flow_control: Update changed_members in the root block.

commit-id:d1a5121c

Author: liorgold2

crates/cairo-lang-lowering/src/lower/block_builder.rs

@@ -15,7 +15,9 @@ use semantic::{ConcreteTypeId, ExprVarMemberPath, TypeLongId};
 use super::context::{LoweredExpr, LoweringContext, LoweringFlowError, LoweringResult, VarRequest};
 use super::generators;
 use super::generators::StatementsBuilder;
-use super::refs::{SemanticLoweringMapping, StructRecomposer, merge_semantics};
+use super::refs::{
+    SemanticLoweringMapping, StructRecomposer, find_changed_members, merge_semantics,
+};
 use crate::db::LoweringGroup;
 use crate::diagnostic::{LoweringDiagnosticKind, LoweringDiagnosticsBuilder};
 use crate::ids::LocationId;
@@ -397,6 +399,15 @@ impl<'db> BlockBuilder<'db> {
             closure_info,
         )
     }
+
+    /// Marks the following as changed members:
+    /// (1) the changed members of `parent_builder`,
+    /// (2) the members whose value was changed between `parent_builder` and `self`.
+    pub fn set_changed_member_paths(&mut self, parent_builder: &Self) {
+        self.changed_member_paths.extend(parent_builder.changed_member_paths.iter().cloned());
+        self.changed_member_paths
+            .extend(find_changed_members(&parent_builder.semantics, &self.semantics));
+    }
 }
 
 impl<'db> DebugWithDb<'db> for BlockBuilder<'db> {
@@ -559,8 +570,9 @@ impl<'db> StructRecomposer<'db> for BlockStructRecomposer<'_, '_, 'db> {
 /// * Variables mapped to the same lowered variable across all input blocks are kept as-is.
 /// * Local variables that appear in only a subset of the blocks are removed.
 /// * Variables with different mappings across blocks are remapped to a new lowered variable.
-// TODO(lior): Remove `allow(dead_code)` once the function is used.
-#[allow(dead_code)]
+///
+/// Note that the returned [BlockBuilder] has an empty [BlockBuilder::changed_member_paths].
+/// Use [BlockBuilder::set_changed_member_paths] to set it if necessary.
 pub fn merge_sealed_block_builders<'db>(
     ctx: &mut LoweringContext<'db, '_>,
     sealed_blocks: Vec<SealedGotoCallsite<'db>>,

crates/cairo-lang-lowering/src/lower/flow_control/lower_graph.rs

@@ -203,9 +203,10 @@ impl<'mt, 'db, 'a> LowerGraphContext<'db, 'mt, 'a> {
 
         match match_info {
             Ok(match_info) => {
-                if let Some((new_builder, lowered_expr)) =
+                if let Some((mut new_builder, lowered_expr)) =
                     merge_sealed_block_builders(self.ctx, self.sealed_blocks, self.location)
                 {
+                    new_builder.set_changed_member_paths(&builder);
                     builder.finalize(self.ctx, BlockEnd::Match { info: match_info });
                     (Ok(lowered_expr), new_builder)
                 } else {

crates/cairo-lang-lowering/src/lower/refs.rs

@@ -308,6 +308,22 @@ fn compute_remapped_variables<'db>(
     Value::Scattered(Box::new(Scattered { concrete_struct_id, members }))
 }
 
+/// Returns an iterator to all the [MemberPath]s that appear in both mappings and have different
+/// values.
+pub fn find_changed_members<'db, 'a>(
+    semantics0: &'a SemanticLoweringMapping<'db>,
+    semantics1: &'a SemanticLoweringMapping<'db>,
+) -> impl Iterator<Item = MemberPath<'db>> + 'a {
+    semantics0.scattered.iter().filter_map(|(path, value0)| {
+        if let Some(value1) = semantics1.scattered.get(path) {
+            if value0 != value1 {
+                return Some(path.clone());
+            }
+        }
+        None
+    })
+}
+
 /// A trait for deconstructing and constructing structs.
 pub trait StructRecomposer<'db> {
     fn deconstruct(