This patch removes many annotations that are not relevant anymore since
we don't support or test back-deploying to macOS < 10.13. It also cleans
up raw usage of target triples to identify versions of dylibs shipped on
prior versions of macOS, and uses the target-agnostic Lit features
instead. Finally, it reorders both the Lit backdeployment features and
the corresponding availability macros in the library in a way that makes
more sense, and reformulates the Lit backdeployment features in terms of
when a version of LLVM was introduced instead of encoding the system
versions on which it hasn't been introduced yet. Although one can be
derived from the other, encoding the negative form is extremely
error-prone.
Fixes#80901
We were not making any distinction between e.g. the "Apple-flavored"
libc++ built from trunk and the system-provided standard library on
Apple platforms. For example, any test that would be XFAILed on a
back-deployment target would unexpectedly pass when run on that
deployment target against the tip of trunk Apple-flavored libc++. In
reality, that test would be expected to pass because we're running
against the latest libc++, even if it is Apple-flavored.
To solve this issue, we introduce a new feature that describes whether
the Standard Library in use is the one provided by the system by
default, and that notion is different from the underlying standard
library flavor. We also refactor the existing Lit features to make a
distinction between availability markup and the library we're running
against at runtime, which otherwise limit the flexibility of what we can
express in the test suite. Finally, we refactor some of the
back-deployment versions that were incorrect (such as thinking that LLVM
10 was introduced in macOS 11, when in reality macOS 11 was synced with
LLVM 11).
Fixes#82107
This addresses cases (currently failing) where we throw a null
pointer-to-object and fixes#64953.
We are trying to satisfy the following bullet from the C++ ABI 15.3:
* the handler is of type cv1 T* cv2 and E is a pointer type that can be
converted to the type of the handler by either or both of:
- a standard pointer conversion (4.10 [conv.ptr]) not involving
conversions to private or protected or ambiguous classes.
- a qualification conversion.
The existing implementation assesses the ambiguity of bases by computing
the offsets to them; ambiguous cases are then when the same base appears
at different offsets. The computation of offset includes indirecting
through the vtables to find the offsets to virtual bases.
When the thrown pointer points to a real object, this is quite efficient
since, if the base is found, and it is not ambiguous and on a public
path, the offset is needed to return the adjusted pointer (and the
indirections are not particularly expensive to compute).
However, when we throw a null pointer-to-object, this scheme is no
longer applicable (and the code currently bypasses the relevant
computations, leading to the incorrect catches reported in the issue).
-----
The solution proposed here takes a composite approach:
1. When the pointer-to-object points to a real instance (well, at least,
it is determined to be non-null), we use the existing scheme.
2. When the pointer-to-object is null:
* We note that there is no real object.
* When we are processing non-virtual bases, we continue to compute the
offsets, but for a notional dummy object based at 0. This is OK, since
we never need to access the object content for non-virtual bases.
* When we are processing a path with one or more virtual bases, we
remember a cookie corresponding to the inner-most virtual base found so
far (and set the notional offset to 0). Offsets to inner non-virtual
bases are then computed as normal.
A base is then ambiguous iff:
* There is a recorded virtual base cookie and that is different from the
current one or,
* The non-virtual base offsets differ.
When a handler for a pointer succeeds in catching a base pointer for a
thrown null pointer-to-object, we still return a nullptr (so the
adjustment to the pointer is not required and need not be computed).
Since we noted that there was no object when starting the search for
ambiguous bases, we know that we can skip the pointer adjustment.
This was originally uploaded as https://reviews.llvm.org/D158769.
Fixes#64953
