[Clang] Treat constexpr-unknown value as invalid in evaluateValue

Author: dtcxzyw

clang/lib/AST/Decl.cpp

@@ -2587,6 +2587,9 @@ APValue *VarDecl::evaluateValueImpl(SmallVectorImpl<PartialDiagnosticAt> &Notes,
       !Notes.empty())
     Result = false;
 
+  if (Eval->Evaluated.allowConstexprUnknown())
+    Result = false;
+
   // Ensure the computed APValue is cleaned up later if evaluation succeeded,
   // or that it's empty (so that there's nothing to clean up) if evaluation
   // failed.

clang/lib/AST/ExprConstant.cpp

@@ -3628,8 +3628,6 @@ static bool evaluateVarDeclInit(EvalInfo &Info, const Expr *E,
   if (AllowConstexprUnknown) {
     if (!Result)
       Result = &Info.CurrentCall->createConstexprUnknownAPValues(VD, Base);
-    else
-      Result->setConstexprUnknown();
   }
   return true;
 }

clang/lib/CodeGen/CGExprConstant.cpp

@@ -1884,9 +1884,11 @@ llvm::Constant *ConstantEmitter::tryEmitPrivateForVarInit(const VarDecl &D) {
   // Try to emit the initializer.  Note that this can allow some things that
   // are not allowed by tryEmitPrivateForMemory alone.
   // Bail out on constexpr-unknown values since they are invalid in CodeGen.
-  if (APValue *value = D.evaluateValue();
-      value && !value->allowConstexprUnknown())
+  if (APValue *value = D.evaluateValue()) {
+    assert(!value->allowConstexprUnknown() &&
+           "Constexpr unknown values are not allowed in CodeGen");
     return tryEmitPrivateForMemory(*value, destType);
+  }
 
   return nullptr;
 }

clang/test/SemaCXX/constant-expression-cxx11.cpp

@@ -122,9 +122,9 @@ namespace CaseStatements {
 }
 
 extern int &Recurse1;
-int &Recurse2 = Recurse1; // expected-note {{declared here}}
+int &Recurse2 = Recurse1; // pre-cxx23-note {{declared here}}
 int &Recurse1 = Recurse2;
-constexpr int &Recurse3 = Recurse2; // expected-error {{must be initialized by a constant expression}} expected-note {{initializer of 'Recurse2' is not a constant expression}}
+constexpr int &Recurse3 = Recurse2; // expected-error {{must be initialized by a constant expression}} pre-cxx23-note {{initializer of 'Recurse2' is not a constant expression}}
 
 extern const int RecurseA;
 const int RecurseB = RecurseA; // expected-note {{declared here}}