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//===- LICM.h - Loop Invariant Code Motion Pass -------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs loop invariant code motion, attempting to remove as much
// code from the body of a loop as possible. It does this by either hoisting
// code into the preheader block, or by sinking code to the exit blocks if it is
// safe. This pass also promotes must-aliased memory locations in the loop to
// live in registers, thus hoisting and sinking "invariant" loads and stores.
//
// This pass uses alias analysis for two purposes:
//
// 1. Moving loop invariant loads and calls out of loops. If we can determine
// that a load or call inside of a loop never aliases anything stored to,
// we can hoist it or sink it like any other instruction.
// 2. Scalar Promotion of Memory - If there is a store instruction inside of
// the loop, we try to move the store to happen AFTER the loop instead of
// inside of the loop. This can only happen if a few conditions are true:
// A. The pointer stored through is loop invariant
// B. There are no stores or loads in the loop which _may_ alias the
// pointer. There are no calls in the loop which mod/ref the pointer.
// If these conditions are true, we can promote the loads and stores in the
// loop of the pointer to use a temporary alloca'd variable. We then use
// the SSAUpdater to construct the appropriate SSA form for the value.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_SCALAR_LICM_H
#define LLVM_TRANSFORMS_SCALAR_LICM_H
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/IR/PassManager.h"
namespace llvm {
/// Performs Loop Invariant Code Motion Pass.
class LICMPass : public PassInfoMixin<LICMPass> {
public:
PreservedAnalyses run(Loop &L, AnalysisManager<Loop> &AM);
};
} // end namespace llvm
#endif // LLVM_TRANSFORMS_SCALAR_LICM_H
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