Fixing issue #4034. Removing unused vars goto mappings. (#4069)

crates/cairo-lang-lowering/src/db.rs

@@ -357,6 +357,9 @@ fn concrete_function_with_body_lowered(
     optimize_remappings(&mut lowered);
     reorder_statements(db, &mut lowered);
     reorganize_blocks(&mut lowered);
+    // Removed blocks may have caused some remappings to be redundent, so they need to be removed,
+    // as SierraGen drop additions assumes all remappings are of used variables.
+    optimize_remappings(&mut lowered);
     Ok(Arc::new(lowered))
 }
 

crates/cairo-lang-lowering/src/test.rs

@@ -151,7 +151,8 @@ fn test_function_lowering_phases(
     apply_stage("after_lower_implicits", &|lowered| lower_implicits(&db, function_id, lowered));
     apply_stage("after_optimize_remappings2", &optimize_remappings);
     apply_stage("after_reorder_statements3", &|lowered| reorder_statements(&db, lowered));
-    apply_stage("after_reorganize_blocks (final)", &reorganize_blocks);
+    apply_stage("after_reorganize_blocks", &reorganize_blocks);
+    apply_stage("after_optimize_remappings3 (final)", &optimize_remappings);
 
     let after_all = db.concrete_function_with_body_lowered(function_id).unwrap();
 

crates/cairo-lang-lowering/src/test_data/lowering_phases

@@ -1095,7 +1095,52 @@ Statements:
 End:
   Return(v34, v35, v25)
 
-//! > after_reorganize_blocks (final)
+//! > after_reorganize_blocks
+Parameters: v26: core::RangeCheck, v27: core::gas::GasBuiltin
+blk0 (root):
+Statements:
+  (v16: core::gas::BuiltinCosts) <- core::gas::get_builtin_costs()
+End:
+  Match(match core::gas::withdraw_gas_all(v26, v27, v16) {
+    Option::Some(v28, v29) => blk1,
+    Option::None(v30, v31) => blk4,
+  })
+
+blk1:
+Statements:
+  (v34: core::RangeCheck, v35: core::gas::GasBuiltin, v17: core::panics::PanicResult::<((),)>) <- test::foo(v28, v29)
+End:
+  Match(match_enum(v17) {
+    PanicResult::Ok(v18) => blk2,
+    PanicResult::Err(v20) => blk3,
+  })
+
+blk2:
+Statements:
+  (v19: ()) <- struct_destructure(v18)
+  (v21: ((),)) <- struct_construct(v19)
+  (v22: core::panics::PanicResult::<((),)>) <- PanicResult::Ok(v21)
+End:
+  Return(v34, v35, v22)
+
+blk3:
+Statements:
+  (v25: core::panics::PanicResult::<((),)>) <- PanicResult::Err(v20)
+End:
+  Return(v34, v35, v25)
+
+blk4:
+Statements:
+  (v11: core::array::Array::<core::felt252>) <- core::array::array_new::<core::felt252>()
+  (v12: core::felt252) <- 375233589013918064796019u
+  (v14: core::array::Array::<core::felt252>) <- core::array::array_append::<core::felt252>(v11, v12)
+  (v13: core::panics::Panic) <- struct_construct()
+  (v15: (core::panics::Panic, core::array::Array::<core::felt252>)) <- struct_construct(v13, v14)
+  (v24: core::panics::PanicResult::<((),)>) <- PanicResult::Err(v15)
+End:
+  Return(v30, v31, v24)
+
+//! > after_optimize_remappings3 (final)
 Parameters: v26: core::RangeCheck, v27: core::gas::GasBuiltin
 blk0 (root):
 Statements:

tests/bug_samples/issue4034.cairo

@@ -0,0 +1,7 @@
+#[test]
+fn var_dropped_after_merge_remapping() {
+    let mut x: u32 = 0;
+    if (x == 0 && x != 1 && false) {
+        x = x + 1;
+    }
+}

tests/bug_samples/lib.cairo

@@ -26,6 +26,7 @@ mod issue3345;
 mod issue3658;
 mod issue3863;
 mod issue4007;
+mod issue4034;
 mod issue4036;
 mod loop_only_change;
 mod inconsistent_gas;