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+//===- LoopSimplify.h - Loop Canonicalization Pass --------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs several transformations to transform natural loops into a
+// simpler form, which makes subsequent analyses and transformations simpler and
+// more effective.
+//
+// Loop pre-header insertion guarantees that there is a single, non-critical
+// entry edge from outside of the loop to the loop header.  This simplifies a
+// number of analyses and transformations, such as LICM.
+//
+// Loop exit-block insertion guarantees that all exit blocks from the loop
+// (blocks which are outside of the loop that have predecessors inside of the
+// loop) only have predecessors from inside of the loop (and are thus dominated
+// by the loop header).  This simplifies transformations such as store-sinking
+// that are built into LICM.
+//
+// This pass also guarantees that loops will have exactly one backedge.
+//
+// Indirectbr instructions introduce several complications. If the loop
+// contains or is entered by an indirectbr instruction, it may not be possible
+// to transform the loop and make these guarantees. Client code should check
+// that these conditions are true before relying on them.
+//
+// Note that the simplifycfg pass will clean up blocks which are split out but
+// end up being unnecessary, so usage of this pass should not pessimize
+// generated code.
+//
+// This pass obviously modifies the CFG, but updates loop information and
+// dominator information.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
+#define LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H
+
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+
+/// This pass is responsible for loop canonicalization.
+class LoopSimplifyPass : public PassInfoMixin<LoopSimplifyPass> {
+public:
+  PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
+};
+
+/// Simplify each loop in a loop nest recursively.
+///
+/// This takes a potentially un-simplified loop L (and its children) and turns
+/// it into a simplified loop nest with preheaders and single backedges. It will
+/// update \c AliasAnalysis and \c ScalarEvolution analyses if they're non-null.
+bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, ScalarEvolution *SE,
+                  AssumptionCache *AC, bool PreserveLCSSA);
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H