[clang][Interp] Fix some dummy-related FIXME comments

Author: tbaederr

clang/lib/AST/Interp/Interp.h

@@ -1569,9 +1569,7 @@ bool OffsetHelper(InterpState &S, CodePtr OpPC, const T &Offset,
     APSInt NewIndex =
         (Op == ArithOp::Add) ? (APIndex + APOffset) : (APIndex - APOffset);
     S.CCEDiag(S.Current->getSource(OpPC), diag::note_constexpr_array_index)
-        << NewIndex
-        << /*array*/ static_cast<int>(!Ptr.inArray())
-        << static_cast<unsigned>(MaxIndex);
+        << NewIndex << /*array*/ static_cast<int>(!Ptr.inArray()) << MaxIndex;
     Invalid = true;
   };
 
@@ -1598,7 +1596,7 @@ bool OffsetHelper(InterpState &S, CodePtr OpPC, const T &Offset,
     }
   }
 
-  if (Invalid && !Ptr.isDummy() && S.getLangOpts().CPlusPlus)
+  if (Invalid && S.getLangOpts().CPlusPlus)
     return false;
 
   // Offset is valid - compute it on unsigned.
@@ -2110,6 +2108,9 @@ inline bool ArrayDecay(InterpState &S, CodePtr OpPC) {
     return true;
   }
 
+  if (!CheckRange(S, OpPC, Ptr, CSK_ArrayToPointer))
+    return false;
+
   if (!Ptr.isUnknownSizeArray() || Ptr.isDummy()) {
     S.Stk.push<Pointer>(Ptr.atIndex(0));
     return true;

clang/lib/AST/Interp/Pointer.h

@@ -384,11 +384,6 @@ class Pointer {
   bool isUnknownSizeArray() const {
     if (!isBlockPointer())
       return false;
-    // If this points inside a dummy block, return true.
-    // FIXME: This might change in the future. If it does, we need
-    // to set the proper Ctor/Dtor functions for dummy Descriptors.
-    if (!isRoot() && isDummy())
-      return true;
     return getFieldDesc()->isUnknownSizeArray();
   }
   /// Checks if the pointer points to an array.
@@ -560,8 +555,6 @@ class Pointer {
 
     if (!asBlockPointer().Pointee)
       return false;
-    if (isDummy())
-      return false;
 
     return isElementPastEnd() || getSize() == getOffset();
   }

clang/lib/AST/Interp/Program.cpp

@@ -144,8 +144,12 @@ std::optional<unsigned> Program::getOrCreateDummy(const ValueDecl *VD) {
   if (auto It = DummyVariables.find(VD); It != DummyVariables.end())
     return It->second;
 
+  QualType QT = VD->getType();
+  if (const auto *RT = QT->getAs<ReferenceType>())
+    QT = RT->getPointeeType();
+
   Descriptor *Desc;
-  if (std::optional<PrimType> T = Ctx.classify(VD->getType()))
+  if (std::optional<PrimType> T = Ctx.classify(QT))
     Desc = createDescriptor(VD, *T, std::nullopt, true, false);
   else
     Desc = createDescriptor(VD, VD->getType().getTypePtr(), std::nullopt, true,

clang/test/AST/Interp/arrays.cpp

@@ -580,3 +580,18 @@ constexpr ptrdiff_t d3 = &melchizedek[0] - &melchizedek[1]; // ok
 /// GH#88018
 const int SZA[] = {};
 void testZeroSizedArrayAccess() { unsigned c = SZA[4]; }
+
+#if __cplusplus >= 202002L
+constexpr int test_multiarray2() { // both-error {{never produces a constant expression}}
+  int multi2[2][1]; // both-note {{declared here}}
+  return multi2[2][0]; // both-note {{cannot access array element of pointer past the end of object}} \
+                       // both-warning {{array index 2 is past the end of the array (that has type 'int[2][1]')}}
+}
+
+/// Same but with a dummy pointer.
+int multi22[2][2]; // both-note {{declared here}}
+int test_multiarray22() {
+  return multi22[2][0]; // both-warning {{array index 2 is past the end of the array (that has type 'int[2][2]')}}
+}
+
+#endif