Merge pull request github#18502 from jketema/consteval

C++: Support `if consteval` and `if ! consteval`

Author: jketema

cpp/downgrades/1aa71a4a687fc93f807d4dfeeef70feceeced242/old.dbscheme

@@ -0,0 +1,17 @@
+class Stmt extends @stmt {
+  string toString() { none() }
+}
+
+class Location extends @location_stmt {
+  string toString() { none() }
+}
+
+predicate isConstevalIf(Stmt stmt) {
+  exists(int kind | stmts(stmt, kind, _) | kind = 38 or kind = 39)
+}
+
+from Stmt stmt, int kind, int kind_new, Location location
+where
+  stmts(stmt, kind, location) and
+  if isConstevalIf(stmt) then kind_new = 7 else kind_new = kind // Turns consteval if into a block with two block statements in it
+select stmt, kind_new, location

cpp/downgrades/1aa71a4a687fc93f807d4dfeeef70feceeced242/semmlecode.cpp.dbscheme

@@ -0,0 +1,5 @@
+description: Support (not) consteval if
+compatibility: full
+consteval_if_then.rel: delete
+consteval_if_else.rel: delete
+stmts.rel: run stmts.qlo

cpp/downgrades/1aa71a4a687fc93f807d4dfeeef70feceeced242/stmts.ql

@@ -0,0 +1,4 @@
+---
+category: feature
+---
+* A new class `ConstevalIfStmt` was introduced, which represents the C++23 `if consteval` and `if ! consteval` statements.

cpp/downgrades/1aa71a4a687fc93f807d4dfeeef70feceeced242/upgrade.properties

@@ -912,6 +912,10 @@ private predicate namedStmtChildPredicates(Locatable s, Element e, string pred)
     or
     s.(ConstexprIfStmt).getElse() = e and pred = "getElse()"
     or
+    s.(ConstevalIfStmt).getThen() = e and pred = "getThen()"
+    or
+    s.(ConstevalIfStmt).getElse() = e and pred = "getElse()"
+    or
     s.(Handler).getParameter() = e and pred = "getParameter()"
     or
     s.(IfStmt).getInitialization() = e and pred = "getInitialization()"

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

@@ -876,6 +876,25 @@ private predicate subEdge(Pos p1, Node n1, Node n2, Pos p2) {
     p2.nodeAfter(n2, s)
   )
   or
+  // NotConstevalIfStmt -> { then, else } ->
+  exists(ConstevalIfStmt s |
+    p1.nodeAt(n1, s) and
+    p2.nodeBefore(n2, s.getThen())
+    or
+    p1.nodeAt(n1, s) and
+    p2.nodeBefore(n2, s.getElse())
+    or
+    p1.nodeAt(n1, s) and
+    not exists(s.getElse()) and
+    p2.nodeAfter(n2, s)
+    or
+    p1.nodeAfter(n1, s.getThen()) and
+    p2.nodeAfter(n2, s)
+    or
+    p1.nodeAfter(n1, s.getElse()) and
+    p2.nodeAfter(n2, s)
+  )
+  or
   // WhileStmt -> condition ; body -> condition ; after dtors -> after
   exists(WhileStmt s |
     p1.nodeAt(n1, s) and

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

@@ -47,7 +47,7 @@ abstract class TranslatedFlexibleCondition extends TranslatedCondition, Conditio
 {
   TranslatedFlexibleCondition() { this = TTranslatedFlexibleCondition(expr) }
 
-  final override predicate handlesDestructorsExplicitly() { none() } // TODO: this needs to be revisted when we get unnamed destructors
+  final override predicate handlesDestructorsExplicitly() { none() } // TODO: this needs to be revisited when we get unnamed destructors
 
   final override TranslatedElement getChild(int id) { id = 0 and result = this.getOperand() }
 

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

@@ -166,7 +166,7 @@ private predicate ignoreExpr(Expr expr) {
 }
 
 /**
- * Holds if the side effects of `expr` should be ignoredf for the purposes of IR generation.
+ * Holds if the side effects of `expr` should be ignored for the purposes of IR generation.
  *
  * In cases involving `constexpr`, a call can wind up as a constant expression. `ignoreExpr()` will
  * not hold for such a call, since we do need to translate the call (as a constant), but we need to

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

@@ -1098,6 +1098,61 @@ class TranslatedConstExprIfStmt extends TranslatedIfLikeStmt {
   override predicate hasElse() { exists(stmt.getElse()) }
 }
 
+class TranslatedConstevalIfStmt extends TranslatedStmt {
+  override ConstevalIfStmt stmt;
+
+  override Instruction getFirstInstruction(EdgeKind kind) {
+    if not this.hasEvaluatedBranch()
+    then
+      kind instanceof GotoEdge and
+      result = this.getInstruction(OnlyInstructionTag())
+    else result = this.getEvaluatedBranch().getFirstInstruction(kind)
+  }
+
+  override TranslatedElement getChildInternal(int id) {
+    id = 0 and
+    result = this.getThen()
+    or
+    id = 1 and
+    result = this.getElse()
+  }
+
+  override predicate hasInstruction(Opcode opcode, InstructionTag tag, CppType resultType) {
+    not this.hasEvaluatedBranch() and
+    opcode instanceof Opcode::NoOp and
+    tag = OnlyInstructionTag() and
+    resultType = getVoidType()
+  }
+
+  override Instruction getALastInstructionInternal() {
+    if not this.hasEvaluatedBranch()
+    then result = this.getInstruction(OnlyInstructionTag())
+    else result = this.getEvaluatedBranch().getALastInstruction()
+  }
+
+  override TranslatedElement getLastChild() { result = this.getEvaluatedBranch() }
+
+  override Instruction getInstructionSuccessorInternal(InstructionTag tag, EdgeKind kind) {
+    tag = OnlyInstructionTag() and
+    result = this.getParent().getChildSuccessor(this, kind)
+  }
+
+  override Instruction getChildSuccessorInternal(TranslatedElement child, EdgeKind kind) {
+    (child = this.getThen() or child = this.getElse()) and
+    result = this.getParent().getChildSuccessor(this, kind)
+  }
+
+  TranslatedStmt getEvaluatedBranch() {
+    result = getTranslatedStmt(stmt.getRuntimeEvaluatedBranch())
+  }
+
+  predicate hasEvaluatedBranch() { stmt.hasRuntimeEvaluatedBranch() }
+
+  TranslatedStmt getThen() { result = getTranslatedStmt(stmt.getThen()) }
+
+  TranslatedStmt getElse() { result = getTranslatedStmt(stmt.getElse()) }
+}
+
 abstract class TranslatedLoop extends TranslatedStmt, ConditionContext {
   override Loop stmt;