[SlotIndexes] Further pack indices to improve spill placement time (#182640)

This patch makes it so that renumbering indices when inserting
instructions into the SlotIndexes analysis renumbers the entire list if
the list is otherwise densely packed. This fixes a case we saw on
AArch64 with a lot of spills where every single spill instruction
insertion required a renumbering of most of the instructions in a large
function, making the operation approximately quadratic.

This is not NFC as heuristics depend on the SlotIndex numbers, although
this should mostly be a wash as LRs should be extended ~equally.
6 files changed
tree: aa2467bb0d0130a484d12a8dd5f56f0331b09738
  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

The LLVM Compiler Infrastructure

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