Finding operator delete[] is still problematic, without it the extension
is a security hazard, so reverting until the problem with operator
delete[] is figured out.

This reverts the following PRs:
Reland [MS][clang] Add support for vector deleting destructors (llvm#133451)
[MS][clang] Make sure vector deleting dtor calls correct operator delete (llvm#133950)
[MS][clang] Fix crash on deletion of array of pointers (llvm#134088)
[clang] Do not diagnose unused deleted operator delete[] (llvm#134357)
[MS][clang] Error about ambiguous operator delete[] only when required (llvm#135041)

Whereas it is UB in terms of the standard to delete an array of objects
via pointer whose static type doesn't match its dynamic type, MSVC
supports an extension allowing to do it.
Aside from array deletion not working correctly in the mentioned case,
currently not having this extension implemented causes clang to generate
code that is not compatible with the code generated by MSVC, because
clang always puts scalar deleting destructor to the vftable. This PR
aims to resolve these problems.

It was reverted due to link time errors in chromium with sanitizer
coverage enabled,
which is fixed by https://github.com/llvm/llvm-project/pull/131929 .

The second commit of this PR also contains a fix for a runtime failure
in chromium reported
in
https://github.com/llvm/llvm-project/pull/126240#issuecomment-2730216384
.

Fixes https://github.com/llvm/llvm-project/issues/19772

This caused link errors when building with sancov. See comment on the PR.

> Whereas it is UB in terms of the standard to delete an array of objects
> via pointer whose static type doesn't match its dynamic type, MSVC
> supports an extension allowing to do it.
> Aside from array deletion not working correctly in the mentioned case,
> currently not having this extension implemented causes clang to generate
> code that is not compatible with the code generated by MSVC, because
> clang always puts scalar deleting destructor to the vftable. This PR
> aims to resolve these problems.
>
> Fixes https://github.com/llvm/llvm-project/issues/19772

This reverts commit d6942d54f677000cf713d2b0eba57b641452beb4.

Whereas it is UB in terms of the standard to delete an array of objects
via pointer whose static type doesn't match its dynamic type, MSVC
supports an extension allowing to do it.
Aside from array deletion not working correctly in the mentioned case,
currently not having this extension implemented causes clang to generate
code that is not compatible with the code generated by MSVC, because
clang always puts scalar deleting destructor to the vftable. This PR
aims to resolve these problems.

Fixes https://github.com/llvm/llvm-project/issues/19772

Identified with misc-include-cleaner.

Virtual function pointer entries in v-tables are signed with address
discrimination in addition to declaration-based discrimination, where an
integer discriminator the string hash (see
`ptrauth_string_discriminator`) of the mangled name of the overridden
method. This notably provides diversity based on the full signature of
the overridden method, including the method name and parameter types.
This patch introduces ItaniumVTableContext logic to find the original
declaration of the overridden method.
On AArch64, these pointers are signed using the `IA` key (the
process-independent code key.)

V-table pointers can be signed with either no discrimination, or a
similar scheme using address and decl-based discrimination. In this
case, the integer discriminator is the string hash of the mangled
v-table identifier of the class that originally introduced the vtable
pointer.
On AArch64, these pointers are signed using the `DA` key (the
process-independent data key.)

Not using discrimination allows attackers to simply copy valid v-table
pointers from one object to another. However, using a uniform
discriminator of 0 does have positive performance and code-size
implications on AArch64, and diversity for the most important v-table
access pattern (virtual dispatch) is already better assured by the
signing schemas used on the virtual functions. It is also known that
some code in practice copies objects containing v-tables with `memcpy`,
and while this is not permitted formally, it is something that may be
invasive to eliminate.

This is controlled by:
```
  -fptrauth-vtable-pointer-type-discrimination
  -fptrauth-vtable-pointer-address-discrimination
```

In addition, this provides fine-grained controls in the
ptrauth_vtable_pointer attribute, which allows overriding the default
ptrauth schema for vtable pointers on a given class hierarchy, e.g.:
```
  [[clang::ptrauth_vtable_pointer(no_authentication, no_address_discrimination, 
                                  no_extra_discrimination)]]
  [[clang::ptrauth_vtable_pointer(default_key, default_address_discrimination,
                                  custom_discrimination, 0xf00d)]]
```

The override is then mangled as a parametrized vendor extension:
```
"__vtptrauth" I
 <key>
 <addressDiscriminated>
 <extraDiscriminator>
E
```

To support this attribute, this patch adds a small extension to the
attribute-emitter tablegen backend.

Note that there are known areas where signing is either missing
altogether or can be strengthened. Some will be addressed in later
changes (e.g., member function pointers, some RTTI).
`dynamic_cast` in particular is handled by emitting an artificial
v-table pointer load (in a way that always authenticates it) before the
runtime call itself, as the runtime doesn't have enough information
today to properly authenticate it. Instead, the runtime is currently
expected to strip the v-table pointer.

---------

Co-authored-by: John McCall <rjmccall@apple.com>
Co-authored-by: Ahmed Bougacha <ahmed@bougacha.org>

This combines the previously posted patches with some additional work
I've done to more closely match MSVC output.

Most of the important logic here is implemented in
AArch64Arm64ECCallLowering. The purpose of the
AArch64Arm64ECCallLowering is to take "normal" IR we'd generate for
other targets, and generate most of the Arm64EC-specific bits:
generating thunks, mangling symbols, generating aliases, and generating
the .hybmp$x table. This is all done late for a few reasons: to
consolidate the logic as much as possible, and to ensure the IR exposed
to optimization passes doesn't contain complex arm64ec-specific
constructs.

The other changes are supporting changes, to handle the new constructs
generated by that pass.

There's a global llvm.arm64ec.symbolmap representing the .hybmp$x
entries for the thunks. This gets handled directly by the AsmPrinter
because it needs symbol indexes that aren't available before that.

There are two new calling conventions used to represent calls to and
from thunks: ARM64EC_Thunk_X64 and ARM64EC_Thunk_Native. There are a few
changes to handle the associated exception-handling info,
SEH_SaveAnyRegQP and SEH_SaveAnyRegQPX.

I've intentionally left out handling for structs with small
non-power-of-two sizes, because that's easily separated out. The rest of
my current work is here. I squashed my current patches because they were
split in ways that didn't really make sense. Maybe I could split out
some bits, but it's hard to meaningfully test most of the parts
independently.

Thanks to @dpaoliello for extensive testing and suggestions.

(Originally posted as https://reviews.llvm.org/D157547 .)

Partial progress towards replacing in-tree uses of `Type::getPointerTo()`.
This needs to be done before deprecating the API.

Reviewed By: nikic, barannikov88

Differential Revision: https://reviews.llvm.org/D152321

Remove uses of to-be-deprecated API.

Explicitly pass loaded type when creating loads, in preparation
for the deprecation of these APIs.

There are still a couple of uses left.