[clang][Interp] Fix Pointer::toAPValue() LValuePath order

[tbaeder]

Summary

See the comment I added for an explanation. This fixes the commented-out testcases I added in https://reviews.llvm.org/D134523.

[tbaeder]

Meh, looks like I forgot to fix up the commit message for https://github.com/llvm/llvm-project/commit/4d2d426a51e122231443d89b196b0c6e91a5b147.

clang/lib/AST/Interp/Pointer.cpp

if (isUnknownSizeArray()) {
           llvm_unreachable("Invalid field type");
         }
       }
 
       IsOnePastEnd = isOnePastEnd();
     }
   }
 
-  return APValue(Base, Offset, Path, IsOnePastEnd, IsNullPtr);
+  // We assemble the LValuePath starting from the innermost pointer to the
+  // outermost one. SO in a.b.c, the first element in Path will refer to
+  // the field 'c', while later code expects it to refer to 'a'.
+  // Just invert the order of the elements.
+  decltype(Path) RealPath;
+  RealPath.resize(Path.size());
+  for (unsigned I = 0, N = Path.size(); I != N; ++I)
+    RealPath[N - 1 - I] = Path[I];
+
+  return APValue(Base, Offset, RealPath, IsOnePastEnd, IsNullPtr);
 }
 
 bool Pointer::isInitialized() const {
   assert(Pointee && "Cannot check if null pointer was initialized");
   Descriptor *Desc = getFieldDesc();
   assert(Desc);
   if (Desc->isPrimitiveArray()) {
     if (Pointee->IsStatic)

clang/test/AST/Interp/records.cpp

BoolPair v[4] = {
     {true,  false},
     {true,  true },
   };
 };
 // Init
 constexpr FourBoolPairs LT;
 // Copy ctor
 constexpr FourBoolPairs LT2 = LT;
-// FIXME: The copy constructor call above
-//   works, but APValue we generate for it is
-//   not sufficiently correct, so the lvalue-to-rvalue
-//   conversion in ExprConstant.c runs into an assertion.
-//static_assert(LT2.v[0].first == false, "");
-//static_assert(LT2.v[0].second == false, "");
-//static_assert(LT2.v[2].first == true, "");
-//static_assert(LT2.v[2].second == false, "");
+static_assert(LT2.v[0].first == false, "");
+static_assert(LT2.v[0].second == false, "");
+static_assert(LT2.v[2].first == true, "");
+static_assert(LT2.v[2].second == false, "");