Yi Kong | 878f994 | 2023-12-13 12:55:04 +0900 | [diff] [blame^] | 1 | //===- llvm/Analysis/LoopUnrollAnalyzer.h - Loop Unroll Analyzer-*- 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 file implements UnrolledInstAnalyzer class. It's used for predicting |
| 10 | // potential effects that loop unrolling might have, such as enabling constant |
| 11 | // propagation and other optimizations. |
| 12 | // |
| 13 | //===----------------------------------------------------------------------===// |
| 14 | |
| 15 | #ifndef LLVM_ANALYSIS_LOOPUNROLLANALYZER_H |
| 16 | #define LLVM_ANALYSIS_LOOPUNROLLANALYZER_H |
| 17 | |
| 18 | #include "llvm/ADT/APInt.h" |
| 19 | #include "llvm/ADT/DenseMap.h" |
| 20 | #include "llvm/Analysis/ScalarEvolution.h" |
| 21 | #include "llvm/IR/InstVisitor.h" |
| 22 | |
| 23 | // This class is used to get an estimate of the optimization effects that we |
| 24 | // could get from complete loop unrolling. It comes from the fact that some |
| 25 | // loads might be replaced with concrete constant values and that could trigger |
| 26 | // a chain of instruction simplifications. |
| 27 | // |
| 28 | // E.g. we might have: |
| 29 | // int a[] = {0, 1, 0}; |
| 30 | // v = 0; |
| 31 | // for (i = 0; i < 3; i ++) |
| 32 | // v += b[i]*a[i]; |
| 33 | // If we completely unroll the loop, we would get: |
| 34 | // v = b[0]*a[0] + b[1]*a[1] + b[2]*a[2] |
| 35 | // Which then will be simplified to: |
| 36 | // v = b[0]* 0 + b[1]* 1 + b[2]* 0 |
| 37 | // And finally: |
| 38 | // v = b[1] |
| 39 | namespace llvm { |
| 40 | class Instruction; |
| 41 | |
| 42 | class UnrolledInstAnalyzer : private InstVisitor<UnrolledInstAnalyzer, bool> { |
| 43 | typedef InstVisitor<UnrolledInstAnalyzer, bool> Base; |
| 44 | friend class InstVisitor<UnrolledInstAnalyzer, bool>; |
| 45 | struct SimplifiedAddress { |
| 46 | Value *Base = nullptr; |
| 47 | ConstantInt *Offset = nullptr; |
| 48 | }; |
| 49 | |
| 50 | public: |
| 51 | UnrolledInstAnalyzer(unsigned Iteration, |
| 52 | DenseMap<Value *, Value *> &SimplifiedValues, |
| 53 | ScalarEvolution &SE, const Loop *L) |
| 54 | : SimplifiedValues(SimplifiedValues), SE(SE), L(L) { |
| 55 | IterationNumber = SE.getConstant(APInt(64, Iteration)); |
| 56 | } |
| 57 | |
| 58 | // Allow access to the initial visit method. |
| 59 | using Base::visit; |
| 60 | |
| 61 | private: |
| 62 | /// A cache of pointer bases and constant-folded offsets corresponding |
| 63 | /// to GEP (or derived from GEP) instructions. |
| 64 | /// |
| 65 | /// In order to find the base pointer one needs to perform non-trivial |
| 66 | /// traversal of the corresponding SCEV expression, so it's good to have the |
| 67 | /// results saved. |
| 68 | DenseMap<Value *, SimplifiedAddress> SimplifiedAddresses; |
| 69 | |
| 70 | /// SCEV expression corresponding to number of currently simulated |
| 71 | /// iteration. |
| 72 | const SCEV *IterationNumber; |
| 73 | |
| 74 | /// While we walk the loop instructions, we build up and maintain a mapping |
| 75 | /// of simplified values specific to this iteration. The idea is to propagate |
| 76 | /// any special information we have about loads that can be replaced with |
| 77 | /// constants after complete unrolling, and account for likely simplifications |
| 78 | /// post-unrolling. |
| 79 | DenseMap<Value *, Value *> &SimplifiedValues; |
| 80 | |
| 81 | ScalarEvolution &SE; |
| 82 | const Loop *L; |
| 83 | |
| 84 | bool simplifyInstWithSCEV(Instruction *I); |
| 85 | |
| 86 | bool visitInstruction(Instruction &I); |
| 87 | bool visitBinaryOperator(BinaryOperator &I); |
| 88 | bool visitLoad(LoadInst &I); |
| 89 | bool visitCastInst(CastInst &I); |
| 90 | bool visitCmpInst(CmpInst &I); |
| 91 | bool visitPHINode(PHINode &PN); |
| 92 | }; |
| 93 | } |
| 94 | #endif |