First pass implementing RULE-0-2-1, unused variables.

change_notes/2026-02-12-unused-variable-reorganization.md

@@ -0,0 +1,3 @@
+ - `M0-1-3`, `RULE-2-8` - `UnusedLocalVariable.ql`, `UnusedMemberVariable.ql`, `UnusedGlobalOrNamespaceVariable.ql`, `UnusedObjectDefinition.ql`, `UnusedObjectDefinitionStrict.ql`:
+   - The organization of unused variable analysis has been reorganized to be usable in MISRA C++ rule 0.2.1, with no expected noticeable change in results.
+   - New filtering passes begin by filtering out variables that have an existing access (`.getAnAccess()`), which should improve performance in later filtering passes and overall query performance.

cpp/autosar/src/rules/M0-1-3/UnusedGlobalOrNamespaceVariable.ql

@@ -18,11 +18,6 @@ import cpp
 import codingstandards.cpp.autosar
 import codingstandards.cpp.deadcode.UnusedVariables
 
-from PotentiallyUnusedGlobalOrNamespaceVariable v
-where
-  not isExcluded(v, DeadCodePackage::unusedGlobalOrNamespaceVariableQuery()) and
-  // No variable access
-  not exists(v.getAnAccess()) and
-  // Exclude members whose value is compile time and is potentially used to inintialize a template
-  not maybeACompileTimeTemplateArgument(v)
+from ThirdPassUnused::UnusedGlobalOrNamespaceVariable v
+where not isExcluded(v, DeadCodePackage::unusedGlobalOrNamespaceVariableQuery())
 select v, "Variable '" + v.getQualifiedName() + "' is unused."

cpp/autosar/src/rules/M0-1-3/UnusedLocalVariable.ql

@@ -18,58 +18,10 @@ import cpp
 import codingstandards.cpp.autosar
 import codingstandards.cpp.deadcode.UnusedVariables
 
-// Collect constant values that we should use to exclude otherwise unused constexpr variables.
-//
-// For constexpr variables used as template arguments or in static_asserts, we don't see accesses
-// (just the appropriate literals). We therefore take a conservative approach and do not report
-// constexpr variables whose values are used in such contexts.
-//
-// For performance reasons, these special values should be collected in a single pass.
-predicate excludedConstantValue(string value) {
-  value = any(ClassTemplateInstantiation cti).getTemplateArgument(_).(Expr).getValue()
-  or
-  value = any(StaticAssert sa).getCondition().getAChild*().getValue()
-}
-
-/**
- * Defines the local variables that should be excluded from the unused variable analysis based
- * on their constant value.
- *
- * See `excludedConstantValue` for more details.
- */
-predicate excludeVariableByValue(Variable variable) {
-  variable.isConstexpr() and
-  excludedConstantValue(getConstExprValue(variable))
-}
-
-// TODO: This predicate may be possible to merge with M0-1-4's getUseCount(). These two rules
-// diverged to handle `excludeVariableByValue`, but may be possible to merge.
-int getUseCountConservatively(Variable v) {
-  result =
-    count(VariableAccess access | access = v.getAnAccess()) +
-      count(UserProvidedConstructorFieldInit cfi | cfi.getTarget() = v) +
-      // In case an array type uses a constant in the same scope as the constexpr variable,
-      // consider it as used.
-      countUsesInLocalArraySize(v)
-}
-
-predicate isConservativelyUnused(Variable v) {
-  getUseCountConservatively(v) = 0 and
-  not excludeVariableByValue(v)
-}
-
-from PotentiallyUnusedLocalVariable v
-where
-  not isExcluded(v, DeadCodePackage::unusedLocalVariableQuery()) and
-  // Local variable is never accessed
-  not exists(v.getAnAccess()) and
-  // Sometimes multiple objects representing the same entities are created in
-  // the AST. Check if those are not accessed as well. Refer issue #658
-  not exists(LocalScopeVariable another |
-    another.getDefinitionLocation() = v.getDefinitionLocation() and
-    another.hasName(v.getName()) and
-    exists(another.getAnAccess()) and
-    another != v
-  ) and
-  isConservativelyUnused(v)
+// 10.1, 41.0
+// 10.9, 45.9
+// 11.0, 52.3
+// 13.1, 59.3
+from ThirdPassUnused::UnusedLocalVariable v
+where not isExcluded(v, DeadCodePackage::unusedLocalVariableQuery())
 select v, "Local variable '" + v.getName() + "' in '" + v.getFunction().getName() + "' is not used."

cpp/autosar/src/rules/M0-1-3/UnusedMemberVariable.ql

@@ -19,13 +19,6 @@ import codingstandards.cpp.autosar
 import codingstandards.cpp.FunctionEquivalence
 import codingstandards.cpp.deadcode.UnusedVariables
 
-from PotentiallyUnusedMemberVariable v
-where
-  not isExcluded(v, DeadCodePackage::unusedMemberVariableQuery()) and
-  // No variable access
-  not exists(v.getAnAccess()) and
-  // No explicit initialization in a constructor
-  not exists(UserProvidedConstructorFieldInit cfi | cfi.getTarget() = v) and
-  // Exclude members whose value is compile time and is potentially used to inintialize a template
-  not maybeACompileTimeTemplateArgument(v)
+from ThirdPassUnused::UnusedMemberVariable v
+where not isExcluded(v, DeadCodePackage::unusedMemberVariableQuery())
 select v, "Member variable '" + v.getName() + "' is unused."

cpp/common/src/codingstandards/cpp/deadcode/UnusedObjects.qll

@@ -17,18 +17,15 @@ import codingstandards.cpp.alertreporting.DeduplicateMacroResults
 class UnusedObjectDefinition extends VariableDeclarationEntry {
   UnusedObjectDefinition() {
     (
-      getVariable() instanceof BasePotentiallyUnusedLocalVariable
+      getVariable() instanceof FirstPassUnused::UnusedLocalVariable
       or
-      getVariable() instanceof BasePotentiallyUnusedGlobalOrNamespaceVariable
+      getVariable() instanceof FirstPassUnused::UnusedGlobalOrNamespaceVariable
     ) and
-    not exists(VariableAccess access | access.getTarget() = getVariable()) and
     getVariable().getDefinition() = this
   }
 
   /* Dead objects with these attributes are reported in the "strict" queries. */
-  predicate hasAttrUnused() {
-    getVariable().getAnAttribute().hasName(["unused", "used", "maybe_unused", "cleanup"])
-  }
+  predicate hasAttrUnused() { hasAttrUnused(getVariable()) }
 }
 
 /* Configuration to use the `DedupMacroResults` module to reduce alert noise */