1 //===- LCSSA.h - Loop-closed SSA transform Pass -----------------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This pass transforms loops by placing phi nodes at the end of the loops for 11 // all values that are live across the loop boundary. For example, it turns 12 // the left into the right code: 13 // 14 // for (...) for (...) 15 // if (c) if (c) 16 // X1 = ... X1 = ... 17 // else else 18 // X2 = ... X2 = ... 19 // X3 = phi(X1, X2) X3 = phi(X1, X2) 20 // ... = X3 + 4 X4 = phi(X3) 21 // ... = X4 + 4 22 // 23 // This is still valid LLVM; the extra phi nodes are purely redundant, and will 24 // be trivially eliminated by InstCombine. The major benefit of this 25 // transformation is that it makes many other loop optimizations, such as 26 // LoopUnswitching, simpler. 27 // 28 //===----------------------------------------------------------------------===// 29 30 #ifndef LLVM_TRANSFORMS_UTILS_LCSSA_H 31 #define LLVM_TRANSFORMS_UTILS_LCSSA_H 32 33 #include "llvm/IR/PassManager.h" 34 35 namespace llvm { 36 37 /// Converts loops into loop-closed SSA form. 38 class LCSSAPass : public PassInfoMixin<LCSSAPass> { 39 public: 40 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 41 }; 42 } // end namespace llvm 43 44 #endif // LLVM_TRANSFORMS_UTILS_LCSSA_H 45
