[DAG] Replace DAGCombiner::ConstantFoldBITCASTofBUILD_VECTOR with SelectionDAG::FoldConstantBuildVector (#147037)

DAGCombiner can already constant fold build vectors of constants/undefs
to a new vector type, but it has to be incredibly careful after
legalization to not affect a target's canonicalized constants.

This patch proposes we move the implementation inside SelectionDAG to
make it easier for targets to manually use the constant folding whenever
it deems it safe to do so.

I've also altered the method to take the BuildVectorSDNode input
directly and consistently use the same SDLoc.
4 files changed
tree: ddfa6acd0c63309589333161989fe49d7e426969
  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. libunwind/
  16. lld/
  17. lldb/
  18. llvm/
  19. llvm-libgcc/
  20. mlir/
  21. offload/
  22. openmp/
  23. polly/
  24. runtimes/
  25. third-party/
  26. utils/
  27. .clang-format
  28. .clang-format-ignore
  29. .clang-tidy
  30. .git-blame-ignore-revs
  31. .gitattributes
  32. .gitignore
  33. .mailmap
  34. CODE_OF_CONDUCT.md
  35. CONTRIBUTING.md
  36. LICENSE.TXT
  37. pyproject.toml
  38. README.md
  39. SECURITY.md
README.md

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