fix(ssa): Resolve value IDs in terminator before comparing to array (#…

…6448)

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

@@ -74,8 +74,9 @@ pub(crate) struct DataFlowGraph {
     blocks: DenseMap<BasicBlock>,
 
     /// Debugging information about which `ValueId`s have had their underlying `Value` substituted
-    /// for that of another. This information is purely used for printing the SSA, and has no
-    /// material effect on the SSA itself.
+    /// for that of another. In theory this information is purely used for printing the SSA,
+    /// and has no material effect on the SSA itself, however in practice the IDs can get out of
+    /// sync and may need this resolution before they can be compared.
     #[serde(skip)]
     replaced_value_ids: HashMap<ValueId, ValueId>,
 

compiler/noirc_evaluator/src/ssa/opt/array_set.rs

@@ -105,13 +105,15 @@ impl<'f> Context<'f> {
                     // If the array comes from a load we may potentially being mutating an array at a reference
                     // that is loaded from by other values.
                     let terminator = self.dfg[block_id].unwrap_terminator();
+
                     // If we are in a return block we are not concerned about the array potentially being mutated again.
                     let is_return_block =
                         matches!(terminator, TerminatorInstruction::Return { .. });
                     // We also want to check that the array is not part of the terminator arguments, as this means it is used again.
                     let mut array_in_terminator = false;
                     terminator.for_each_value(|value| {
-                        if value == array {
+                        // The terminator can contain original IDs, while the SSA has replaced the array value IDs; we need to resolve to compare.
+                        if !array_in_terminator && self.dfg.resolve(value) == array {
                             array_in_terminator = true;
                         }
                     });