Address feedback.

Author: MichaelRFairhurst

c/misra/src/rules/RULE-8-15/RedeclarationOfObjectWithUnmatchedAlignment.ql

@@ -15,21 +15,10 @@
 
 import cpp
 import codingstandards.c.misra
-
-predicate lexicallyEqualExpr(Expr a, Expr b) {
-  a.toString() = b.toString() and
-  a.getNumChild() = b.getNumChild() and
-  forall(Expr aChild, Expr bChild, int i |
-    aChild = a.getChild(i) and
-    bChild = b.getChild(i) and
-    i < a.getNumChild()
-  |
-    lexicallyEqualExpr(aChild, bChild)
-  )
-}
+import semmle.code.cpp.valuenumbering.HashCons
 
 predicate lexicallyEqual(AttributeArgument a, AttributeArgument b) {
-  lexicallyEqualExpr(a.getValueConstant(), b.getValueConstant()) or
+  hashCons(a.getValueConstant()) =  hashCons(b.getValueConstant()) or
   a.getValueType() = b.getValueType()
 }
 

c/misra/src/rules/RULE-8-15/RedeclarationOfObjectWithoutAlignment.ql

@@ -46,10 +46,9 @@ newtype TAttributeDeclLocation =
  * This should give us a highly reliable means of finding which attributes are
  * associated with which `DeclarationEntry`s.
  *
- * One note of caution: the associated `Variable` must be treated with caution,
- * as there are multiple instances of that `Variable` if it is declared
- * multiple times, they equal each other, and `getLocation()` on each variable
- * returns every location result. This class must act on `DeclarationEntry`s to
+ * One note of caution: the location of the associated `Variable` must be
+ * treated with caution, as calls to `getLocation()` on a redeclared `Variable`
+ * can return multiple results. This class must act on `DeclarationEntry`s to
  * deliver reliable results.
  */
 class DeclarationEntryAttribute extends Attribute {

c/misra/src/rules/RULE-8-17/MoreThanOneAlignmentSpecifierOnDeclaration.ql

@@ -20,9 +20,12 @@ where
   not isExcluded(v, AlignmentPackage::moreThanOneAlignmentSpecifierOnDeclarationQuery()) and
   first = v.getAnAttribute() and
   last = v.getAnAttribute() and
-  first != last and
+  not first = last and
   first.hasName("_Alignas") and
   last.hasName("_Alignas") and
+  // Handle double reporting: the first Attribute should really be first, and the last Attribute
+  // should really be last. This implies the first is before the last. This approach also ensures
+  // a single result for variables that have more than two alignment specifiers.
   not exists(Attribute beforeFirst |
     beforeFirst.getLocation().isBefore(first.getLocation(), _) and
     v.getAnAttribute() = beforeFirst