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use std::mem::take;
use cubecl_ir::{
Arithmetic, BinaryOperator, Bitwise, ElemType, Instruction, Operation, UIntKind, Variable,
};
use crate::{AtomicCounter, Optimizer};
use super::OptimizerPass;
/// Replace expensive operations with less expensive equivalent ones.
/// Example
/// ```rust,ignore
/// let a = x % 16;
/// let b = x / 8;
/// let c = x * 15;
/// ```
/// to
/// ```rust,ignore
/// let a = x & 15;
/// let b = x >> 3;
/// let c = (x << 4) - x;
/// ```
pub struct ReduceStrength;
impl OptimizerPass for ReduceStrength {
fn apply_post_ssa(&mut self, opt: &mut Optimizer, changes: AtomicCounter) {
for block in opt.node_ids() {
let ops = take(&mut *opt.block(block).ops.borrow_mut());
let mut new_ops = Vec::with_capacity(ops.capacity());
for (_, inst) in ops.into_iter() {
let op = match inst.operation.clone() {
Operation::Arithmetic(op) => op,
_ => {
new_ops.push(inst);
continue;
}
};
match op {
Arithmetic::Mul(op)
if inst.ty().elem_type() == ElemType::UInt(UIntKind::U32) =>
{
let (const_val, dyn_val) = match (op.lhs.as_const(), op.rhs.as_const()) {
(None, Some(val)) => (val.as_u32(), op.lhs),
(Some(val), None) => (val.as_u32(), op.rhs),
_ => {
new_ops.push(Instruction::new(Arithmetic::Mul(op), inst.out()));
continue;
}
};
match const_val {
val if val.is_power_of_two() => {
new_ops.push(Instruction::new(
Bitwise::ShiftLeft(BinaryOperator {
lhs: dyn_val,
rhs: val.trailing_zeros().into(),
}),
inst.out(),
));
changes.inc();
}
val if (val + 1).is_power_of_two() => {
let temp = *opt.allocator.create_local(inst.ty());
new_ops.push(Instruction::new(
Bitwise::ShiftLeft(BinaryOperator {
lhs: dyn_val,
rhs: (val + 1).trailing_zeros().into(),
}),
temp,
));
new_ops.push(Instruction::new(
Arithmetic::Sub(BinaryOperator {
lhs: temp,
rhs: dyn_val,
}),
inst.out(),
));
changes.inc();
}
val if (val - 1).is_power_of_two() => {
let temp = *opt.allocator.create_local(inst.ty());
new_ops.push(Instruction::new(
Bitwise::ShiftLeft(BinaryOperator {
lhs: dyn_val,
rhs: (val - 1).trailing_zeros().into(),
}),
temp,
));
new_ops.push(Instruction::new(
Arithmetic::Add(BinaryOperator {
lhs: temp,
rhs: dyn_val,
}),
inst.out(),
));
changes.inc();
}
_ => {
new_ops.push(Instruction::new(Arithmetic::Mul(op), inst.out()));
}
}
}
Arithmetic::Div(op) if is_pow2(op.rhs) => {
let (const_val, dyn_val) = match (op.lhs.as_const(), op.rhs.as_const()) {
(None, Some(val)) => (val.as_u32(), op.lhs),
(Some(val), None) => (val.as_u32(), op.rhs),
_ => {
new_ops.push(Instruction::new(Arithmetic::Div(op), inst.out()));
continue;
}
};
new_ops.push(Instruction::new(
Bitwise::ShiftRight(BinaryOperator {
lhs: dyn_val,
rhs: const_val.trailing_zeros().into(),
}),
inst.out(),
));
changes.inc();
}
Arithmetic::Modulo(op) if is_pow2(op.rhs) => {
let const_val = op.rhs.as_const().unwrap().as_u32();
new_ops.push(Instruction::new(
Bitwise::BitwiseAnd(BinaryOperator {
lhs: op.lhs,
rhs: (const_val - 1).into(),
}),
inst.out(),
));
changes.inc();
}
_ => {
new_ops.push(inst);
}
}
}
opt.block(block).ops.borrow_mut().extend(new_ops);
}
}
}
fn is_pow2(var: Variable) -> bool {
var.ty.elem_type() == ElemType::UInt(UIntKind::U32)
&& var
.as_const()
.is_some_and(|it| it.as_u32().is_power_of_two())
}