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 
34 namespace llvm {
35 
36 /// Converts loops into loop-closed SSA form.
37 class LCSSAPass : public PassInfoMixin<LCSSAPass> {
38 public:
39   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
40 };
41 } // end namespace llvm
42 
43 #endif // LLVM_TRANSFORMS_UTILS_LCSSA_H
44