1 //===- LICM.h - Loop Invariant Code Motion 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 performs loop invariant code motion, attempting to remove as much 11 // code from the body of a loop as possible. It does this by either hoisting 12 // code into the preheader block, or by sinking code to the exit blocks if it is 13 // safe. This pass also promotes must-aliased memory locations in the loop to 14 // live in registers, thus hoisting and sinking "invariant" loads and stores. 15 // 16 // This pass uses alias analysis for two purposes: 17 // 18 // 1. Moving loop invariant loads and calls out of loops. If we can determine 19 // that a load or call inside of a loop never aliases anything stored to, 20 // we can hoist it or sink it like any other instruction. 21 // 2. Scalar Promotion of Memory - If there is a store instruction inside of 22 // the loop, we try to move the store to happen AFTER the loop instead of 23 // inside of the loop. This can only happen if a few conditions are true: 24 // A. The pointer stored through is loop invariant 25 // B. There are no stores or loads in the loop which _may_ alias the 26 // pointer. There are no calls in the loop which mod/ref the pointer. 27 // If these conditions are true, we can promote the loads and stores in the 28 // loop of the pointer to use a temporary alloca'd variable. We then use 29 // the SSAUpdater to construct the appropriate SSA form for the value. 30 // 31 //===----------------------------------------------------------------------===// 32 33 #ifndef LLVM_TRANSFORMS_SCALAR_LICM_H 34 #define LLVM_TRANSFORMS_SCALAR_LICM_H 35 36 #include "llvm/Analysis/LoopInfo.h" 37 #include "llvm/IR/PassManager.h" 38 #include "llvm/Transforms/Scalar/LoopPassManager.h" 39 40 namespace llvm { 41 42 /// Performs Loop Invariant Code Motion Pass. 43 class LICMPass : public PassInfoMixin<LICMPass> { 44 public: 45 PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM, 46 LoopStandardAnalysisResults &AR, LPMUpdater &U); 47 }; 48 } // end namespace llvm 49 50 #endif // LLVM_TRANSFORMS_SCALAR_LICM_H 51
