1 //===------ CodeGeneration.cpp - Code generate the Scops using ISL. ----======//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // The CodeGeneration pass takes a Scop created by ScopInfo and translates it
11 // back to LLVM-IR using the ISL code generator.
12 //
13 // The Scop describes the high level memory behaviour of a control flow region.
14 // Transformation passes can update the schedule (execution order) of statements
15 // in the Scop. ISL is used to generate an abstract syntax tree that reflects
16 // the updated execution order. This clast is used to create new LLVM-IR that is
17 // computationally equivalent to the original control flow region, but executes
18 // its code in the new execution order defined by the changed schedule.
19 //
20 //===----------------------------------------------------------------------===//
21 
22 #include "polly/CodeGen/IslNodeBuilder.h"
23 #include "polly/CodeGen/IslAst.h"
24 #include "polly/CodeGen/Utils.h"
25 #include "polly/DependenceInfo.h"
26 #include "polly/LinkAllPasses.h"
27 #include "polly/ScopInfo.h"
28 #include "polly/Support/ScopHelper.h"
29 #include "llvm/IR/Module.h"
30 #include "llvm/IR/Verifier.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Analysis/AliasAnalysis.h"
33 #include "llvm/Analysis/BasicAliasAnalysis.h"
34 #include "llvm/Analysis/GlobalsModRef.h"
35 #include "llvm/Analysis/PostDominators.h"
36 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
37 
38 using namespace polly;
39 using namespace llvm;
40 
41 #define DEBUG_TYPE "polly-codegen"
42 
43 namespace {
44 class CodeGeneration : public ScopPass {
45 public:
46   static char ID;
47 
48   CodeGeneration() : ScopPass(ID) {}
49 
50   /// @brief The datalayout used
51   const DataLayout *DL;
52 
53   /// @name The analysis passes we need to generate code.
54   ///
55   ///{
56   LoopInfo *LI;
57   IslAstInfo *AI;
58   DominatorTree *DT;
59   ScalarEvolution *SE;
60   RegionInfo *RI;
61   ///}
62 
63   /// @brief The loop annotator to generate llvm.loop metadata.
64   ScopAnnotator Annotator;
65 
66   /// @brief Build the runtime condition.
67   ///
68   /// Build the condition that evaluates at run-time to true iff all
69   /// assumptions taken for the SCoP hold, and to false otherwise.
70   ///
71   /// @return A value evaluating to true/false if execution is save/unsafe.
72   Value *buildRTC(PollyIRBuilder &Builder, IslExprBuilder &ExprBuilder) {
73     Builder.SetInsertPoint(Builder.GetInsertBlock()->getTerminator());
74     Value *RTC = ExprBuilder.create(AI->getRunCondition());
75     if (!RTC->getType()->isIntegerTy(1))
76       RTC = Builder.CreateIsNotNull(RTC);
77     return RTC;
78   }
79 
80   bool verifyGeneratedFunction(Scop &S, Function &F) {
81     if (!verifyFunction(F))
82       return false;
83 
84     DEBUG({
85       errs() << "== ISL Codegen created an invalid function ==\n\n== The "
86                 "SCoP ==\n";
87       S.print(errs());
88       errs() << "\n== The isl AST ==\n";
89       AI->printScop(errs(), S);
90       errs() << "\n== The invalid function ==\n";
91       F.print(errs());
92       errs() << "\n== The errors ==\n";
93       verifyFunction(F, &errs());
94     });
95 
96     return true;
97   }
98 
99   // CodeGeneration adds a lot of BBs without updating the RegionInfo
100   // We make all created BBs belong to the scop's parent region without any
101   // nested structure to keep the RegionInfo verifier happy.
102   void fixRegionInfo(Function *F, Region *ParentRegion) {
103     for (BasicBlock &BB : *F) {
104       if (RI->getRegionFor(&BB))
105         continue;
106 
107       RI->setRegionFor(&BB, ParentRegion);
108     }
109   }
110 
111   bool runOnScop(Scop &S) override {
112     AI = &getAnalysis<IslAstInfo>();
113 
114     // Check if we created an isl_ast root node, otherwise exit.
115     isl_ast_node *AstRoot = AI->getAst();
116     if (!AstRoot)
117       return false;
118 
119     LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
120     DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
121     SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
122     DL = &S.getRegion().getEntry()->getParent()->getParent()->getDataLayout();
123     RI = &getAnalysis<RegionInfoPass>().getRegionInfo();
124     Region *R = &S.getRegion();
125     assert(!R->isTopLevelRegion() && "Top level regions are not supported");
126 
127     Annotator.buildAliasScopes(S);
128 
129     simplifyRegion(R, DT, LI, RI);
130     assert(R->isSimple());
131     BasicBlock *EnteringBB = S.getRegion().getEnteringBlock();
132     assert(EnteringBB);
133     PollyIRBuilder Builder = createPollyIRBuilder(EnteringBB, Annotator);
134 
135     IslNodeBuilder NodeBuilder(Builder, Annotator, this, *DL, *LI, *SE, *DT, S);
136 
137     // Only build the run-time condition and parameters _after_ having
138     // introduced the conditional branch. This is important as the conditional
139     // branch will guard the original scop from new induction variables that
140     // the SCEVExpander may introduce while code generating the parameters and
141     // which may introduce scalar dependences that prevent us from correctly
142     // code generating this scop.
143     BasicBlock *StartBlock =
144         executeScopConditionally(S, this, Builder.getTrue());
145     auto SplitBlock = StartBlock->getSinglePredecessor();
146     Builder.SetInsertPoint(SplitBlock->getTerminator());
147     NodeBuilder.addParameters(S.getContext());
148     Value *RTC = buildRTC(Builder, NodeBuilder.getExprBuilder());
149     SplitBlock->getTerminator()->setOperand(0, RTC);
150     Builder.SetInsertPoint(StartBlock->begin());
151 
152     NodeBuilder.create(AstRoot);
153 
154     NodeBuilder.finalizeSCoP(S);
155     fixRegionInfo(EnteringBB->getParent(), R->getParent());
156 
157     assert(!verifyGeneratedFunction(S, *EnteringBB->getParent()) &&
158            "Verification of generated function failed");
159     return true;
160   }
161 
162   void printScop(raw_ostream &, Scop &) const override {}
163 
164   void getAnalysisUsage(AnalysisUsage &AU) const override {
165     AU.addRequired<DominatorTreeWrapperPass>();
166     AU.addRequired<IslAstInfo>();
167     AU.addRequired<RegionInfoPass>();
168     AU.addRequired<ScalarEvolutionWrapperPass>();
169     AU.addRequired<ScopDetection>();
170     AU.addRequired<ScopInfo>();
171     AU.addRequired<LoopInfoWrapperPass>();
172 
173     AU.addPreserved<DependenceInfo>();
174 
175     AU.addPreserved<AAResultsWrapperPass>();
176     AU.addPreserved<BasicAAWrapperPass>();
177     AU.addPreserved<LoopInfoWrapperPass>();
178     AU.addPreserved<DominatorTreeWrapperPass>();
179     AU.addPreserved<GlobalsAAWrapperPass>();
180     AU.addPreserved<PostDominatorTree>();
181     AU.addPreserved<IslAstInfo>();
182     AU.addPreserved<ScopDetection>();
183     AU.addPreserved<ScalarEvolutionWrapperPass>();
184     AU.addPreserved<SCEVAAWrapperPass>();
185 
186     // FIXME: We do not yet add regions for the newly generated code to the
187     //        region tree.
188     AU.addPreserved<RegionInfoPass>();
189     AU.addPreserved<ScopInfo>();
190     AU.addPreservedID(IndependentBlocksID);
191   }
192 };
193 }
194 
195 char CodeGeneration::ID = 1;
196 
197 Pass *polly::createCodeGenerationPass() { return new CodeGeneration(); }
198 
199 INITIALIZE_PASS_BEGIN(CodeGeneration, "polly-codegen",
200                       "Polly - Create LLVM-IR from SCoPs", false, false);
201 INITIALIZE_PASS_DEPENDENCY(DependenceInfo);
202 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass);
203 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass);
204 INITIALIZE_PASS_DEPENDENCY(RegionInfoPass);
205 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass);
206 INITIALIZE_PASS_DEPENDENCY(ScopDetection);
207 INITIALIZE_PASS_END(CodeGeneration, "polly-codegen",
208                     "Polly - Create LLVM-IR from SCoPs", false, false)
209