1//===- LoopSimplify.h - Loop Canonicalization 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 performs several transformations to transform natural loops into a
10// simpler form, which makes subsequent analyses and transformations simpler and
11// more effective.
12//
13// Loop pre-header insertion guarantees that there is a single, non-critical
14// entry edge from outside of the loop to the loop header. This simplifies a
15// number of analyses and transformations, such as LICM.
16//
17// Loop exit-block insertion guarantees that all exit blocks from the loop
18// (blocks which are outside of the loop that have predecessors inside of the
19// loop) only have predecessors from inside of the loop (and are thus dominated
20// by the loop header). This simplifies transformations such as store-sinking
21// that are built into LICM.
22//
23// This pass also guarantees that loops will have exactly one backedge.
24//
25// Indirectbr instructions introduce several complications. If the loop
26// contains or is entered by an indirectbr instruction, it may not be possible
27// to transform the loop and make these guarantees. Client code should check
28// that these conditions are true before relying on them.
29//
30// Note that the simplifycfg pass will clean up blocks which are split out but
31// end up being unnecessary, so usage of this pass should not pessimize
32// generated code.
33//
34// This pass obviously modifies the CFG, but updates loop information and
35// dominator information.
36//
37//===----------------------------------------------------------------------===//
38#ifndef LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
39#define LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
40
41#include "llvm/IR/PassManager.h"
42#include "llvm/Support/Compiler.h"
43
44namespace llvm {
45
46class AssumptionCache;
47class DominatorTree;
48class Loop;
49class LoopInfo;
50class MemorySSAUpdater;
51class ScalarEvolution;
52
53/// This pass is responsible for loop canonicalization.
54class LoopSimplifyPass : public PassInfoMixin<LoopSimplifyPass> {
55public:
56 LLVM_ABI PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
57};
58
59/// Simplify each loop in a loop nest recursively.
60///
61/// This takes a potentially un-simplified loop L (and its children) and turns
62/// it into a simplified loop nest with preheaders and single backedges. It will
63/// update \c DominatorTree, \c LoopInfo, \c ScalarEvolution and \c MemorySSA
64/// analyses if they're non-null, and LCSSA if \c PreserveLCSSA is true.
65LLVM_ABI bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI,
66 ScalarEvolution *SE, AssumptionCache *AC,
67 MemorySSAUpdater *MSSAU, bool PreserveLCSSA);
68
69} // end namespace llvm
70
71#endif // LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
72