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feat: simplify explicit equality assertions to assert equality directly #3708

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merged 3 commits into from
Dec 12, 2023
Merged

feat: simplify explicit equality assertions to assert equality directly #3708

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bcd4fba
feat: simplify explicit equality assertions
TomAFrench Dec 6, 2023
da6d62e
Merge branch 'master' into tf/simplify-explicit-equality-assertions
kevaundray Dec 9, 2023
101ec98
feat: simplify constraints on NOT instructions
TomAFrench Dec 8, 2023
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83 changes: 77 additions & 6 deletions compiler/noirc_evaluator/src/ssa/ir/instruction.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -433,12 +433,74 @@ impl Instruction {
_ => None,
}
}
Instruction::Constrain(lhs, rhs, ..) => {
Instruction::Constrain(lhs, rhs, msg) => {
if dfg.resolve(*lhs) == dfg.resolve(*rhs) {
// Remove trivial case `assert_eq(x, x)`
SimplifyResult::Remove
} else {
SimplifyResult::None
match (&dfg[dfg.resolve(*lhs)], &dfg[dfg.resolve(*rhs)]) {
(
Value::NumericConstant { constant, typ },
Value::Instruction { instruction, .. },
)
| (
Value::Instruction { instruction, .. },
Value::NumericConstant { constant, typ },
) if *typ == Type::bool() => {
match dfg[*instruction] {
Instruction::Binary(Binary {
lhs,
rhs,
operator: BinaryOp::Eq,
}) if constant.is_one() => {
// Replace an explicit two step equality assertion
//
// v2 = eq v0, u32 v1
// constrain v2 == u1 1
//
// with a direct assertion of equality between the two values
//
// v2 = eq v0, u32 v1
// constrain v0 == v1
//
// Note that this doesn't remove the value `v2` as it may be used in other instructions, but it
// will likely be removed through dead instruction elimination.

SimplifiedToInstruction(Instruction::Constrain(
lhs,
rhs,
msg.clone(),
))
}
Instruction::Not(value) => {
// Replace an assertion that a not instruction is truthy
//
// v1 = not v0
// constrain v1 == u1 1
//
// with an assertion that the not instruction input is falsy
//
// v1 = not v0
// constrain v0 == u1 0
//
// Note that this doesn't remove the value `v1` as it may be used in other instructions, but it
// will likely be removed through dead instruction elimination.
let reversed_constant = FieldElement::from(!constant.is_one());
let reversed_constant =
dfg.make_constant(reversed_constant, Type::bool());
SimplifiedToInstruction(Instruction::Constrain(
value,
reversed_constant,
msg.clone(),
))
}

_ => None,
}
}

_ => None,
}
}
}
Instruction::ArrayGet { array, index } => {
Expand Down Expand Up @@ -795,10 +857,19 @@ impl Binary {
let zero = dfg.make_constant(FieldElement::zero(), Type::bool());
return SimplifyResult::SimplifiedTo(zero);
}
if operand_type.is_unsigned() && rhs_is_zero {
// Unsigned values cannot be less than zero.
let zero = dfg.make_constant(FieldElement::zero(), Type::bool());
return SimplifyResult::SimplifiedTo(zero);
if operand_type.is_unsigned() {
if rhs_is_zero {
// Unsigned values cannot be less than zero.
let zero = dfg.make_constant(FieldElement::zero(), Type::bool());
return SimplifyResult::SimplifiedTo(zero);
} else if rhs_is_one {
let zero = dfg.make_constant(FieldElement::zero(), operand_type);
return SimplifyResult::SimplifiedToInstruction(Instruction::binary(
BinaryOp::Eq,
self.lhs,
zero,
));
}
}
}
BinaryOp::And => {
Expand Down
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