From 59b88a6464fbebefd4e7d6c7b199601315dba661 Mon Sep 17 00:00:00 2001
From: Tom French <tom@tomfren.ch>
Date: Tue, 2 Apr 2024 13:36:48 +0100
Subject: [PATCH] feat: improve optimisations on range constraints

---
 .../noirc_evaluator/src/ssa/ir/instruction.rs     | 10 +++++-----
 .../src/ssa/ir/instruction/call.rs                | 15 ++++++++++-----
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/compiler/noirc_evaluator/src/ssa/ir/instruction.rs b/compiler/noirc_evaluator/src/ssa/ir/instruction.rs
index dd190c112f..a887b27997 100644
--- a/compiler/noirc_evaluator/src/ssa/ir/instruction.rs
+++ b/compiler/noirc_evaluator/src/ssa/ir/instruction.rs
@@ -573,12 +573,12 @@ impl Instruction {
             Instruction::IncrementRc { .. } => None,
             Instruction::DecrementRc { .. } => None,
             Instruction::RangeCheck { value, max_bit_size, .. } => {
-                if let Some(numeric_constant) = dfg.get_numeric_constant(*value) {
-                    if numeric_constant.num_bits() < *max_bit_size {
-                        return Remove;
-                    }
+                let max_potential_bits = dfg.get_value_max_num_bits(*value);
+                if max_potential_bits < *max_bit_size {
+                    Remove
+                } else {
+                    None
                 }
-                None
             }
         }
     }
diff --git a/compiler/noirc_evaluator/src/ssa/ir/instruction/call.rs b/compiler/noirc_evaluator/src/ssa/ir/instruction/call.rs
index 5b268de239..a284714608 100644
--- a/compiler/noirc_evaluator/src/ssa/ir/instruction/call.rs
+++ b/compiler/noirc_evaluator/src/ssa/ir/instruction/call.rs
@@ -240,11 +240,16 @@ pub(super) fn simplify_call(
             let max_bit_size = dfg.get_numeric_constant(arguments[1]);
             if let Some(max_bit_size) = max_bit_size {
                 let max_bit_size = max_bit_size.to_u128() as u32;
-                SimplifyResult::SimplifiedToInstruction(Instruction::RangeCheck {
-                    value,
-                    max_bit_size,
-                    assert_message: Some("call to assert_max_bit_size".to_owned()),
-                })
+                let max_potential_bits = dfg.get_value_max_num_bits(value);
+                if max_potential_bits < max_bit_size {
+                    SimplifyResult::Remove
+                } else {
+                    SimplifyResult::SimplifiedToInstruction(Instruction::RangeCheck {
+                        value,
+                        max_bit_size,
+                        assert_message: Some("call to assert_max_bit_size".to_owned()),
+                    })
+                }
             } else {
                 SimplifyResult::None
             }