1//===- LCSSA.h - Loop-closed SSA transform 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 transforms loops by placing phi nodes at the end of the loops for
10// all values that are live across the loop boundary. For example, it turns
11// the left into the right code:
12//
13// for (...) for (...)
14// if (c) if (c)
15// X1 = ... X1 = ...
16// else else
17// X2 = ... X2 = ...
18// X3 = phi(X1, X2) X3 = phi(X1, X2)
19// ... = X3 + 4 X4 = phi(X3)
20// ... = X4 + 4
21//
22// This is still valid LLVM; the extra phi nodes are purely redundant, and will
23// be trivially eliminated by InstCombine. The major benefit of this
24// transformation is that it makes many other loop optimizations, such as
25// LoopUnswitching, simpler.
26//
27//===----------------------------------------------------------------------===//
28
29#ifndef LLVM_TRANSFORMS_UTILS_LCSSA_H
30#define LLVM_TRANSFORMS_UTILS_LCSSA_H
31
32#include "llvm/IR/PassManager.h"
33
34namespace llvm {
35
36/// Converts loops into loop-closed SSA form.
37class LCSSAPass : public PassInfoMixin<LCSSAPass> {
38public:
39 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
40};
41} // end namespace llvm
42
43#endif // LLVM_TRANSFORMS_UTILS_LCSSA_H
44