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  1. //===- LCSSA.h - Loop-closed SSA transform Pass -----------------*- C++ -*-===//
  2. //
  3. // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  4. // See https://llvm.org/LICENSE.txt for license information.
  5. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  6. //
  7. //===----------------------------------------------------------------------===//
  8. //
  9. // This pass transforms loops by placing phi nodes at the end of the loops for
  10. // all values that are live across the loop boundary.  For example, it turns
  11. // the left into the right code:
  12. //
  13. // for (...)                for (...)
  14. //   if (c)                   if (c)
  15. //     X1 = ...                 X1 = ...
  16. //   else                     else
  17. //     X2 = ...                 X2 = ...
  18. //   X3 = phi(X1, X2)         X3 = phi(X1, X2)
  19. // ... = X3 + 4             X4 = phi(X3)
  20. //                          ... = X4 + 4
  21. //
  22. // This is still valid LLVM; the extra phi nodes are purely redundant, and will
  23. // be trivially eliminated by InstCombine.  The major benefit of this
  24. // transformation is that it makes many other loop optimizations, such as
  25. // LoopUnswitching, simpler.
  26. //
  27. //===----------------------------------------------------------------------===//
  28.  
  29. #ifndef LLVM_TRANSFORMS_UTILS_LCSSA_H
  30. #define LLVM_TRANSFORMS_UTILS_LCSSA_H
  31.  
  32. #include "llvm/IR/PassManager.h"
  33.  
  34. namespace llvm {
  35.  
  36. /// Converts loops into loop-closed SSA form.
  37. class LCSSAPass : public PassInfoMixin<LCSSAPass> {
  38. public:
  39.   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
  40. };
  41. } // end namespace llvm
  42.  
  43. #endif // LLVM_TRANSFORMS_UTILS_LCSSA_H
  44.