1 //===- LoopVectorize.h ------------------------------------------*- 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 is the LLVM loop vectorizer. This pass modifies 'vectorizable' loops
10 // and generates target-independent LLVM-IR.
11 // The vectorizer uses the TargetTransformInfo analysis to estimate the costs
12 // of instructions in order to estimate the profitability of vectorization.
13 //
14 // The loop vectorizer combines consecutive loop iterations into a single
15 // 'wide' iteration. After this transformation the index is incremented
16 // by the SIMD vector width, and not by one.
17 //
18 // This pass has three parts:
19 // 1. The main loop pass that drives the different parts.
20 // 2. LoopVectorizationLegality - A unit that checks for the legality
21 //    of the vectorization.
22 // 3. InnerLoopVectorizer - A unit that performs the actual
23 //    widening of instructions.
24 // 4. LoopVectorizationCostModel - A unit that checks for the profitability
25 //    of vectorization. It decides on the optimal vector width, which
26 //    can be one, if vectorization is not profitable.
27 //
28 // There is a development effort going on to migrate loop vectorizer to the
29 // VPlan infrastructure and to introduce outer loop vectorization support (see
30 // docs/Proposal/VectorizationPlan.rst and
31 // http://lists.llvm.org/pipermail/llvm-dev/2017-December/119523.html). For this
32 // purpose, we temporarily introduced the VPlan-native vectorization path: an
33 // alternative vectorization path that is natively implemented on top of the
34 // VPlan infrastructure. See EnableVPlanNativePath for enabling.
35 //
36 //===----------------------------------------------------------------------===//
37 //
38 // The reduction-variable vectorization is based on the paper:
39 //  D. Nuzman and R. Henderson. Multi-platform Auto-vectorization.
40 //
41 // Variable uniformity checks are inspired by:
42 //  Karrenberg, R. and Hack, S. Whole Function Vectorization.
43 //
44 // The interleaved access vectorization is based on the paper:
45 //  Dorit Nuzman, Ira Rosen and Ayal Zaks.  Auto-Vectorization of Interleaved
46 //  Data for SIMD
47 //
48 // Other ideas/concepts are from:
49 //  A. Zaks and D. Nuzman. Autovectorization in GCC-two years later.
50 //
51 //  S. Maleki, Y. Gao, M. Garzaran, T. Wong and D. Padua.  An Evaluation of
52 //  Vectorizing Compilers.
53 //
54 //===----------------------------------------------------------------------===//
55 
56 #ifndef LLVM_TRANSFORMS_VECTORIZE_LOOPVECTORIZE_H
57 #define LLVM_TRANSFORMS_VECTORIZE_LOOPVECTORIZE_H
58 
59 #include "llvm/IR/PassManager.h"
60 #include "llvm/Support/CommandLine.h"
61 #include <functional>
62 
63 namespace llvm {
64 
65 class AssumptionCache;
66 class BlockFrequencyInfo;
67 class DemandedBits;
68 class DominatorTree;
69 class Function;
70 class Loop;
71 class LoopAccessInfoManager;
72 class LoopInfo;
73 class OptimizationRemarkEmitter;
74 class ProfileSummaryInfo;
75 class ScalarEvolution;
76 class TargetLibraryInfo;
77 class TargetTransformInfo;
78 
79 extern cl::opt<bool> EnableLoopInterleaving;
80 extern cl::opt<bool> EnableLoopVectorization;
81 
82 /// A marker to determine if extra passes after loop vectorization should be
83 /// run.
84 struct ShouldRunExtraVectorPasses
85     : public AnalysisInfoMixin<ShouldRunExtraVectorPasses> {
86   static AnalysisKey Key;
87   struct Result {
88     bool invalidate(Function &F, const PreservedAnalyses &PA,
89                     FunctionAnalysisManager::Invalidator &) {
90       // Check whether the analysis has been explicitly invalidated. Otherwise,
91       // it remains preserved.
92       auto PAC = PA.getChecker<ShouldRunExtraVectorPasses>();
93       return !PAC.preservedWhenStateless();
94     }
95   };
96 
97   Result run(Function &F, FunctionAnalysisManager &FAM) { return Result(); }
98 };
99 
100 /// A pass manager to run a set of extra function simplification passes after
101 /// vectorization, if requested. LoopVectorize caches the
102 /// ShouldRunExtraVectorPasses analysis to request extra simplifications, if
103 /// they could be beneficial.
104 struct ExtraVectorPassManager : public FunctionPassManager {
105   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM) {
106     auto PA = PreservedAnalyses::all();
107     if (AM.getCachedResult<ShouldRunExtraVectorPasses>(F))
108       PA.intersect(FunctionPassManager::run(F, AM));
109     PA.abandon<ShouldRunExtraVectorPasses>();
110     return PA;
111   }
112 };
113 
114 struct LoopVectorizeOptions {
115   /// If false, consider all loops for interleaving.
116   /// If true, only loops that explicitly request interleaving are considered.
117   bool InterleaveOnlyWhenForced;
118 
119   /// If false, consider all loops for vectorization.
120   /// If true, only loops that explicitly request vectorization are considered.
121   bool VectorizeOnlyWhenForced;
122 
123   /// The current defaults when creating the pass with no arguments are:
124   /// EnableLoopInterleaving = true and EnableLoopVectorization = true. This
125   /// means that interleaving default is consistent with the cl::opt flag, while
126   /// vectorization is not.
127   /// FIXME: The default for EnableLoopVectorization in the cl::opt should be
128   /// set to true, and the corresponding change to account for this be made in
129   /// opt.cpp. The initializations below will become:
130   /// InterleaveOnlyWhenForced(!EnableLoopInterleaving)
131   /// VectorizeOnlyWhenForced(!EnableLoopVectorization).
132   LoopVectorizeOptions()
133       : InterleaveOnlyWhenForced(false), VectorizeOnlyWhenForced(false) {}
134   LoopVectorizeOptions(bool InterleaveOnlyWhenForced,
135                        bool VectorizeOnlyWhenForced)
136       : InterleaveOnlyWhenForced(InterleaveOnlyWhenForced),
137         VectorizeOnlyWhenForced(VectorizeOnlyWhenForced) {}
138 
139   LoopVectorizeOptions &setInterleaveOnlyWhenForced(bool Value) {
140     InterleaveOnlyWhenForced = Value;
141     return *this;
142   }
143 
144   LoopVectorizeOptions &setVectorizeOnlyWhenForced(bool Value) {
145     VectorizeOnlyWhenForced = Value;
146     return *this;
147   }
148 };
149 
150 /// Storage for information about made changes.
151 struct LoopVectorizeResult {
152   bool MadeAnyChange;
153   bool MadeCFGChange;
154 
155   LoopVectorizeResult(bool MadeAnyChange, bool MadeCFGChange)
156       : MadeAnyChange(MadeAnyChange), MadeCFGChange(MadeCFGChange) {}
157 };
158 
159 /// The LoopVectorize Pass.
160 struct LoopVectorizePass : public PassInfoMixin<LoopVectorizePass> {
161 private:
162   /// If false, consider all loops for interleaving.
163   /// If true, only loops that explicitly request interleaving are considered.
164   bool InterleaveOnlyWhenForced;
165 
166   /// If false, consider all loops for vectorization.
167   /// If true, only loops that explicitly request vectorization are considered.
168   bool VectorizeOnlyWhenForced;
169 
170 public:
171   LoopVectorizePass(LoopVectorizeOptions Opts = {});
172 
173   ScalarEvolution *SE;
174   LoopInfo *LI;
175   TargetTransformInfo *TTI;
176   DominatorTree *DT;
177   BlockFrequencyInfo *BFI;
178   TargetLibraryInfo *TLI;
179   DemandedBits *DB;
180   AssumptionCache *AC;
181   LoopAccessInfoManager *LAIs;
182   OptimizationRemarkEmitter *ORE;
183   ProfileSummaryInfo *PSI;
184 
185   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
186   void printPipeline(raw_ostream &OS,
187                      function_ref<StringRef(StringRef)> MapClassName2PassName);
188 
189   // Shim for old PM.
190   LoopVectorizeResult runImpl(Function &F, ScalarEvolution &SE_, LoopInfo &LI_,
191                               TargetTransformInfo &TTI_, DominatorTree &DT_,
192                               BlockFrequencyInfo &BFI_, TargetLibraryInfo *TLI_,
193                               DemandedBits &DB_, AssumptionCache &AC_,
194                               LoopAccessInfoManager &LAIs_,
195                               OptimizationRemarkEmitter &ORE_,
196                               ProfileSummaryInfo *PSI_);
197 
198   bool processLoop(Loop *L);
199 };
200 
201 /// Reports a vectorization failure: print \p DebugMsg for debugging
202 /// purposes along with the corresponding optimization remark \p RemarkName.
203 /// If \p I is passed, it is an instruction that prevents vectorization.
204 /// Otherwise, the loop \p TheLoop is used for the location of the remark.
205 void reportVectorizationFailure(const StringRef DebugMsg,
206     const StringRef OREMsg, const StringRef ORETag,
207     OptimizationRemarkEmitter *ORE, Loop *TheLoop, Instruction *I = nullptr);
208 
209 /// Reports an informative message: print \p Msg for debugging purposes as well
210 /// as an optimization remark. Uses either \p I as location of the remark, or
211 /// otherwise \p TheLoop.
212 void reportVectorizationInfo(const StringRef OREMsg, const StringRef ORETag,
213                              OptimizationRemarkEmitter *ORE, Loop *TheLoop,
214                              Instruction *I = nullptr);
215 
216 } // end namespace llvm
217 
218 #endif // LLVM_TRANSFORMS_VECTORIZE_LOOPVECTORIZE_H
219