[clang][Interp] Fix handling PointerToIntegral casts

We need to always emit the diagnostic, but still do the cast.
This is also what the current interpreter does.

clang/lib/AST/Interp/Interp.cpp

@@ -533,17 +533,6 @@ bool CheckPure(InterpState &S, CodePtr OpPC, const CXXMethodDecl *MD) {
   return false;
 }
 
-bool CheckPotentialReinterpretCast(InterpState &S, CodePtr OpPC,
-                                   const Pointer &Ptr) {
-  if (!S.inConstantContext())
-    return true;
-
-  const SourceInfo &E = S.Current->getSource(OpPC);
-  S.CCEDiag(E, diag::note_constexpr_invalid_cast)
-      << 2 << S.getLangOpts().CPlusPlus << S.Current->getRange(OpPC);
-  return false;
-}
-
 bool CheckFloatResult(InterpState &S, CodePtr OpPC, const Floating &Result,
                       APFloat::opStatus Status) {
   const SourceInfo &E = S.Current->getSource(OpPC);

clang/lib/AST/Interp/Interp.h

@@ -113,10 +113,6 @@ bool CheckThis(InterpState &S, CodePtr OpPC, const Pointer &This);
 /// Checks if a method is pure virtual.
 bool CheckPure(InterpState &S, CodePtr OpPC, const CXXMethodDecl *MD);
 
-/// Checks if reinterpret casts are legal in the current context.
-bool CheckPotentialReinterpretCast(InterpState &S, CodePtr OpPC,
-                                   const Pointer &Ptr);
-
 /// Sets the given integral value to the pointer, which is of
 /// a std::{weak,partial,strong}_ordering type.
 bool SetThreeWayComparisonField(InterpState &S, CodePtr OpPC,
@@ -1722,8 +1718,9 @@ template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool CastPointerIntegral(InterpState &S, CodePtr OpPC) {
   const Pointer &Ptr = S.Stk.pop<Pointer>();
 
-  if (!CheckPotentialReinterpretCast(S, OpPC, Ptr))
-    return false;
+  const SourceInfo &E = S.Current->getSource(OpPC);
+  S.CCEDiag(E, diag::note_constexpr_invalid_cast)
+      << 2 << S.getLangOpts().CPlusPlus << S.Current->getRange(OpPC);
 
   S.Stk.push<T>(T::from(Ptr.getIntegerRepresentation()));
   return true;