The layout and the size of an ObjC interface can change after its
corresponding implementation is parsed when synthesized ivars or ivars
declared in categories are added to the interface's list of ivars. This
can cause clang to mis-compile if the optimization that emits fixed
offsets for ivars (see 923ddf65f4e21ec67018cf56e823895de18d83bc) uses an
ObjC class layout that is outdated and no longer reflects the current
state of the class.

For example, when compiling `constant-non-fragile-ivar-offset.m`, clang
emits 20 instead of 24 as the offset for `IntermediateClass2Property` as
the class layout for `SuperClass2`, which is created when the
implementation of IntermediateClass3 is parsed, is outdated when the
implementation of `IntermediateClass2` is parsed.

This commit invalidates the stale layout information of the class and
its subclasses if new ivars are added to the interface.

With this change, we can also stop using ObjC implementation decls as
the key to retrieve ObjC class layouts information as the layout
retrieved using the ObjC interface as the key will always be up to date.

rdar://139531391

As part of the "RemoveDIs" work to eliminate debug intrinsics, we're
replacing methods that use Instruction*'s as positions with iterators. The
call-sites updated in this patch are those where the dyn_cast_or_null cast
utility doesn't compose well with iterator insertion. It can distinguish
between nullptr and a "present" (non-null) Instruction pointer, but not
between a legal and illegal instruction iterator. This can lead to
end-iterator dereferences and thus crashes.

We can improve this in the future (as parent-pointers can now be accessed
from ilist nodes), but for the moment, add explicit tests for end()
iterators at the five call sites affected by this.

This reverts commit 81fc3add1e627c23b7270fe2739cdacc09063e54.

This breaks some LLDB tests, e.g.
SymbolFile/DWARF/x86/no_unique_address-with-bitfields.cpp:

lldb: ../llvm-project/clang/lib/AST/Decl.cpp:4604: unsigned int clang::FieldDecl::getBitWidthValue() const: Assertion `isa<ConstantExpr>(getBitWidth())' failed.

Save the bitwidth value as a `ConstantExpr` with the value set. Remove
the `ASTContext` parameter from `getBitWidthValue()`, so the latter
simply returns the value from the `ConstantExpr` instead of
constant-evaluating the bitwidth expression every time it is called.

To authenticate pointers, CodeGen needs access to the key and
discriminators that were used to sign the pointer. That information is
sometimes known from the context, but not always, which is why `Address`
needs to hold that information.

This patch adds methods and data members to `Address`, which will be
needed in subsequent patches to authenticate signed pointers, and uses
the newly added methods throughout CodeGen. Although this patch isn't
strictly NFC as it causes CodeGen to use different code paths in some
cases (e.g., `mergeAddressesInConditionalExpr`), it doesn't cause any
changes in functionality as it doesn't add any information needed for
authentication.

In addition to the changes mentioned above, this patch introduces class
`RawAddress`, which contains a pointer that we know is unsigned, and
adds several new functions for creating `Address` and `LValue` objects.

This reapplies d9a685a9dd589486e882b722e513ee7b8c84870c, which was
reverted because it broke ubsan bots. There seems to be a bug in
coroutine code-gen, which is causing EmitTypeCheck to use the wrong
alignment. For now, pass alignment zero to EmitTypeCheck so that it can
compute the correct alignment based on the passed type (see function
EmitCXXMemberOrOperatorMemberCallExpr).

This reverts commit d9a685a9dd589486e882b722e513ee7b8c84870c.

The commit broke ubsan bots.

To authenticate pointers, CodeGen needs access to the key and
discriminators that were used to sign the pointer. That information is
sometimes known from the context, but not always, which is why `Address`
needs to hold that information.

This patch adds methods and data members to `Address`, which will be
needed in subsequent patches to authenticate signed pointers, and uses
the newly added methods throughout CodeGen. Although this patch isn't
strictly NFC as it causes CodeGen to use different code paths in some
cases (e.g., `mergeAddressesInConditionalExpr`), it doesn't cause any
changes in functionality as it doesn't add any information needed for
authentication.

In addition to the changes mentioned above, this patch introduces class
`RawAddress`, which contains a pointer that we know is unsigned, and
adds several new functions for creating `Address` and `LValue` objects.

This reapplies 8bd1f9116aab879183f34707e6d21c7051d083b6. The commit
broke msan bots because LValue::IsKnownNonNull was uninitialized.

This reverts commit 8bd1f9116aab879183f34707e6d21c7051d083b6.

It appears that the commit broke msan bots.