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feat: replace modulo operations with truncations where possible #4329

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Feb 12, 2024
Merged

feat: replace modulo operations with truncations where possible #4329

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17 changes: 17 additions & 0 deletions compiler/noirc_evaluator/src/ssa/ir/instruction/binary.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,9 +38,9 @@
Or,
/// Bitwise xor (^)
Xor,
/// Bitshift left (<<)

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Unknown word (Bitshift)
Shl,
/// Bitshift right (>>)

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Unknown word (Bitshift)
Shr,
}

Expand Down Expand Up @@ -141,6 +141,23 @@
let zero = dfg.make_constant(FieldElement::zero(), operand_type);
return SimplifyResult::SimplifiedTo(zero);
}
if operand_type.is_unsigned() {
// lhs % 2**bit_size is equivalent to truncating `lhs` to `bit_size` bits.
// We then convert to a truncation for consistency, allowing more optimizations.
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if let Some(modulus) = rhs {
let modulus = modulus.to_u128();
if modulus.is_power_of_two() {
let bit_size = modulus.ilog2();

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Unknown word (ilog)
return SimplifyResult::SimplifiedToInstruction(
Instruction::Truncate {
value: self.lhs,
bit_size,
max_bit_size: operand_type.bit_size(),
},
);
}
}
}
}
BinaryOp::Eq => {
if dfg.resolve(self.lhs) == dfg.resolve(self.rhs) {
Expand Down Expand Up @@ -231,7 +248,7 @@
return SimplifyResult::SimplifiedTo(zero);
}

// `two_pow_rhs` is limited to be at most `2 ^ {operand_bitsize - 1}` so it fits in `operand_type`.

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Unknown word (bitsize)
let two_pow_rhs = FieldElement::from(2u128).pow(&rhs_const);
let two_pow_rhs = dfg.make_constant(two_pow_rhs, operand_type);
return SimplifyResult::SimplifiedToInstruction(Instruction::binary(
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