C++: Simplify consteval if to be just a single class with an isNot predicate

Author: jketema

cpp/ql/lib/change-notes/2024-01-16-consteval-if.md

@@ -1,4 +1,4 @@
 ---
 category: feature
 ---
-* New classes `ConstevalIfStmt` and `NotConstevalIfStmt` were introduced, which represent the C++23 `if consteval` and `if ! consteval` statements.
+* A new class `ConstevalIfStmt` was introduced, which represents the C++23 `if consteval` and `if ! consteval` statements.

cpp/ql/lib/semmle/code/cpp/PrintAST.qll

@@ -912,9 +912,9 @@ private predicate namedStmtChildPredicates(Locatable s, Element e, string pred)
     or
     s.(ConstexprIfStmt).getElse() = e and pred = "getElse()"
     or
-    s.(ConstevalOrNotConstevalIfStmt).getThen() = e and pred = "getThen()"
+    s.(ConstevalIfStmt).getThen() = e and pred = "getThen()"
     or
-    s.(ConstevalOrNotConstevalIfStmt).getElse() = e and pred = "getElse()"
+    s.(ConstevalIfStmt).getElse() = e and pred = "getElse()"
     or
     s.(Handler).getParameter() = e and pred = "getParameter()"
     or

cpp/ql/lib/semmle/code/cpp/controlflow/internal/CFG.qll

@@ -876,8 +876,8 @@ private predicate subEdge(Pos p1, Node n1, Node n2, Pos p2) {
     p2.nodeAfter(n2, s)
   )
   or
-  // ConstevalOrNotConstevalIfStmt -> { then, else } ->
-  exists(ConstevalOrNotConstevalIfStmt s |
+  // NotConstevalIfStmt -> { then, else } ->
+  exists(ConstevalIfStmt s |
     p1.nodeAt(n1, s) and
     p2.nodeBefore(n2, s.getThen())
     or

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedStmt.qll

@@ -1098,8 +1098,8 @@ class TranslatedConstExprIfStmt extends TranslatedIfLikeStmt {
   override predicate hasElse() { exists(stmt.getElse()) }
 }
 
-class TranslatedConstevalOrNotConstevalIfStmt extends TranslatedStmt {
-  override ConstevalOrNotConstevalIfStmt stmt;
+class TranslatedConstevalIfStmt extends TranslatedStmt {
+  override ConstevalIfStmt stmt;
 
   override Instruction getFirstInstruction(EdgeKind kind) {
     if not this.hasEvaluatedBranch()

cpp/ql/lib/semmle/code/cpp/stmts/Stmt.qll

@@ -446,7 +446,27 @@ class ConstexprIfStmt extends ConditionalStmt, @stmt_constexpr_if {
  * }
  * ```
  */
-class ConstevalOrNotConstevalIfStmt extends Stmt, @stmt_consteval_or_not_consteval_if {
+class ConstevalIfStmt extends Stmt, @stmt_consteval_or_not_consteval_if {
+  override string getAPrimaryQlClass() { result = "ConstevalIfStmt" }
+
+  override string toString() {
+    if this.isNot() then result = "if ! consteval ..." else result = "if consteval ..."
+  }
+
+  /**
+   * Holds if this is a 'not consteval if' statement.
+   *
+   * For example, this holds for
+   * ```cpp
+   * if ! consteval { return true; }
+   * ```
+   * but not for
+   * ```cpp
+   * if consteval { return true; }
+   * ```
+   */
+  predicate isNot() { this instanceof @stmt_not_consteval_if }
+
   /**
    * Gets the 'then' statement of this '(not) consteval if' statement.
    *
@@ -515,7 +535,9 @@ class ConstevalOrNotConstevalIfStmt extends Stmt, @stmt_consteval_or_not_constev
    * ```
    * there is no result.
    */
-  Stmt getCompileTimeEvaluatedBranch() { none() }
+  Stmt getCompileTimeEvaluatedBranch() {
+    if this.isNot() then result = this.getElse() else result = this.getThen()
+  }
 
   /**
    * Holds if this '(not) constexpr if' statement has a compile time evaluated statement.
@@ -544,7 +566,9 @@ class ConstevalOrNotConstevalIfStmt extends Stmt, @stmt_consteval_or_not_constev
    * ```
    * there is no result.
    */
-  Stmt getRuntimeEvaluatedBranch() { none() }
+  Stmt getRuntimeEvaluatedBranch() {
+    if this.isNot() then result = this.getThen() else result = this.getElse()
+  }
 
   /**
    * Holds if this '(not) constexpr if' statement has a runtime evaluated statement.
@@ -561,44 +585,6 @@ class ConstevalOrNotConstevalIfStmt extends Stmt, @stmt_consteval_or_not_constev
   predicate hasRuntimeEvaluatedBranch() { exists(this.getRuntimeEvaluatedBranch()) }
 }
 
-/**
- * A C/C++ 'consteval if'. For example, the `if consteval` statement
- * in the following code:
- * ```cpp
- * if consteval {
- *   ...
- * }
- * ```
- */
-class ConstevalIfStmt extends ConstevalOrNotConstevalIfStmt, @stmt_consteval_if {
-  override string getAPrimaryQlClass() { result = "ConstevalIfStmt" }
-
-  override string toString() { result = "if consteval ..." }
-
-  override Stmt getCompileTimeEvaluatedBranch() { result = this.getThen() }
-
-  override Stmt getRuntimeEvaluatedBranch() { result = this.getElse() }
-}
-
-/**
- * A C/C++ 'not consteval if'. For example, the `if ! consteval` statement
- * in the following code:
- * ```cpp
- * if ! consteval {
- *   ...
- * }
- * ```
- */
-class NotConstevalIfStmt extends ConstevalOrNotConstevalIfStmt, @stmt_not_consteval_if {
-  override string getAPrimaryQlClass() { result = "NotConstevalIfStmt" }
-
-  override string toString() { result = "if ! consteval ..." }
-
-  override Stmt getCompileTimeEvaluatedBranch() { result = this.getElse() }
-
-  override Stmt getRuntimeEvaluatedBranch() { result = this.getThen() }
-}
-
 private class TLoop = @stmt_while or @stmt_end_test_while or @stmt_range_based_for or @stmt_for;
 
 /**

cpp/ql/test/library-tests/ir/ir/PrintAST.expected

@@ -24138,7 +24138,7 @@ ir23.cpp:
 #   10| [TopLevelFunction] bool consteval_2()
 #   10|   <params>: 
 #   11|   getEntryPoint(): [BlockStmt] { ... }
-#   12|     getStmt(0): [NotConstevalIfStmt] if ! consteval ...
+#   12|     getStmt(0): [ConstevalIfStmt] if ! consteval ...
 #   12|       getThen(): [BlockStmt] { ... }
 #   13|         getStmt(0): [ReturnStmt] return ...
 #   13|           getExpr(): [Literal] 1
@@ -24169,7 +24169,7 @@ ir23.cpp:
 #   28| [TopLevelFunction] bool consteval_4()
 #   28|   <params>: 
 #   29|   getEntryPoint(): [BlockStmt] { ... }
-#   30|     getStmt(0): [NotConstevalIfStmt] if ! consteval ...
+#   30|     getStmt(0): [ConstevalIfStmt] if ! consteval ...
 #   30|       getThen(): [BlockStmt] { ... }
 #   31|         getStmt(0): [ReturnStmt] return ...
 #   31|           getExpr(): [Literal] 1
@@ -24192,7 +24192,7 @@ ir23.cpp:
 #   39|               Type = [BoolType] bool
 #   39|               Value = [Literal] 1
 #   39|               ValueCategory = prvalue
-#   41|     getStmt(1): [NotConstevalIfStmt] if ! consteval ...
+#   41|     getStmt(1): [ConstevalIfStmt] if ! consteval ...
 #   41|       getThen(): [BlockStmt] { ... }
 #   42|         getStmt(0): [ExprStmt] ExprStmt
 #   42|           getExpr(): [AssignExpr] ... = ...