[clang][Interp] Load value from MemberExpr if required

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -1272,12 +1272,23 @@ bool ByteCodeExprGen<Emitter>::VisitMemberExpr(const MemberExpr *E) {
   if (DiscardResult)
     return this->discard(Base);
 
+  // MemberExprs are almost always lvalues, in which case we don't need to
+  // do the load. But sometimes they aren't.
+  const auto maybeLoadValue = [&]() -> bool {
+    if (E->isGLValue())
+      return true;
+    if (std::optional<PrimType> T = classify(E))
+      return this->emitLoadPop(*T, E);
+    return false;
+  };
+
   if (const auto *VD = dyn_cast<VarDecl>(Member)) {
     // I am almost confident in saying that a var decl must be static
     // and therefore registered as a global variable. But this will probably
     // turn out to be wrong some time in the future, as always.
     if (auto GlobalIndex = P.getGlobal(VD))
-      return this->emitGetPtrGlobal(*GlobalIndex, E);
+      return this->emitGetPtrGlobal(*GlobalIndex, E) && maybeLoadValue();
+    return false;
   }
 
   if (Initializing) {
@@ -1295,8 +1306,8 @@ bool ByteCodeExprGen<Emitter>::VisitMemberExpr(const MemberExpr *E) {
     const Record::Field *F = R->getField(FD);
     // Leave a pointer to the field on the stack.
     if (F->Decl->getType()->isReferenceType())
-      return this->emitGetFieldPop(PT_Ptr, F->Offset, E);
-    return this->emitGetPtrField(F->Offset, E);
+      return this->emitGetFieldPop(PT_Ptr, F->Offset, E) && maybeLoadValue();
+    return this->emitGetPtrField(F->Offset, E) && maybeLoadValue();
   }
 
   return false;

clang/test/AST/Interp/cxx03.cpp

@@ -10,3 +10,17 @@ namespace NonInitializingMemberExpr {
                                                                                               // both-note {{required by}} \
                                                                                               // both-note {{subexpression not valid}}
 }
+
+
+namespace NonLValueMemberExpr {
+  struct PODType {
+    int value;
+  };
+
+#define ATTR __attribute__((require_constant_initialization))
+  struct TT1 {
+    ATTR static const int &subobj_init;
+  };
+
+  const int &TT1::subobj_init = PODType().value;
+}