C++: add support for enums in HashCons

cpp/ql/src/semmle/code/cpp/valuenumbering/HashCons.qll

@@ -43,6 +43,8 @@ import cpp
 private cached newtype HCBase =
   HC_IntLiteral(int val, Type t) { mk_IntLiteral(val,t,_) }
   or
+  HC_EnumConstantAccess(EnumConstant val, Type t) { mk_EnumConstantAccess(val,t,_) }
+  or
   HC_FloatLiteral(float val, Type t) { mk_FloatLiteral(val,t,_) }
   or
   HC_StringLiteral(string val, Type t) {mk_StringLiteral(val,t,_)}
@@ -179,6 +181,17 @@ private predicate mk_IntLiteral(int val, Type t, Expr e) {
   t = e.getType().getUnspecifiedType()
 }
 
+private predicate analyzableEnumConstantAccess(EnumConstantAccess e) {
+  strictcount (e.getValue().toInt()) = 1 and
+  strictcount (e.getType().getUnspecifiedType()) = 1 and
+  e.getType().getUnspecifiedType() instanceof Enum
+}
+
+private predicate mk_EnumConstantAccess(EnumConstant val, Type t, Expr e) {
+  analyzableEnumConstantAccess(e) and
+  val = e.(EnumConstantAccess).getTarget() and
+  t = e.getType().getUnspecifiedType()
+}
 
 private predicate analyzableFloatLiteral(Literal e) {
   strictcount (e.getValue().toFloat()) = 1 and
@@ -446,6 +459,10 @@ cached HC hashCons(Expr e) {
   | mk_IntLiteral(val, t, e) and
     result = HC_IntLiteral(val, t))
   or
+  exists (EnumConstant val, Type t
+  | mk_EnumConstantAccess(val, t, e) and
+    result = HC_EnumConstantAccess(val, t))
+  or
   exists (float val, Type t
   | mk_FloatLiteral(val, t, e) and
     result = HC_FloatLiteral(val, t))
@@ -521,6 +538,7 @@ cached HC hashCons(Expr e) {
  */
 predicate analyzableExpr(Expr e, string kind) {
   (analyzableIntLiteral(e) and kind = "IntLiteral") or
+  (analyzableEnumConstantAccess(e) and kind = "EnumConstantAccess") or
   (analyzableFloatLiteral(e) and kind = "FloatLiteral") or
   (analyzableStringLiteral(e) and kind = "StringLiteral") or
   (analyzableNullptr(e) and kind = "Nullptr") or

cpp/ql/test/library-tests/valuenumbering/HashCons/HashCons.expected

@@ -67,3 +67,5 @@
 | test.cpp:150:3:150:5 | ... ++ | 150:c3-c5 150:c9-c11 151:c3-c5 151:c9-c11 152:c10-c12 |
 | test.cpp:150:3:150:11 | ... + ... | 150:c3-c11 151:c3-c11 |
 | test.cpp:156:14:156:20 | 0 | 156:c14-c20 156:c3-c9 157:c10-c16 |
+| test.cpp:171:3:171:6 | (int)... | 171:c3-c6 172:c3-c6 |
+| test.cpp:171:3:171:6 | e1x1 | 171:c3-c6 172:c3-c6 |

cpp/ql/test/library-tests/valuenumbering/HashCons/test.cpp

@@ -156,3 +156,19 @@ void* test11() {
   nullptr == nullptr;
   return nullptr;
 }
+
+enum t1 {
+  e1x1 = 1,
+  e1x2 = 2
+};
+
+enum t2 {
+  e2x1 = 1,
+  e2x2 = 2
+};
+
+int test12() {
+  e1x1 == e2x1;
+  e1x1 == e2x2;
+  return e1x2;
+}