chore: mark casts as able to be deduplicated (#6996)

compiler/noirc_evaluator/src/ssa.rs

@@ -171,7 +171,7 @@ fn optimize_all(builder: SsaBuilder, options: &SsaEvaluatorOptions) -> Result<Ss
         )?
         .run_pass(Ssa::simplify_cfg, "Simplifying (2nd)")
         .run_pass(Ssa::flatten_cfg, "Flattening")
-        .run_pass(Ssa::remove_bit_shifts, "After Removing Bit Shifts")
+        .run_pass(Ssa::remove_bit_shifts, "Removing Bit Shifts")
         // Run mem2reg once more with the flattened CFG to catch any remaining loads/stores
         .run_pass(Ssa::mem2reg, "Mem2Reg (2nd)")
         // Run the inlining pass again to handle functions with `InlineType::NoPredicates`.

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

@@ -473,6 +473,9 @@ impl Instruction {
             // removed entirely.
             Noop => true,
 
+            // Cast instructions can always be deduplicated
+            Cast(_, _) => true,
+
             // Arrays can be mutated in unconstrained code so code that handles this case must
             // take care to track whether the array was possibly mutated or not before
             // deduplicating. Since we don't know if the containing pass checks for this, we
@@ -484,7 +487,6 @@ impl Instruction {
             // with one that was disabled. See
             // https://github.com/noir-lang/noir/pull/4716#issuecomment-2047846328.
             Binary(_)
-            | Cast(_, _)
             | Not(_)
             | Truncate { .. }
             | IfElse { .. }