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feat: skip redundant range checks in brillig #4460

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Mar 1, 2024
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feat: skip redundant range checks in brillig #4460

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59 changes: 31 additions & 28 deletions compiler/noirc_evaluator/src/brillig/brillig_gen/brillig_block.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -624,37 +624,40 @@ impl<'block> BrilligBlock<'block> {
}
Instruction::RangeCheck { value, max_bit_size, assert_message } => {
let value = self.convert_ssa_single_addr_value(*value, dfg);
// Cast original value to field
let left = SingleAddrVariable {
address: self.brillig_context.allocate_register(),
bit_size: FieldElement::max_num_bits(),
};
self.convert_cast(left, value);
// SSA generates redundant range checks. A range check with a max bit size >= value.bit_size will always pass.
if value.bit_size > *max_bit_size {
// Cast original value to field
let left = SingleAddrVariable {
address: self.brillig_context.allocate_register(),
bit_size: FieldElement::max_num_bits(),
};
self.convert_cast(left, value);

// Create a field constant with the max
let max = BigUint::from(2_u128).pow(*max_bit_size) - BigUint::from(1_u128);
let right = self.brillig_context.make_constant(
FieldElement::from_be_bytes_reduce(&max.to_bytes_be()).into(),
FieldElement::max_num_bits(),
);
// Create a field constant with the max
let max = BigUint::from(2_u128).pow(*max_bit_size) - BigUint::from(1_u128);
let right = self.brillig_context.make_constant(
FieldElement::from_be_bytes_reduce(&max.to_bytes_be()).into(),
FieldElement::max_num_bits(),
);

// Check if lte max
let brillig_binary_op = BrilligBinaryOp::Integer {
op: BinaryIntOp::LessThanEquals,
bit_size: FieldElement::max_num_bits(),
};
let condition = self.brillig_context.allocate_register();
self.brillig_context.binary_instruction(
left.address,
right,
condition,
brillig_binary_op,
);
// Check if lte max
let brillig_binary_op = BrilligBinaryOp::Integer {
op: BinaryIntOp::LessThanEquals,
bit_size: FieldElement::max_num_bits(),
};
let condition = self.brillig_context.allocate_register();
self.brillig_context.binary_instruction(
left.address,
right,
condition,
brillig_binary_op,
);

self.brillig_context.constrain_instruction(condition, assert_message.clone());
self.brillig_context.deallocate_register(condition);
self.brillig_context.deallocate_register(left.address);
self.brillig_context.deallocate_register(right);
self.brillig_context.constrain_instruction(condition, assert_message.clone());
self.brillig_context.deallocate_register(condition);
self.brillig_context.deallocate_register(left.address);
self.brillig_context.deallocate_register(right);
}
}
Instruction::IncrementRc { value } => {
let rc_register = match self.convert_ssa_value(*value, dfg) {
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