Revert "[clang][bytecode] Fix incorrect offset in elem() (llvm#155157)"

This reverts commit 0f4db1a.

This breaks the armv8-quick builder:
https://lab.llvm.org/buildbot/#/builders/154/builds/20676

Author: tbaederr

clang/lib/AST/ByteCode/EvaluationResult.cpp

@@ -178,8 +178,8 @@ bool EvaluationResult::checkFullyInitialized(InterpState &S,
 static void collectBlocks(const Pointer &Ptr,
                           llvm::SetVector<const Block *> &Blocks) {
   auto isUsefulPtr = [](const Pointer &P) -> bool {
-    return P.isLive() && P.isBlockPointer() && !P.isZero() && !P.isDummy() &&
-           P.isDereferencable() && !P.isUnknownSizeArray() && !P.isOnePastEnd();
+    return P.isLive() && !P.isZero() && !P.isDummy() && P.isDereferencable() &&
+           !P.isUnknownSizeArray() && !P.isOnePastEnd();
   };
 
   if (!isUsefulPtr(Ptr))

clang/lib/AST/ByteCode/Pointer.h

@@ -694,20 +694,15 @@ class Pointer {
     assert(asBlockPointer().Pointee);
     assert(isDereferencable());
     assert(getFieldDesc()->isPrimitiveArray());
-    assert(I < getFieldDesc()->getNumElems());
 
     unsigned ElemByteOffset = I * getFieldDesc()->getElemSize();
-    if (isArrayRoot()) {
-      unsigned ReadOffset = BS.Base + sizeof(InitMapPtr) + ElemByteOffset;
-      assert(ReadOffset + sizeof(T) <=
-             BS.Pointee->getDescriptor()->getAllocSize());
-      return *reinterpret_cast<T *>(BS.Pointee->rawData() + ReadOffset);
-    }
+    if (isArrayRoot())
+      return *reinterpret_cast<T *>(asBlockPointer().Pointee->rawData() +
+                                    asBlockPointer().Base + sizeof(InitMapPtr) +
+                                    ElemByteOffset);
 
-    unsigned ReadOffset = BS.Base + ElemByteOffset;
-    assert(ReadOffset + sizeof(T) <=
-           BS.Pointee->getDescriptor()->getAllocSize());
-    return *reinterpret_cast<T *>(BS.Pointee->rawData() + ReadOffset);
+    return *reinterpret_cast<T *>(asBlockPointer().Pointee->rawData() + Offset +
+                                  ElemByteOffset);
   }
 
   /// Whether this block can be read from at all. This is only true for

clang/test/AST/ByteCode/invalid.cpp

@@ -58,11 +58,3 @@ namespace Casts {
   /// Just make sure this doesn't crash.
   float PR9558 = reinterpret_cast<const float&>("asd");
 }
-
-
-/// This used to crash in collectBlock().
-struct S {
-};
-S s;
-S *sp[2] = {&s, &s};
-S *&spp = sp[1];