feat: Optimize x < 0 for unsigned x to false (#2206)

* feat: Optimize `x < 0` for unsigned `x` to false * chore: add `Type::is_unsigned(&self)` method
noir-lang · Aug 8, 2023 · 25bc969 · 25bc969
1 parent c74b228
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diff --git a/crates/noirc_evaluator/src/ssa/ir/instruction.rs b/crates/noirc_evaluator/src/ssa/ir/instruction.rs
@@ -593,6 +593,11 @@ 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);
+                }
             }
             BinaryOp::And => {
                 if lhs_is_zero || rhs_is_zero {

diff --git a/crates/noirc_evaluator/src/ssa/ir/types.rs b/crates/noirc_evaluator/src/ssa/ir/types.rs
@@ -37,6 +37,11 @@ pub(crate) enum Type {
 }
 
 impl Type {
+    /// Returns whether the `Type` represents an unsigned numeric type.
+    pub(crate) fn is_unsigned(&self) -> bool {
+        matches!(self, Type::Numeric(NumericType::Unsigned { .. }))
+    }
+
     /// Create a new signed integer type with the given amount of bits.
     pub(crate) fn signed(bit_size: u32) -> Type {
         Type::Numeric(NumericType::Signed { bit_size })