include/llvm/Transforms/Utils/LCSSA.h

   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