Merge pull request #732 from fjatWbyT/fix-constexpr-array-size-a0-1-1

A0-1-1: Fix useless assignment false positive on constexpr array size

Author: lcartey

change_notes/2024-10-04-fix-constexpr-arr-size-fp-a0-1-1.md

@@ -0,0 +1,2 @@
+- `A0-1-1` - `UselessAssignments.qll`:
+  - Remove (dead code) useless assignment false positive when integer constant expression is used to define the size of an array.

cpp/autosar/test/rules/A0-1-1/UselessAssignment.expected

@@ -12,3 +12,5 @@
 | test.cpp:94:11:94:17 | new | Definition of $@ is unused. | test.cpp:94:6:94:7 | b4 | b4 |
 | test.cpp:95:11:95:17 | 0 | Definition of $@ is unused. | test.cpp:95:6:95:7 | b5 | b5 |
 | test.cpp:103:11:103:17 | 0 | Definition of $@ is unused. | test.cpp:103:6:103:7 | c5 | c5 |
+| test.cpp:132:43:132:45 | {...} | Definition of $@ is unused. | test.cpp:132:7:132:18 | unused_array | unused_array |
+| test.cpp:134:29:134:31 | 0 | Definition of $@ is unused. | test.cpp:134:17:134:26 | unused_int | unused_int |

cpp/autosar/test/rules/A0-1-1/test.cpp

@@ -123,4 +123,16 @@ template <typename T> void test_range_based_for_loop_template() {
                                //             template
     elem;
   }
-}
+}
+
+#include <cstdint>
+
+std::int32_t test_constexpr_array_size() {
+  constexpr int constexpr_array_size = 7;      // COMPLIANT
+  int unused_array[constexpr_array_size] = {}; // NON_COMPLIANT
+
+  constexpr int unused_int = {}; // NON_COMPLIANT
+
+  std::int32_t used_array[] = {-1, 0, 1}; // COMPLIANT
+  return used_array[1];
+}

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

@@ -3,6 +3,7 @@
  */
 
 import cpp
+import codingstandards.cpp.deadcode.UnusedVariables
 import codingstandards.cpp.enhancements.ControlFlowGraphEnhancements
 
 /** If a variable may escape from the local context */
@@ -47,7 +48,9 @@ class InterestingStackVariable extends StackVariable {
     // Ignore variables in uninstantiated templates
     not this.isFromUninstantiatedTemplate(_) and
     // Ignore compiler generated variables, such as those generated for range based for loops
-    not this.isCompilerGenerated()
+    not this.isCompilerGenerated() and
+    // Explicitly ignore (propagated) constants that may be used to define sizes of local arrays
+    not countUsesInLocalArraySize(this) > 0
   }
 }