[DirectX] Denote `dx.resource.getpointer` with `IntrInaccessibleMemOnly` and `IntrReadMem` (#193593)

`IntrConvergent` was originally added to `dx.resource.getpointer` to
prevent optimization passes (`SimplifyCFG`, `GVN`) from sinking the
intrinsic out of control flow branches, which would create phi nodes on
the returned pointer.

Using `IntrInaccessibleMemOnly` and `IntrReadMem` semantics still
prevent passes from merging or sinking identical calls across branches.
However, this allows the call to be moved within a single control flow
path.

Updates relevant tests and adds a new test to demonstrate a now legal
potential optimization.

This was discovered when
https://github.com/llvm/llvm-project/pull/188792 caused the following
failure:
https://github.com/llvm/llvm-project/actions/runs/24577221310/job/71865579618.
When emitting convergence control tokens, each resource access is then a
user of the convergence control tokens, which makes it's use more
unnecessarily restrictive for optimizations and in this case would
prevent a loop unroll from taking place.

Assisted by: Claude Opus 4.6
4 files changed
tree: 253d8c43918f39a39f9ddf268163b574addbf760
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. flang-rt/
  11. libc/
  12. libclc/
  13. libcxx/
  14. libcxxabi/
  15. libsycl/
  16. libunwind/
  17. lld/
  18. lldb/
  19. llvm/
  20. llvm-libgcc/
  21. mlir/
  22. offload/
  23. openmp/
  24. orc-rt/
  25. polly/
  26. runtimes/
  27. third-party/
  28. utils/
  29. .clang-format
  30. .clang-format-ignore
  31. .clang-tidy
  32. .git-blame-ignore-revs
  33. .gitattributes
  34. .gitignore
  35. .mailmap
  36. CODE_OF_CONDUCT.md
  37. CONTRIBUTING.md
  38. LICENSE.TXT
  39. pyproject.toml
  40. README.md
  41. SECURITY.md
README.md

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