| 1 | //===- LCSSA.h - Loop-closed SSA transform Pass -----------------*- C++ -*-===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | // |
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| 9 | // This pass transforms loops by placing phi nodes at the end of the loops for |
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| 10 | // all values that are live across the loop boundary. For example, it turns |
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| 11 | // the left into the right code: |
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| 12 | // |
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| 13 | // for (...) for (...) |
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| 14 | // if (c) if (c) |
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| 15 | // X1 = ... X1 = ... |
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| 16 | // else else |
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| 17 | // X2 = ... X2 = ... |
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| 18 | // X3 = phi(X1, X2) X3 = phi(X1, X2) |
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| 19 | // ... = X3 + 4 X4 = phi(X3) |
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| 20 | // ... = X4 + 4 |
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| 21 | // |
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| 22 | // This is still valid LLVM; the extra phi nodes are purely redundant, and will |
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| 23 | // be trivially eliminated by InstCombine. The major benefit of this |
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| 24 | // transformation is that it makes many other loop optimizations, such as |
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| 25 | // LoopUnswitching, simpler. |
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| 26 | // |
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| 27 | //===----------------------------------------------------------------------===// |
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| 28 | |
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| 29 | #ifndef LLVM_TRANSFORMS_UTILS_LCSSA_H |
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| 30 | #define LLVM_TRANSFORMS_UTILS_LCSSA_H |
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| 31 | |
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| 32 | #include "llvm/IR/PassManager.h" |
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| 33 | |
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| 34 | namespace llvm { |
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| 35 | |
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| 36 | /// Converts loops into loop-closed SSA form. |
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| 37 | class LCSSAPass : public PassInfoMixin<LCSSAPass> { |
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| 38 | public: |
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| 39 | PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); |
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| 40 | }; |
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| 41 | } // end namespace llvm |
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| 42 | |
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| 43 | #endif // LLVM_TRANSFORMS_UTILS_LCSSA_H |
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| 44 | |
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