Fix(common/cpp): useless assignment false positive on constexpr array size.

Author: fjatWbyT

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/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
   }
 }