[SPIR-V] Fix BB ordering & register lifetime (#111026)

The "topological" sorting was behaving incorrectly in some cases: 
the exit of a loop could have a lower rank than a node in the loop.
This causes issues when structurizing some patterns, and also codegen
issues as we could generate BBs in the incorrect order in regard to the
SPIR-V spec.

Fixing this ordering alone broke other parts of the structurizer, which
by luck worked. Had to fix those.

Added more test cases, especially to test basic patterns.

I also needed to tweak/disable some tests for 2 reasons:
 - SPIR-V now required reg2mem/mem2reg to run. Meaning dead stores
   are optimized away. Some tests require tweaks to avoid having the
   whole function removed.
 - Mem2Reg will generate variable & load/stores. This generates
   G_BITCAST in several cases. And there is currently something wrong
   we do with G_BITCAST which causes MIR verifier to complain.
   Until this is resolved, I disabled -verify-machineinstrs flag on
   those tests.

---------

Signed-off-by: Nathan Gauër <brioche@google.com>
92 files changed
tree: e9ae30d295609eda1e9cc13fe23248e5ba1b9a7d
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. libc/
  11. libclc/
  12. libcxx/
  13. libcxxabi/
  14. libunwind/
  15. lld/
  16. lldb/
  17. llvm/
  18. llvm-libgcc/
  19. mlir/
  20. offload/
  21. openmp/
  22. polly/
  23. pstl/
  24. runtimes/
  25. third-party/
  26. utils/
  27. .clang-format
  28. .clang-tidy
  29. .git-blame-ignore-revs
  30. .gitattributes
  31. .gitignore
  32. .mailmap
  33. CODE_OF_CONDUCT.md
  34. CONTRIBUTING.md
  35. LICENSE.TXT
  36. pyproject.toml
  37. README.md
  38. SECURITY.md
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