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
40namespace llvm {
41
42/// Performs Loop Invariant Code Motion Pass.
43class LICMPass : public PassInfoMixin<LICMPass> {
44public:
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