[clang][Interp] Don't diagnose non-const reads from the evaluating decl

Author: tbaederr

clang/lib/AST/Interp/EvalEmitter.cpp

@@ -56,6 +56,7 @@ EvaluationResult EvalEmitter::interpretExpr(const Expr *E,
 EvaluationResult EvalEmitter::interpretDecl(const VarDecl *VD,
                                             bool CheckFullyInitialized) {
   this->CheckFullyInitialized = CheckFullyInitialized;
+  S.EvaluatingDecl = VD;
 
   if (const Expr *Init = VD->getAnyInitializer()) {
     QualType T = VD->getType();
@@ -69,6 +70,7 @@ EvaluationResult EvalEmitter::interpretDecl(const VarDecl *VD,
   if (!this->visitDecl(VD, S.inConstantContext()) && EvalResult.empty())
     EvalResult.setInvalid();
 
+  S.EvaluatingDecl = nullptr;
   return std::move(this->EvalResult);
 }
 

clang/lib/AST/Interp/Interp.cpp

@@ -322,7 +322,7 @@ bool CheckConstant(InterpState &S, CodePtr OpPC, const Descriptor *Desc) {
   };
 
   if (const auto *D = Desc->asVarDecl();
-      D && D->hasGlobalStorage() && !IsConstType(D)) {
+      D && D->hasGlobalStorage() && D != S.EvaluatingDecl && !IsConstType(D)) {
     diagnoseNonConstVariable(S, OpPC, D);
     return S.inConstantContext();
   }

clang/lib/AST/Interp/InterpState.h

@@ -121,6 +121,8 @@ class InterpState final : public State, public SourceMapper {
   InterpFrame *Current = nullptr;
   /// Source location of the evaluating expression
   SourceLocation EvalLocation;
+  /// Declaration we're initializing/evaluting, if any.
+  const VarDecl *EvaluatingDecl = nullptr;
 };
 
 } // namespace interp