[clang][CodeGen][SPIR-V] Fix incorrect SYCL usage, implement missing interface (#109415)

This is primarily meant to address the issue identified in #109182,
around incorrect usage of `-fsycl-is-dev

[clang][CodeGen][SPIR-V] Fix incorrect SYCL usage, implement missing interface (#109415)

This is primarily meant to address the issue identified in #109182,
around incorrect usage of `-fsycl-is-device`; we now have AMDGCN
flavoured SPIR-V which retains the desired behaviour around the default
AS and does not depend on the SYCL language being enabled to do so.
Overall, there are three changes:

1. We unconditionally use the `SPIRDefIsGen` AS map for AMDGCNSPIRV
target, as there is no case where the hack of setting default to private
would be desirable, and it can be used for languages other than OCL/HIP;
2. We implement `SPIRVTargetCodeGenInfo::getGlobalVarAddressSpace` for
SPIR-V in general, because otherwise using it from languages other than
HIP or OpenCL would yield 0, incorrectly;
3. We remove the incorrect usage of `-fsycl-is-device`.

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[Clang][CodeGen] Start migrating away from assuming the Default AS is 0 (#88182)

At the moment, Clang is rather liberal in assuming that 0 (and by extension unqualified) is always a safe default. Th

[Clang][CodeGen] Start migrating away from assuming the Default AS is 0 (#88182)

At the moment, Clang is rather liberal in assuming that 0 (and by extension unqualified) is always a safe default. This does not work for targets that actually use a different value for the default / generic AS (for example, the SPIRV that obtains from HIPSPV or SYCL). This patch is a first, fairly safe step towards trying to clear things up by querying a modules' default AS from the target, rather than assuming it's 0, alongside fixing a few places where things break / we encode the 0 == DefaultAS assumption. A bunch of existing tests are extended to check for non-zero default AS usage.

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[IR] Change representation of getelementptr inrange (#84341)

As part of the migration to ptradd
(https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699),
we need to change the

[IR] Change representation of getelementptr inrange (#84341)

As part of the migration to ptradd
(https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699),
we need to change the representation of the `inrange` attribute, which
is used for vtable splitting.

Currently, inrange is specified as follows:

```
getelementptr inbounds ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, inrange i32 1, i64 2)
```

The `inrange` is placed on a GEP index, and all accesses must be "in
range" of that index. The new representation is as follows:

```
getelementptr inbounds inrange(-16, 16) ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, i32 1, i64 2)
```

This specifies which offsets are "in range" of the GEP result. The new
representation will continue working when canonicalizing to ptradd
representation:

```
getelementptr inbounds inrange(-16, 16) (i8, ptr @vt, i64 48)
```

The inrange offsets are relative to the return value of the GEP. An
alternative design could make them relative to the source pointer
instead. The result-relative format was chosen on the off-chance that we
want to extend support to non-constant GEPs in the future, in which case
this variant is more expressive.

This implementation "upgrades" the old inrange representation in bitcode
by simply dropping it. This is a very niche feature, and I don't think
trying to upgrade it is worthwhile. Let me know if you disagree.

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[Clang][CodeGen]`vtable`, `typeinfo` et al. are globals

All data structures and values associated with handling virtual functions / inheritance, as well as RTTI, are globals and thus can only reside

[Clang][CodeGen]`vtable`, `typeinfo` et al. are globals

All data structures and values associated with handling virtual functions / inheritance, as well as RTTI, are globals and thus can only reside in the global address space. This was not taken fully taken into account because for most targets, global & generic appear to coincide. However, on targets where global & generic ASes differ (e.g. AMDGPU), this was problematic, since it led to the generation of invalid bitcasts (which would trigger asserts in Debug) and less than optimal code. This patch does two things:

ensures that vtables, vptrs, vtts, typeinfo are generated in the right AS, and populated accordingly;
removes a bunch of bitcasts which look like left-overs from the typed ptr era.

Reviewed By: yxsamliu

Differential Revision: https://reviews.llvm.org/D153092

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