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 | |