feat: optimize out range checks on limiting cases

compiler/noirc_evaluator/src/ssa/ir/instruction.rs

@@ -426,7 +426,7 @@
             // These can fail.
             Constrain(..) | ConstrainNotEqual(..) | RangeCheck { .. } => true,
 
             // This should never be side-effectful
             MakeArray { .. } | Noop => false,
 
             // Some binary math can overflow or underflow
@@ -1036,7 +1036,7 @@
             Instruction::DecrementRc { .. } => None,
             Instruction::RangeCheck { value, max_bit_size, .. } => {
                 let max_potential_bits = dfg.get_value_max_num_bits(*value);
-                if max_potential_bits < *max_bit_size {
+                if max_potential_bits <= *max_bit_size {
                     Remove
                 } else {
                     None
@@ -1472,3 +1472,32 @@
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::ssa::{opt::assert_normalized_ssa_equals, ssa_gen::Ssa};
+
+    #[test]
+    fn removes_range_constraints_on_constants() {
+        let src = "
+        acir(inline) fn main f0 {
+          b0(v0: Field):
+            range_check Field 0 to 1 bits
+            range_check Field 1 to 1 bits
+            range_check Field 255 to 8 bits
+            range_check Field 256 to 8 bits
+            return
+        }
+        ";
+        let ssa = Ssa::from_str_simplifying(src).unwrap();
+
+        let expected = "
+        acir(inline) fn main f0 {
+          b0(v0: Field):
+            range_check Field 256 to 8 bits
+            return
+        }
+        ";
+        assert_normalized_ssa_equals(ssa, expected);
+    }
+}