),
rhs: ScoreboardValue::Static(*value),
operation: *operation,
})),
));
}
// Useless math operation (a + 0, a - 0)
Node::BinaryOperation(BinaryOperation {
id,
lhs,
rhs: ScoreboardValue::Static(0),
operation: ScoreboardOperation::Plus | ScoreboardOperation::Minus,
}) => {
commands.commands.push(OptimizeCommand::new(
node_id,
Replace(Node::FastStore(FastStore {
id: *id,
value: *lhs,
})),
));
}
// Useless math operation (a * 1, a / 1, a % 1)
Node::BinaryOperation(BinaryOperation {
id,
lhs,
rhs: ScoreboardValue::Static(value @ 0..=1),
operation:
ScoreboardOperation::Times
| ScoreboardOperation::Divide
| ScoreboardOperation::Modulo,
}) => {
let kind = match value {
0 => OptimizeCommandKind::Replace(Node::FastStore(FastStore {
id: *id,
value: ScoreboardValue::Static(0),
})),
1 => OptimizeCommandKind::Replace(Node::FastStore(FastStore {
id: *id,
value: *lhs,
})),
_ => unreachable!(),
};
commands.commands.push(OptimizeCommand::new(node_id, kind));
}
// `let b = a - a` => `let b = 0`
Node::BinaryOperation(BinaryOperation {
id,
lhs: ScoreboardValue::Scoreboard(lhs),
rhs: ScoreboardValue::Scoreboard(rhs),
operation: ScoreboardOperation::Minus,
}) if lhs == rhs => {
commands.commands.push(OptimizeCommand::new(
node_id,
OptimizeCommandKind::Replace(Node::FastStore(FastStore {
id: *id,
value: ScoreboardValue::Static(0),
})),
));
}
// `let b = a / a` => `let b = 1`
Node::BinaryOperation(BinaryOperation {
id,
lhs: ScoreboardValue::Scoreboard(lhs),
rhs: ScoreboardValue::Scoreboard(rhs),
operation: ScoreboardOperation::Divide,
}) if lhs == rhs => {
commands.commands.push(OptimizeCommand::new(
node_id,
OptimizeCommandKind::Replace(Node::FastStore(FastStore {
id: *id,
value: ScoreboardValue::Static(1),
})),
));
}
&Node::Call(Call { id }) => {
let function = commands.optimizer.get_function(id);
if function.is_empty() {
commands
.commands
.push(OptimizeCommand::new(node_id, Delete));
} else {
// If the called function is only called from here, the function may be inlined.
// Additionally, the function may be inlined, if it is not directly recursive,
// and does not call the calling function
let calls_no_function = || {
commands
.stats
.call_graph
.get_called_functions(id)
.next()
.is_none()
};
if commands.get_call_count(id) == 1
|| calls_no_function()
|| (self.aggressive_function_inlining
&& !function.calls_function(&node_id.0)
&& !commands
.infinite_loop_detector
.detect_infinite_loop(&commands.optimizer.functions, id))
{
commands
.commands
.push(OptimizeCommand::new(node_id, InlineFunction));
// This command modifies a lot of nodes, so return here to not destroy the internal state.
return;
}
}
}
Node::Execute(ExecuteRaw(components)) => {
for (index, component) in components.iter().enumerate() {
if let &ExecuteRawComponent::Node(Node::Call(Call { id })) = component {
let function = commands.optimizer.get_function(id);
if function.is_empty() {
commands.commands.push(OptimizeCommand::new(
node_id,
UpdateExecuteRaw(index, ExecuteRawUpdate::Delete),
));
break;
}
let calls_no_function = || {
commands
.stats
.call_graph
.get_called_functions(id)
.next()
.is_none()
};
let has_single_node = function.nodes.len() == 1;
if has_single_node
&& (commands.get_call_count(id) == 1 || calls_no_function())
{
let node = function.nodes()[0].clone();
commands.commands.push(OptimizeCommand::new(
node_id,
UpdateExecuteRaw(index, ExecuteRawUpdate::Replace(node)),
));
break;
}
}
}
}
// If the branch does the same thing in both cases - remove it
Node::Branch(branch) if *branch.pos_branch == *branch.neg_branch => {
let new_command = branch.pos_branch.as_ref().clone();
if branch.condition.is_effect_free() {
commands
.commands
.push(OptimizeCommand::new(node_id, Replace(new_command)));
} else {
commands
.commands
.push(OptimizeCommand::new(node_id, InsertAfter(new_command)));
commands.commands.push(OptimizeCommand::new(
node_id,
Replace(Node::Condition(branch.condition.clone())),
));
}
}
// Checks if the branch depends on a condition that was just calculated
// ToDo: Instead of only checking the last condition, check as long as the condition is valid
Node::Branch(Branch {
condition,
pos_branch,
neg_branch,
}) => {
let mut could_optimize = false;
// first try to run some trivial optimizations on the condition
if let Some(new_condition) = simplify_condition(condition) {
match new_condition {
SimplifiedCondition::False | SimplifiedCondition::True => {
let inlined_branch =
matches!(new_condition, SimplifiedCondition::True);
commands.commands.push(OptimizeCommand::new(
node_id,
InlineBranch(inlined_branch),
));
}
SimplifiedCondition::NewCondition(condition) => {
commands.commands.push(OptimizeCommand::new(
node_id,
UpdateBranchCondition(condition),
));
}
}
return;
}
if let Some((prev_id, prev_node)) = commands.optimizer.previous_node(&node_id) {
if let Some((result_index, condition)) =
merge_condition(prev_node, condition)
{
commands
.commands
.push(OptimizeCommand::new(prev_id, Delete));
commands.commands.push(OptimizeCommand::new(
node_id,
SetCondition(condition, result_index),
));
could_optimize = true;
}
}
// Otherwise check if one of the branches is a nop or a single command
if !could_optimize {
for (branch, flag) in [(&**pos_branch, true), (&**neg_branch, false)] {
if let &Node::Call(Call { id }) = branch {
let function = commands.optimizer.get_function(id);
match function.nodes() {
[] => commands.commands.push(OptimizeCommand::new(
node_id,
UpdateBranch {
branch: flag,
new_node: Node::Nop,
},
)),
[single] => commands.commands.push(OptimizeCommand::new(
node_id,
UpdateBranch {
branch: flag,
new_node: single.clone(),
},
)),
_ => {}
}
}
}
}
}
_ => (),
}
}
}
}
enum SimplifiedCondition {
True,
False,
NewCondition(Condition),
}
impl From<bool> for SimplifiedCondition {
fn from(val: bool) -> Self {
match val {
true => SimplifiedCondition::True,
false => SimplifiedCondition::False,
}
}
}
/// Simplifies trivial conditions
fn simplify_condition(condition: &Condition) -> Option<SimplifiedCondition> {
match condition {
&Condition::Compare {
comparison,
lhs: ScoreboardValue::Static(lhs_val),
rhs: ScoreboardValue::Static(rhs_val),
} => Some(comparison.evaluate(lhs_val, rhs_val).into()),
Condition::Compare { .. } => None,
Condition::And(parts) | Condition::Or(parts) => {
let is_and = matches!(condition, Condition::And(_));
let mut new_parts = parts.clone();
let mut anything_changed = false;
for (index, part) in parts.iter().enumerate().rev() {
match simplify_condition(part) {
None => {}
Some(simplified_cond) => {
anything_changed = true;
if is_and && matches!(simplified_cond, SimplifiedCondition::False)
|| !is_and && matches!(simplified_cond, SimplifiedCondition::True)
{
return Some(simplified_cond);
}
match simplified_cond {
SimplifiedCondition::False | SimplifiedCondition::True => {
new_parts.remove(index);
}
SimplifiedCondition::NewCondition(condition) => {
new_parts[index] = condition;
}
}
}
}
}
if !anything_changed {
return None;
}
if new_parts.is_empty() {
return Some(if is_and {
SimplifiedCondition::True
} else {
SimplifiedCondition::False
});
}
if new_parts.len() == 1 {
return Some(SimplifiedCondition::NewCondition(
new_parts.into_iter().next().unwrap(),
));
}
match is_and {
true => Some(SimplifiedCondition::NewCondition(Condition::And(new_parts))),
false => Some(SimplifiedCondition::NewCondition(Condition::Or(new_parts))),
}
}
}
}
/// Tries to merge the condition and the previous node into one node
/// eg: `a := b > c; d := a == 1 => d := b > c`
fn merge_condition(prev_node: &Node, condition: &Condition) -> Option<(Vec<usize>, Condition)> {
match condition {
Condition::Compare {
comparison: ScoreboardComparison::Equal,
lhs: ScoreboardValue::Scoreboard(id),
rhs: ScoreboardValue::Static(1),
}
| Condition::Compare {
comparison: ScoreboardComparison::NotEqual,
lhs: ScoreboardValue::Scoreboard(id),
rhs: ScoreboardValue::Static(0),
} => {
if let Node::FastStoreFromResult(FastStoreFromResult {
id: cond_id,
command,
}) = prev_node
{
if id == cond_id {
if let Node::Condition(condition) = &**command {
return Some((vec![], condition.clone()));
}
}
}
}
Condition::Compare {
comparison: ScoreboardComparison::Equal,
lhs: ScoreboardValue::Scoreboard(id),
rhs: ScoreboardValue::Static(0),
}
| Condition::Compare {
comparison: ScoreboardComparison::NotEqual,
lhs: ScoreboardValue::Scoreboard(id),
rhs: ScoreboardValue::Static(1),
} => {
if let Node::FastStoreFromResult(FastStoreFromResult {
id: cond_id,
command,
}) = prev_node
{
if id == cond_id {
if let Node::Condition(condition) = &**command {
return Some((vec![], condition.not()));
}
}
}
}
Condition::Or(values) | Condition::And(values) => {
for (index, inner_condition) in values.iter().enumerate() {
if let Some((mut result_index, condition)) =
merge_condition(prev_node, inner_condition)
{
result_index.push(index);
return Some((result_index, condition));
}
}
}
Condition::Compare { .. } => (),
}
None
}
/// Checks for a write to `id` after `node` and returns with false
/// If it is read before a write.
/// Also returns false if no further write in this branch exists
fn write_after_write(optimizer: &GlobalOptimizer, id: ItemId, node: NodeId) -> bool {
for (_, other_node) in optimizer.iter_at(&node) {
let mut branches = false;
other_node.scan(&mut |node| {
if matches!(node, Node::Branch(_) | Node::Call(_)) {
branches = true;
}
});
if branches {
return false;
}
let mut writes_id = false;
let mut reads_id = false;
other_node.variable_accesses(&mut |access| match access {
VariableAccess::Read(ScoreboardValue::Scoreboard(target_id))
| VariableAccess::ReadWrite(ScoreboardValue::Scoreboard(target_id))
if target_id == &id =>
{
reads_id = true;
}
VariableAccess::Write(target_id, _) if target_id == &id => {
writes_id = true;
}
_ => {}
});
if reads_id {
return false;
}
if writes_id {
return true;
}
}
false
}